1985 300SD Brake Problem - PeachParts Mercedes-Benz Forum

Lain · #1 02-01-2011, 05:36 PM

Ok, first I'll admit that I have committed the heinous crime of not paying enough attention to my car and being cheap... Second, sorry if this has already been asked, I don't know what to search for. Anyway, a week ago my front driver's side brake started scraping metal to metal, so I got it home and parked it 'till I could replace the brake pad. I didn't have time to work on it for a couple days, so I left it parked out front of the house. Two days later, I go out to the car and get in to take it to ye olde brick-and-mortar car parts store to get new pads... and lo and behold the brake pedal falls to the floor.

Anyway, I notice that the rear brakes are still working due to the car being able to stop. I looked under where the car was parked and there was a puddle under the same brake that was scraping. The first thing that comes to mind is that somehow it started leaking brake fluid from that caliper, but the master cylinder and booster are right above that same spot. Anyone know what I managed to break?

engatwork · #2 02-01-2011, 05:48 PM

Brake pad wears out, metal wears down and finally the piston pushes out of the caliper. Have a spare caliper in hand when you make the repair.

tbomachines · #3 02-01-2011, 07:05 PM

Quote:

Originally Posted by engatwork

Brake pad wears out, metal wears down and finally the piston pushes out of the caliper. Have a spare caliper in hand when you make the repair.

Yup, and it also means you've exceeded thoroughly SCARY levels of ignoring your brakes! In the very least replace both sides in front (you'll probably get pads as a pair anyways) and check the rears, replace if they're getting down there.

vstech · #4 02-01-2011, 08:03 PM

OK, if you just started feeling the brake grinding noise, there is no way the piston could have fallen out. more likely the fluid level got low, and air is in your master cylinder. I'd look and see how much fluid is in there, both front and rear chambers, and then bleed the brakes and see if fluid is leaking.
new pads are easy to change at least!

Lain · #5 02-03-2011, 08:03 PM

Ok, it was the piston leaking fluid. Here's another dumb question, how do I bleed it? It's full of air, as far as I can tell.

vstech · #6 02-03-2011, 08:07 PM

... if the piston is leaking fluid, you know you have to change the pair of calipers on that axle right? or at least get a rebuild kit, and replace the seals... unless it is leaking at a hose, or from the bleeders.
are both pads worn evenly and equally?
where exactly do you see the fluid escaping?

engatwork · #7 02-03-2011, 09:56 PM

My recommendation would be to try to purchase a good quality rebuilt caliper and replace it. Inspect the other one and replace it if there are any concerns. The worst brake failure I have ever seen where the dude was still driving the car was one there the rotors had worn down to the point that they had come apart. What was left of the pad was rubbing on the ribbing that is used to connect the two sections of the rotor. I don't remember the exact make but it was either a Buick or Pontiac.

vstech · #8 02-04-2011, 10:19 AM

Quote:

Originally Posted by engatwork

My recommendation would be to try to purchase a good quality rebuilt caliper and replace it. Inspect the other one and replace it if there are any concerns. The worst brake failure I have ever seen where the dude was still driving the car was one there the rotors had worn down to the point that they had come apart. What was left of the pad was rubbing on the ribbing that is used to connect the two sections of the rotor. I don't remember the exact make but it was either a Buick or Pontiac.

the accepted practice with our brakes *(any brakes really) is if ONE wheel is affected, and needs a rebuilt caliper, BOTH calipers on that axle should be replaced! a serious imbalance issue can arise if you only change one caliper!

engatwork · #9 02-04-2011, 05:50 PM

vstech I totally agree with you. If I am going to change calipers on a car they both get changed, front or back. They wear out at the same rate if they are working properly. I have found that brake fluid changes every couple years makes calipers last a good bit longer (if the pads/rotors are being maintained).

Lain · #10 02-05-2011, 03:37 PM

Closure to those who are still interested in this thread, I replaced both calipers on the front axle and new pads, then new brake fluid. I did make another mistake, I didn't know that the brake fluid reservoir had split chambers, which made for an interesting time bleeding the brakes (why isn't anything coming out of the bleeder screw?! Is something stuck?!) Finally topped off the reservoir then gravity bled the whole system, brakes now completely functional. Thanks for the help guys!

engatwork · #11 02-05-2011, 04:56 PM

How'd the rotor look?