TR5/TR250 a type transmission rebuild for tr250

[vrod]

does anyone have any experience tearing apart and rebuilding the a type overdrive tranny in a tr250 (same as tr6 up to 1972) I would like to tear into it myself, just for the learning experience. The last time it needed work, I took it to a guy who supposedly had rebuilt trannys for one of the top 3 british parts suppliers. Needless to say that the overdrive only lasted about 2 months, when I took it back to him he ended up putting one of his used overdrives in and cleaning out the particles from the damaged parts, now my sychronizers in 2nd and 3rd are making noises again. Any advice would be much appreciated

 

[vrod]

forgot to mention that my overdrive is slipping out under hard acceleration. Maybe the pump is weak, or the clutch in the overdrive is worn

 

[Alan_Myers]

Hi, The first thing to consider is if both the gearbox and the overdrive are original to your car. Do you know for certain that they are?

The reason I ask is that the basic gearbox was used by Triumph in a number of cars and there are many, many variations. There were at least two different A-type ODs, too. Your OD should be the later one, with smaller accummulator piston that makes the OD engage a little more softly. The TR4 and earlier A-type used a larger piston that tends to "bang" the OD into action. In fact, for hard driving, the IRS cars really should have upgraded rear drivetrain to handle the earlier type OD.

Assuming both gearbox and OD are original to your car, that might help simplify the job and finding parts, to a degree. You'll need a good, correct factory manual, plus the OD supplementary manual would be helpful.

To work on the gearbox, there are at minimum two special tools you'll need to buy. The Roadster Factory sells them for about $100 apiece. These are almost essential to taking the gears off the mainshaft, it's an almost impossible job without them.

According the manuals, you'll need 14 additional special tools to work on the OD. However, I'm sure some could be made up or worked around. However, others will be mandatory. I know a high pressure gauge is necessary, for example. The A-type operates at up to 400 lbs. psi.

There are some upgrades possible to both the gearbox and the OD unit. These include things like roller bearings to replace bushings, roller-type thrust bearings and stronger gears or shafts. I don't know all the details. You might inquire at some of the British specialists.

What I'm leading up to is that I have no plans to work on my own overdrive, which will be rebuilt before use. I'm relatively mechanically inclined and enjoy working on cars and motorcycles, have built more than a few engines and some gearboxes, even worked in the service dept. of an auto dealer when I was much younger. But, the OD is a specialty just in itself. I'd rather have an expert who knows these things inside and out and has all the necessary tools and test equipment to do the work, do it once and do it right. That's my opinion. I'm still looking for that A-type "expert" though!

There are some tests you can do to the OD unit, to help find out if the slippage is due to a worn clutch, softened springs or too-low pressure. First check that the filters are clean, that the actuating valve is clear and the oil is correct and fresh.

I think you would be wise to rebuild (or have rebuilt) both the gearbox and the OD at the same time, since they share oil and some of the residue from the gearbox can end up in the OD, and vice versa. At least, if one is rebuilt, the other should be thoroughly cleaned before putting them back together and using them.

Happy holidays!

 

[vrod]

yea, your probably right about finding a specialized professional to do the rebuild and their out there, Quantum mechanics is one that I can think of, I guess when you get burned and you recognize the weaknesses of the standard tranny, I tend to start looking at the most logical solutions like may be converting to the toyota supra 5 speed which has better ratios in the first 4 gears and does not leak oil every where. I tend to drive my car quite a bit compared to most triumph owners so I look at solutions that you can live with every day rather than the purity of the original design.

 

[Geo Hahn]

A few comments --

I don't think there is any particular weakness in the standard gearbox, in fact is may be the strong point in these notably durable cars. I wouldn't walk away from it because of bad experiences with one rebuilder.

If you do decide to go with a modern box here's a useful link to someone with a sound reputation --

https://www.blindmoosefab.com/hvda.htm

Not cheap but then your rebuildable OD gearbox will be of significant value to someone on eBay.

As for specialized tools -- this is yet another reason to join your local Triumph club. Most have a formal or informal arrangement of tool sharing. Given that you live in the absolute hotbed of TR enthusiasts (Ohio) I would expect local club members would be very helpful -- if not with tools and hand-on help then at least with references for competent local shops.

Our local club had a tech session where 2 members rebuilt another member's gearbox while we watched. 2 sessions -- first for teardown & inspection and the second for reassembly when the parts came in. Amazing to see it done so smoothly and quickly though it convinced me that this is a task I prefer to leave to the pro.