Transmission:Manual, Clutch                                                                          FAQ Home

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

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.

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).

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.

It's not leaking.
The light always comes on when I push the button.
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 on.
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.

First check the fluid.  Very important to have the correct fluid and level in an M46.
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 tunnel.
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.

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.
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 to ground?
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

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.

• 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.

[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
 hydraulic)
 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.