• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR2/3/3A TR3 Replacement Gearbox

Share this page

RedTR3

RedTR3

Jedi Trainee
Offline
My TR3 has a non-working overdrive (been that way since I got it 5 years ago, not sure why OD is not working) and it leaks oil like a sieve, so a rebuild or replacement is on the horizon. I really don't need the overdrive...

So can this be replaced with a rebuilt non-OD unit? There's a guy on eBay that sells these TR6 units he claims will fit TR3.

Or anyone have a another source for rebuilt units? thanks

<https://cgi.ebay.com/ebaymotors/Triumph-T...=item4cf42b6b41>
 
Personally, I'd pull it apart myself. Leaks are usually just bad seals and/or plugged vents (although a distorted OD adapter plate is another possibility). There is a good series of articles on the Buckeye Triumphs site, and another on the VTR site. Even doing the OD isn't that hard (I just put mine back together last night, and should be doing a pressure test instead of playing on the computer).

Putting in a TR6 box is quite do-able (I have one myself), but it does involve some adaptation and modification.

The box is perhaps 3/8" longer overall, so the rear mount has to move backwards. Easiest way IMO is to elongate the holes in the rear crossmember (but I also had to pound down the folded edge for clearance).

Your gearbox tunnel won't have clearance for the starter bulge on the TR6 box, so you'll need to do some massaging there. Make sure you leave enough clearance, as it will communicate a surprising amount of noise to the cockpit if the tunnel touches the bulge.

Depending on which gearbox you get (TR6 had lots of minor variations), you may have to install longer studs in the back of the engine block. But they can't be too long, or it makes the gearbox hard to install. (Guess who cut them too long the first time, and had to trim them down already in the car
grin.gif
)

You'll probably notice the higher 1st gear ratio, but IMO that is a Good Thing.

If it is a late TR6 gearbox, the speedo drive ratio will be wrong. I don't recall offhand if you can use the TR3 gear, or have to find the early TR6 gear.

And of course you'll need the non-OD speedo cable.

The TR6 shift lever is different, of course, but you can make your TR3 lever work. You'll probably have to drill the top cover, though.

You'll also lose the dipstick, unless you rebuild your old cover with the TR6 components (which also solves the shift lever problem).

Clearance is a little tight between the shifter mechanism and the back of the hole in the tunnel, but it cleared on my cars. Definitely obvious (with the boot off) that it moved backwards, though.

OTOH, I'm sure there are any number of people on this list that would LOVE to trade you a good working non-OD box for your old, worn-out, non-working OD :laugh:

PS, if you are interested, I have the original box from TS13571L, that worked just fine when removed. I'll even deliver!
:cowboy:
 
Hi Randall,

Didn't know that about the TR6 "Bulge"....

I will have to compare the two covers that I have. The one that I am restoring has a TR6 tranny in it mated to the original A Type that came with the car. The parts car was unmodified and had the non syncro box in it. Maybe I will take some pics for comparison.

Cheers,
Tush
 
Later 3A's already have the bulge, Tush, so you should be fine. It changed around TS50,000 (when the later starter came in).
 
Thanks Randall,

Maybe a good idea to remove the box and replace the seals. Can you give me an idea of the number of labor hours required for a decent mechanic to do this?

Also, there must be some "might-as-wells" to consider in the job also

Thanks, Tim
 
Red- I have the OD in my 60 3A...and really love it. Took me a while after restoration to really get it adjusted properly...but now love it! My car has a 4:11 rear end from the factory...and the OD really makes a huge difference. One thing for you to consider for the long run is what having the OD might add to the value to your car...today or some day down the road. Randall is right (again)...you will have a long line waiting to make you a swap your OD for a non-OD tranny! I have seen several non-OD trannys listed recently. Will look around. Gil NoCal
 
If it were me I'd get the OD working, if you really don't care I'll swap you a good regular box for your OD box in the same condition.
 
TR3driver said:
...OTOH, I'm sure there are any number of people on this list that would LOVE to trade you a good working non-OD box for your old, worn-out, non-working OD...
Click to expand...

I'd be in that queue -- got a good TR4 box that I would happily swap for a OD needing work -- but I suppose you've figured out by now that what you've is worth keeping & sorting out.
 
