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

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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.