79 240d brakes go bye bye....but just for a few minutes? - PeachParts Mercedes-Benz Forum

joegolden · #1 05-17-2013, 10:41 PM

After about 30 minutes of extreme stop and go traffic this evening I get within 2 redlights of my on ramp to I-75....I cant wait

I am almost there! Home Free!

I come to that 2nd to last light and whoa! brake pedal to the floor and I barely got her stopped. I was so glad I was stopping slowly and not slamming on the brakes. I pull off into the gas station parking lot and start pumping them. absolutely NO resistance

Straight to the floor.

Since I was so close to the open freeway I eased back out into traffic and creeped down the road with my hazards on. I knew I could get her home due to fast moving traffic on 75 at this point. I made it the 20 miles home and did not touch the pedal once until my exit. I prayed..I applied.. and what do ya know....TOTALLY back to normal. Excellent feel and stopping power. 100% back to normal. I even ran a few errands around town late tonight and they seem as if nothing ever happened..

What the hell happened? I would rather get a jump start on this before it goes completely out.. you know?

I did noticed this week a squealing sound has started at start up... warm or cold.. like a squealing belt but I cant tell what/where its coming from. Related maybe?

Thanks guys in advance. The Town car has not been getting the thumbs up like my 240d....I mean I get at least 3 compliments everyday in the 240...Its gotta be the hubcaps!

Stretch · #2 05-18-2013, 01:58 AM

If the pedal dropped to the floor - it went the whole length of the stroke - but you still have the correct fluid level =>

I'd suspect the master cylinder

However you should check all parts of a braking system - especially the flexible hoses.

If you have leaks / low brake fluid level then you've got more investigative work to do.

I hope you checked the fluid level before driving off again.

ah-kay · #3 05-18-2013, 02:16 AM

I think your brake fluid was boiling. When it boils it is vapor and hence no brake. It could be one of the followings:

1) The caliper got hot when you were in heavy stop and go traffic.
2) The other reason could be your brake is binding and the caliper got hot, hence the fluid boils.
3) You have contamination in your fluid which lowers the boiling point.

Check the calipers and then flush all brake fluid. It has to be seen to.

nelbur · #4 05-18-2013, 08:11 PM

I agree with the "boiled fluid" theory. Brake fluid that has picked up a lot of water will boil at lower temps, and if one caliper is sticking, you can boil fluid in that caliper blowing the fluid back into the master cylinder. You stopped because you still had the rear brakes, assuming it was a front caliper sticking. See if one wheel center is hotter than the others. If so, that is your problem caliper. Fix it, and use fresh high boiling point Dot 4 fluid.

79Mercy · #5 05-20-2013, 01:00 AM

I had this problem on 76 300D a few years ago after long drives the brake fluid would boil and i would loose brakes until it cooled down. Flushed the brake system with new DOT 4 fluid and i back in business. Brake fluid honestly should be replaced about every 2 years, its a cheap preventative maintenance which will extend the life span of costly brake system parts and will prevent failures which can be dangerous.

Zulfiqar · #6 05-20-2013, 10:19 AM

yep - sounds like a boiling problem. I bet if you flush the fluid you may even find it a bit emulsified too and loaded with specks of rust etc.

New fluid always gives great pedal feel no matter what car.

If you lack a pressure bleeder and even a helper - this works like a charm.

http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_x_9020969-P_x_x?cm_mmc=ACQ-_-Google-_-enhancedRM-_-9020969&ci_src=17588969&ci_sku=9020969&ci_gpa=pla&ci_kw=&gclid=CPGdlsbwpLcCFU1p7AodgwIA_A#utm_source=acq&utm_medium=google&utm_campaign=enhancedrm&utm_content=9020969

takes an hour tops with 1 quart fluid bottle.