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Triumph TR6 - Master Cylinder Problem -- Brakes Locking

A couple of months ago I had the master cylinder replaced on my '72 TR6. I didn't know anything about brakes so I had someone who was knowledgeable (atleast from what I've been told by the local Triumph association was, I still have no reason to doubt them) work on them. The trouble is that after about 5 minutes of driving, all 4 brakes lock up and, of course, the engine overheats and dies. The brake pedal is not depressed but it is solid as a rock. The only thing that relieves the problem is to let it sit for about an hour or so and then drive it to the next safest place.

Now, the guy I took it to lives far away and offered to work on it, it's just that I don't want to have it towed all the way over there. I'd rather just see if I can fix it myself and save myself that hassel, but I know very little about brake systems. Are there any suggestion on why this might be happening and are there any quick fixes?
George C.

Hi George

assuming that the MC is now good and was replaced due to pitting caused by moisture in the braking fluid, I would suspect that the problem is that one or more slave cylinders (rear)or caliper pistons are also corroded and are unable to effectivly retract. This is a common problem on any aging vehicle. To prevent such problems in the future, blead out all of the hydrulic systems biannuallly... typical dot 3 or 4 brake fluid is hygroscopic in nature and readily absorbs atmospheric moisture. When brake caliper pistons etc fail to retract the brake pads stay in contact with the rotors or drums causing over heating of the brakes, expansion of the components, and brake lock up. The brake fluid will begin to boil causing a further locking of the brakes, usually identified by a pulsation through the brake peddle.

I suspect that you will need a partial brake overhaul... it is not rocket science and can be completed by anyone who has a will to learn. A few notes: 1. KEEP ALL BRAKE FLUID OFF AND AWAY FROM ALL PAINTED SURFACES! 2. work on one side off the car till complete then on the other so you have a complete intact mirrored model to refer to. 3. Whatever components that are discovered at fault on one side should be replaced on both sides of the vehicle. 4.refer to a manual for correct torquing and wear specs.

Best wishes...wish I was closer to help you out,
Rob
Rob Gibbs

Hi George The first thing to check out is the brake booster or (servo) the chances of all the calipers and cylinders sticking due to corossion and releasing although possible are pretty remote. Somwhere during the replacement of the Master Cyl a part was replaced that allowed the booster to be somewhat opperating during driving conditions, It has to be in that region
Clive Parker

Thanks Clive. The calipers and cylinders are all brand new. I've pretty much gone through an entire overhaul over the past 3 years, so this has been the last stumbling block on my brakes actually operating properly.
George C.

George-I would think that if all 4 wheels lock and the problem wasn't present before the MC was replaced, the MC is the likely culprit. Perhaps the pistons are binding in the bores or the valve at the end of the cylinder isn't allowing the fluid to return to the reservoir when the pedal is released.
Berry Price
BTP Price

I am not familiar with the TR-6 master cylinder set up,(yet), but I have seen this on other cars. The rod that comes out of the front of the booster into the rear of the Master cylinder may be too long. Most that I have seen have some adjustment of some kind. You must allow the master cylinder piston to retract fully in order to expose the bleed off port which allows fluid to excape into the resevoir. It could also be the pedal travel that needs to be adjusted so that there is a slight amount of free play before engaging the booster?
Ed Bell

Ed-I think you are right about the piston not fully retracting and allowing the return port to be uncovered. Unfortunately, the pedal travel or MC pushrod is not adjustable.
George-If you could get the brakes to go into lockup mode, you might try loosening the two nuts that hold the MC to the servo and moving the MC forward a small amount. If the brakes unlock, this would confirm that the problem is the return port being blocked.
Berry Price
BTP Price

I'll give that a shot, I haven't driven her in a month and a half because I just returned from a trip.

A couple of weeks before my trip, the guy who was working on it said that there was some sort of spacer between the MC and I'm guessing the servo that he was unfamiliar with and he thought that that might have been the problem as he had forgotten to put them back into place. He came over and we replaced the spacers with a few washers and that seemed to have fixed the problem for about a week, until it happened again, the day before my trip. I didn't have time (or money) to have it looked at the time, so she has been just sitting.

As I remember, though, when it locked up the last time, I had thought about doing just that; loosening the two nuts that hold the master cylinder, then re-tightening them, but that did not fix the problem this time. The best I could do was let it sit for an hour and come back to it and drive it straight home. I will try again sometime in the near future, unfortunately, going to school full-time, working, and enlisted in the reserves, time is a valuable commodity.
George C.

This thread was discussed between 02/07/2006 and 04/07/2006

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