More Stuck Stuff!

With the transmission out and on the bench, it was time to fix it! The problem was with the shifter, and it is a very common problem with this series of transmissions. The spring-loaded detent pins that center the shifter seize in place, making it very difficult to shift, and also making it hard to find 3rd gear. The fix is "easy" but it requires removal of the transmission. I've already documented how "not easy" that part was, with nearly every bolt seriously stuck. As you'll see, the trans had stuck stuff too!


I bought parts from BimmerDiffs.com, which specializes in the parts and tools needed for this very fix, among other things. They also have an excellent, step-by-step procedure with tons of photos. You can find it on their Guides and Videos page. Since it's so good, I won't be going through the step-by-step. Instead, I'll just show some of the extraordinary efforts required. These are the special tools, called "drifts", to insert all the bushings and caps - you couldn't do it without them:

The basic idea is that you remove the old pins and the bushings they slide in, and then drive new bushings in with the drifts, and then put in the new pins. Easy-peasy, except when the old pins and bushings won't come out. Of course, that is why the transmission won't shift right, so when you're doing this repair they are always stuck.

The procedure document suggested that perhaps you could bend a screwdriver tip and snag the hole at the bottom of the hollow pin and pull it out. No dice. I tried driving a long screw into that hole - the hardened pin just laughed at me. So, back to the Internet, where I found a suggestion to tighten a collet into the pin, and then use that with a slide hammer to get it out. A collet is a sort of expanding device used to hold cutting bits tightly in place. Here's a picture of three from my mini-mill - you can see the slots that allow it to expand, and the threaded hole in the bottom that allows you to put in a bolt to expand it. This style of collet is actually made to tightly hold whatever's in the hole in the collet, but a similar looking design can expand the collet to fill an external hole.

Collets are expensive, and there was no way I was going to use one of mine with a slide hammer! So, I decided to make my own. I made one from a piece of 1/2" aluminum rod. The six photos below show the basic operations:

1. Cut off an inch-long piece.
2. "Face" it to make the end exactly perpendicular to the rod.
3. Center-drill it with a stiff, short bit that put the hole right in the middle.
4. Drill it through with a 3/16" bit.
5. Drill again, all but the last quarter-inch with a 5/16" bit.
6. Tap (cut internal threads) it to fit a 3/8-16 bolt. 

My reasoning was that the ramp left by the tapered tip of the 5/16" bit would allow the bolt threaded into the collet to push the end out, increasing the diameter around 1/8 of an inch.

Then I moved to the bandsaw, and cut the slots to allow the collet to expand.

One more operation: I had to turn down part of the shank of the 3/8-16 bolt I was using, so the ears on my slide hammer would fit over it:

It was pretty satisfying to thread the bolt into that homemade collet, and see the end flare out! I had a pretty official looking arrangment here:

I put it into the pin, and started to tighten. I hoped that friction would allow me to continue to tighten the bolt, but I was wrong, and the collet was too short to hold while tightening. I tried it, and it popped right back out without budging the pin.

So, round 2. I started this time with a 5/8" aluminum rod, the largest that will pass through my little lathe's chuck. I turned the first inch down to 1/2" diameter, and then used the bolt to determine a total length. I didn't even measure it - just held the bolt up and marked. I made it into a collet using the exact same procedure as above, with one addition: I had to drill an additional larger clearance hole from the rear, to a depth of about half the length of the collet, to allow clearance for the bolt shank until it reached the threaded part.

Then, I moved to the mill and milled flats on the 5/8" part, so I could hold it with a wrench. A real machinist has a fixture called an indexing head (or dividing head). It allows the machinist to work on round stock at precise angles. I don't own this beautiful example of a dividing head - I include this Internet photo in case someone is looking for that perfect birthday gift for me!

Since I didn't have one of those floating around, I improvised. I wanted to put flats on the round shank 180 degrees from each other. I drilled a 5/8" (0.625") hole in a piece of wood with parallel edges, and my collet (nominally 5/8", actual measurement 0.629") was a nice friction fit. I milled one side, turned the block over, and milled the other.

When I was done, I had a right nice looking tool:

I used the same bolt as before, held the collet with an adjustable wrench on the flats, and turned the bolt in. I was able to really tighten that puppy down, and bam, bam, bam! It worked great, and in a couple of minutes I had both pins out:

The next step was to remove the bushing that the pins slide in, or in this case, didn't slide. The instructions said to use a small screwdriver to hammer the bushing out, without scratching or damaging the bore. Yeah, right. Those bushings were practically welded in from years of heat and friction. Using a combination of screwdrivers, awls and pin punches, I finally got them both out, but it was not pretty, and each bore had a small gouge where the seam in the collet was:

I cobbled up a flap sander to clean up the bore a little. It didn't remove the gouge, but it at least smoothed off any burrs:

Then I used the appropriate drift to drive in new bushings. The pins fit (one felt a little tight, but would move without binding). The final step was to reinstall the springs, caps and spring clips. Here the instructions had an interesting semantic difference. For the other uses of the drifts, you would "drive" the bushings in. For this, you were to "press" them in. I made a little handle for the drift, and with a good bit of effort managed to press in the caps far enough to install the spring clips. Success!

Of course, I have to reassemble the entire car to know if this really worked, but I am cautiously hopeful. And making the tool that made it possible has given me a pretty good sense of accomplishment!