Did I screw up?
 

It recently occured to me that I may have caused damage to my brakes. I had taken my '85 300Dturbo out for a 15-20 minute drive and came back home and parked her. Then I decided to give her a wash.

I was hosing her down and got to the wheels, and the brakes were still hot, so there was steam coming out from the brakes when the water would hit the discs. I didn't really think much of it and just finished washing and drying. That was about a week ago.

Now im getting weird brakeing...the brake pedal is a little stiffer than usual, and if I pump them 2-3 times while up to speed, on the 3rd time it seems like I lose vacuum assist. Either that or they stop working all together, Im really not sure what non-assisted brakes feel like... im not sure if its a vacuum problem or a disc problem. After I get going again braking will be adequate leading me to believe it's vacuum related.

I kind of hope it's a disc problem, because Im sure the rotors could be replaced or machined. And then I could have an excuse to rebuild the calipers and replace the brake hoses (speaking of which, they are $50 each at the local MB dealer! :D) And even replace the crappy brake pads my dad had a brake shop put in there. I say "excuse" because my parents are always paranoid of me ruining something. I figure it's a 20 year old car and could use new brake parts but...

Anyways I will investigate the problem further. Does anybody have any insight?

Weird. I don't know what you mean by "they stop working all together"
It isn't a good idea to spray water on hot discs, interesting that they got that hot...could have warped them, I suppose...
You could have a vacuum issue, you might have a failing master cylinder as well...If you are really losing brakes altogether, and the master is dying, you could have an unsafe situation on your hands in short order. You want to make sure this is not the case, because when masters die, you have zero brakes... :eek:

Well the pedal does not drop to the floor, so I am assuming the master cylinder is ok. It just gets incredibly hard to press down when this occurs, I dont think I got the pedal to move more than a centimeter or two when this happens. Like I said i'll investigate further.

I would think water wouldnt hurt them. They have to be made to withstand weather operation, rain, sleet, snow, puddles, small streams, etc.

Sounds like a vacuum problem. Water generally won't hurt the brakes. Just think, when you drive in the rain, water surely gets on the rotors and doesn't cause a problem.
Check the vacuum pump, and check for vacuum leaks.

Sounds like a vacuum / booster issue.
Does the engine shutoff normally?
If you apply braking pressure a few times, with the engine off, does the pedal become harder to push after 2 or 3 applications of the brake?
When you have done this. Keep foot hard on brake pedal and start engine. Does the pedal drop down a little?
Does the pedal slowly sink towards the floor?

When did you last change the brake fluid? It may have water contamination causing brake fade.
The above tests should prove vacuum / booster / master cylinder are OK.

Warped rotors will give you a pulsation in the pedal, a "thump thump thump" feeling of the pedal pushing back. If you don't have that, you didn't warp the rotors.

The loss of assist indicates a vacuum booster problem or low vacuum condition. Check your piping for leaks, check your brake booster for leaks, and check that your vacuum pump is working correctly.

Washing the car and wetting the brakes had nothing to do with it.

This may be a longshot, but I'll just throw it out there for consideration. A stream of cold water on hot calipers with a torn boot could wick water in between the piston and caliper bore where it would not go during normal driving. Rust could then develop to hinder piston movement. But I would think that this would happen only on 1 or 2 wheels, not all evenly, so there would be a corresponding unevenness in braking.

Almost every car has a vacuum booster sized for 2-3 assisted pedal presses if the vacuum source is lost while driving. If boost is lost, braking takes considerably more effort.

You can experience this by shutting off the car, then pressing the pedal a few times. With no vacuum source, the boost will be 'used up' after a few presses, and you will feel what the unassisted pedal is like on your car. Go ahead and press hard, it won't break the car. Unassisted brakes will take more effort, but you can press hard enough to stop the car if you have to.

Gassers have an almost unlimited source of vacuum in the intake manifold, but diesels have a relatively small vacuum pump. Pushing 2-3 times on the pedal will drain the reservoir, and it will be a few seconds until the vacuum pump can draw the booster back down to the vacuum it needs for power assist.

Do check everything else, and look for other vacuum leaks.

Best Regards,
Jim

My '81 300SD had a similar problem and it was not caused by washing the brakes. I replaced the vacuum pump and have had no furter problems. By the way the vacuum pump is easy to replace. I used one off a donor car. The allen head screws that secure the pump make for easy removal and replacement and rebuild kits are available if you don't have a parts car

Lee

I would 1st ask why where your brakes steaming hot? Maybe you have one or more stuck calipers. Were all the brakes eqauly hot?

Another thing to check would be the vacuum pump.

Use a vaccum gauge to check what vaccum you have before rebuilding or changing pump. Read the vaccum available at pump source only and if it is at specification check out your vaccum lines and fittings for leaks with a minivac type tester if vaccum is far less when system is hooked back to the pump. Threads posted in archives search should give you a lot of guidance. Good maintenance check anyways on these older cars. Also by coincidence you may have only one half your braking system working yet pedal not reaching floor. Just jack up one wheel and have friend hold brake pedal on and try to turn that wheel by hand. Jack up other end of car and repeat. If after holding the pedal down for a minute and the wheel turns that half of your master cylinder is bypassing. Like most posts do not see how the wash could have affected the brakes in the method you describe other than a lot of soap getting on the disks and pads. (and I mean a lot) If that is the case should rain wash or wear off in a few days. So if brakes are gradually improving give them a day or so before looking for a problem. :)

i used to wash my car immediately after driving it all the time, and the brakes would always steam and there wasnt anything wrong with them, but i do drive pretty fast and brake hard (some day ill break that habit). since then ive gotten new slotted rotors but i havent washed it after driving it lately so i havent been able to see if theres a difference.

looks like youve got almost 200k miles, you probably will need new rotors soon too, but that wouldnt cause the problem youre having. when i got new rotors it made the pedal travel less when i pressed it. cheap pads would just make them squeal.

AFAIK, with MB, you change the pads then the next time you change pads and rotors. At least that is what my shop (Gilly) tells me. I still think your issue is a coincidence issue. Maybe you could take apart your calipers and regrease them and clean anything moving. I always wire wheel the slid pins and put the best grease I can find in them. Also I flush brakes as per MB spec (once every 2 years, IIRC) In fact, all my vehicles always get fresh fluid every year.

I still think it has something to do with the booster. Could you hook a vacuum source to it and see if it gets easier? If so, you might ahve a bad source somewhere.

The pedal does drop further when I start the engine with the foot on the brake and depleted vacuum. The door locks work perfectly and the engine shuts off immediately, so no vacuum leaks there anyways. I did spill diesel fuel on the rubber 3 way connector near the brake booster a while back, and the connector is now hard and discolored (black and white) so that may be an issue. I didnt expect diesel fuel to do that to rubber.

I figure i just lose vacuum after 2 or 3 pumps, and then the brakes become unassisted. I just thought it would take more than that to deplete vaccuum assistance, that seems almost unsafe if you were not expecting it in an emergency situation. I bled and flushed the brakes with new fluid about 4 months ago i think.