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 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 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 recoat the exhaust tubing and repaint the engine sheet metal. Also I expected that some other cosmetic work would be necessary.

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.

The clutch still looked pretty good. The thickness of the friction material around the shallower rivet heads is the wear indicator, and it's almost as good as a new disk. If it were nearing the end of its life, this would be a good time to replace it, but it clearly has plenty of mileage left in it.

Here 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. 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 opposite the teeth. There is a fair amount of slippage where the slider contacts the band, so that side experiences most of the wear. The opposite side, under the dog teeth, slides back and forth only about 1 cm, so it wears differently, losing metal only under the teeth and eventually 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 12K miles earlier and it still looked virtually new.

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.

The slider's teeth have a depression in the center and a dome near each point. Those 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 hub were replaced in 2012, about 12K miles back, and the parts still look virtually new.

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.