Brake problems 300D, much help needed! - PeachParts Mercedes-Benz Forum

Rudebutler · #1 09-18-2007, 08:20 PM

My 83 300D has about 206000 miles on it. I bought it a year ago-great shape, no records.

Last night the rear brakes froze on me. As Paris Hilton would say, they were "hot." I pulled over and they released on their own, but I developed a leak in the metal brake line on the driver's side rear. After a brief inspection, I can see that all the metal lines are rusty and in need of replacement. I'm plenty willing to do the work-it seems straight forward enough. Here are my questions:

1. The car is parked at the high school where I work. Not the worst place, but I really need to get it home to replace all the lines. I have read that you can replace the metal lines in 2 pieces using double flanges and a connector. Could I just cut into the good part of the lines, remove the defective section, and put in a new section of metal tubing just to get me home? (Could it be a long term temporary fix?)

2. If I can do the above, what size is the metal brake line? It looks awfully small.

3. Does anyone know a link for instructions on using the flange tool? Never had the opportunity to learn.

OK, on to the tougher questions. I adjusted the parking brake using the star wheel adjusters 1.5 weeks ago. Everything was happy-used it a few times no problems. I did not use it yesterday at all. Do you think this caused the rear brakes to seize?

The rear wheels still seem to bind a bit. I tried to loosen the star wheel adjustment, but wheels still don't exactly turn freely. Is there a way I can completely release all tension to the parking brakes?

Thanks for reading all this!

barry123400 · #2 09-18-2007, 08:43 PM

Sounds like the master cylinder internal rubber is not clearing the return port. This maybe leaving pressure in the rear brake system causing the rear brakes not to release properly. If you loosen a rear bleeder screw and let a very small amount of fluid flow out the brakes should release till you use them again.
Whatever you see as a leak cannot be one or it would let the brakes release. Both rear brakes at the same time is signifigant. You are also right in that if the brake lines are very rusty they should be changed. Also look for a pinched brake line that feeds both rear sides. If pinched off bad enough it might retain fluid pressure to some extent.
The only other thing I can think of is you did damage a line and pinched it off but the line forward of the pinch damage is leaking. That is a very unlikley senatio though.
Anyways if you lock up the brakes try releasing a little brake fluid on a rear caliper as your first test. If both back brakes release you know where to look. Patching in a section of brake line is questionable at this point in my opinion. I doubt it could really contribute much unless there is evidence of a pinched off line. There will also be a slight residual drag on brakes with tired calipers. But the rear wheels should not get hot. Perhaps you have a friend that knows more about brakes and he could have a look with you. He does not have to be mercedes specific as it is a straightforward system.

Rudebutler · #3 09-18-2007, 09:26 PM

Barry-

Thanks for the reply! It's definitely leaking brake fluid-dripping to the ground when I press the pedal with engine running. I can't see exactly where the leak is as the leaking section is behind suspension parts.

The brakes aren't frozen now. But the rear wheels don't spin completely freely, either. I am wondering whether the parking brakes are still engaging slightly or if I severely warped the rotors. Is there a way I can push in the pads without removing them? I will try opening a valve and see what effect that has.

I don't think there is a pinch in the line-it would have to be pretty severe to cut off the fluid completely. I can run my hand along the parts I can't see and it feels intact. You rmaster cylander theory sounds quite plausible.

I only want to patch in a section of brake line so that I have brakes all the way around for the drive home. I work in a congested area-lots of traffic lights and I have to cross a major bridge, too. I'll need them! So, if I can't get this to work RELIABLY I'll have to get towed. Hate to spend the $$$, but not worth hurting anyone, either!

Rudebutler · #4 09-18-2007, 09:34 PM

RR-

Replacing everything in the rear sounds like a great idea! Thanks for your input on the parking brake, too. It didn't make sense to me that that would be the culprit, but I am still getting quite the education!

I have free towing with Geico, but I think that just gets me to the closest shop of their choosing. Do you think they would let me join AAA already needing a tow?

t walgamuth · #5 09-18-2007, 11:27 PM

If the fronts are working fine I would just drive it carefully home, if it is not too far, personally.

ON the brake hard lines I would replace the entire section from flared fitting to flared fitting. Cutting brake lines and flaring them can be tricky. Standard lines are available in many lengths and you can connect them together with double female fittings.

Tom W

rrgrassi · #6 09-18-2007, 09:13 PM

You are really better off replacing the enire line, but you should do it on both sides. The emergency brake is what you adjusted, and it is a separate system, so by not using it, you did not cause the brakes to seize. It is possible that you adjusted them too tight, though. You will have to remove the caliper and rear hub to inspect it. Do you have AAA? If you have the AAA Plus you get a 50 mile tow for free. Have it towed to your house so you can work on it.

Do not try to patch a leaky line, it just introduces a new weak spot. When you dis assemble the rear brakes, check everything. It may be easier for you to just replace the rotors, pad, calipers, rubber hoses and metal lines, and inspect the e-brake shoes, as they may be fine. IIRC the metal line inner diameter is 3 or 4 mm. Take a sample to the parts store. A line flanger is pretty easy to use. It's basically a clamp with holes in it to hold the unflanged line. The "flanger" looks like a gear puller, but has a tapered head. Tightening this is what creates the flange.