Hi!

i have a brake issue with my 2004 2,5 L AWD DSC.
the brakes are sticking after a while driving. Often after 15-20 mins. I have changed head cylinder and gone over all calipers. When i loosen the vacum hose from the brakebooster the brakes release. I'm still thinking its the abs-unit. The brakebooster should not make the brakes stick? Pls help! Anyone have any ideas?

Kindly,
Johan

 

I recently posted about a similar problem, only disconnecting the vacuum line had no effect. In researching the forum, it was reported that sometimes, when fitting a new master cylinder, it doesn't release all of the way when you take your foot off the brake which doesn't allow the brake fluid to flow back into the reservoir and the brakes stay pressurized. There is a push rod from the brake pedal to the back of the master cylinder which is adjustable. You can access it by removing the master cylinder and having someone sit inside the car and push the brake pedal to the floor. You would want to use a 7mm socket on the end of the rod and turn it to the right, holding the lower part of the rod that it's threaded into. This will shorten the rod which might cure the problem.
I've also heard that the return spring in the brake booster can be a problem. No first-hand knowledge though.

 

thanks a lot for your answer!
i have tried this to, adjusting the rod in the brake booster. With no luck unfortunatly.
The problems accured after a brake line replacement in the rear(both sides). The guy who did the job said that there was problem bleeding the brakes after the replacement but he got the job done somehow. After that the brakes intermittent lock up. The brakes somehow build up pressure. And after a while(when the discs get very hot) it loosen up. When i disconnect the brakebooster from the vacum line, the pressure also release. When i drive without the brakebooster(hard to brake) the brakes never build up pressure.

I have bought a second hand brake booster and abs unit(master cylinder already replaced). But the more research i do, i only get more and more uncertain what the actual problem is. And the abs unit have to be re- programmed after installation as i understand?

 

I don't believe that the ABS unit has to be programmed, just make sure that it has the same Bosch part number or you'll create a new problem. I read a post where someone said that it could be air in the system, probably near the calipers. When they heat up, the air expands and pressurizes the system; about as good a theory as any. I tried adjusting the brake booster rod and shortened it as much as it would go with no luck. One thing I noticed is when you put the back of the master cylinder into the booster, it doesn't sit flush, even with the rod adjusted all the way in. Right now my brakes are marginal because of what feels to be air in the system. Pressure bled it twice and still have almost no pedal with the engine running. I used to be a mechanic in another life and bled out many clutch and brake systems, but never had so much trouble as I've had with this car. Probably been through a gallon of brake fluid. Planning on taking it to a mechanic in my area and see if he can cure the problem. Good luck with tracking down the sticking brake issue..

 

I dont think its air, because when i disconnect the vacum line from the brakebooster the brakes never build up pressure. I drove for a month without the brakebooster and never had this problem. I just cant figure out why it has that effect. How the brakebooster intermittent lock up the brakes🤔. Thats why i go for the abs unit. The numbers match so i will give it a try. I tried to drive disconnecting the abs unit but then dashboard went crazy. Abs lamp, DSC warning, gearbox fault, engine lamp etc...

 

In re-reading your posts, our issues are more similar similar than not. I had the mechanic replace all four brake lines and the left rear caliper. He was following the traditional two-person bleeding method and could never get a good pedal. After taking the car home, the sticking brake problems began. Having once been a mechanic myself, I purchased the following:

• A Motive pressure brake bleeder
• An extra two quarts of Bosch DOT-4 brake fluid
• A kit to bench-bleed the master cylinder .

I bench-bled the master cylinder and pressure bled the entire brake system. Better pedal, but brakes still sticking. After more researching on the forum, I found out that I still was not bleeding them properly. Apparently if you don't position the catch container above the bleed fitting it will suck air back in. Just purchased to Motive catch containers specifically made tor that purpose that can be attached above the caliper. I'm planning to go out over the weekend to give this a third try! After that, the car's going into a new shop I'm trying out to have the front wheel bearing hubs replaced. If the problem still persists by then they're going to address it ( Ihope).

Are we having fun yet?

 

When this problem is solved i will celebrate! It's been a year since the brake issue began..
Yes maybe it is air that messes things up. I follow your advice and bleed the brakes once again before i go for the abs unit.
if you dont want the bleeder screws to suck air use a hose that fits tight on the screw!(transparent so you easily se airbubbles.) The other end in a bottle. I find this way very easy, you can bleed all by your self the old way.

 

I've been using 1/4-inch clear hose which seems to fit the bleed fittings fairly tightly. I also spread a little grease on the bleeder threads to seal them up from the looseness in the bleed fitting to the caliper when the fitting is open. The pressure bleeder works well and keeps a constant pressure on the fluid in the brake fluid reservoir and allows you go around the car doing one at a time, stopping occasionally re-pressurize the system. I'm making my final attempt this weekend and will report back.