Manual Transmission Rebuild


Created: 4/1/99

Last updated: 


Author/source: DAS


Photos will be added later

Introduction:

In fall/winter 1998, I removed and rebuilt the manual transmission in my 1981 DMC VIN 5429. This writeup is my notes on the subject while still fresh in my mind. The original purpose was twofold, first to replace the aging clutch, thought to be original at 30K miles (about the limit for most Deloreans) replace the slave cylinder as long as it was out, and diagnose and repair a symptom best described as a crunch going into third gear, and instability in staying in fourth gear. I had had Stephen Wynn test drive the car at one of our club Tech days and his comment was "feels like bad third gear synchro, but third gear problems would be very unusual".

In most cases, I followed the DMC Technical Manual. In a few cases it is either unclear or has you do extra work. The only description in the manual that I would have been afraid to attempt was removal of the 1-2 synchros since the work is required to be done with the items heated to 400 degrees and then pressed on using a hydralic press. The other BIG THING TO NOTICE IS THAT THE DRAWINGS ARE REVERSED anywhere they show the postion of the ring gear assembly. If you follow the manual you WILL end up with a car with 5 speeds in reverse and one forward.

Removal of the transmission from the car:

The manual is essentially correct, although it severely understates the difficulty in removing the shift linkage. The difficult part is where it says "remove the mount brackets from the transmission end cover" (Step 5). The crossgate linkage must be removed to get tools into place. A swivel is needed to get to the bolt in the center of the linkage bracket. You need about 6-inch double-jointed fingers to get the socket on the bolt.

The other difficulty is the two of the three small metal shields that are apparently installed with the engine out of the car. Iíve been told that it is common to leave out the lower one.  The one on the side opposite the starter holds the magnetic sensor that is only used for some non-existent test equipment.. Removal of the side cover is best accomplished with a long socket extension where the ratchet ends up behind the catalytic converter. The lower plate is removed with standard wrench while lifting the engine slightly. You may have to knock the screws out after loosening them all the way against the frame. Do not forget to set this cover back in place under the engine before you put the transmission in place, it wonít go in after. I believe in re-installing all of the covers, it's up to you. 

Removing the axles is simple, but be sure to hang them in place with wires. If the car is rolled around with the axles allowed to dangle on their own, the outer CV joint boots will be ruined. Itís probably better to remove the axles all the way and repack the CV joints while theyíre out.

There is no reason to remove the aluminum coolant tubes as long as youíre not totally an animal with the trans.

Disassembly of the Transmission (F:06:01)

Remove the axle flanges as detailed on F:04:01. The written procedure assumes that you have already done this.

Remove the bellhousing. The written procedure assumes that you have already done this.

On step 3 the 5th speed detent ball cover cannot be removed with a screwdriver. A small pair of channel-locks works better. In an extreme case I had to grind flats on the screw so I could use a wrench and then replace the screw, but the trans was on the car at the time and I could not get a good angle with the pliers. PJ Grady sells a replacement screw that has an allen head but it has the wrong threads. I made one from hardware store parts that worked just fine.

Where Step 5 says to remove both shaft nuts, you probably don't need to remove the large one on the output (lower) shaft unless you are planning to later remove it from the housing and disassemble it. Just remove the rightmost bolt shown in Figure 12 and only loosen the other two. Note - if you later decide that the lower (output) gear train has to be removed, you will have to reassemble the transmission, so that you can lock it, to loosen the shaft nut.

Removing the shaft nuts is easier said than done, after several tries my recommendation is to remove the bellhousing first. Then fabricate a bar at least 3í long and attach it across the front of the transmission using two of the bellhousing screws. The input shaft nut can be removed using a breaker bar with a 1-1/16" socket and an additional length of pipe, with the other bar keeping the transmission from rolling across the floor. I used the same assembly that I use for adjusting the doors. If you need to remove the shaft nut from the output (lower) shaft, you can use a large crescent wrench and a length of pipe to make the handle longer. In the case of both nuts, once you break over the staking, they are not all that tight. Torque specification on these is 120 ft-lb, but the nuts being staked makes the breakaway torque pretty high.

