Thread: Front brakes stay on afte release brake pedal Calipers or Master? Need brake expert.

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Hey guys. I am having a brake problem. My rod sat for a little while but had this problem since I bought it. The front brakes will hold even after I release the brake pedal. If I do a normal stop they only hold for about 3-5 seconds. If I do a harder stop the front brakes may stay on for 30 seconds or more depending on how hard I push the pedal. If I push on the pedal hard they will stay stuck longer.

On my rod I have 4 front calipers. 2 on either side and all 4 calipers are sticking not just one or 2.
Would this be the calipers or the master cylinder? My calipers are a little rusty. I bought a rebuild kit for all of my calipers and new brake lines (flexible) but I am thinking it can't be the hoses or the calipers since all 4 stick.

What do you guys think? Master cylinder? Crud in the lines? Could all 4 flexible lines collapse and keep the brakes on?

Thanks.

Do you have a residual valve between the Mc and the calipers?
Why do you have 4 calipers up front, or do you mean 4 pistons?

what residual valves are you using...ted

Check for "free play" in your master cylinder push rod. Also, could be rotten rubber front brake hoses. They will swell up and not allow the fluid to return.

Got a return spring on the pedal??
Also as John said, got freeplay in the rod???

No I mean 4 front calipers. 2 per wheel. That is how the car came. Stops pretty good.

By residual pressure valve is that a proportioning valve? If not how can I test this part?

Is the best way to check to see if the rod is holding is to jack up the car, push on the pedal hard and lock the brake and loosen the bolts on the master to the booster. If it releases it is the rod adjustment?

Yes it has a return spring and I have tried pulling up on the brake pedal when they lock up and it didn't help. The pedal was at the top of its travel.

It is only the front brakes. Rears are fine.

This is the first time I have ever seen both front brakes lock up. I have had sticking calipers on one side before but never this.

Thanks Again. I appreciate it.

i'd say calipers

Is the best way to check to see if the rod is holding is to jack up the car, push on the pedal hard and lock the brake and loosen the bolts on the master to the booster. If it releases it is the rod adjustment?

Yes that would prove if it is the rod. But I would almost bet that if it was that way since you have owned it as stated,that whoever built it hooked the lines up backwards at the master cylinder.Most cylinders have a residual pressure valve built in them for the rear drum brakes and if the lines are hooked backwards it would act just like your symptoms. Also you don't say if this is a power brake system,if it is,will it do the same thing without the engine running ?
If it'll do it with the engine running and will not with the engine off it might indicate a booster problem. All 4 calipers and/or all 4 hoses going bad at one time is highly unlikely.

Thanks guys.

It is a power brake system. It is a GM master cylinder and booster. I will try to get a pic of it today to show it. It has one large metal rod that holds down the fluid res. cover.

The line on the very front of the master cylinder should operate the front brakes and the rear line should operate the rear brakes correct?

I have front and rear discs, no drums.

Thanks Again.

Greg,in most (not all) the rear chamber serves the front brakes.

Brake drag with power disc brakes front and rear could be caused by one or more of the following conditions:

Booster pin length incorrect
If the pin from the booster that pushes on the master is too long, the master will not return to the correct rest position when you release the brake pedal, retaining a residual pressure in the system. Try shimming the master off the booster about 1/32" and see if the drag disappears. [ basicly what you mentioned above ] If it does, remove the master and adjust the booster pin inward.





A pre-load pressure on the booster
If your pedal linkage binds it may retain a pre load pressure on the booster which causes the booster to apply pressure to the master.

Wrong master cylinder
If you use a drum master for disc brakes it will cause the front calipers to drag. A drum master has a 10 lb residual pressure valve in it that holds too much residual pressure on the calipers causing excessive drag.

Had the same thing on my 68 camaro, replaced EVERYTHING but the front hose's, so about 600.00 later I replaced the hose's and fixed the problem!