Help diagnosing brake issue
 

I recently purchased a 1980 SC Coupe, it has an odd brake issue that I'd love some help diagnosing. Here are the bullet points.
-The brake pedal travels down normally about 3 inches then becomes rock hard and won't compress further
-The brake master cylinder was recently replaced
-The brakes are not dragging, and the car rolls easily
-Under heavy braking, the left front tire always locks first

My current thought is that either the BMC was not put in correctly, or there is some kind of binding in the front right calipers that is keeping the pistons from compressing fully. What are your thoughts?

Thanks,
-Tom

Short of rebuilding the calipers. Try bleeding the brakes and use the gold ATE brake fluid.

But before that check to insure BMC, Booster, hardlines and T connectors under the stone guard calipers are not leaking. If you have brake switches, make sure those are properly torqued.

Remember, place a block behind the pedal before you bleed the brakes. YOU DO NOT WANT TO LET THE PEDAL DROP TO THE FLOOR WHILE BLEEDING BY FOOT/FRIEND method. It may damages the BMC.

Jim

DRACO,
Thanks for the reply. I have a sinking feeling that I might end up having to rebuild the caliper anyway. Any reason to do the left one if it appears to be working correctly? I'm about to put the car up for a month or two while I travel for work. I might just bring the caliper with me and rebuild it in the hotel. Time to look at the Bentley Book. Given the symptoms, is it at all possible that the PO's recent BMC install is to blame?
Thanks again,
-Tom

Yes, it is possible for the slow response of the pedal. PO may have not properly bleed the brakes or used incorrect fluid. Pedal should respond at top of the pedal throw not 3 inches from the top

But the imbalance could also be corner balance or wheel alignment related.

A quick and dirty test is. drive her like you stole her and quickly before she cools down. Raise the front and have a helper press the brakes as you spin each wheel and see if they brake at the same rate. Unfortunately there is no load on the wheels but it will give you some guidance as to which is binding or not responding properly. As a control test, do this while she is cold to obtain a gauge of what to expect.

Jim

Yes, you want to do them in pairs if it calls for a Caliper Rebuild.

Rubber hoses collapsed very common.

OK, thanks for the answers guys. DRACO, when I first get on the pedal, it responds fine, and linearly. It's the total lack of movement about three inches in that worries me, and also makes the car damn near impossible to heal-toe downshift. Which in turn makes the 915 transmission a lot harder to drive. Some pressure is getting to the brakes when it gets that hard though, as it's in that rock hard zone that I can get the front left to lock up.

3 inches is a lot of pedal travel. does't sound right.

Our cars thankfully are over engineered for the most part.

It will lock up if allot of load is exerted. However, your situation is not safe. Especially if you AX/DE.

Do the easy stuff first to insure it is done properly then move on to a rebuild/replacement.

My 2 cents.