I have a 1983 Mercedes 300SD. The front brakes are locking up.
Calipers/brake hose on front driver side has been recently replaced and
the front passenger side has new pads (caliper looks fine). Does anyone
Just a shot in the dark. I had a volvo 240 that I did pads on once and
used cheap pads. The tolerances were a little off. They were a little
large. large enogh that when they heated up they would expand enough in
their window that they didn't want to move. I had to bang on them to
get them in.(I should have known then that somethign was up.) As I was
driving once I hit the brakes, and they did not return to an idle
position, they kept depressed, heated up, then were slowing the car
down more and more until they started boiling the brake fluid. So once
I decided it was safe to pull over my pedal went to the floor. Don't
know if this is your problem, but just thought I might throw it out
I fixed my problem by pulling the pads out, scraping the sides on
asphalt to wear them down, and sticking them back in. To this day I buy
high quality pads, but still scrape the edges on the ground too wear
down the paint a little.
Good luck with it. I get to do my front pads this weekend on my 84
300D. I hope I don't run into the same problem.
Thanks Bill and Trader4 for your response,
My problem appears to be almost identical to Bill's as far as the
calipers not disengaging, and the car's speed starting to slow down (it
almost appeared to be a transmission problem). the first time, I got
stuck on the by-pass not able to move faster than 10-15 mph.
I thought I fixed the problem by replacing the driver-side front
caliper and hose, and replacing the pads on both front sides.
apparently this did not fix the problem. During my next drive I was
headed to work about 30 mile from home and the lockup started again
about 15 miles out. I was aware of what was happening so pull over and
waited for a few minutes. I was able to turn around and drive back home
slowly. Calipers are still partially engaged. By the time I made it
home and stopped both of the front brakes were smoking.
Later that night, I went back and bleed the master cyclinder and both
front brake lines and was able to drive around town without noticing
any problem. This evening will be the real test.
There may be something to the oversize brake pad, Bill. I will
definitely check it out.
If anyone have other ideas, I am open to suggestion.
Sure doesn't sound like a problem related to bleeding. Air in the
system would lead to a soft pedal, but I can't conceive how it would
create the problem you are describing. Did you have a firm pedal
before bleeding? One thing is for sure, I wouldn't be taking this on
30 mile trips until I figured out what is going on. At the very least,
after this severe heating, the pads are likely shot
Since you started with a bad caliper on one side, replaced that and the
pads on the other side and now have this problem on both sides, I vote
for Bill's idea. Which is that something in the pad/caliper interface
is binding. Are you sure they are the right pads? Still have the old
ones to compare with?
The only other scenario that comes to mind is that sometimes when you
put new pads on an existing caliper, that can lead to immediate failure
of the caliper. What happens is the piston has become corroded on the
most exposed part, which had been outside the caliper with the old thin
pads. If you push the piston back in, now the bad part is inside the
cylinder, where it binds. But that would only possibly explain one
side, not the new side, which would have to be a deffective part.
When I replaced the caliper/brakes, I had a good hard petal. When I
return after the "severe smoking" the petal was soft or spongy. The
truth is I'm never really satisfied with the bleed results. When I
bleed the back I feel certian that all the air is out because of how
the fluid flows. But with the front, I don't feel as certian.
As fall as the pads being in a bind, it didn't appear to be the case,
but I am not ruling anything out yet. Since the problem is
intermiitent, i must be cautious as to how i drive the car.
Any chance water got into the system? Never seen this happen, but just
theorizing, it would seem plausible that if you had water in the brake
fluid, when the caliper gets hot, it might vaporize, which would give
you a soft pedal. Also, it would seem possible that the steam would
then keep pressure in the system, making the brakes not fully release.
That makes the caliper hotter, more steam, making it worse, etc.
This is possible; I often wondered about contamination. One thought
that came to mind is that I had a container resembling a brake bottle
but had powersteering fluid in it. I normally would not put this in
intentionally, but I was concern that I put some powersteering in
unknowingly. To cover the possibility, I sucked all of the fluid out of
the master cylinder on the front brake side to remove the majority of
it (not sure how to remove it all fron the back brake side). This was
done before the 30 mile trip.
Contamination is a possible, and I will continue to monitor the fluid
as well as other suggestions noted from this cite.
have to remove one and pump the pedal a couple of times.
Contamination of brake fluid sometimes blocks the return hole.
How long ago did you change the brake fluid? , it has to be replaced at
least every 2 years.
Make sure you only use the right fluid, wrong fluids brake down the
I'm using Dot 3 fluid and I partially changed the fluid (through
bleeding and removing it from the front wheel section of the master
cyclinder) about aweek ago. I believe if there is contamination, it
probable been there for some time.
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