Any common problems resulting in loose-like brakes? - PeachParts Mercedes-Benz Forum

azitizz · #1 01-31-2010, 04:03 PM

Hi there, I have a 85 300TD wagon and have all of a sudden started experiencing looser brakes. They still work but you have to push down further and there doesnt seem to be the resistance there was before. This seemed to happen quite suddenly. When parked (with the car running) and feeling, when I push down on the brakes I can feel when the resistance actually does begin it seems to release even a bit further to the ground after a second or two.

The brake fluid is still full and Ive never known there to be a problem with them before. The weather is pretty cold here (-20 to -25 C) however thats never been a factor before. Any thoughts on where I can begin looking? ( I want to spend as little time as possible outside!) Ill need a heated Garage of course to do any real work though.
Thanks

pawoSD · #2 01-31-2010, 04:16 PM

The hoses between the body and calipers might be bulging/failing. If they look old or you have never replaced them, replace them ASAP!

Or, the seals in the master cylinder might be failing, causing reduced pressure.

azitizz · #3 02-01-2010, 10:52 PM

Thank you. Ill be having a chance to look at this tomorrow. Wondering if anyone knows what kind of brake fluid I can use (other than name brand $$$Mercedes)? Im imagining Ill be needing to bleed the system at the least. I should probably replace the fluid anyways but my manual only says to use only mercedes approved brake fluid. I know theres other stuff out there that will be just as good and cheaper.

mobetta · #4 02-02-2010, 12:16 AM

I use dot4 fluid.

you can do all the hoses plus the master for about $100 in parts/ if you order from the right places- dont know about up north, prolly more $$

t walgamuth · #5 02-02-2010, 02:48 AM

It sounds like an internal leak failure in the master cylinder. It is leaking from one side to the other so it is not running out on the ground. Or if the fluid level is going down but not running out anywhere it may be filling up your booster.

Since they don't cost much if it were mine I would probably just change the mc and be done with it....unless by chance it is already brand new.

winmutt · #6 02-02-2010, 10:37 AM

I concur with everyone else, MC. Fix it sooner than later.

konstan · #7 02-02-2010, 11:06 AM

The first point of failure are the rubber hoses that go from the brake calipers to the metal fittings. If you don't remember when they were replaced last time, replace them.

Master cylinder is cheap and easy to replace, so if you haven't already done so, go ahead and do it. If you are not losing fluid, this might be it.

Check all the hard lines (steel lines) too... if they rust, they may develop slow leak, then its not too long before the brakes are completely gone.

Take the wheels off, one by one, and start looking... I think it will be obvious once you dig in there... Yeah I know -20C is no fun to do anything in... I could let you use my garage.. Winnipeg - you are just a short drive from Omaha...

Chas H · #8 02-02-2010, 11:49 AM

Quote:

Originally Posted by mobetta

I use dot4 fluid.

you can do all the hoses plus the master for about $100 in parts/ if you order from the right places- dont know about up north, prolly more $$

Use the recommended fluid. There is a difference between DOT 3 and DOT 4.

azitizz · #9 02-03-2010, 09:48 PM

Thanks for the replies.
I never noticed there were two separate reservoirs until yesterday when I got a chance to take off the wheels and take a better look. The one in the front was full but the one in the rear was empty so I was mistaken into thinking they were both full.

I checked the rear lines and the left side flexible line had some minor cracks in it but no sign of leakage. I plan to replace them all anyway as I dont know when they were last done.
Would an empty rear reservoir correspond to a rear brake line leak?

Would this possibly rule out the mater Cylinder as the culprit? (the Mercedes parts dealership quoted me over $500 for a new MC!) I found brand new ones online and from Canadian sources for as low as $60. Not sure if thats a gamble though. Is there an obvious quality difference? Sure is a price difference.

I filled up the reservoir again and bled the line I took off and it works fine again, however I know this is temporary. I'm just waiting for the parts to be shipped.

I alos was considering getting new brake pads as they may need replacing withing the next year. But when I was about to choose them I got 3 different versions. One that says for ATE Calliper 123, one for a Bendix 123 and the other simply said it was for 123 models.
All 3 options had an OEM selection. I wasnt sure if thre was a big difference between the models if they are all for 123s. The callipers appear to be original so I was just going to go for the general 123 option but perhaps someone could shed some light on the differences?

unkl300d · #10 02-03-2010, 09:59 PM

Best bet is to make sure you spec the pad for your particular caliper.
The manufacturer is stamped on an open space but you have to clean it up to see. Sometimes not that obvious.

Might as well replace the pads. Then you can eyeball the calipers for leaks.
Pad wear patterns can also shed light on calipers behavior.

I forget what's the idea behind the rear reservoir..... I only recall that one must be sure to top out both after refilling.

winmutt · #11 02-03-2010, 11:04 PM

Chances are that fluid leaked into brake booster, make sure it is empty when you replace the booster.

babyjames · #12 02-03-2010, 11:28 PM

Since you'll already be bleeding the system, it wouldn't hurt anything to change those rear flex hoses. If they have cracks, especially at the caliper end where the fitting is crimped onto the rubber, they're done for.

As for the pads, it makes no difference r.e. the brand of caliper. There is a break around m.y. 1979. The year of the car is much more important.

If possible, a few days prior to actual installation, clean the area surrounding the hard-line/flex-hose junction THOROUGHLY and apply your favorite penetrating oil to the unoin. BE VERY CAREFUL WITH THESE!!! If you toast the flats on the fitting (especially on the p.s.) your day will not go as planned. Napa carries metric brake hard-lines, so don't waste time/money getting one from MB, as it probably won't fit any better than, say, a 36" chunk from Napa. If you have a bubble flare tool then you can cut either down to fit exactly. Regardless, this entails considerable extra effort. Cooking the thing a little is advisable, though I prefer an electric heat gun under circumstances such as these....

Jay.

Diesel911 · #13 02-04-2010, 12:15 AM

Quote:

Originally Posted by azitizz

Thanks for the replies.
I never noticed there were two separate reservoirs until yesterday when I got a chance to take off the wheels and take a better look. The one in the front was full but the one in the rear was empty so I was mistaken into thinking they were both full.

I checked the rear lines and the left side flexible line had some minor cracks in it but no sign of leakage. I plan to replace them all anyway as I dont know when they were last done.
Would an empty rear reservoir correspond to a rear brake line leak?

Would this possibly rule out the mater Cylinder as the culprit? (the Mercedes parts dealership quoted me over $500 for a new MC!) I found brand new ones online and from Canadian sources for as low as $60. Not sure if thats a gamble though. Is there an obvious quality difference? Sure is a price difference.

I filled up the reservoir again and bled the line I took off and it works fine again, however I know this is temporary. I'm just waiting for the parts to be shipped.

I alos was considering getting new brake pads as they may need replacing withing the next year. But when I was about to choose them I got 3 different versions. One that says for ATE Calliper 123, one for a Bendix 123 and the other simply said it was for 123 models.
All 3 options had an OEM selection. I wasnt sure if thre was a big difference between the models if they are all for 123s. The callipers appear to be original so I was just going to go for the general 123 option but perhaps someone could shed some light on the differences?

You fixed what was causing the problem. However, changing the Hoses is a good idea.
Unless you are buying your brake parts local; where they can easily be returned it is best you get under the Car and identify what company's Brake Calipers you actually have.
It is hard to read but I know that the ATE Brake Calipers are marked with an styalized ATE with the A being larger and the other letters getting smaller as you read left to right. Sort of like a Trialngle with the A being the tallest part.