taylorcom
Well-Known Member
I hope I don't have to source any more parts, as they seem rare now.
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Rear brakes over-heating, possibly fading on 3.0CS
- Thread starter taylorcom
- Start date
taylorcom
Well-Known Member
Yesterday I replaced the left rear brake hose, which seemed newer than the other one and in better condition (I could blow air through it). Drove about 5 miles roundtrip up a hill and back down today. Brakes worked fine. The rear wheels s still got warmer than the fronts, which were cold (it's a 55F morning). I wouldn't think it's normal for the rear brakes to heat up more than the fronts, which do most of the work.
It is not normal for the rears to heat up more than the fronts. Are you sure the emergency brake is not grabbing? Try finding a stretch of tarmac with little activity and a slight hill. Head uphill, stop, put the car in neutral and see that it freely rolls back. Then turn around, reverse up the same hill, car in neutral and see how it rolls. Both tests should result in the same roll downhill.
If it passes that test, try bleeding your brake system but this time run a lot of fluid out the rear brakes. If the rears still heat up after than, then its time to replace the proportioning valve. Double check this on realoem, but I'm pretty sure that the e3 valve is the same part. If so, the e3 part will be cheaper than an e9 part.
If it passes that test, try bleeding your brake system but this time run a lot of fluid out the rear brakes. If the rears still heat up after than, then its time to replace the proportioning valve. Double check this on realoem, but I'm pretty sure that the e3 valve is the same part. If so, the e3 part will be cheaper than an e9 part.
taylorcom
Well-Known Member
I'll try that test, thanks. When you say run a lot of fluid out the rear brakes, approximately how much fluid do you mean, per brake?
That pressure regulator is NLA, does someone else sell one?
Taylor - say six ounces per side.
Further to Chris' comment, I should have been more specific on the regulator. Nobody sells new ones, so if you need to find a replacement you will be seeking a used one. I bought a used one from a california company who used to have a large stock of used BMW parts, who is no longer in business. I saved a couple of dollars by specifying the e3 part instead of the e9 part. Were I seeking one today, I would likely contact Al Taylor.
Our parts listing FAQ indicates that PMB performance sells rebuild kits. They also sell entire kits for the Porsche 914, which used this same regulator, so this likely means that they can rebuild the part for you.
Further to Chris' comment, I should have been more specific on the regulator. Nobody sells new ones, so if you need to find a replacement you will be seeking a used one. I bought a used one from a california company who used to have a large stock of used BMW parts, who is no longer in business. I saved a couple of dollars by specifying the e3 part instead of the e9 part. Were I seeking one today, I would likely contact Al Taylor.
Our parts listing FAQ indicates that PMB performance sells rebuild kits. They also sell entire kits for the Porsche 914, which used this same regulator, so this likely means that they can rebuild the part for you.
Centric rebuilt mine many years ago so others must as well.
I believe Carl has them.
taylorcom
Well-Known Member
I should take a closer look at the emergency brakes (the cable for one of which broke a while ago). Is the e9 emergency brake a drum brake? What problems should I look for?
The parking brake on the 3.0 is a simple and well designed system. It is a drum setup within the rear rotor, like many. They need to be adjusted from time to time but not frequently. There is the cable adjustment at the brake lever and there is an adjuster between the two shoes. The adjuster at the shoes can cease up but that wouldn’t cause any binding or drag. Cleaning the parking brake hardware and making sure it is lubricated and operating freely may not solve your problem but it certainly wouldn’t hurt.
taylorcom
Well-Known Member
OCCoupe, Are the parking brake cables available anywhere?
Yes, through bmw or walloth and nesh.
taylorcom
Well-Known Member
I just tried Ohmess' rolling-up-and-down-the-hill test and noticed no difference either way. When I got back home, the brake over-heating problem was, as always, most noticeable at the left rear wheel. That is also the wheel with the broken parking brake cable. The right rear wheel was only slightly hotter than the front wheels. I'll try running a lot of fluid through both rear brakes and see if that helps.
Taylorcom...It's pretty clear (to me) that your brakes need complete rebuilding. The first hose you replaced was plugged. I would guess that the remaining 5 may not be in the best of shape. An emergency brake cable is broken and you are essentially driving the car with no way to stop the car if a remaining hose (or another brake component) fails The rear brakes continue to overheat after the hose replacement which means other components (calipers, pressure regulator, and/or master cylinder) need attention.
