TR4/4A TR4 Transmission Question [non overdrive]

[TR3TR6]

I rebuilt a TR4 transmission, replaced the bearings, seals and everything else that showed any wear. Installed it in my TR3A and in worked good for about a year and then it started popping out of 2nd gear. Any suggestions as to what to check or look for? I've looked at the synchro's, and they look good.

 

[JerryVV]

Cracked Top Hat Bushing will cause that to happen.

 

[TR3TR6]

Does the top hat bushing go by another name? Where is that located?

 

[TR3driver]

Aka "bush, 2nd gear". Located on the mainshaft, with 2nd gear riding on it.

They also seem to frequently be sized wrong.

 

[tdskip]

Randall - wrong size as in replacement parts are the wrong size? Any ideas on correct ones?

(no vendor bashing intent, just trying to help)

 

[TR3TR6]

Thanks Randall. That part isn't cheap. I noticed that Moss has a two-piece steel replacement for more bucks. Is that pretty common for that bronze bushing to crack? If the bushing checks out okay, is there anything else that will cause 2nd gear to pop out that your aware of? Thanks.

 

[sail]

I recall some top hat replacements need adjustment to fit the spec for gear float.
An easier one to fix would be if the selector shafts tension springs are too loose.

 

[TR3driver]

Yes, wrong size as in the replacement parts do not fit correctly. I've heard that both from other people, and had it happen to me. The bushes are supposed to move easily on the shaft, and the gear move on the bush. Then the bush is supposed to be slightly longer than the gear. I went through 3 or 4 of each, then finally wound up reusing the old one in one case, and lapping the new one out larger for the other one.

Sorry, no idea on who has the right ones. I got the impression that this is one of those situations where all the parts originally came from the same source, and it's simply luck of the draw whether you get a good one or not.

The top hat breaking was a common enough problem that the factory started using steel instead of bronze in the late TR6 boxes. ISTR they also used the 2-piece steel bush for awhile, perhaps in early Stags.

Excess float on the mainshaft can cause problems, which in turn could be caused by the big circlip breaking or popping out of it's groove. I would also double-check that the alignment dowels between gearbox and engine are in place, although that's not a common problem with TR3s.

Check the TRF TR6 parts book, it has a page on mismatched gearbox components. Friend of mine had a very persistent problem with popping out of 2nd, that was eventually traced to mis-matched components being used by a rebuilder.

I don't know of anything else, but I'm still a neophyte when it comes to transmissions. You could try giving Herman van den Akker a call; although I don't know if he is still willing to talk about TR boxes or not.

 

[vivdownunder]

Occasionally the spring that holds the detent ball into the notch in the 1st/2nd selector shaft breaks, or needs tightening a touch. Check that the selector fork isn't bent and its fixing is secure.

Avoid push/tow starting the car in second gear. The jolt when dropping the clutch is a suspect for broken 2nd gear top hat bushes.

Viv.

 

[sail]

From The Greasy Hands Guide:

"The detents and springs are probably the most important parts in the top cover. If these are not working properly, the transmission can jump out of gear, with 2nd gear being the most common problem."


Greasy Hands Guide Reassembly


I'm no expert but worth a shot, better than taking the whole thing apart again if you don't need to. You can feel this adjustment through the shift lever although you must take the cover off to adjust. Then get a fish scale and measure it. I added a washer with one of the springs to get the correct release. FYI I reused my top hat bushing with a mix of new and existing spacers. Daunting project.

 

[TR4nut]

Thanks Randall. That part isn't cheap. I noticed that Moss has a two-piece steel replacement for more bucks. Is that pretty common for that bronze bushing to crack? If the bushing checks out okay, is there anything else that will cause 2nd gear to pop out that your aware of? Thanks.

I put one of these steel ones in a few months ago when I rebuilt my gearbox for the 3A. Not sure it is worth the price, but I will say the fit was excellent, I had purchased a bronze one and can confirm it had fit issues - couldn't even get it on the gear/mainshaft properly.

 

[TR3TR6]

Thanks everyone, I will report back on what I find problem wise, after I tear into it again.