Maintenance FAQ for 7xx/9xx/90 Cars
Transmission Shifting Troubles. [Query:] My Volvo 745T has gradually
been developing a shifting problem over the years and it has recently become
a lot worse. I have the manual transmission and I find that I have
trouble putting it into first gear and to a lesser degree second gear.
These problems occur about every 4 out of 5 times I shift into those gears.
They either go into those gears smoothly on the first try or completely
refuse to go in(requiring a 3-2-1 shift maneuver). The other gears work
fine and the car is generally in good mechanical shape. It
has been suggested that this problem may be caused by shift cables or possibly
the synchronizers on those gears.
Adjustments. [Response 1:
Jerry Andersch] I'd start by making sure the clutch cable is
properly adjusted. There should be about 1/8" slack in it before it begins
to pull the release arm. Adjustment is made under the car at the end of
the clutch cable. Threading it in or out will produce the right amount
of slack. If the cable is out of adjustment it may not fully disengage
the clutch and as a result getting it in to first gear from a dead stop
and shifting to other gears, may be difficult. Of course there could be
other problems but I'd begin here with the easiest and virtually cost free
potential solution. Hope this is the answer. [Response: Rollie] I
had similar problem after I replaced the clutch but it turned out to be
an adjustment that I'd made on the shift linkage.
Fluid Change. [Response: Robert
Abel] I had this problem in my M46 (190,000 miles). In fact, it got
so bad that I was locked out of gear in traffic once - that was a fun one.
Changed the fluid to synthetic 10w30 motor oil. Ran the car for a week.
Changed the fluid again. Problem fixed. Now shifts easily every time.
The only thing I can figure is that the old fluid was not allowing the
synchros to properly rotate. Once the new fluid had its chance, everything's
good. [Response: Ozzie] The guy I bought my car from at 129K was
selling the beast because of the 1st, 2nd gear problem. I changed the fluid
to find it a little better, then I changed to Redline MTL.
This stuff works wonders, its a little expensive (8 or 9 bones a quart---you
need two), but not near what a new/used tranny costs.
Shifting Technique. [Ozzie:]
A couple of tricks for you M47 owners with 1st gear problems: either shift
into 2nd then 1st, or shift into 1st as you're coming to a stop.
The synchros engage better. Another trick I learned a month ago,
for those with a worn clutch and the grinding into reverse problem....put
that puppy in first, then slide it into reverse--NO GRINDING--just another
trick to put off replacing the clutch and surrounding pieces and parts
(rear main seal,etc.)
Overall Diagnostics. [Response:
Gary DeFrancesco] Your problem sounds like the beginnings of what I experienced
with my M46 tranny last year. In my case, the problem came on somewhat
suddenly, then progressively got worse. After awhile, I no longer had 2nd
gear at all.
How many miles
are on your tranny? Has the oil ever been changed? Unfortunately, many
auto manufacturers do not consider changing the manual tranny oil a regular
maintenance item. Hence, there are manual trannys out there with a lot
of miles on the factory oil, and they sometimes fail. In my case, I think
the tranny oil was first changed at 164,000, which is shortly after I bought
the car. At about 175,000, the shifting problems started. I think the wear
was well underway when the oil was changed, by then the it was too late
to prevent the long term problems. I tried Redline MTL in a desperate attempt
to revive the tranny. It did not work. I ended up replacing the tranny
with another one from wreck.
In your case,
I would go ahead and change the oil. Look at the magnet in the drain plug.
If there are a lot of metal filings, then there is some significant wear
occurring. Maybe a good synthetic oil such as Redline MTL will help. I
think your synchros are starting to go. Don't know what a set of synchros
cost, but being a Volvo part.... Such a repair will require a total tranny
tear down, so you should also replace all the bearings and seals. Since
your problem is mostly with 1st gear, you may have a problem with the 1st
gear damper if you car is equipped with one. If this is the case, you may
also need a 1st gear wheel which is obscenely expensive.
If an oil change does
not help, and your clutch is working fine (if you get grinding into reverse,
then your clutch is not releasing correctly which can cause your shifting
problems), then you may want to look for another tranny from a wreck.
Try to find one with some known history, relatively low mileage, and evidence
of being maintained (ie., oil changes). Finding a M46 for a 745T
can be very expensive. I was getting quotes of $650 - $950. Remember,
a 740T with manual tranny is not a common configuration in this country.
I ended up getting a M46 out of a 240. These trannys are much cheaper
($300 - $400 range) and are the SAME tranny as what goes into the 740.
