TR6 TR6 brakes failing

Thankyou for reading my post. I have a 1975 TR6 that I don't get to enjoy as much as I would like. I have had it out for a couple of long rides this Summer and each time after about 30-45 minutes of normal driving the brakes become soft and progressively fail. I can pump them up to get myself to a slow stop but the pedal goes all the way to the floor. After it sits for 30 minutes I can get back in and the pedal is firm again and they work for a while and the process repeats itself. I have a new master cylinder (2years old) and both resevoirs are full. The vacuum assist hose from the intake manifold is new and conected properly to the booster. There are no apparent leaks at all four corners nor in the engine compartment. The car does not pull when braking (when their working). It makes me nervous to drive of course and the problem is if I take it to a mechanic the brakes will probably work fine when he tests it. It would be helpful to have some input from experts to help guide me when I go to the mechanics. I use Castrol DOT3 fluid, the car is garaged and covered when not in use. Any thoughts would be greatly appreciated. Thanks.

Sounds like you have something hanging up, maybe the emergency brake. Things are getting hot, your brake fluid boils and in 30 minutes it's all cool and normal again.

Sounds like the master cylinder is failing. They have a 100% failure rate and 2 years sounds about right for an off the shelf new master. On a brighter side, since the system is not leaking, it may just be some trash or FOB in the tip over valve.

Is your brake fluid perfectly clear or is it dark in color at all?

My impression is that the fluid is a little darker than I recall as new. If the seals in the brake cylinders are bad would this show up in the resevoir or does this more likely mean seals in the master cylinder? I don't see any particulate matter in the bottom of the resevoir. Would excessive heat "burn" the fluid into a darker color? Thanks for all the input.

I just recently did my whole brake system over in my Spitfire. The brake fluid was dark, which I always attribute to deteriorating rubber seals in the master cylinder. Since everything on the car has been 30 year old OEM parts, I figured the brake fluid must have been DOT 3. Dot 3 I have read is not good for British Automotive braking systems.
I rebuilt my master cylinder, replaced both rear wheel cylinders, front and rear brake pads and shoes and completely flushed and refilled with DOT 4 synthetic fluid. I was out all day today driving rather hard on the brakes and they never changed. Nice firm, strong pedal all day. If you are mechanically inclined, you can get away with all this for about $200. Rockauto.com has all the parts at very reasonable prices. Actually the best prices I found anywhere and the shipping is incredibly fast.

This is just my 2 cents and others may offer a different opinion.

Stirkle said:

I just recently did my whole brake system over in my Spitfire.... Rockauto.com has all the parts at very reasonable prices. Actually the best prices I found anywhere and the shipping is incredibly fast.

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Just curious: who is (are) the supplier of the various components you got? Lucas/TRW? Delphi? Repco? other?

I nearly forgot. Welcome to the Forum.

I think that you may want to look into replacing the seals, if not each of the components and possibly switch to silicon fluid.

Andrew Mace said:

Stirkle said:

I just recently did my whole brake system over in my Spitfire.... Rockauto.com has all the parts at very reasonable prices. Actually the best prices I found anywhere and the shipping is incredibly fast.

Click to expand...

Just curious: who is (are) the supplier of the various components you got? Lucas/TRW? Delphi? Repco? other?

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The 2 rear wheel cylinders and new shoes (not re-man) were Beck-Arnley, the master kit was a Girling packet inside a Dorman box. The front pads were no name plain box and the synthetic DOT 4 brake fluid was Prestone from Autozone.

vettedog72 said:

Sounds like the master cylinder is failing. They have a 100% failure rate and 2 years sounds about right for an off the shelf new master.

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Does this include TRF new girling units, which replacement is the best, is rebuilt better than new--???

vettedog72 said:

They have a 100% failure rate and 2 years sounds about right for an off the shelf new master.

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Wow, that's almost unbelievable huh?

Hi I was just passing by and I noticed you were using DOT 3 fluid that is a no no. You might first try flushing the system and refilling with Castrol GTLMA Dot 4 fluid. I am not fond of synthetic brake fluid and neither are British cars--Fwiw---Keoke

Allan
I am thinking of the OEM's and OEM replacements. I would hope TRF has some good, regular duty, long lasting masters. If I had a master that needed service, I would not get a new cylinder, I would have it serviced by Apple or White Post. I have had work done by both of these companies and they made a purse out of the sow's ear as far as i am concerned. The cost is not much of a factor; the rebuild is less expensive by about $50.

Frankly, I never had a master that acted as the original poster described; my presentments were LEAKS of the paint remover that is also called DOT3 brake fluid.