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TR4/4A How to check TR3/4A Trans for wear?


Darth Vader
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Now that I have the trans on the bench to replace the broken taper pin what is the best way to check out the trans to see if it is in reasonably good condition seeing as how it's been sitting for 20 years? What should I look for when shifting thru the gears? What are the obvious signs of worn synchs etc. ? Any related advice would be most helpful.


Luke Skywalker
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From my experience, it is very difficult to assess transmission condition on the bench without a teardown. By removing the shift cover, it will be possible to see the gears and wear patterns but normal wear and excessive wear don't look much different to me. The counter shaft and bearings are a major weak area and remain hidden.
I'd put it in the car and drive it. It really isn't that difficult to remove again if you've got a howl or other issue. If it doesn't, you've saved a bunch of money.


Great Pumpkin - R.I.P
I'm inclined to agree with Tom, but there are a few things you can do with it on the bench.

One is to hook up something to spin it. I use a 1/2" drill motor with a short length of radiator hose clamped to the drill chuck and to the input shaft of the gearbox. Others have mounted a pulley to the output flange and used a belt & washing machine motor to spin it that way. With it spinning, you can go through the synchromesh gears (2-4 on a TR3 box, 1-4 on a TR4-onwards box) and get a crude check on whether the synchros work at all. Not an exhaustive test, but if it flunks you know you've got a problem.

Another is to remove the top cover, push each synchro ring up against its associated gear, and measure the gap between the ring and the "dog teeth" on the gear. Anything less than about .035" indicates a worn synchro ring. (They will still work at .025" but it's best to leave some margin for wear.) Of course, you'll want to have a new gasket for the top cover; but they are reasonably cheap from any of the usual suspects or you can cut one from thin gasket material.

If you are so inclined, it's not terribly difficult to tear the box down enough to remove and inspect the countershaft and thrust washers. This is by far the most fragile part of the gearbox (in terms of excess wear and/or damage being likely) so might be worthwhile if you don't know the box's history. Getting to this point is reasonably straightforward (though you will likely have to kludge something together to get the tail housing off). Check out the gearbox articles on the Buckeye Triumphs and VTR sites. All of the tricky clearance checking and so on only applies if you go further and disassemble the mainshaft.

OTOH if it was working OK when the car was parked 20 years ago, then I wouldn't bother with any of this. I might change the seals if they weren't reasonably fresh when it was parked, but nothing else is likely to deteriorate from long storage.
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