TR3driver said:
I'm sure there are any number of people on this list that would LOVE to trade you a good working non-OD box for your old, worn-out, non-working OD :laugh:
Click to expand...
...and a near-equal number of people still drying out their keyboards after salivating over the prospect of finally getting that OD gearbox for their car!

drooling-5.gif
 
OK, you've talked me into it! I'll start making plans to do this next fall

Now what else should I consider while the Gearbox is out. Probably the clutch and release bearing? (I'm not sure of its age; I've had the car about 5 years now).
 
I would say as a minimum:

New input, countershaft, mid, and tailshaft bearings. New mainshaft snap ring (get a couple in case it gets bent on your first attempt to install it!). Gaskets, of course. New thrust washers for the countershaft.

The retaining screw for the clutch lever is almost always broken...if you're lucky you can replace it without any colateral damage. So at least the retaining bolt. New bushings for the clutch shaft are cheap, while you are there.

New release bearing is a good idea, as is a new clutch disc. New locking plates for the front bearing retainer.

Extras to do a good job...replace the three synchros...look over all the gears, as a couple more may need replacement...if so, that gets into real money. There is a good chance the first gear teeth will be chewed up. New clutch if the pressure plate is heat checked...or weak springs.

The above is for the main gearbox. I am sure someone else can fill you in on OD details.

It sounds daunting...but it is actually pretty fun digging into these gearboxes. Just take your time and don't rush...be ready for surprises...

John
 
tdskip said:
Red - good decision to keeep it and get it working. It will be worth the effort.
Click to expand...
And expense but I agree, swapping for a non-od would have been a mistake. Good luck with it. Tom
 
If you work on the od yourself, the expense is not that bad - of course depending on whats wrong. Quite often its just a replacement thrust washer or two, as well as renewing of the pistons. If so, parts total can be kept in the $100-$200 range.
 
The gearbox itself is not a terrible job to rebuild. I just did one for a TR250, new bearings, thrust washers, seals, bushings, syncros, layshaft, reverse shaft. Total for the parts was around $200 or so. Just make sure you pay attention to how things come apart. Havn't been into an OD unit yet but I've got one sitting at the shop that is completely toasted I may play around with one day if I ever have a spare minute and can find a few of the parts it needs.
 
BRSLimited said:
Havn't been into an OD unit yet but I've got one sitting at the shop that is completely toasted I may play around with one day if I ever have a spare minute and can find a few of the parts it needs.
Click to expand...
"Completely toasted" can be expensive, as practically every component is subject to damage after something breaks. But overall, I'd say the OD is easier to do than the main gearbox. Fewer moving parts, fewer clearances to check and adjust, etc.

However, I believe I have run into a major "gotcha" that I've never heard mentioned before. Nelson mentioned observing erratic high pressure as a result of too many shims in the accumulator spring causing the spring to reach coil bind before the relief port was uncovered. I believe I managed to shim mine just to the point where the port could be partially uncovered, which regulated the pressure at the limited speed I could turn on the bench; but the spring would bind and not allow the port to be fully uncovered, which allowed the pressure to go too high at max rpm.

The kicker is that new accumulator springs don't seem to be available at the moment. I've ordered from 3 different vendors, and apparently all have put them on backorder.
 
My 71 TR6 gear box is being rebuilt actually the last time I had a discussion with my rebuilder the gear box and A type OD is finished. There are upgrades to these gear boxes other than just replacing the bearings and seals, I had an uprated layshaft installed, which is harder. double bearing inside the layshaft gear set, and uprated thrust washers. New reverse, steel bushings, I belive I got that right, also on the OD unit the cone clutch was shipped to UK to be relined with better materials. I read thru articles on how to disassembly a gear box and wanted no part of it, if you have the money I would out source the rebuild. some specialized tools are required and tolerances that must be correct or jumping out of gears can be an issue when its back in the car. just my opinion.

Hondo
 
Another item to replace is the pilot bushing that is in the end of the crankshaft. You will have to remove the flywheel, slide in the new pilot bushing, then put the flywheel back on. Costs a few dollars and takes about an hour at most. Soak the oil-lite bushing in oil for a few days or a week to allow the oil to soak into all the pores in the bushing. The inside diameter of the new pilot bushing will not be waorn and it will guide the front free end of you input shaft to the gearbox in the true center for longer life for the input bearing and the gear just inside the gearbox.
 
Easy box to rebuild. There are a few upgrades as said but I say try doing it yourself!
 
Back
Top