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Triumph TR6 - Overdrive transmission Lay shaft

I have a 68 TR250 I rebuilt the transmssion about 4 years ago. At that time I had to replace the lay shaft bearing with a bearing repair kit, the needle bearing had there own outer race that fit into the lay shaft. I run 20W50 oil changed it at least one a year.
The other week I was out driving a lost all for sycro ring in about 1/2 hr. I am assuming the lay shaft bearing have failed.
I look in the acheives and found an artical discussing a racing beaering that can be fitted.
Can anyone give me some information about these racing bearings ?
Has anyone else had a similar problem?
Phil Law

Phil - Most will tell you to check your clutch and the end thrust in your engind rear main bearing. This is well documented in the archives for TR6's.

To get into the archives, you have to join up. It's worth it (free).

As to your gearbox, if the bearings for the lower layshaft (sometimes called the countershaft) have failed after 4 years, I'd be surprised. But if they are the originals, and they are gone, you will need to change them.

The TR-250's and maybe into the early TR6's had the needle bearing (sometimes called shell bearings) like yours with an outer cage design. If you need to change yours I assume the originals are still available from TR suppliers or from a local Bearing Store. To get them out, use a large tap and screw into them till you can get a good grip and pull them out.

If the layshaft and/or the countershaft with the gears on it, have become scored where they run on the needle bearings, all these will need to be changed. If so, I'd go for the newer design. The new ones require a cir-clip to hold them in and the newer open cage don't need to be pressed in. They slide in.

Recently, with a failed starter, did you by chance (bad luck) have the need to jump start, push start or bump start the car going down a hill BACKWARDS when you popped the clutch in reverse gear to start the car? If you did, then it's probably the spacer between 1st and 2nd gears or the one between 3rd and 4th along the upper mainshaft that has broken into about 12 - 15 pieces about 1/4" by 1/4". Most probably the top-hat bushing next to these has broken with the top-hat flange cracked or completely separated.

Drain the oil and check for steel chunks. With a micrometer, measure the thickness of the chunks and if you know the thickness of the ones that were there 4 years ago, this will tell you if these chunks are from the spacer rings.

It could be that you put in a set of bad synchros that were machined too thin. There were about 10,000 rings (or was it 10,000 sets of rings?) that were all machined too thin and if they were close to (or less than) 0.410" thick, they wear out in no time - some have reported less than a year. Others say a week. The new sets have been correctd and measure about 0.440" thick - but some old sets are still in some stock-rooms.

If you look at a syncho ring axially, holding it vertical with the large diameter machined circular face against a flat wall or similar, you will notice that on the other side axially back about 1/4" back, there are some slots and some step bumps. There are 3 short step bumps and 3 longer step bumps that were there when they cast the bronze to make the rings. Measure from the front machined circular face to the top of the 3 longer step bumps. A good synchro ring will be about 0.440" thick from the front flat machined surface to the high step bumps.

If they measure less than 0.410", you have the answer as to why you lost the synchros. Did some stop working earlier, or did thay all "disapear" at the same time?

I re-built my own TR3A gearbox this summer. The overdrive was fine and all is right again. During the last 14 summers (80,000 miles), I have used Valvoline VC211 20W50 VR1 which means "Racing Oil" in my gearbox and overdrive.

Right now, I'm converting an older TR3 gearbox to go into another TR3A. The owner gave me an old dismantled overdrive that had a broken mainshaft and lots of other parts needed to be replaced too. He also gave me a dismantled overdrive from an Austin Healey (I believe).

I sourced a gearbox input shaft and its matching overdrive mainshaft that had come from a later TR3A.

I changed all the bearings in the gearbox as well as the overdrive including the needle bearings that support the lower layshaft and coutershaft. I have just about completed the re-assembly.

Don Elliott, Original Owner, 1958 TR3A
Don Elliott

Phil-In re-reading your post, I think your problem maybe in the clutch instead of the trans. If it is difficult or impossible to shift into reverse without grinding gears, it is probably clutch related. Try jacking up the left rear wheel, shift into any gear (engine not running), depress the clutch, and try to turn the left rear wheel. It should spin freely, if not, the clutch is not releasing. This is very common with TR6s and the cause is worn pivot points in the linkage, broken pin in the clutch fork, hydraulics, and engine thrust washers that have worn. You will find much info in the archieves on the subject.
Berry Price
BTP Price

Thanks for the information.
To anwer some of your questions, there have been no problems with the starter, I lost all the syncros in a period of about 1/2 hr. while driving, each gear drop out in order 2, 3, and then fourth gear.
Its not the clutch as I have already changed the transmission to a space non overdrive transmission, it works great. Just runs a little slower.
I haven't drained the oil yet this is a winter project.
Phil Law

Then you'll have to go inside the gearbox, remove the synchros, measure them as I wrote above and you will know. If they measure about 0.440", then keep looking and maybe you are right that the layshaft ass'y is bad.

Don Elliott
Don Elliott

Having recently rebuilt my tranny and added OD I think that a quick check for any up and down movement in the layshaft assembly will alay or confirm your suspicions. Regardless, I would first expect to find a substantial amount of metalic particulate in the tranny oil...a magnetic drain plug can reveal much.
Rob Gibbs

I want to correct a point in my long discourse above.

With reference to the dimension 0.410" being too small and the synchros should have a dimension of 0.440" ---

This dimension refers (not to the longer tangs as I wrote) but is the distance from the front machined face of the synchro ring to the top height of the three shorter tangs.

I hope this has not caused anyone any grief.

Don Elliott
Don Elliott

If anyone is able to survive the grief up to the point of having the synchros in their hands, I think they'll be OK, Don. I'm sure they'll figure out which surfaces to compare, the ones between .410 and .440. Your explanations really do clarify things for me, thank you for all you contribute to this board, especially the affection you have for the breed.

For some reason, I just remembered reading Henry Manney's (I think that's right, middle initial N?) articles in older Road and Track magazines? He had such a cool, quirky love for the odd British car. Some of them I'd only heard of through his articles. Velocette? Jowett Jupiter? Anyway, cheers!

This thread was discussed between 05/11/2004 and 11/11/2004

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