TR4/4A Speedo Drive removal (non-OD)

[Darrell_Walker]

The gearbox on my 66TR4A (non-OD) is a bit leaky, and one of those places (which think I can fix without removing the transmission) is the speedo drive. On my TR8, this part just pulled out after removing the retaining plate. On my TR4A, I've removed the retaining bolt (that comes in from the top), but I'm unable to get the drive assembly to budge. I've tried pulling on it using the cable nut to give me more leverage, and I've tried to rotate the brass housing that protrudes from the gearbox case, and I can't get any movement. Before I break something, is there anything else I need to do before removing it? Any tips/tricks to removing it? Other than the parts diagram in the manual, I can't find any mention of it. Thanks!

 

[CJD]

That can be a problem to remove. It is a slip fit with an o-ring seal...so once the lock bolt is removed, nothing fancy is holding it in. The o-ring hardens over time and locks the assembly into the tailhousing. And, because of the o-ring, heating is rarely effective at loosening it. The only option is to spray PB blaster over a couple days, and gradually increase the amount of force on it. Start trying to use the cable nut to turn it, then vise grips without damaging the nut threads, and finally a pipe wrench. If you are lucky, it will loosen before any damage is done. Sometimes there is no other way than to ruin the drive, though.

 

[Darrell_Walker]

Success! I wasn't able to get it to budge by trying to rotate it, so I used a pry bar (screwdriver) between the housing and the cable nut, and was able to slowly pry it out. I wasn't able to get any rotation until the o-ring was quite a ways out of the gearbox case, and it fought be all the way out. Hopefully cleaning it up will help in putting it back, because I discovered the retaining bolt goes into a hole, not a groove around the housing, so it will be fun to get lined up. The only casualty was the nut on the speedo cable, it is still functional, but I'll be ordering a new cable.

 

[Darrell_Walker]

OK, next question. I want to change the seal inside the housing as well as the o-ring. It appears that the threaded end where the cable attaches is separate from the rest of the housing, and that the two parts trap the seal inside. There is a very tiny hole near the end that sticks out of the gearbox, but if there is a pin in there I don't see how to get it out, other than maybe drilling. Are the two brass halves threaded together? Is there a pin?

 

[Darrell_Walker]

This diagram on the Rimmer site shows that the two parts do indeed come apart, just not how. One reason I think they might be threaded is that there are two flats just under the threads for the cable nut, and a slot on the other end that would work with a giant screwdriver. But it isn't clear in this diagram if they are indeed threaded or not. And it doesn't show any pin.

 

[Darrell_Walker]

OK, got it apart. After probing around in the little hole, I was pretty sure there wasn't a pin in there. I don't know if it was punched to lock the two parts together, or something else. Anyway, I ran a little drill bit in there just a tap to clean it out. And with quite a bit of effort, I was able to get them apart. The flats on the cap (I found that's what it is called, at least on the Moss site) are 5/8", but I don't have a wrench that thin. But I did have a metric wrench out of sheet metal (came with something or another) that was a close fit, and with some angle iron in the slots on the other end, I was able to get them apart.

 

[Sarastro]

Here's a tip for those places where yo need a thin wrench: go to a bike shop and look for a "cone wrench" in the required size--which will be metric, unfortunately, but you may find a metric size that works. They are used for assembling the bearing cones in bike wheels.

 

[CJD]

Excellent! Normally there would be a pin, but I guess someone had been there previously and already drilled it out. It's a huge win when you can save the drive. Once it and the case are cleaned it should easily slide in and out.

 

[Darrell_Walker]

Excellent! Normally there would be a pin, but I guess someone had been there previously and already drilled it out. It's a huge win when you can save the drive. Once it and the case are cleaned it should easily slide in and out.

Hmm, I don't see any sign in the part the threaded out that there was a pin. Anyway, I'll probably just use a drop of thread locker when I put it back together.