The only differences I could find was what was bolted to the gear box to
make it mate to the different cars. Swap these few parts (shifting
cage, selector rod, tranny mount, and maybe the drive shaft coupling and
clutch fork), and the tranny is ready to go right into the car. No
other changes need to be made.
Driving a Manual Transmission. [Tips from Volvo TSB 890-43-4, 06/97,
courtesy of Service Technicians’ Society ] Systematic testing and diagnosis
continues to be a primary rule for technicians. Some problems, though,
can only be confirmed while driving the car. Shifting and noise problems
can be tricky without a standardized procedure within a particular shop.
Volvo has outlined a manual transmission test drive procedure that would
apply to most, if not all, manuals. The first step is preparation with
checking the transmission oil level before test driving. Transmission warmup
also is needed before the test drive. Volvo states that manual transmissions
with an aluminum case should be driven for about 20 minutes to achieve
normal operating temperature. With the car stationary, engine
idling, clutch pedal depressed and shift lever in Neutral, release the
clutch pedal and listen for mechanical
noise. Note whether the noise occurs with
the pedal depressed or released. Repeat this step 10 times to check for
intermittent noise. With the car stationary and the engine idling,
fully depress the clutch pedal and wait three seconds, put the lever into
Reverse, then 1st gear, and then Reverse again. Move the lever to Neutral
and release the clutch pedal. Repeat the procedure, but wait for 20 seconds
instead of three. Note any changes: differences in noise or difficulty
in selecting gears after the different wait time.
Check the point of clutch engagement,
and whether the clutch sticks or causes noise when the pedal is depressed.
Put the lever in Reverse and accelerate to about 2500 rpm, listening for
any noise and noting any other problems. Next, drive the car
on a highway with little traffic. Select 1st gear, and accelerate, shifting
1-2 and 2-3 at about 4000 rpm. Then shift 3-4 and 4-5 at as high an engine
speed as can be done safely, but no higher than 4000 rpm. Engine brake
the car, downshifting through all gears at about 3000 rpm. Note any difficulties
selecting a gear, whether gears jump out of engagement, and whether there
is any noise during any shift. Repeat the test, upshifting at 5000 rpm
and downshifting at 3000 rpm.
Drive the car in 4th gear at about 60
mph and begin 1 minute of constant acceleration, as traffic and speed limits
allow. Upshift to 5th gear, release the clutch for a moment, depress the
clutch and downshift back to 4th gear. Repeat six times, noting any problems.
Whether you elect to use this procedure or develop a modified one of your
own for local conditions, being able to repeat the sequence to demonstrate
a problem is a plus. The test procedure also helps to confirm that the
repair fixed the problem. A re-test need not repeat test steps that initially
were satisfactory. However, there’s always the slight possibility that
another problem occurred as a result of the repair procedure. Become a
creature of good, thorough habits when diagnosing. Unpredictable procedures
will mislead you more often than not.
M-46 Laycock Overdrive Unit: Basic Operation. [Discussion and
Analysis by Duane Hoberg]
The following describes the power flow
and the fluid flow for control of the Laycock OD.
Refer to the OD
diagram for the numbers.
Non-OD Operation. Assume the output
shaft from transmission through center of OD. During Non-OD operation,
splines on end of trans shaft mesh with Sprague clutch cam (67) and internal
of planetary carrier (70). Cone clutch (43) is pushed onto annulus
/output case (55) by springs (51) through bearing (46)and its carrier (44).
Reverse and engine braking. Trans output
shaft turns the planetary carrier (70). Since planetary carrier gears
(75) are in contact with the sun gear (78) and the annulus case (55), and
the cone clutch (43) is in contact with output case (55), the complete
system acts as a locked unit. The Sprague clutch freewheels
allowing the case (55) to "turn backwards".
Forward gears one through four. As for
reverse adding transmission output shaft drives Sprague cam (67) jamming
rollers (66) against output case (55) eliminating slippage of cone clutch
under higher torque and load conditions.
OD engagement. At all times transmission
output shaft is rotating, fluid is being pumped by pump (12) through check
ball (18) through filter (30) to passages leading to the actuating pistons
(49) and the solenoid (39). This fluid, under about 15 PSI, is always
present behind the actuating pistons (49), at the top of the Pressure Relief
Valve (between 22 & 23), and at the rear most port on the solenoid.
