TR2/3/3A Aftermarket brake master cylinder 1961 TR 3A

Well, brakes on the TR 3A froze up today, so I guess I need to rebuild or replace the master cylinder? Has anyone had good luck with any of the aftermarket cylinders?
thanks
Tom

I'd do a lot more investigation before assuming the MC is bad. Although it is possible, IMO it is very unlikely.

First of all, try loosening the outlet fitting a half turn or so. If you get a spurt of fluid and the brakes free up, then at least you know the MC was holding pressure. If not, the problem is somewhere else (like maybe the residual pressure valve near the RF wheel).

If the MC is holding pressure, then double-check that the pedal is not holding pressure against the MC, due to a stiff pivot or too-long pushrod. The MC pushrod must be allowed to return fully against the stop inside the MC.

Sorry, no advice on aftermarket cylinders; except the ones I've seen are obviously non-original. I've always just rebuilt the original. For it to hold pressure when it shouldn't, the rod or clip inside the MC must be apart; so you might need to find a donor cylinder to replace them. Only the seals and the little Belleville washer come with the rebuild kits.

PS, this diagram is from the TR4 manual, so it shows the integral reservoir instead of remote. But the MC operation is the same (even the parts interchange), in case you'd like to see how it should work. If you zoom in far enough (look for the magnifying glass), you should be able to see in the upper diagram how the fluid is made free to return to the reservoir, by having the clip and rod lift the 'foot' valve away from the inlet port.

Check the rubber hoses first, they will collapse and hold pressure on the brakes.

Marv

Went out this morning and jacked the car up. The wheels turned freely, so the pressure had released over night. However, when I pumped the brake pedal by hand they locked up again|Where do I start? MC or residual brake valve. Can't remember if the residual pressure valve has been gutted in the past or not. I know I have had it off before and cleaned it!
thanks
tom

Yeh these cars are getting older all the way around. I just recently replaced the rubber hoses on a tr3 I have driven since the early 70s and they did not leak, yet, but they made me nervous. I guess what I am saying is to do a complete brake job; however, I did not replace the metal lines and in some parts of the country that is a good idea. Anymore, I purchase new clutch and brake MCs and put those in rather than rebuild. I often get them from BPNW, but I live close by them, and they have worked well for a few cars and many years. My experience has been that the parts from TRF are usually the closet to OEM, but again I look for sales and would get the best deal on something like that because I think the suppliers are all actually pretty good.

tomnanney said:

Where do I start? MC or residual brake valve.

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The test I gave above is easy and quick. I've even done it on the side of the road (on a Stag) and it did turn out that the MC piston was not returning fully. But letting that drop or two of fluid out was enough to release the brakes and let us continue on from Phoenix to LA. Stuff a rag underneath if you are worried about the escaping fluid damaging the paint. Or, if you prefer, you could loosen the fitting at the top of the RPV. Either way, if the brakes release, the problem is at the MC. If not, it is somewhere else.

I agree with Marv about the rubber hoses, it's happened to me as well. But it seems unlikely to me that all 3 of them failed at the same time. (Assuming that you mean all 4 wheels locked up.)

TR3driver said:

The test I gave above is easy and quick. I've even done it on the side of the road (on a Stag) and it did turn out that the MC piston was not returning fully. But letting that drop or two of fluid out was enough to release the brakes and let us continue on from Phoenix to LA. Stuff a rag underneath if you are worried about the escaping fluid damaging the paint. Or, if you prefer, you could loosen the fitting at the top of the RPV. Either way, if the brakes release, the problem is at the MC. If not, it is somewhere else.

I agree with Marv about the rubber hoses, it's happened to me as well. But it seems unlikely to me that all 3 of them failed at the same time. (Assuming that you mean all 4 wheels locked up.)

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thanks for the replys. it was the MC. I pulled it off today, and the piston was stuck in the end.
the bore looks okay other than some dunk at the end, so I'll rebuild it put it back on. Also going to rebuild the clutch master and the slave while it's down. I appreciate all the responses!
tom

Be exceptionally careful if rebuilding a M/C as it only takes a tiny score in the bore to cause total failure of the system. Stainless steel sleeves give peace of mind.

If only one front wheel locks it's usually that side's flexible hose collapsed internally. Fluid still gets forced through under braking, but there's insufficient return pressure to overcome the blockage and release the brake. The opposite side often follows, so replace in pairs, or in general it's best to replace all three flexible hoses every 10 years.

Viv

vivdownunder said:

... in general it's best to replace all three flexible hoses every 10 years.

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FWIW - at my last replacement the TRF 'rubber' front hoses were out of stock so they offered me the braided steel instead. I would not have gone that route but figured I'd try them.

In my opinion these greatly improved the already very good brakes on the TR3A -- incredibly firm pedal. I still used a rubber hose on the rear as that makes it easy to clamp them off should a problem arise on the road (an option I have used more than once).

Good idea Geo I never thought of that, right on.

I like the "braided SS" hoses as well. The firmer feel helps compensate for the softer pedal caused by using DOT 5. But I've got them all around, since I've never had to clamp off a brake hose to get home.

TR3driver said:

...I've never had to clamp off a brake hose to get home.

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I once experimented with lubing the rear brake shoes with diff lube (thanks to a failed seal). I discovered that (on the set I was using at least) diff lube will dissolve whatever is used to bond the shoes to the steel backing - both shoes were lying in the bottom of the drum. Oh, I was 400 miles from home.

Fortunately it was 400 miles of freeway so front brakes were good enough.