Beck TD, Part 49: Transmission Rebuild

"I'll always remember my first transmission rebuild..." said no romantic songwriter ever. But I suspect it's true, for the same reason you remember your first true love. The joys, the sorrows, and most of all the memory of your boneheaded mistakes stay with you.

But my first is done, and it works well! The story is one of perseverance over setbacks, which makes the eventual success even more sweet. After all the study detailed in Part 48, I was very confident that I could reassemble the trans in a couple of hours. So much so, I asked Troy Nace to help by removing Beck's interior while I was finishing the rebuild. He did so, and then he and I removed the problematic trans in the car. I was just sure that we'd be driving around by the end of the afternoon.


The rebuild started with prosaic pressing of new bearings into place:

Easy stuff, except that something always happens. In this case, when I pried the old seal out of the front extension that goes around the input shaft, it didn't all come out. The metal shell stayed behind, precisely sized to fix tight, and have nothing at all to grab. It took several minutes of careful work with a tiny punch and a brass hammer to tap the shell away from the housing all the way around. After that, I could grab it with needle nosed pliers and pull it out.

When learning how the trans works, I spent a lot of time playing with the assembly of the synchronizers. That was the only part that wasn't carefully detailed on the videos referenced in Part 48, and it is extremely fussy to keep everything aligned. I figured out a method that worked well, and I'll detail it for myself should I ever do it again, as well as for others trying to get it done.

Here are the parts of the 1st-2nd synchronizer, which mates to the spline in the middle of the main shaft. There is one more brass synchro cone not shown. See the two semi-circular springs? Those need to be installed in a particular orientation, such that the hooked end of both springs are in the same dog, and they go different directions.

My spacially challenged brain couldn't keep that orientation straight as I flipped from one side to the other. I finally came up with a simple mark, made with a Sharpie. It should align with one of the dog holes, and the line on each side shows which way that side's spring should go. The mark is visible in the depression for the shift fork.

Here's the setup: put the synchro cone on the bottom side, carefully aligning it with the dog holes. Then drop the dogs in place, and refer to the mark to set the first spring. Add the second cone, flip the whole mechanism, and temporarily remove the first cone to insert the other spring in the direction indicated by the mark. In the right hand picture, you can see one spring in place in the dog.

I confidently assembled everything, and after I drove the shaft into place for the layshaft, the trans was locked up and wouldn't rotate. I tried all sorts of things, and with Troy's help, disassembled and reassembled the trans about 4 times that afternoon. No joy, and I glumly went home to consult the experts.

I had actually had an idea, because I realized that in Part 48, I had called out an incorrect orientation for one gear. But, when I disassembled again the next morning, I found that I had installed it correctly. I had only blogged it wrong! I kept looking, and finally realized the problem. I had used the procedure from the video to press the bearing on the main shaft, using the tail flange to press it in place. It turns out that wasn't enough, and the bearing wasn't fully seated. There was enough of a gap to create a bind.

I found just the right piece of pipe to reach down into the rear bearing housing, and used the 20-ton press to seat the bearing. Back on track! Now I had to permanently install that rear flange, and Jake R. had warned me that it was often a press fit. I had to put the entire trans into the press to get that flange seated.

After doing that, the trans was stuck in 4th gear. Once again, I pondered... and tried putting the washer and nut on that rear flange. Sure enough, that drew everything together and freed up the input synchro cone.

Everything was free, and I could with difficulty get the trans into every gear, but I wanted to check it further before putting it back into the car. I devised a crazy test fixture that worked very well, using a special electric motor with a gearbox built in to reduce the speed to 150 RPM. That's slow enough that I could easily see and evaluate.

First, I made a simple bracket to hold the trans in place at the rear:

I needed a way to marry the motor to the input shaft in the trans, and for that I attacked a dead clutch disc with an angle grinder. When it fell apart, it yielded the splined hub at the right:

At the band saw, I cut off those protruding ears, leaving the inner hub. Now I needed a shaft, and I found one in the junk box. It was even drilled at one end to allow clearance for the input shaft's nose. I drilled the other end the diameter of the motor's shaft:

Once that was done, I cross-drilled and tapped two holes for #6-32 brass screws to hold it to the motor shaft. Those screws are so small and soft, I knew they would shear if something bound up, protecting the trans from harm. I also spent some time making an aluminum fixture to hold the shaft in perfect alignment with the hub.

With everything lined up, I tack welded the shaft to the hub, and my fixture was complete. Here it all is, spinning the trans. For this initial run-in, I used 30 weight motor oil, which is lighter than the eventual gear oil.

I carefully worked the shift rods to select each gear, After convincing myself that all was well (and taking a good chunk of skin off one knuckle,) I reinstalled the shifter, and then over a couple of days I would occasionally spin the motor and select all forward gears over and over. As I hoped, the new syncho cones quickly mated to the gears, and shifting got easier and easier.

This afternoon, Troy and I reinstalled the trans, and it works perfectly in the car, based on a "test drive" on my EZ-Car Lift. I can't take it out on the road right now, because I don't have any tires on the wheels. That will be another story, but for now... I REBUILT A TRANSMISSION, AND IT WORKS!

One more photo. I went down this whole path because the replacement used trans I bought had a problem shifting into 4th gear. Basically, it wouldn't unless you double-clutched the shift. That's the old technique used before synchronizers were invented, and having to do so always points to a synchro problem. In this case, the 4th gear synchro had a big notch (circled) worn out of it! That's enough slack to basically guarantee that the synchro will misalign the gears 100% of the time.

People rebuild transmissions all the time. I think Jake R. was in his teens when he did his first. But I am inordinately proud of this one!

Continue on to Part 50...