Non-OD fluid control and flow. The solenoid
not energized, blocks the fluid from reaching the area under the dashpot
(just above 24). The pressure generated by the pump is sufficient
to push the relief valve (between 25 & 27) down and the fluid is dumped
through the side of the relief valve onto the trans output shaft just forward
of the cam follower to bathe the cam (not shown inside 13) and the bearing
The 4 springs (51) have enough pressure
to overcome this pressure and keep the cone clutch (43) pressed against
the annulus case (55).
OD actuated. Solenoid energized.
Solenoid internal piston moves toward front of solenoid piston bore, opening
path between the back port and the middle port on the solenoid bore.
This action also blocks a port on the front of the solenoid bore plug.
Fluid is now free to pass to a
metered port between the solenoid housing and the bottom of the Pressure
Control Valve Dashpot (above 24). Since this is a very small opening
the pressure build up is slow to allow a slow buildup of pressure.
Since the dashpot has a larger surface area than the top of the relief
valve (between 25 & 27), the dashpot will push the relief valve up
closing the relief port and increasing the pressure behind the actuating
pistons (49) and the underside of the dashpot.
As the pressure increases behind
the actuating pistons, the pistons push on the bars (52) which then pulls
the cone clutch (43) off the annulus case (55) and into the brake ring
(42) which stops the cone clutch (43),bearing (46), and sun gear (78) from
spinning. As the cone clutch unit slides on the trans output shaft,
the planetary gear carrier (70) is still driven by the trans output shaft.
When the sun gear stops spinning,
The planetary gear carrier (70) still driven by the trans output shaft,
spins the planetary gears (75) on the stationary sun gear (78), and cause
the annulus case (55) to rotate faster than the output shaft of the transmission.
The Sprague clutch (66 & 67) allows this by freewheeling since the
output case (55) is still linked to the transmission output shaft splines.
Engagement fluid pressure is maintained
by the springs (below 25) inside the dashpot (above 24) pushing up on the
relief valve (between 22 & 23) and fluid pushing down on the relief
valve from above. Excess pressure is dumped through the side of the
relief valve as in non OD operation.
OD disengagement. Solenoid power is
removed. Inner solenoid piston is returned to "normal"position by
a spring between the plug on the end of the solenoid bore and the piston.
Solenoid reverts to blocking the fluid from reaching the area under the
dashpot. Pressure that is under the dashpot bleeds back through the
meteringport and passes from the middle port on the solenoid bore through
the front plug hole and into the OD.
As the fluid under the dashpot
bleeds off, the Pressure Relief Valve (between 22 & 23) falls, reopening
the side port dump. Pressure behind the actuating pistons falls allowing
the springs to push the cone clutch back onto the annulus case. Since
the sun gear is now free to rotate, the drive reverts to through the Sprague
That is the operation of an OD in a LARGE
M-46 Overdrive Fails to Engage: Basic Diagnostics. [Query:] 740T
car has a 4 speed manual transmission plus overdrive. The overdrive is
the push-button type on the end of the shifter. When the car
is hot it will not shift into overdrive. I just changed the transmission
fluid and cleaned the strainer but I still have the problem. Here are some
It's not leaking.
[Response 1: Duane Hoberg] In
all the OD's that I have worked on (net included), electrical problems
The light always comes on when I push
It never shifts by itself but it does
occasionally slip out. This happens when it gets hot and I try to drive
in OD at about 40-45 MPH.
The relay has never been changed or worked
It started happening suddenly. The problem
seems to have started around the same time as the weather got warmer. I
wonder if the problem may have actually started sometime over the winter
but the cold weather delayed the effect. It is usually below zero here
(Atlantic Canada) all winter.
The oil & strainer looked fine. I
was expecting the worse.
It doesn't make any funny noises at all.
rank the highest. Second is bad
seals on the solenoid piston allow fluid past and allowing a self-engage
situation. Third is bad piston seals on units prior to 1985.
[Response 2: Basic Diagnostics by Paul
First check the fluid. Very important
to have the correct fluid and level in an M46.
[Further O/D Functional Notes: Abe Crombie.
See Duane Hoberg's extensive M-46 notes
above and the OD
exploded parts diagram] The OD is engaged by closing a relief
port with the od solenoid. The relief port is connected to the lower portion
of the relief valve. When the relief valve is "relaxed" it regulates a
pressure of about 1 bar (15psi+/-) and the apply pistons for od don't have
enough pressurre to lift and engage cone clutch to cause od shift. When
the solenoid closes the relief port the relief valve gets its spring compressed
and now regulates a pressure of 30 bar (450 psi) and the pistons lift the
cone clutch of the output shaft outer annulus and pull it into the brake
ring which causes the planetary gears to increase output shaft---->overdrive.