Do step 10 (remove pivot interlock) before Step 6 - this gets it out of the way. It just unscrews from the case.

Step 6 refers to figure 12 - that makes no sense. Also - you will need to use a gear puller, pull the whole thing off as an assembly. Unlock the gears first. Do not pull using the ears on the 5-th gear dog (they will snap off). The gears on the output (lower) shaft are a slip fit and a puller is not necessary.

After separating the case, DO NOT play with the reverse gear shift fork. If you shift it overcenter, the detent ball will fall in and lock the lever/bar in place. If this happens remove the reverse light switch and press the ball back into place while moving the lever back.

Observations:

In my case, the sliding gear that goes between 3 and 4th gear had the points ground off the teeth. These are on the INSIDE of the slider and not easy to see. In addition, the brass synchro (blocking) ring was noticeably worn and shinier than the others. Normally the brass is dull.

The other transmission that I used as a donor had the differential (spider) gears broken, probably through an attempt at drag racing or spinning the tires on ice and then catching pavement. The pieces of spider gear then lodged between the ring gear and the case just about where the drain plug goes, this caused a 1" hole to be blown in the case and an immediate loss of all the oil. This did not damage any of the other gears in the trans.

Reassembly:

The two halves of the case are assembled without a gasket. This requires an Anerobic sealant, NOT RTV. The recommended sealant is called Hylomar. Thanks to advice from one of the list members, I went to my local Jaguar dealer - Jaguar part number JLM-9709 at $8.70 per tube. Since I did this job, Hylomar has also become available repackaged by Permatex and is much easier to find. The main benefit of this sealer is that it is non-hardening and does not change composition in constant contact with gasoline or oil. Spread it as smoothly as you can, on both of the mating surfaces of the case. It starts out with a very runny consistency but the carrier evaporates almost immediately. It does not harden, so donít worry if it does not look very smooth. It will compress and squirt out as you torque the fasteners, so go easy on it.

There is a small plastic plug called a "breather" that shows up in the parts manual. DMC part number is 103047, page 4/1/1 location 18. This plugs into a small hole (about 1/4". Note that this hole is necessary to allow for expansion of air inside the trans as it heats up. If you just leave the hole open dirt gets in. If you plug the hole you will tend to blow oil out of the seals, probably around the axle flanges. I bought the breather part, it actually appears to be a transit plug that has no vent. According to Rob Grady, he has never seen anything in the hole in the transmission.

Hint - put the gear oil back in before you put the trans in the car. If youíve ever refilled the transmission with the almost 1 gallon of 90-weight through a 1/4" hose youíll know why.

Someone had told me to remove the water pipes. I didn't, having just replaced all the hoses last summer I really didn't want to open the system up again. It would have made it easier to get the trans back in but was not really necessary.

I made a couple of guide pins by cutting the heads off of two long screws of the size that hold the bellhousing to the engine. This worked great and helped line everything up. An old trick from working on Chevys. Just don't make the pins too long, about 3 1/2 inches. You'll need a clutch alignment tool. I used the input shaft from the donor trans for this, but the tool is available from Grady. I'm sure there are Volvo tools that would work too, I didn't look. 

Reattaching the lower flywheel cover plate with all 4 screws appears to require that the engine be lifted. I just put in the two outer screws. I've been told that a lot of people just leave the plate off completely. Mine was in place with one screw when I took it apart.

Bleeding the hydraulic system is still a pain in the neck, although having done it a few times I can do it in about ten minutes now instead of the 2 hours it took the first time. (Hint - take off the engine cover). And I'd really like to punish the designer of the shift linkage. The trick on that is to install the upper part (the cable attachment) BEFORE installing the crossgate linkage (opposite of the removal instructions above), otherwise it is impossible to get a socket on the middle bolt.

 



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