Brakes Question

Somebody may have put the wrong fluid in the master cylinder. Easy way to tell is to remove the cap and see if the rubber on the inside of the cap is deformed as if the wrong fluid is in there it will deform the rubber on the cap....or the Proportioning valve in the MBC could be going bad...or the parking brake could be on....

Ok thanks.. I was told by the dealership that my master cylinder needed to be replaced but I was also told by elsewhere that the master cylinder wouldnt cause the brakes to lock up. I will have what you suggested checked out

GA to you. As an apprentice i rebored master cylinders, so i can say i know how they work. I read your replies in the Gremlins thread and i agree with you on this one. My car owner manuals say that the brake fluid must be replaced at 2 yearly intervals, i guess we know why!

To the O.P.; Brake fluid absorbs moisture from the air and this reacts with the rubbers and creats gunk that stops components within the master cylinder from working. By putting direct force on the pedal it is difficult to feel the gunk trying to stop the components from moving but the springs trying to return the components to the rest position can struggle to do so. This results in the brake line remaning somewhat pressurised. For a full explanation see Andys' comments in the Gremlin thread.

The wrong fluid? Unlikely. DOT3 and DOT4 are all you will find on the parts shelves of an auto parts store. The rubber inside the cap changes shape to keep air out of the system, effectively moving down as fluid is displaced from the master cylinder. COMPLETELY NORMAL. The parking brake works on the rear brakes, not the front brakes. Take it to a brake specialist. I had a similar problem on more than one F150 from the 1980s, front brakes sticking. I replaced the calipers and pads and the problem persisted, so I changed the master cylinder. Still did it. Solved the problem by selling the truck and never bought another F150 from the 1980s. In talking with brake specialists, this wasn't uncommon for those particular vehicles. I figured I had wasted way more time than the truck was worth (to me). Most mechanics will charge little or nothing to diagnose the problem. You can then fix it yourself if you want to.

If you think that no one ever adds motor oil or transmission fluid to a master, why do you think the aftermarket has started to sell just the rubber covers that go under the master cylinder cap?

You've got to be kidding!

What do u think Lyn?

I think it's deja vu all over again: Self Applying Brakes - Ghost or Gremlins?

And that is redundant again!

It might be your master cylinder but I would first investigate if your brake calipers have seized. The pads will be lightly dragging on your disk while everything is cool. However the slight drag the pad puts on the disk heats pad and disc so they expand and more drag is created.

Regardless of the root cause of your brake problem, this is a very dangerous condition. Your brakes can suddenly catastrophically fail by locking up one to four wheels or suddenly release the drag by permanently removing all braking capabilities while your foot is hard on the accelerator. Get this fixed by a reputable shop quickly.

Thanks for the advice since I have already replaced my callers and brake pads my next step will be the master cylinder and brake booster? Wish me luck!!!!!

NO!!! Stop it!

Figure out what is wrong, and fix that!

Why did you replace calipers and pads... were they worn, or was that an incorrect response to this issue? Did YOU, in fact, do the work, or have a shop do it?

Locking Calipers or ABS issue ? Without pressing the brake pedal ? Is your ABS system kicking in ? Is it a solid or intermittent braking ? Is it one side or both ? Does the brake pedal go to the floor without touching on its own ? Most problems are usually "loss" of braking power. Only thing that can trigger front braking without driver brake pedal being depressed is mechanical foot pedal problem or ABS kicking in. To force a caliper to squelch on the rotors and create smoke (high rpm I am sure) is difficult. I would also check the power assist on the master cylinder. Depending on your car, there are usually lines that either are connected to a power booster, power steering pump for brake assist. Not sure if that helps but all I could rattle off at the moment- Good Luck !!!

You'd feel the ABS kicking in, a pulsating. It's a digital device, not analog

Hi Folks,i have had this occur after fitting Pattern parts on Motorbikes,without enough Free play between the Piston and Lever the system begins to Pressure up.I think this is caused by fluid not returning to the Master cylinder because of stroke length but the result is the same,after a short Distance the brakes go on harder and harder until it's futile.Maybe manufacturing tolerances or over eager assembly workers thinking less free play = Sharper Brakes may be responsible.So i would go for seeing if their is any play it 's usually small but .5mm too much can make all the difference .

Thats a good description of the problem.....exactly what happens.

One possible problem is a collapsed rubber hose. I had this happen to me once whereas when I pushed the brake pedal the brakes would apply but not fully release. After the vehicle sat for several hours the pressure would bleed off and release the brakes.

Good thought, but the hose issue usually only happens to one side. To have two hoses fail at the same time, and in the same manner would be very odd.

Very true.

GA.

You badly wanted to award that GA at some point, didn't you?

I don't know what you are talking about.

Just to bring attention to an additional problem that you may have. If your front brakes have been smoking, there's a very real possibility that you now have warped rotors and damaged seals on your calipers.

Once the initial problem is rooted out, I'd have the entire braking system checked out. Brakes are about the single most important feature on your car...............they need to be in perfect working condition.

And check the wheel bearings, too.

Well put, also damaged bearings are possible..... Lyn was first!!!

Thanks Andy. And thanks for not yelling at us. Apparently if lyn and I show any concern for the safety of the OP, we turn into egotistical losers.

I'd explain, but it's not worth wasting your time.

Yes, we know, but, I owe you one.

Has the master cylinder been separated from the booster recently?

If so, perhaps while they were disconnected the 'finger' protruding from the booster which pushes on the piston in the master cylinder was adjusted in length - it is adjustable - if it has been lengthened - ie screwed out - what you describe will occur.

I made that mistake once years ago and immediately adjusted it back - the problem went away.