You may need to do more than to unscrew the relief valve plug and filter
plugs and blow through the hole you will see in the relief valve bore just
above the threads. When you back up if the od attempts to try to
engage it will try to lift the cone clutch off the annulus and reverse
will slip. The only power flow in reverse is by the cone clutch inner lining
being pushed onto the annulus by the piston return coil springs.
Second check the OD switch and wiring.
The former can die a painful death (causing intermittent problems) and
the latter can be chaffed as it runs under the carpet and through the transmission
Third, check the oil pressure in 4th gear.
Pressure is critical as it is used to engage/disengage the OD. Connect
a pressure gauge to the port directly below the OD solenoid valve.
Pressure should read 21 psig at 70 km/h or ~40 mph. On OD engagement,
pressure should rise to 520-600 psig. If the pressure is not within
this range (typically low) replace the solenoid valve.
If all is correct and the OD still slips,
remove/clean the relief valve located at the bottom of the OD unit.
Note: you must replace the transmission cross member to do this.
While you're doing this, replace the OD filter (located under a plug directly
beside the relief valve.
Next, replace the OD switch in the transmission
case. If the unit still slips, there is a (big) problem in the OD
clutch. Have the unit rebuilt.
[Response 3: Filters & Fluid]
A frequent cause (not yours) is clogged filters inside the OD unit. Can
be cleaned (with white spirit) without removing gearbox or OD. Also synthetic
ATF (or redline MTL) will help. The reason it does not engage when the
car is warm is that the gearbox oil is also hot - and thus thinner, so
it's pressure drops. Synthetic oils do not change their properties (so
much) when heated, this is one of their advantages.
[Response 4: O/D Relay] Bosch relays have
a serious habit of becoming intermittent and/or temperature sensitive.
98% of the time, it's solder connections on the printed circuit boards
inside the relay assembly. You can pop the plastic cover off and examine
the backside of the PCB with a magnifying glass. More often than not, you'll
find microscopic cracks in the solder around some of the connections. I
have been quite lucky re-soldering and reviving virtually ALL the relays
in my family's Volvos.
[Response 5: Electrical Wiring to Solenoid]
Check the wiring to (and connections at) the overdrive solenoid.
[Response 6: Basic O/D Electrical Diagnostics]
There are a couple of good diagnostics and inspections that you or a willing
mechanic can easily perform. Given that you changed the oil, at least you
know where the OD is, so maybe you and/or a friend can dive right in..
Wire up an indicator light to the "hot"
terminal on the solenoid, and confirm that there's 12 volts present when
the OD engages -- and that the test light goes out when OD disengages.
[Response 7:Rebuild] Finally,
it may be time for an OD rebuild. The OD uses the pressure of the
oil in the tranny to engage. When the tranny is cold, the pressure
is greater, so the OD works. When it gets hot, the pressure is less
so the OD does not work. You really have two choices, find a reputable
shop to rebuild your OD, or find a used OD. If you are playing around
with extra boost in your car, you will want to have the OD rebuilt to handle
the extra power.
Then the question is, when you push the
button but the OD fails to engage, did the light still come on? How is
the condition of the ground lead at the solenoid, and is it solidly connected
If the light fails to come on (when it
should) then the problem is electrical and not inside the OD. You can confirm
this by feeding 12 volts to the solenoid directly -- note that you must
only do this in forward gear (reverse OD is not healthy!).
If appears that the solenoid is getting
power but OD fails to engage, the next candidate is the solenoid itself.
Sometimes a shop will have a known-good one to substitute (which is good,
because they're not cheap). Sometimes an enterprising mechanic can disassemble,
clean, and reclaim a solenoid -- but I wouldn't hang my hat on it (I've
done a couple). If the problem is the solenoid, replace the OD solenoid
NOW! My OD acted like this for a year and a half, then the overdrive
turned into tiny bits and ate up the shaft from the transmission too
M-46 Overdrive Self-Engages. [Tip from Duane Hoberg:] If the
"clutch" only slips in second gear and no other, and the OD does not appear
to function, you have a problem with the solenoid on the overdrive allowing
the OD function to "self engage" without input from you.
The solenoid in its OFF position acts as
a stopper to keep fluid from an area that creates the pressure build up
necessary to move parts internal to the OD and "engage" the "fifth" gear.
