Transmission:Manual, Clutch                                                                          FAQ Home

   Volvo Maintenance FAQ for 7xx/9xx/90 Cars                                                                                                                     Version 5.0

Manual Transmission Shifting Troubles

Test Driving a Manual Transmission

Manual M-46 Laycock Overdrive Unit: Basic Operation

Manual M-46 Overdrive Fails to Engage: Basic Diagnostics

Manual M-46 Overdrive Self-Engages

M-46 Overhaul and Rebuild Procedures

M-46 Leaks

Overdrive Filter Cleaning

Manual Transmission Overdrive Solenoid

Manual Overdrive Clutch Slipping

Manual Overdrive: New Pistons and Seals Needed

Replace Broken M-46 with Unit from 240 Car

New Clutch Needed; Other Preventive Maintenance?

M47 5-Speed Noise in Gear: Bearings Bad

Manual 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.

Test 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.

Manual 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.

  1. 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).
  1. 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".
  1. 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.
  1. 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.
  1. 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 (46).

  2. The 4 springs (51) have enough pressure to overcome this pressure and keep the cone clutch (43) pressed against the annulus case (55).
  1. 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.
  1. 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 clutch.
That is the operation of an OD in a LARGE nutshell.

Manual 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 basic conditions: [Response 1:  Duane Hoberg]  In all the OD's that I have worked on (net included), electrical problems
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 Grimshaw] [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.
[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.. Try these: [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.

Manual 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" occurs.

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.

M-46 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 attached OD drawing.  See the more detailed discussion at Overdrive Rebuild: M-46 Transmission which includes a parts list and another link to the diagram. Warnings:

M-46 Leaks.  [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.

Overdrive 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 overdrives.

Manual 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.

Manual 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 a gearbox.

Manual 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.

Replace 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 modification.
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.

New 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.

M47 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.

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