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Car Forum / Mercedes-Benz Cars / December 2006Front Brakes lockup
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 have any suggestions. 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 there. 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. Bill > 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 [quoted text clipped - 17 lines] > > Bill I would help if we had more info as to exactly what "locking up" means. 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. Thanks again, JJ > 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 [quoted text clipped - 17 lines] > > Bill > Thanks Bill and Trader4 for your response, > [quoted text clipped - 21 lines] > > JJ 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. Thanks again jj > > Thanks Bill and Trader4 for your response, > > [quoted text clipped - 42 lines] > 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 [quoted text clipped - 8 lines] > Thanks again > jj 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. Thanks, JJ > > 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 [quoted text clipped - 15 lines] > then keep pressure in the system, making the brakes not fully release. > That makes the caliper hotter, more steam, making it worse, etc. > 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 [quoted text clipped - 55 lines] >>cylinder, where it binds. But that would only possibly explain one >>side, not the new side, which would have to be a deffective part. It may be a bad master cylinder, if the pedal is released fluid must be able to flow back to the reservoir. If the valves of the master cylinder are blocked pressure may build up due to heat. How can I tell if the valve of the master cyclinder is blocked. Thanks, JJ > > 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 [quoted text clipped - 59 lines] > able to flow back to the reservoir. If the valves of the master cylinder > are blocked pressure may build up due to heat. > How can I tell if the valve of the master cyclinder is blocked. > [quoted text clipped - 65 lines] >>able to flow back to the reservoir. If the valves of the master cylinder >>are blocked pressure may build up due to heat. You can check it by pushing the pistons in. If you have new pads you 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 rubber seals. 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. Thanks, JJ > > How can I tell if the valve of the master cyclinder is blocked. > > [quoted text clipped - 73 lines] > Make sure you only use the right fluid, wrong fluids brake down the > rubber seals. Thanks everyone for you help. All indications is leading me to believe that I have an intermitten master cyclinder problem. JJ > > How can I tell if the valve of the master cyclinder is blocked. > > [quoted text clipped - 73 lines] > Make sure you only use the right fluid, wrong fluids brake down the > rubber seals. Replaced master cylinder and brakes are now working fine. Thanks, JJ > > 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 [quoted text clipped - 59 lines] > able to flow back to the reservoir. If the valves of the master cylinder > are blocked pressure may build up due to heat. |
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