When ON the solenoid valve moves only 1/8 to 3/16 of an inch and allows
the fluid past. The seals internal to all this are two very small
O-rings. There can be over time a small amount of leakage past the
"end" O-ring and into the electrical area of the solenoid. If this
leakage is great enough the valve cannot return to the OFF position and
the OD then becomes self engaging. There are all sorts of causes
for this to occur, age is one and poor electrical contact which causes
heat which bakes the O-rings hard being another.
The solenoid has to be removed and shaken
to test it. Yes, that is the test. It must rattle freely or
it is bad.
In case anyone is wondering how this can
be: Normal drive in the OD for gears 1 to 4 is via a Sprague clutch.
(Only works in one direction and very very positive). OD is via planetary
gearing which requires a stationary sun gear to accomplish. Hydraulics
push the sun gear carrier (which almost everyone calls the cone clutch)
into a brake ring which is part of the outside case of the OD. During
the transition from Sprague clutch drive to planetary gear drive, the planetary
gear drive is trying to make the output shaft move faster but cannot because
the sun gear is not stationary and the Sprague clutch is just sitting there
trying to drive but cannot. It is this in between area where "slippage"
The pump in the OD is a piston style driven
off the output shaft of the transmission. The pressure necessary
to move ( not engage just move) the internal parts of the OD begins at
around 15 mph and with good actuating piston seals is sufficient to maintain
OD contact at about 25 mph. Second gear range in the M46. After
that, the OD is engaged and the OD "doesn't work" when the button
is pushed. Only because it is already engaged. Change
the OD solenoid.
Overhaul and Rebuild Procedures. [Extensive Discussion courtesy
of Duane Hoberg]
Tips on dismantling and overhauling the
Laycock J type Overdrive. Numbers refer to parts as numbered on the
drawing. See the more detailed discussion at Overdrive
Rebuild: M-46 Transmission which includes a parts list and another
link to the diagram.
After removing the OD from the vehicle, clean
the outside well.
Prior to separating the OD housing, remove
the rear output flange (61) if necessary. A pipe wrench is suitable
for holding the flange.
Remove the nuts (53) holding the bars (52)
over the actuating pistons and remove the bars.
Remove the nuts and washers (82,83,84)holding
valve body (2), clutch ring (42) and rear case (54) together gradually.
Working your way around the case, loosen each nut a little at time to release
the tension from the springs (51) gradually. Note the two copper
washers and possibly plastic "sleeves" on the upper pair of studs. These
washers and sleeves will have to be replaced on the same two studs to prevent
leakage after reassembly. With a soft (brass or plastic) drift, drive
the brake ring (42) from whatever case it stuck to, working around the
ring for even removal.
With the rear case separated from the brake
ring, remove the return springs (51), cone clutch (43), bearing and carrier
(44 through 48),sun gear (78) and the planetary gear system (70 to 76)
as a unit from the front of the annulus ring/output case (55). The
cone clutch may stick a little but will release as the inside of the cone
clutch has clutch material in contact with the output case. The planetary
system may decide to stay with the annulus case and is OK to remain with
the case. If needed, to remove the annulus case from the rear case,
put the nut (64) back on the output shaft and strike with a plastic mallet
to drive the case from the bearing (59).
Removal of the one way roller clutch (65 to
68) requires a special tool or lotsa patience and grease to reinstall.
It is not recommended that this clutch be removed unless damaged.
By inserting your thumb into the center of the clutch, it should turn one
way and one way only. If using your left thumb inserted into the
center, rotation counter clockwise should occur. Clockwise rotation
should lock the bearing and try to turn the case.
To remove the bearing (46) from the cone clutch
(43), remove spring clip (48) and sun gear (78) from cone clutch. Spray
a little penetrating lubricant of choice at the joint between the bearing
and the cone clutch. Using two pry bars, place bars between cone clutch
and the bearing carrier (44) at a point other than the flanges. Pry
the bearing off the clutch. Remove the retaining clip (47), flip
the carrier over, and drive the bearing out of the carrier with a drift
or similar device.
Reverse is the opposite of disassembly.
The thrust bearing (46) can be driven into
the carrier (44) by drift around the outer race if the carrier is on a
flat stable surface. A press method is preferable but not necessary.
