Rear brakes over-heating, possibly fading on 3.0CS

[taylorcom]

Progress so far: I think the over-heating in the LR brake is not due to problems with the parking brake because when I removed the caliper the wheel started turning well. Next steps are 1) rebuild or find a rebuilt LR caliper and 2) replace the LR parking brake cable, which snapped off a while ago.

To get the old pistons out of the calipers (for rebuilding), I'm thinking of stepping on the brake pedal with the caliper off the disc and the brake line connected. Does anyone have advice on that (beyond putting a pan under the caliper to catch spilled fluid)?

The parking brake shoes look okay, btw.

Any good ideas on any of the above will be appreciated. Thanks

 

[taylorcom]

here's a pic I took of one of the pistons so I could get the orientation of the "C" when I reinstall it. pretty funky looking

 

[mulberryworks]

Progress so far: I think the over-heating in the LR brake is not due to problems with the parking brake because when I removed the caliper the wheel started turning well. Next steps are 1) rebuild or find a rebuilt LR caliper and 2) replace the LR parking brake cable, which snapped off a while ago.

To get the old pistons out of the calipers (for rebuilding), I'm thinking of stepping on the brake pedal with the caliper off the disc and the brake line connected. Does anyone have advice on that (beyond putting a pan under the caliper to catch spilled fluid)?

The parking brake shoes look okay, btw.

Any good ideas on any of the above will be appreciated. Thanks

Yes, if your hydraulics are good, stepping on the brakes with the caliper off can push the pistons out, but if one is sticking, you'll only push out the free one. DON'T use compressed air as it can launch the pistons with some real velocity and damage it or you. Instead you can use a grease gun to slowly push the stuck one out. You might have to block the others in place with some wood to get the stuck one out. Here's a video.

 

[taylorcom]

I've got the caliper off the car and have replaced the inner seal on one of the pistons. But I'm having trouble getting the piston back into the caliper. It doesn't want to go further than you see in the pic. Is this normal? I lubricated everything with brake fluid, but still no go. What's the protocol for getting it back in place? The pic below shows the rebuilt piston on top, old stuck piston below it:

 

[Stevehose]

What are you using for leverage on the piston? Typically you'd remove both pistons, clean, and install with new seals all at once.

 

[Dick Steinkamp]

Did you hone the cylinders?

It may be an optical illusion, but the one you are trying to install looks like it is starting in crooked

I've used a C clamp to reinstall pistons.

...and like Steve said....both pistons need to be removed from the bores as step 1. Then the caliper needs to be thoroughly cleaned and the passages flushed, then the bores and pistons inspected for serviceability (scratches, nicks, etc), cylinders honed and then recleaned, pistons reinstalled with plenty of the proper lubricant (brake fluid works in a pinch). A new hardware kit and new bleeder valves are recommended. During this process, don't get anything near any of the brake parts that contain anything other than brake fluid or brake clean.

 

[taylorcom]

What are you using for leverage on the piston? Typically you'd remove both pistons, clean, and install with new seals all at once.

For leverage on the piston I used a C clamp. The stuck piston at bottom of the pic wouldn't come out, so I decided to do them one at a time, get one done then put caliper back on car and force the other one out. The rubber inner ring that came in the rebuild kit seems a bit taller and thinner than the original one. The piston seems jammed now, so I may have to put it back on car and try to pop it out again by stomping on the brake. It might be better use of my time to search for a rebuilt caliper.

 

[taylorcom]

Did you hone the cylinders?

View attachment 127064

It may be an optical illusion, but the one you are trying to install looks like it is starting in crooked

I've used a C clamp to reinstall pistons.

...and like Steve said....both pistons need to be removed from the bores as step 1. Then the caliper needs to be thoroughly cleaned and the passages flushed, then the bores and pistons inspected for serviceability (scratches, nicks, etc), cylinders honed and then recleaned, pistons reinstalled with plenty of the proper lubricant (brake fluid works in a pinch). A new hardware kit and new bleeder valves are recommended. During this process, don't get anything near any of the brake parts that contain anything other than brake fluid or brake clean.
View attachment 127065

I did not hone the cylinders and did not disassemble the calipers. I cleaned them with a rag. I lubricated everything with brake fluid. It does not seem practical to do both cylinders at once, since they would not both pop out at once.

 

[Dick Steinkamp]

You don't have to disassemble the callipers. In fact, I'd advise against it.

If the parts I was replacing were different then the parts in the kit, I'd be concerned.

 

[Stevehose]

100lbs of compressed air will pop it out, put a piece of wood in there to keep it from hitting the other side. I cut off a schrader valve from an inner tube and cram it in the brake line hole, then hit it with the air.

 

[Ohmess]

100lbs of compressed air will pop it out, put a piece of wood in there to keep it from hitting the other side. I cut off a schrader valve from an inner tube and cram it in the brake line hole, then hit it with the air.

I've done this too.

 

[Ohmess]

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!)

This post is very helpful. I purchased a used e3 proportioning valve when I had the bits of rubber problem with mine, but did so in part because I was under some time pressure to take my car on a trip. I still have the old valve; and this post makes it seem like disassembly and cleaning is what is needed to get that baby working again.

 

[Bert Poliakoff]

I've got the caliper off the car and have replaced the inner seal on one of the pistons. But I'm having trouble getting the piston back into the caliper. It doesn't want to go further than you see in the pic. Is this normal? I lubricated everything with brake fluid, but still no go. What's the protocol for getting it back in place? The pic below shows the rebuilt piston on top, old stuck piston below it:

I had the same problem re building a set of E12 calipers. Turned out I had left the old seal in that fits into the bore of the caliper. My pistonss were also frozen onto the seals and I couldn't move them I took them to a brake rebuilding shop and they blew them out for me. It took them over 200lbs of air pressure to get the pistons out

 

[taylorcom]

You don't have to disassemble the callipers. In fact, I'd advise against it.

If the parts I was replacing were different then the parts in the kit, I'd be concerned.

It's a kit from Centric I bought a few years ago from RockAuto.

 

[Bert Poliakoff]

Centric, as far as I know, offers the only kit that also includes the "0" rings to use if you split the E12-E24 calipers

 

[taylorcom]

Yes, my kit has the O rings.

 

[Redrumm3]

The piston does not look centered in the bore. It appears cocked. It they are not straight they will not go back in. You also have the bleed valve open, correct?

 

[JFENG]

put caliper back on car and force the other one out.

I always use compressed air and never had a problem with it. Just exercise common sense: block of wood in the caliper to prevent a piston from flying out and hitting the other side, small clamp to restrain pistons that you don’t want to come out, wrap the whole assembly in an old towel to keep droplets of brake fluid spraying everywhere when a piston pops out.

Assembly: I have always used Castrol red rubber grease, but any grease compatible with DOT 3/4 should be ok (Miller’s, Rtc). This type of grease makes assembly a bit easier and doesn’t absorb water so it may help delay rust formation on the bores and pistons.

What is Red Rubber Grease, such as Castrol and Girling, why and how it is used for hydraulic brakes, clutch and suspension lubrication. Technical information and selected applications.

John

 

[taylorcom]

The piston does not look centered in the bore. It appears cocked. It they are not straight they will not go back in. You also have the bleed valve open, correct?

Are you taking into account the chamfered edge? It looked straight to me.

 

[taylorcom]

So I put it back on the car, popped the piston out by stomping on brake pedal. It popped out easily. Put it back in and again it seemed to hang up, probably on the inner gasket. I used a pry bar to wiggle it in and that took a lot of pushing. I now wonder if it will retract properly. I used brake fluid for lube. Are they normally that hard to reinstall?