Transmission Refresh (2026)

This is the five-speed transmission that came with my 912. I replaced the first-gear synchro parts in 2012 (see Continuing Restoration). At that time, I didn't touch the higher gears, as they looked good, and I was reluctant to do extensive work on the box unless it was clearly necessary. The first-gear synchro replacement was a success, and the transmission worked well for many years. Eventually, however, second gear started grinding occasionally on upshifts as well as downshifts. It's the kind of problem that many people would ignore until it got really bad; then, they would finally remove the box for repair and discover that many more parts were worn. I'd like to avoid that experience.

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Here's a CV joint and axle. I put new boots on both axles in 2012, but by now they are worn out. That's mostly from age, not use; the joints themselves look good. Black is the normal color of the molybdenum grease I use; it isn't dirty. I cleaned the CV joints well and replaced the boots. They were relubed, of course, before going back onto the car.

The axles were removed before the engine and transmission. That isn't strictly necessary for the transmission removal, but it gets them out of the way.

The engine and transmission must be removed together. Just as well, since I wanted to repaint the engine sheet metal. Also I expected that some other cosmetic work would be necessary, especially the rusty exhaust tubing. The rust is inconsequential from a performance and reliability standpoint, but it's profoundly ugly and virtually cries out for refinishing.

I got a fancy transmission jack to help with the engine. It was also useful for my Triumph's transmission work. The transmission showed some oil leakage; it appeared to come from the speedometer drive, a common problem. I eventually found a mangled o-ring in the speedometer drive, which probably was not inserted correctly last time I worked on the box.

The clutch still looked pretty good. The thickness of the friction material around the shallower rivet heads is the wear indicator, and I'd guess it's still about 60-70% of its thickness when new. If the clutch was nearing the end of its life, this would be a good time to replace it, but it clearly has plenty of mileage left. Replacing it, when the time comes, isn't a huge job, but a new clutch kit for this car is something upwards of $500.

On the left, below, is a close-up of the second-gear sychro assembly as it came out of the transmission. You can see a lot of spalling along the surface of the synchro band; a little unusual, at least in my experience. On the right is a picture of the same synchro in early 2012, showing no sign of that spalling. The car has gone 12,000 miles since then. The good news is that the synchro hub's teeth (AKA dog teeth) are perfect. If I had waited longer to fix the problem, they almost certainly would not be. It's a $150 part.

This is a good place for a discussion of synchro wear. The synchro is essentially a conical clutch, consisting of the slider and the edge of the band farthest from the teeth. There is a fair amount of slippage where the slider contacts the band, so that edge experiences the most wear. The other side, under the dog teeth, slides back and forth only about 1 cm, so it wears differently, losing metal only under the teeth and sometimes forming a groove at the tooth edge.

The two pictures below compare the old and new second-gear synchro bands. An end view of the band shows how the side that contacts the synchro slider is worn, causing the central dome to appear to have moved toward the dog-tooth side. The slider side often becomes shiny from wear. The tooth side has been abraded a bit by the dog teeth, but no groove has formed yet.

Bands that exhibit those characteristics--a groove and/or shininess--must be replaced, as those are a sign of significant wear. But that degree of wear isn't evident here. So, except for the spalling, this band actually shows only modest wear. The spalling is a greater concern and is the most likely cause of the occasional grinding.

It's a dirty little secret of all high-end cars that high parts prices often motivate the reuse of parts that normally would be replaced. Many rebuilders would continue to use this band after flipping it over, so the less-worn edge faces the synchro slider, giving it a few thousand more miles. I don't think that's a good practice, but it's done regularly.

Interestingly, the third-gear band looked about the same, but it was still working normally. I suspected that it would have developed the same behavior in short order, so I decided to replace it. 4th and 5th were good, but they seemed to show early indications of the same problem. I took a big dose of Fukitol and shelled out another $180 for new 4th and 5th synchros as well. I left first gear as it was, since it was replaced only 12,000 miles earlier and it still looked virtually new.

Why did this corrosion occur? I don't know for sure, but I suspect that it is simply a consequence of age. The coating on the synchro band has changed over the years, evidenced by a change from a black material to the light gray of the newer bands. Presumably the new material is more resistant to this kind of wear. The older four bands clearly are made of the old material, and they may even be original. They have been sitting for decades in oil that may not have been replaced as often as it should, becoming corrosive from oxidation. In any case, the box now has five new bands, and it should be healthy for a long time.

The teeth on the slider looked very good, too. The two pictures below show the two sides of the 2-3 slider. The 4-5 was just as good; no surprise, as it gets less wear than the 2-3..

The slider's teeth have a depression in the center and a dome near each point. The domes often wear down as the slider is used. As with the synchro hub, the teeth should be sharp. Rounding of the teeth or wear-down of the domes is cause for replacement.

The completed gear stacks and a close-up of the 2-3 gears. The shifters have not been installed yet.

The 4-5 gears and first gear. In any transmission, 4th and 5th gears get the least wear; 2nd probably gets the most, as it is the target of frequent downshifts. The first-gear synchro band and tooth ring (below right), replaced in 2012, show no visible wear.

Below is the finished gear stack with the selector hardware installed. The selector forks had negligible wear.

I checked the pinion mesh with gear-marking compound. With 13 mils of intermediate-plate gaskets, it was fine. I removed the differential assembly for inspection and cleaning, and to make it easier to clean the case.

The yellow gear-marking compound is simply a dyed grease. I wiped most of it off, but any remaining grease does not contaminate the gear oil.

Finally finished. Here is the transmission, all buttoned up and ready to go into the car. After it's in place, I will fill it with Swepco 201 lube. For the CV joins, I will use the same Swepco molybdenum grease that I have used previously.

Before reinstalling the transmission, I spruced up the engine and engine compartment. I removed the engine sheet metal, cleaned and painted it, and cleaned the engine.

I took advantage of the good accessibility to adjust the valves and clean and regap the plugs. (The plugs had only 1500 miles on them, so it seemed silly to replace them.) The cylinder heads are remarkably clean; an older engine usually has some degree of oil staining. But this engine has only 16,000 miles since its last rebuild, and I've changed the oil frequently.

I also derusted and repainted the exhaust system and cleaned the carb bodies and intake manifolds. I used an electrolytic process to remove the rust after first separating the muffler from the exhaust piping. I painted the pipes with high-temperature ceramic paint and the muffler with engine paint. The last time I did this, the paint flaked off, probably because I didn't derust the pipes adequately. I'm optimistic, if cautiously, that this time it will work better.

Finally, time to reinstall the transmission onto the engine.

I replaced the three boots and a short piece of fuel line in the engine compartment. Cleaned it a bit as well.

Reinstalling the engine and transmission combination is straightforward but a little fiddly. It requires care to avoid damaging anything.

Some pictures of the reinstalled engine and transmission. I think it all looks a lot nicer.

The new firewall boots are shown below, with the repainted and cleaned transmission mount. Below right, the repacked CV joint and new boots.