The bearing (46) MUST BE PRESSED onto the cone clutch (43) with a vise
and spacers or what ever. A socket on the back of the cone clutch
with bolt through bearing and big washers that put pressure on inner race
and the bearing "boss" of the cone clutch only. If bearing is driven
on to cone clutch with an impact method or the pressure on the cone clutch
is not directly under the inner bearing "boss" the cone clutch integrity
will be compromised. READ AS guaranteed failure in many pieces with
many dollars to repair OD unit.
The thrust washer (56) under the roller clutch
(65) fits into a mating recepticle in the annulus (55).
The gaskets (80 & 81) are not interchangable.
The two copper washers (83) are installed
on the upper two studs to prevent a possible leakage condition after reassembly.
Some OD's had plastic "seals" around the studs instead of copper washers.
Leave these in place or replace with eight to ten turns of Teflon tape.
Just enough to contact the inside of the mating hole in the rear case.
Tighten the case nuts (84) gradually and in a criss cross pattern to pull
the cases together and load the springs (51) evenly.
To reseat the annulus case into the rear bearing
(59) (or bearing and annulus into the outer case), use a spacer of some
sort to push against the inside of the rear case (54) to allow the flange
nut (64) with a washer to pull everything into position.
[Query:] My M-46 overdrive leaks; does this require dissassembly?
[Response: Abe Crombie] The leakage is most likely from the upper two nuts/studs
on the OD unit. These are sealed with cone shaped nylon pieces that get
forced into threads. Clean it up and then drive a block and see if
it leaking there. If so then you only need to remove nuts and clean the
stud and case with brake cleaner spray and then apply sealant (silicone,
permatex, etc) to the studs liberally and then re-install nuts. If
you have to remove OD then just before you lift car kill it in reverse
so that the splines in OD will unbind from the trans output shaft.
The OD will slide right off if this is done.
Filter Cleaning. [Tips by Mike Froebel] Cleaning out the filter
is a good idea. There is a special tool to remove those three plugs,
but I've found you can do it with two punches and a large adjustable wrench
if you have 3 hands. The filter is behind the big plug, and the relief
valve is behind the medium one. If you take that on out be careful,
there is 4-5 parts, 2 springs and a bunch of shims that are used to adjust
operating pressure. Change o-ring at the same time. This is
pretty complicated, and mistakes can kill expensive parts. Flaws
of the type reported here are not normal, most mechanics are afraid of
Transmission Overdrive Solenoid. I checked at a few volvo dealers for
the cost of a volvo OD solenoid and the price was between $195 and $215.
Then I ran into the Gear Vendors (World's largest supplier of Overdrive
Auxiliary Transmissions) at the Los Angeles Roadster Show. Their price
for new OD solenoids for the Volvo is $100. I spoke to Homer Eubanks at
800/999-9555 (customer service rep) and he was very, very helpful diagnosing
a problem I had with my OD when it would go off/on/off/on/off and finally
off. He told me that the OD needs servicing and when that is done that
I should have the screen cleaned and air blown through the small oil holes
that go to the solenoid.
Overdrive Clutch Slipping. [Query:] I posted a message
about this problem a couple of weeks ago, or so, and one respondent suggested
engine mounts, but after inspecting them, I doubt that they are the cause
of this problem. The car is an '89 740 Turbo with M-46 plus P overdrive.
When the car is good and hot, the overdrive clutch seems to slip. Starting
out in 1st gear, I get a lurch, during which the engine revs slightly,
then settles to normal. Sometimes, in any forward gear, in overrun, the
engine drops back to idle, as if the overdrive was neither engaged nor
disengaged and was freewheeling. In reverse gear, I get a loud gear whine,
and the car proceeds at a clearly much lower ratio for 20 - 30 yards,
then lurches into its normal ratio. At these times, the overdrive
will not engage at all, but it doesn't feel like the direct drive has disengaged,
because there is no freewheeling. In cool weather, or when the car is not
stinking hot, the overdrive works perfectly. The electrics for the overdrive
all check out. The car is new to me, has 85,000 miles, and seems to have
been very well cared for and driven lightly. Should I just assume that
it has the wrong kind of oil (i.e. Dexron), or should I consider other
things? Is Redline really the magic bullet for these units, or is Volvo's
stuff better? The Volvo manual seems to suggest that Volvo's oil is only
good where ambient temperatures remain above 10 degrees Fahrenheit, not
a safe assumption here in the Boston area. If incorrect oil is the likely
culprit, what should I do to clean out the old stuff? [Response:]
Try draining the trans and O/D. Clean both screens in the O/D. The one
under the rectangular plate as well as the one on top of the big plug once
you get the cover off. Type F will work fine for the trans./O/D. O/D's
can slip both unengaged as well as engaged. They usually slip when engaged
though. This is a first step and it's a lot easier to do them pulling
Overdrive: New Pistons and Seals Needed.
