O.B.1

Got my new to me 928 in but on the first drive ,the front brakes would not release. Got a little warm on the front before I realized what was going on. Any ideas where to start to fix problem. THANKS !!!

GlenL

So you jacked the front and the wheels don't turn or don't turn well. A little friction is expected. Hot wheels are a strong indicator, too.

If they're dragging then it's time to rebuild the calipers.

WallyP

Two possible causes include:
- The brake pedal may be maladjusted. If the pedal rests just a bit too far into the cylinder, the rear cup will just cover the tiny hole that allows fluid to flow from the cylinder back to the reservoir. As the fluid gets warm and expands, the brakes will be slightly applied, causing more heat, which causes more dragging, which causes more heat...
- The brake hoses might be swollen internally, allowing fluid to pass into the calipers, but not back. This is pretty unlikely if both front brakes are staying applied.

Mrmerlin

try flushing the old fluid out then road test, you might figure your in for new brake lines new master cylinder and possible a set of rebuilt calipers.
There is a possibility that the wrong fluid was used and thus has swollen the seals in the system if this is the case then a complete system refresh is in order..
Do a flush first, hopefully it is only old fluid
Also consider removing the vacuum line to the booster for a road test to see if the booster is damaged
I suggest to use only ATE super blue fluid mixing in other fluid can damage the seals

karl ruiter

You don't have the specifics of your car in your sig, but I seem recall it is an early S4. So the early S4 front Brembo calipers don't have a dust boot around the pistons. It is just the piston hanging out there in the breeze and a seal inside the caliper. This is the only time I have ever seen such a thing on a street car. I've had two problem related to this which caused the pistons to stick: build up of crud aound where the piston and caliper meet, and pitting of the sides of the piston. Either of the can mean that the piston can come out, but not want to go back in. The first is easily solved by pulling the calipers, blowing the pistons out with compressed air and just cleaning things up. The 2nd is not too big of a deal either as replacement pistons are easily available. After '89 or so they added dust boots.

You don't want to drive it this way as it can overheat the caliper and boil the fluid and you totally lose your brakes. Ask me how I know.

brutus

If BOTH front brakes are dragging it has to be a booster problem so unhook the VACUUM HOSE. If that stops the car from putting on the brakes it is a defective booster or miss-adjustment of the pedal so that the internal switch in the booster is activated. But my money is on it being the booster which is failing.

JHowell37

Are you sure it was the front brakes and not the rear?

Did the pedal feel strange when the brakes were sticking? Unusually hard?

The first thing I'd do is pull the check valve out of the vacuum booster. Stick a drinking straw, or some other semi-rigid object in the hole and try to feel your way to the bottom of the booster. When you remove it, it should be dry. If there's fluid on it, you need to replace your master cylinder. It only takes about 5 minutes to check this, and it costs almost nothing.

Before I replaced my master cylinder, the rears dragged so bad one day, they turned the rotor hats blue, wore a fairly new pad to almost nothing, and almost made my engine overheat.

frustrated

Or a vibration in the brake pedal. Had to strip my fronts a couple of months ago and as Karl suggested a build up of brake dust and crud was stopping the pots retracting fully.

ZEUS+

Disconnecting the booster vacuum supply will only make it harder to apply the brakes. Raise the front end and loosen the master cylinder. If both wheels release, the problem is in the booster/master area. If they are still locked, the problem is with the calipers or flex hoses.

O.B.1

The 928 is a 87 version,got a appointment with a shop to do a total flush and clean up first. Hopefully that will fix ,if not ,plan B . Thanks for all the responses.