Please do not continue to chase problems and try to patch up this system. Your life (and that of others on the road with you) are not worth saving a few bucks. All hoses should be replaced. Hard brake lines should be examined for any areas that are crimped or rusty and replaced if needed. Calipers need to be replaced or rebuilt. Rotors and pads should be replaced if out of spec or getting close. The master cylinder should be rebuilt or replaced. The rear pressure regulator should be rebuilt or replaced. The power booster should be tested and replaced if not functioning properly. The e-brake system should be cleaned, examined, lubricated and adjusted. The e-brake shoes should be replaced if out of spec. The broken cable should be replaced and the other one examined and replaced if defective.
Please do not drive the car until the above is completed. If you are not comfortable doing these things yourself, transport the car to @sfdon in Alameda or another reputable shop familiar with the E9 and E9 parts sources.
Please do not continue to chase problems and try to patch up this system. Your life (and that of others on the road with you) are not worth saving a few bucks. All hoses should be replaced. Hard brake lines should be examined for any areas that are crimped or rusty and replaced if needed. Calipers need to be replaced or rebuilt. Rotors and pads should be replaced if out of spec or getting close. The master cylinder should be rebuilt or replaced. The rear pressure regulator should be rebuilt or replaced. The power booster should be tested and replaced if not functioning properly. The e-brake system should be cleaned, examined, lubricated and adjusted. The e-brake shoes should be replaced if out of spec. The broken cable should be replaced and the other one examined and replaced if defective.
Please do not drive the car until the above is completed. If you are not comfortable doing these things yourself, transport the car to @sfdon in Alameda or another reputable shop familiar with the E9 and E9 parts sources.
taylorcom
Well-Known Member
Dick, Thanks for the cautionary input. As you may have guessed, I haven't been driving the car beyond short test drives and don't plan to do so until the issues I've mentioned are resolved. The front calipers were replaced not long ago, and I notice no problems there. I come from a family that includes two BMW repair shop owner-operators and so am familiar with repair processes. I also value the constructive advice commenters have provided here.
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taylorcom
Well-Known Member
Again, I appreciate your detailed description of the e9 braking system. I have a question: When you say "The first hose you replaced was plugged. I would guess that the remaining 5 may not be in the best of shape," are you saying there are a total of 6 brake hoses on the car?
I know the front brakes have 2 hoses (one per brake), replaced not long ago) and the rears have 2 hoses (both replaced a few days ago).
Where are the other 2 brake hoses you refer to?
The front calipers have two hoses per...
taylorcom
Well-Known Member
I just looked at mine and you are correct. My 3.0CS' six brake hoses are all fairly recent, so that's done. The RR caliper was replaced with a new one in '94 and now runs cooler with the new hose. The left rear caliper may be original ... it's the one that's overheating the most. I've owned the car since '85 and don't recall replacing it.
Regarding rear brakes and the pressure regulator valve...I recently picked up a 2800/Bavaria that was sitting for 20 years, so as you would imagine, the brake system was toast (frozen calipers, etc.). So I rebuilt all calipers, new hoses, etc. At one point I stopped getting fluid from both the rear calipers even though I did drain fluid through them previously. I removed the pressure regulator valve and disassembled it. I called PMB performance to ask them some questions regarding their kits, and rebuilding those things. Upon inspection, turns out my issues was that is was partially clogged due to old rubber bits that flowed into the valve, not from the valve itself. The seals were still good so cleaned it up and put it back together, and it flows nicely (PMB said that it should be good to go). I know some of this info is posted somewhere on this forum, but always good to know what these things are for and exactly how they work: So to recap what I learned after researching, is that theses things are more or less "T"s under normal circumstances, fluid goes from single line and splits off to each rear. The spring inside has a slight preload on it (via the stud and nut on the end) and is calibrated to ~525lbs. So under hard braking, if the fluid pressure in the valve cylinder reaches this threshold, it will start pushing against a piston which is held against this spring, and therefore will start compressing the spring. This will allow the piston to move forward enough to close off the fluid influent hole, preventing additional pressure building and further actuating the rear calipers. It is a primitive ABS of sorts, and they were likely developed for Porsche (911 and 914s probably) since they have all the weight in the rear and act like a giant pendulum under braking. Bottom line is, if you have a problem with fluid flow to your rear brakes AFTER you change hoses, a dirty valve could be the issue (assuming you confirmed your hardlines are not clogged, which happened to me!). Removal, disassembly, inspection, and cleaning is easier than you may think. But of course, should probably test it under a controlled situation (hard braking in an empty street or parking lot, etc.). PMB rebuilds them for less than $200, always money well spent and peace of mind. (Now if I can only get a pedal going after bleeding this rebuilt system...that's going to be a new post!)
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