[Tip from Joann Kaylor] A year ago I replaced the o-rings in my P
type O/D (essentially the same as the J type hydraulics) I was unable to
locate the blue teflon seals for the operating pistons so I used these
over and placed new new o-rings in the groove underneath the teflon seals.
This worked OK for about 10,000 mi. when slipping and poor shift quality
symptoms began to appear. I discovered that revving the engine to 3,000+
before shifting and staying on the throttle increased internal pressures
sufficiently to engage the O/D,although somewhat harshly. Also it would
stay engaged and not drop out of O/D below 45MPH. Draining the oil revealed
no aluminum or ferrous particles so I assumed I was on the right track.
The blue teflon seals are not available from Volvo or anyone else and for
a good reason. The issue is addressed in TSB 43-14 in which new pistons
and seals replace the two piece teflon / o-ring seal and piston. The new
seals will not fit the old piston due to differences in the grooves
The piston appears to be the same as earlier
J-type and uses a single 3/16" cross section o-ring. Very few people
who deal in Volvo parts are aware of this change but leakage around the
teflon was the reason (loss of operating pressure). I suggest
calling Kevin at Beechmont 800-255-3601 Who knows the P/N's you need and
gives a VCOA discount.Brian Greene of VRC 800-872-2170 has been a good
source of recycled parts not available from Volvo. Replacing only
these pistons restored my O/D's ability to shift when hot.
Broken M-46 with Unit from 240 Car.
[Tip from Tom Fachetti] Having gone
through a real headache when trying to exchange OD units on a
1987 745T, please be advised that Volvo
switched to a Type P (vice Type J) OD unit in 1987. These two units
are not interchangeable and, therefore, be very careful when you are seeking
a replacement. FYI - The Type P is a larger unit that is intended
to handle the added torque of the turbo engine.
[Tip from Gary DiFrancesco] Over the holiday
break, I replaced the sick M46 tranny in my '87 745T. The sick M46 no longer
would go into 2nd gear and repair costs were potentially out of this world.
Many of the bone yards I contacted for a 740 ready M46 usually wanted big
bucks for one, ($650 to $950). Yet, M46s for a 240 were relatively cheep,
($250 to $350). A few knowledgable yards confirmed my idea of using
a M46 from a 240 and adapting it to a 740. I obtained a 240 M46 and intalled
it over the holiday break. I can say with confidence (based on my experience)
that a M46 from a 240 will easily fit into a 740!
These are the changes I needed to make
to the 240 M46 in order for it to fit in a 740:
1. Swap the tranny mount and bracket,
(2 to 4 bolts)
2. Swap shifting cage, (4 bolts)
3. Swap the selector rod, (1 pin)
4. Swap clutch fork and move fork
pivot point, (240 clutch has a cable, 740 uses
5. Swap drive shaft couplings, (1
nut, My 740 uses a rubber coupling instead of a u-joint)
These changes are all easy and fast. Knowing
what I know now, I can make these changes in maybe 20 minutes. Once done,
the tranny installs into the 740 without difficulty or need for further
In my situation, the 240 M46 I obtained
is an earlier version that had the iron case. This is the version with
the lower 1st gear ratio which is desirable. The later Al case M46s had
a higher 1st gear ratio that could pull a house off its foundation.
The 240 M46 came with a Type J OD unit.
I was figuring on swapping it with the Type P OD from my sick M46 since
I have a B230FT engine. Unfortunately this swap was not possible. The output
shaft of the 240 M46 (with iron case) was about 3/16" longer than the shaft
from the Al case M46. So the Type P OD would not go onto the iron case
M46 all the way. Furthermore, I found the spline on the iron case M46 was
shorter and slightly smaller in diameter than that of the Al case M46.
I am not sure of the reason for the changes in the output shafts and OD
units. Obviously there have been some design changes over the years that
has caused some incompatibility with these parts. I put the Type J OD back
onto the iron case M46 and am driving the car just fine. If anyone can
shed some light on these design changes, it would be greatly appreciated.
If a Type P OD can be obtained that will properly fit my iron case 240
M46, I would like to get one.
