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TR2/3/3A Broken TR3 rear differential


Senior Member
I started hearing a noise from the drive train during accel and coast so I changed out the U-joints. That didn't fix and in fact it got much worse after about 15 minutes of driving. I took the cover off the diff and after taking a long look inside I found that I have managed to break three teeth off the pinion gear! (and it still moves!)

So now I am trying to decide on a fix. The mechanic that I use on non-Triumph (modern) repairs has 30 years experience and he said to not try to put in a new gear set myself and in fact, to not even let anyone locally try it because setting backlash on that old axle is a bear. His recomendation is to pick up a rebuilt rear and and drop it into my car. I looked at the parts and by the time I add in new bearings I am up to about $600 in parts that I don't want to destroy with a bad rebuild.

I know that CAR Components does real ends, how is their quality? Is there anyone else out there who can provide a good solid rear end for under the $1,000 that they want?



Luke Skywalker

Ouch, sorry to hear about the breakage.

I agree with your mechanic, that this might not be a DIY job. But you might ask around some more locally before making a final decision. Many truck repair shops should be able to handle rebuilding that diff, although you may need to provide them with the parts and a manual showing TR specifications and special procedures.

While it's apart, it's almost surely worthwhile to go ahead and replace the bearings and seals, but it sounds like you might already be budgeting for that.

You didn't mention what year TR3 yours is. Don't very early TR3 (and TR2) have rather fragile axles? If that's what's on your car, it might be worth looking for a complete later axle assembly, used but in good contdition, as a replacement/upgrade (you probably know that TR4 won't fit). I'm not sure exactly when the stronger axle design was implemented.

There was also a change in bolt size used to attach the crown wheel to the carrier. It might be necessary to drill your carrier out to the later, larger size, if you you can't find a crown wheel that's tapped with the smaller TR3-size holes. A size change will mean getting 10 new bolts and lock washers, too. Early cars used tab-locking washers, but rebuilds and later cars use regular split lock washers (and probably Locktite).

Shop around for a crown wheel and pinion gear set. The prices advertised by the biggest U.S. TR vendors seem pretty darned high. Just be sure it's a matched set.

You'll have a choice of ratios, too, if you want to make a change. 3.7:1 was typically fitted with 4-speed, non-OD gearbox, and is the most commonly found as well as generally the least expensive. Overdrive cars were often fitted with 4.1:1, which are rather hard to find and usually more costly, but will help acceleration combined with any gearbox. Without an overdrive, highway cruising might call for some pretty high rpms.

Some TR6 were fitted with 3.45:1, which will make for more comfortable highway cruising rpms even with a non-OD 4-speed gearbox, but will cost a lot of acceleration. There are a variety of other possible ratios, but these three are the most common and probably most useful.

If you aren't sure what you have in the car now, there are various ways to tell. Probably the easiest with the diff cover already off is to just count the teeth on the crown wheel/pinion. Pinion should have 10 teeth. CW will most likely be either 37 tooth (3.7:1) or 41 tooth (4.1:1).

A few other tips...

If you go the rebuild route, while it's all apart is a good time to check that the diff vent is clear. A shop will probably do this anyway, but you might ask just to be sure. A plugged up vent can cause leaking seals, and it's tricky to clean the vent on a fully assmebled axle without accidentally dropping dirt and grit inside the unit.

While the car is apart is also an ideal time to replace driveshaft u-joints and have the driveshaft balanced. If you do this, just try to avoid the u-joints that don't have a grease zerk fitted.

At the drive shaft, be sure to use new lock nuts on the drive shaft, especially don't reuse old Nylocks. I prefer to replace the bolts, too, *and* use all-metal self-locking nuts (such as jetnuts) *and* use Locktite. TRF sells a good kit of all the necessary hardware, if that's easier.

If they are still good, the outer axle bearings and seals might be left alone and/or done later as a separate project. They can be removed and worked on easily while the diff unit stays in the car. Just be a little careful removing and reinstalling the axle shafts themselves, to not damage the lip seal inside the axle tube. Watch for the shims, too, that control axle end-float. You will find them between the brake backing plate and the axle tube flange on each side. Mark and keep each set of shims together for reinstallation, but expect to have to check and reset axle end float (by changing those shim packs) after having the diff work done.

Best of luck with your repair!


Luke Skywalker
Not an uncommon problem. My first TR3 (1959) came to me with broken teeth in the diff. Luckily, the guy I bought it from was very good friends with my Triumph mechanic, and the mechanic pressured him to swap the rear axle off his parts car for free. (I payed for labor, which still wasn't cheap!)

As I recall, the TR2 axles were fragile, but towards the wheel where there was a taper. I believe the differential was rather robust, just like in later models.



Best to find a used entire rear axle and swap it out. Cheapest route and should last a long time unless it's from the earlier TR2 with the square axle flange behind the brake drums. Check vtr.org classified or email one of the ebay dismantelers. My $.02 ,PeterK


Jedi Knight
Every one tends to forget that the gearset interchanges all the way through the tr6 line. If you have a non od car consider getting the high speed gearset (3.48) that is still available. On the cheap, a good used tr6 center could make a nice donor for a 3. In fact if you would come and get the one in the corner of my garage and hand me a cold one we would both be thrilled.....
MD(mad dog)


It's not just the carrier and R&P but the labor to properly set it up, and then new seals, bearings, etc that add up the costs. That's why (IMO) a good (complete) rear end is easier to swallow, just the R&R to swap it.


Senior Member
My car is one of those interesting TR 3As that is made up of a mishmash of different cars. Although registered as a '59, with a 33,000 SN, it has a late (post 60,000) body. The rear differential is the new style (round flange), but I have the early 10" brakes!
What worries me about trying to get a R&P set locally is just how touchy they can be to get to run quietly and with a good pattern.
I was planning to have all the bearings and seals replaced while I was in the rear end, so I don't have to go back in again. By the time you add up al those parts you are most of the way to a rebuilt axle.

I am really conflicted about buying a diff. that isn't rebuilt; so far all of the units that I have tried to use without rebuilding have gone away pretty quickly. The diff. is the only part of the car that I have not rebuilt, so I guess it was just time for that to die.

Has anyone bought one of the CAR components axles? I know that Charles usually has ggod parts, but I am wondering if their work is up to the usual TRF standard.



Late pre-60000 3A came with round flanges and 10" brakes - same as on my '58. Your TS33nnn is in the range thta had these originally.


Senior Member
God I love British cars! The very concept of documenting engineering changes seems to have a totally unknown concept to them. Trying to match up my car with a new wiring harness and any of the schematics that I had was one of the more interesting projects that I have ever done. I only let out a little of the smoke from the harness.
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