jaybird81

I posted a thread a few days ago about my 81's brakes locking up. I pulled the tires and see no visual leaks of the calipers. the fronts are pretty new and the back are not, but they are not leaking. So I think my problem may be related to the master cylinder or the power brake booster. I believe both to be original. I am willing to invest in a master cylinder to see if it fixes my problem. however if I am doing it should I go for the extra money and replace the booster as well? Is there any sign that my problem could be the master cylinder or the booster? I would hate to swap the master, only to have to take it off again to replace the booster. Any advice would be greatly appreciated.....

Bob Heine

The only time my brakes ever locked up as you describe, it was caused by the rubber brake hoses that connect the calipers to the hard lines.

Replacing the master cylinder and brake booster are fine projects. It is probably a good time to replace those rear calipers as well. It's even possible your brakes locking up will be cured temporarily by replacing the master cylinder because you'll have to bleed the system. The process of bleeding the system will most likely move the chunks of rubber from the clogs in your brake lines into the wheel calipers. The problem will return when new chunks of rubber from the flexible brake lines pass through the fitting into the hard lines again. The rubber chunks act like one-way valves so pressure builds in the caliper when you apply the brake and the chunks hold that pressure quite nicely when you release the pedal. At least that's my theory.

I'm not an expert and as often as not I'm wrong. But quite a few experts have already advised you that the brake lines are probably bad (not leaking bad but crumbling on the inside bad). Starting a new thread probably won't change their advice. You might want to go back and re-read what they said.

It is not surprising that you see no signs of leaking brake fluid at the calipers or flex hoses. The insides of the hoses are crumbling and causing the problem. You can probably get a hint of the problem by bending the flexible lines -- if they are the originals, they should have lots of little cracks by now.

jaybird81

I could see it being the hose if it was one caliper like what happpened to one of the guys that replied to my post. But I had all 4 lock up. Leads me to think it would be a more central problem, no?

Bob Heine

In my case it was a 1974 Fiat X1/9 I bought for my son in 1982. It sat in the garage for several months without being driven while I fixed it up for him. When I took it out for a test drive all four wheels locked up (X1/9s came with 4-wheel disk brakes). I replaced the master cylinder and it stopped fine for about a week. I parked it, waiting for my son to come home and pick it up. The weekend he was coming home on leave, I took it for a test drive just to be sure it was OK and the left rear wheel locked up but recovered more quickly. I swapped the four new lines from my car to his and he never had the problem again.

To be honest, I couldn't tell for sure if one, two, three or all four calipers were locked up. All I knew was that the car was fighting against the brakes and after ten minutes they eased up enough to limp back home. Did you get the brakes to lock up and then jack the car up to determine that all four wheels were locked?

Whenever my master cylinder has gone bad, the symptom is that the pedal slowly goes to the floor after you stop the car.

Like I said, it's not a bad idea to replace anything in your 30ish year old brake system. Do the master cylinder but while before your do the brake bleeding tango, replace those hoses. I put braided stainless flex lines, a new master cylinder and stainless calipers on my '72 almost 25 years ago. Never put it back on the road so now I've replaced the hard lines with stainless, put in a hydroboost and another new master cylinder (even without being used, the master cylinder had rust in it. The fluid seeped out of the stainless calipers so I've changed those from lip seal to o-ring seal.

jaybird81

Bob, I hear ya... I guess I will deffinitly do the hoses as well. The car is getting up there in age and I don't use it that often. So since I am going for the hoses as well, I see you said you went for the stainlees steel, I am thinking about it. Anyone else replace the hoses on your C3 and did you stick with the rubber hoses or did you go for the SS?

rugerm44

Go with SS and be done with it.Brakes are a safety issue and not a place to skemp over a few bucks.Even brand new parts can be defective.I just put on a new mastercyl and upgraded to power brakes.The mastercyl was bad out of the box and it was new not rebuilt.

81_vette!

How do you know where your problem is - between the booster and the master?

I have no braking problems.... but I have a leak under the hood.

I can clearly see fluid is leaking, but am not sure if it is coming from just the master or both. (as both are wet from fluid)

Does the booster itself ever leak?

Apparently the master is leaking and fluid is running down from there... but I wanted to know if the booster was ever subject to leaking.

SanDiegoPaul

There should NEVER be fluid in the booster! Replace the master immediately if it's leaking. Test the booster and replace if needed.

Method:

Depress brake pedal and hold it down, engine off. While brake pedal is down, start engine. If the brake pedal sinks a half inch or so, then the booster is good.

orgsretep8

My 70 front brakes locked up on me recently. I had already installed new calipers and brake hoses when they locked up. I replaced the master cylinder and have not had a problem since.

Indiancreek

If your breakes are not locked up when you begin driving, but lock up later as you drive, the fluid is not returning to the master cylinder when you release them. Could be one or all of them. If you have access to a laser thermometer, when they seem to lock up, check from wheel to wheel to find the wheel/s that are HOT.
If you can get to the bleeder open it and see if the brake releases. If so, I'd look at the hoses. If not the piston itself may be sticking. In either event, I'd at least replace the the caliper and hose in question, if not all, if they are similar in age.
Like the other guys have said, replace with stainless braided hose. If you're using Dot 3 drain the system and replace.
The rubber hoses acctually collapse inside as they loose their strength over time. I make it a practice that whenever I replace a caliper I also replace the hose.

Project80

If fluid can't return to the master because the compensation port or ports are blocked or clogged, this will cause the brakes to stay locked or drag. Have someone gently apply the brake fully as you watch the fluid in the master. You should see a small squirt of fluid appear at one or both chambers.

straub18045

pull the vacuum line off booster, if it does make a noise than it aint working (not keeping vacuum). 'while engine off'

mashinter

It could be the master; it could be the booster. I'd just replace the master and see if that does it.