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TR4/4A Early TR4 - Front Brakes



I now have one of the front brake calipers apart. I know that you're not supposed to split them, but that is the only way that the pistons were going to come out after decades of nil use. Also, I am not going to trust the condition of the 44 year old seal between the 2 halves; Moss shows that they have them in stock. The 2 pistons have badly rusted where they were exposed, but all the "hidden" areas look to be in good condition.

So to today's questions:

1 - Has anyone split a caliper and succesfully put it back together without leaks? If so, what torque values should I use?

2 - Both Moss and TRF show replacement pistons. TRF state that they make their own from Stainless, don't know about Moss. Anyone have any experience with either of these, or others?

As always, thanks for the assistance.


Luke Skywalker
Hi Ian,

Do some searching on the Internet for torque values for those calipers, I don't have the specifics (or maybe someone else here does). I do know there are two different size bolts and each gets torqued differently. Also, be sure the threads on the bolts and in the caliper halves are in good shape, or torque readings will be inaccurate. If you must use tjem to clean up the threads, it's best to use "restoration"-type taps and dies so that the threads aren't overcut on either part, which might make them more prone to loosening.

I highly recommend the stainless steel pistons. I won't use anything else, in spite of the higher cost. The chrome plated ones (original style) go bad way too quickly. Check around for best price on the s/s pistons. (Best guess, TRF or British Parts Northwest).

AFAIK, Moss might be the only source of the o-rings needed in the caliper. One other possibility I cna think of is Pegasus (www.pegasusautoracing.com). I wouldn't use standard o-rings from a hardware store, not knowing how the material will hold up to brake fluid.



Luke Skywalker

I *knew* there was some info out there!

Ya got me curious so using the "Wayback Machine" I looked at the archives on the Buckeye Triumphs website (TR club), where I *thought* I remembered seeing something. They took the data about brake repair off their website, supposedly on the advice of a lawyer who said it was a liability concern.

Sooooooo, I guess I'd better disclaim this by saying "use this info at your own risk and with full awareness of the potential consequences"! Brakes are an important safety related item and should only be serviced with great care by someone familiar with and trained in their function and repair. After the car is reassembled, it needs to be test driven carefully and then inspected to be certain all braking functions are working properly!

https://web.archive.org/web/20030302163140/www.buckeyetriumphs.org/technical/Brakes/Front/Front.htm has an overview of front brake repair and rebuild for TR6, but it's not much different for TR3A through TR250/5.

The author of that article states he torques the 3/8" caliper bolts to 40 ft lbs and the 7/16" bolts to 70 ft lbs.




Thanks for taking the time to research this and also the rear brake response. I always wondered where the Buckeye info was hiding. Your comment re. the stainless pistons makes sense, but I wasn't sure how well the TRF ones were machined and finished.
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