M46 Overdrive Repair
|Text that follows assumes above average
automotive repair knowledge. If you can R & R the
head you can do this. This job should take 5 to 6 hours
barring major problems without removing the transmission.
This is only a compilation of tips that will make the job
go smoother not a complete how to do it.
I strongly suggest obtaining the Bentley Manual or the Volvo Service Manual as an assist in diagnosing and evaluating the OD unit. Going through the effort to R&R the OD then not having it work because of a broken/damaged/corroded wire or switch will destroy your day. As preventive replace the 4th gear switch on the side of the trans. Also get a copy of the parts diagram from your local dealer to help in reassembly and keeping track of which O-ring goes where, (some are so close to the same size that size alone will not help you place them correctly).
Parts needed: Some may be special order. I suggest replacing all these as a preventive measure.
To order the correct parts you will need the number off the unit that is on the right side of the unit. The number begins with 27 then 115xxx and a serial number. Take in the whole number.
My cost was $56 for all but the rear seal.
Special tools needed.
Procedure and tips.
1. Drain transmission and OD unit. When removing OD "pan" catch the filter screen which will fall out when the pan comes down.
2. Remove the Overdrive unit. See Bentley Manual
Tip: Support the transmission forward of the support cross member and remove transmission support and clean the nuts/studs on the OD as best you can. Clean studs allow fingers to remove nuts instead of wrenching them all the way off. See below.
Using the 11mm "C" wrench and 11mm wrench (alternate between them if necessary), remove the two nuts & lock washers at the top of the OD housing to rear trans housing, one each side below the bottom of the shift lever. The nuts are located to the transmission side of the unit just above the front of the "pan". You may have to carefully push the trans to the side to gain enough room to get the wrench to fit on the nut and move it. DO Not use the open end of the wrench, it will not fit properly and will round the nut making removal of the transmission necessary. I found this out pulling the OD from a vehicle in a salvage yard and had to drop the whole trans to get on the nut with a six point socket. Not fun on a 98 degree day.
These two nuts are the most difficult to remove and install. Be patient, I could only move them 1/12 turn at a time until the lock washer was free then used my fingers. Carefully lowering the transmission slightly helps. There is not much clearance between the firewall and the valve cover with wires and hoses in between.
There are a total of ten nuts and studs. Some studs will come out, that's OK. Leave the bottom two until last.
Flex the OD unit by pushing up (do not jack it up or you will bend the output shaft of the trans) on the rear of the unit to allow just enough clearance to get a screwdriver or pry bar between the units to help pry the units apart. Do not drive the pry bar/screwdriver between the units.
Remove the OD unit from the output shaft by moving it straight back in line with the transmission (about 15") while supporting it.
3. Clean well, disassemble the valves, replace O-rings lubricating well with ATF and reassemble. Tips for Overdrive O-rings: Be sure to lube well with fluid before reinstalling.
A. Remove the OD solenoid from the unit AND the pressure port plug just to the right of the pan.
his will allow whatever fluid still left in the unit to drain out as you work and not cause problems by creating a vacuum as you try to pull some of the pistons out.
There are two metal bars visible from the front of the unit. Remove them and remove the pistons below them. These are usually what is causing the OD not to work.
You will probably have to use a pair of pliers to pull the pistons from their bores. They may be a little difficult but if you did step A you won't be pulling against the fluid still in the passages between all the valves and pistons. Sometimes pushing on the other piston helps push the other out.
Removing the O-rings from the pistons. The trick I like to use to remove O-rings is by using a pair of narrow needle nose pliers. Open the pliers and grab the O-ring at points about 90 degrees apart, squeezing the pliers causes the ring to stretch up so the pliers can clamp on it (or I can slip a toothpick underneath it) without touching the piston. Doesn't marr the surface of the piston that way. With new O-rings the pistons will take some effort to install. That's good.
Removing the center
plug. (Check Valve) It will seem very stiff as it has an
O-ring on it. Just underneath the plug is a spring which
holds a check ball into a dimple on a plate inside a pump
sleeve. All parts are necessary. DO not loose them. The
pump sleeve can be removed by pushing
The sleeve must be reinstalled in the same orientation with the slot toward the hole the screen fits into in the bottom of the unit. Remove and replace the O-ring on the sleeve and plug. Lube all well and reinstall. NOTE: The pump piston cannot be removed from the cam follower without damage, leave them attached. When reinstalling the piston and cam follower assembly it must go into the sleeve before the sleeve is seated in the housing. Install the cam follower with the sloped side of the cam follower toward the front of the OD.
The pressure relief valve has many parts and must be replaced in the same sequence and relationship. The plug too has an O-ring on it and will be stiff. Pull the piston with a pair of pliers. Spacer washers and shims are located between the inner spring and the control piston. The outer sleeve can be removed by inserting your thumb, bending your thumb, then pulling the sleeve out. Mine came out without much effort. Some are more difficult than others. Sometimes you need to hook the hole toward the bottom of the sleeve to pull it out. Be careful to not scratch the bore.
The seat at the top of the bore requires a special tool to remove. A piece of stiff wire bent into a hook will work just as well if the seat O-rings allow it to come out. If it doesn't want to release with a little effort do not take it out. The O-rings are holding it in place and are still good. (the later from three different shop's mechanics). The hole in the outer sleeve when reinstalled should line up with the hole in the casting.
Clean surfaces between the OD unit and rear trans housing, install gasket on OD unit, rotate output shaft of trans with eccentric cam so cam lobe is in the extreme down position. Liberally lube the cam. Then lube the cam follower on the OD.
Position cam follower on OD unit in position straight up, centered L & R on hole in housing and pump piston all the way down.
Slide OD over output shaft of trans rotating rear flange to help align splines. The unit should slide up until about « to 3/4 of an inch from the trans. Check alignment of the cam and socket. Adjust position of the cam and follower using the rear output flange. Slide the OD rearward without allowing the studs to clear the holes. With a very sharp forward motion push the OD forward. It will seem to hesitate at the point where the cam contacts the socket then slide "home" as the socket adjusts to the cam. This may take a few tries. Mine took 8 tries over 20 min. Each time I realigned the cam and follower before trying it again and before I tried the sharp forward motion.
Refill with fresh fluid as able. I used a fill device I got from K-Mart that screws to the bottle, has a twist type on/off valve with about a 12" length of clear vinyl tube about «" in diameter. It just fit inside the trans fill hole, and allowed me to turn the bottle upside down into the area just below the intake manifold. Dumped 2.4 quarts into the trans and spilled maybe 2 to 3 ounces after the unit was full. Slick little device.