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Replaced F& R brake pads, brake master cylinder, sloppy brake performance - Printable Version

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+--- Thread: Replaced F& R brake pads, brake master cylinder, sloppy brake performance (/showthread.php?tid=3666)



Replaced F& R brake pads, brake master cylinder, sloppy brake performance - doosky - 05-20-2012

I have an 84 300d which I've been working on since February, I've run into a problem with the brakes.

Last weekend my brake pedal was spongy, so today I put on a reman master cylinder, changed out F & R pads, and while the pedal is firm, the brakes just don't engage how they should. I have to really press down on it to get them to work and even after that the car takes its time to stop, not even close to the braking on my 85 euro 300d.

This car has a vacuum leak, my mechanic hooked up a pressure gauge to the vacuum pump and the needle barely hit 3.5psi, he told me it should be closer to 15psi, so my power locks don't work and I have to manually shut the car off. We checked the vacuum lines under the hood and everything was satisfactory, my mechanic said it could be a bad vacuum pump.

Could a bad vacuum pump be related to the sloppy braking performance?

I was also considering installing new brake lines and flushing the entire system. We bled the system after the new master cylinder was installed, there were no air bubbles left in the system.

The only other issue I noticed with the braking system was when we were replacing the pads, the rear pads were worn down to bare metal, and getting the old pads out wasn't easy. With the passenger rear caliper I had to loosen the bleeder screw in order to compress one of the caliper pistons. There are no leaks anywhere but could I possibly need to replace the caliper?

I need to replace the vacuum pump anyways so I don't have to stall it out to turn it off, so I'll see if that fixes the problem. If not I'll run down the list
* Flush entire brake system
* Replace F&R brake lines
* Replace brake booster

Is this a good course of action or does anyone else have some better ideas, I'd rather not throw parts at it if I don't have to.


RE: Replaced F& R brake pads, brake master cylinder, sloppy brake performance - Hercules - 05-20-2012

Repair or replace vacuum pump First,proper working brakes depend on good vac.May be just faulty ck valves. Recommended to
flush system at least every two years under normal conditions. Brake hoses are due if original,but usually only if cracked,leaking or worn (rubbing) frayed etc. Booster very seldom bad but possible. Easy ck,after repairing vac.step on brake pedal a few times,keep pressure on brake pedal,start engine,after a few seconds pedal should fall a couple of inches and hold,keep pressure on pedal shut off engine,pedal should not rise. Hope the mechanic used a vac.gauge,and was stating inches of vac. lol.
Hope this helps.


RE: Replaced F& R brake pads, brake master cylinder, sloppy brake performance - doosky - 05-20-2012

He was using a dedicated vacuum gauge, and I assumed the reading was in PSI but I guess it could of been inches of vac. Thanks, I guess I'll have to find a reman vacuum pump and will definitely flush the system, hopefully that will do the trick


RE: Replaced F& R brake pads, brake master cylinder, sloppy brake performance - Hercules - 05-20-2012

Your other question? Do you need to replace rear caliper . Some times when brake pads are to the metal the pistons get cocked to one side (hard to push back in). Things to ck to help decide if bad,after stepping on brake a few times ,turn brake disc and compare with other side,or drive a few miles,trying not to use brakes and ck heat being produced from pads and disc by just placing hand near.Should not be HOT,compare with others. If all that seems ok,last test,after a few thousand miles ck wear on pads,should be some what equal.
DO ck for fluid leaks now and after driving a while.