The Type P OD is stronger than the Type
J OD, hence it is used on the Turbo cars. Can anyone tell me where the
weakness of the Type J OD is. Is the weakness only an issue when the overdrive
is engaged? Or is it an overall weakness that affects the OD unit whether
it is engaged or not? Since I don't hot rod this car, am I correct in assuming
that a Type J OD will be fine? After all, many 240 owners with Type J ODs
tow boats and tent trailers which put a fair amount of stress on the OD
even when not engaged. I don't hear anything about that being a problem.
Since I don't tow with this car, running with a Type J OD seems to me to
be okay if I don't hot rod. Any thoughts on this train of thought would
also be greatly appreciated.
If nothing else, it is good to know that
a 240 M46 can very easily be installed into a 740. This can be a
real $ saver for the few of us whose 740 M46 gets sick.
Clutch Needed; Other Preventive Maintenance? [Query:] Our 88
740 Turbo Wagon is in need of a new clutch. Any suggestions as to other
work to do while doing the clutch? Rear oil seal? Shifter bushing? Is it
a given that the flywheel should be re-surfaced? [Response 1:
Gary DiFrancesco] While replacing the rear oil seal, pilot bearing, and
throwout bearing, also look at the clutch fork. It is not unusual for the
pivot point on the clutch fork to wear (clutch fork is about $45 at the
dealer.) When my '87 745T had a new clutch put in, the pivot
point was worn so badly, you could see holes in the metal. If not
replaced, the pivot point would have eventually failed and the clutch would
have been useless. Also look at the pivot bolted to the bell housing.
This rubs against the clutch fork pivot point and can get deformed. It
should be smooth and round on top. If there is wear, replace it.
It is easily removed with a socket (19mm I think), and the bell housing
does not need to be removed to do it. When putting the clutch fork in,
put some grease on the pivot point. [Response 2: Dick
Riess] By all means replace the rear seal. Also pilot, throwout and
you may as well go for the clutch kit which includes a new pressure plate.
To have a super smooth engagement you could have the flywheel resurfaced
also. [Response 3: Tom Frisardi] Only reface the flywheel if
there's a problem. Usually there is, especially in the form of hairline
cracks. Sometimes refacing won't cure this. A fresh flywheel face feels
better, to me at least. Other things that I've had trouble with in the
drivetrains of my 740's that you might want to look out for have been the
center support bearing, the rear transmission mount and the flexible coupling
on the output flange of the transmission.
5-Speed Noise in Gear: Bearings Bad. [Query] Ever since I purchased
the car in November, that M-47 transmission just moans and groans. 1st,2nd,3rd
and 5th are the offenders. 4th appears to be OK. The car has 165,000 kms
on it. Is this a common issue or is the result of poor maintenance in regards
to the tranny oil? I recently changed the oil to find it a nice shade of
silver. It's obvious the damage has been done. I'm just wondering
if this is to be a continuing concern and if it is, are there any tricks
to keep it from occurring any time soon. [Response 1: Mike Froebel]
I hate to say, but what you're seeing is bearing bits. One of the
bearings is coming apart, probably on the countershaft. It's only
going to get worse, I'm afraid. The reason you don't hear it in 4th
is because that gear is not a gear at all, the trans just joins input to
output shaft. This puts no load on your bad bearing. The trouble
with a bad bearing is once the hard surface of the bearing parts has worn
off, there is nothing to prevent rapid deteriation of what is left.
In this type of transmission, then the gears don't mesh properly as the
shaft with the bad bearing moves around. And of course, all
the metal particles grinding everything else. Then instead of a small
parts and large labour bill, you have a large parts and larger labour bill.
I would have this fixed ASAP. As far as only working on one part
of the transmission, I wouldn't recommend it, take the whole thing apart
and see what is wrong. Or try to find a used one, rebuilding these
takes time and patience, and not very many have any experience. [Response
2: Paul] Mike is right, what you are hearing is noise from a bad countershaft
bearing. Don't let this go on, because aside from damage to other
bearings, the alignment between the gears on the Input/Mainshaft and the
countershaft is changing, and those parts will add zeros to the parts bill
in a hurry. Make sure this job is done by someone who has done Volvo tranny's
before if you want it done right.
[Response 3: Henrik] If you see metal
parts in the oil - don't replace just the bad bearing! Look for a used
M47 instead. Just a few hours of labour (two actually if you are handy).
The metal parts has probably made serious damage to other bearings in the
gearbox. In Sweden, you can get a used M47 for about $180 and it's not
worth the money to rebuild the box and take the risk of making things worse
and end up buying a used box.
Maintenance FAQ for 7xx/9xx/90 Cars
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