Pagoda SL Group
W113 Pagoda SL Group => Drive train, fuel, suspension, steering & brakes => Topic started by: wwheeler on December 12, 2010, 05:42:09
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I am having trouble with my right rear brake getting hot.
Some history first. I discovered one of my front wheels did not spin easily when off the ground. Bearings were adjusted correctly and turns out the pistons in the caliper were tight. I "exercised" them to loosen them up which worked well. I then decided to do a preventative check on the others.
One of the things I found was the outer piston on the right rear caliper was totally seized and it's dust cover was deteriorated. The outer pad was very thin but the inner pad (piston still free) was fairly thick. I concluded that the dust seal had deteriorated and allowed debris to seize the piston. I replaced the caliper and pads with new MB pieces and thought my problems would be over. When replacing the caliper, I noticed that brake fluid would continuously drip from the brake line (3 drops /sec) unless capped off.
After a 20 minute test drive with the new caliper, the caliper was very hot to the touch and the other three were cool. There was even a slight smell of bunt pad coming from that wheel. I did some hard stops in forward and reverse hoping that would loosen the pads. After the next test drive, same thing.
I next removed the wheel and brake pads. The pads were tight on the rotor as the rotor would not budge. While removing the pads, I was able to move the pistons back in their bores, but they seemed to push back by themselves. My guess is that the caliper got very hot with the PO and burnt the dust seal and seized the piston and has been idle ever since.
What would cause just this one caliper to engage but not the others? Could it be the brake valve in the rear?
Thank you for your help
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Did you replace the flexible brake hoses? With age they get swollen on the inside and prevent the brake fluid from returning freely and could prevent the caliper from disengaging. They are cheap and it's a good idea to replace all four if they are a few years old and you are experiencing this kind of problem.
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Hello Wallace,
Yes, my guess would be with Hans on the brake hose. You may also want to make sure the emergency brake is releasing on that side. Most likely the hose.
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Thanks for the ideas. I had all of the hoses replaced and the fluid flushed 3 years ago when I bought the car. So I have been hesitant to blame this problem on the hoses. When I remove the pads, the rotor is loose, so I don't think the emergency brake is too tight. All of the major brake components are original if that helps.
I can push the pistons back in their bores by hand using the pads. The pistons go in fairly easy but push back out in about a second. The pads aren't so tight that they lock up the rotor, but they are snug on the rotor. Since the caliper is new, I thought that it still may have air trapped. The way the pistons moved back almost seemed like trapped air. I bled it again two different ways. Using a vacuum pump and then the two man method with the brake pedal. I got some air with the vacuum, but absolutely none with the two man method. So I think all of the air is gone but the pistons still spring back.
I remember that when I exercised the front calipers, the pistons stayed in the bore and didn't push back on their own. That seems normal. It almost seems like there are springs pushing the pistons back out on this rear caliper.
When you disconnect the brake line to the calipers, is it normal for the fluid to continuously drip? The line to the rear caliper did this until I put a rubber plug in it and found a new caliper. It wasn't any pressure, but just a constant drip every second. I don't know if this may be related to my problem.
This is a frustrating problem. Thanks for your help!
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Are the bleeders in the top hole and brake line in the bottom hole? Air will be trapped if not. Fluid will drip by gravity when system is open.
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Yes, the new caliper has the bleeder on top. I did check that after reading a thread about that very subject here recently, thank you.
Looking back at my first post, I am wondering if my first caliper suffered from the same fate. The outer pad was very thin while the inner pad was at least 3 times thinker. Why was the outer pad so thin? Maybe it was the same force pushing the pistons out then as it is now. Could it be that the brake got hot enough for so long from the pads contact on the rotor, that the dust seal hardened and the piston froze? Strange that it is only this one side. The fronts are definitely OK.
I already checked the rear caliper on the other side but will do it again to make sure it is OK and normal.
Any thoughts are greatly appreciated.
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After my recent brake debacle, I am in no position to advise, but I would definitely replace the hose because it's cheap. While it's off, suggest you make sure the metal line is clear. The final possible culprit is the pressure regulating valve. I do recall a post on its causing a lack of braking at the rear wheels.
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You should also "fit" the brake pads to the caliper. They almost always need to be filed down a little on the metal edges of the backing plate so they move in the caliper easily. This can also help reduce brake squeel. Maybe not your problem, but it is not a bad idea to do this. I also put a very small amount of never sieze on the edges of the metal backing plates where the ride on the caliper. Does opening the bleeder release the brake? If so the hose or valve could be the problem, if not it is most likely your caliper.
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I think I have solved the problem but won't know until I take test drive this weekend.
I loosened the bleeder and pushed in on the pistons until they bottomed out. Some fluid came out in the bleeder tube I was using as expected. I closed the bleeder, but the pistons sprung back as they had done before. I kept trying it and noticed each time I did it, it took longer for the pistons to spring back. Encouraged, I did the same procedure 10 more times at which time the pistons stopped springing back!
I never saw very much air come out in the bleed tube, but am sure there must have been an air bubbled lodged near the pistons. Do you typically need to bench bleed a caliper like you do a master cylinder?
Anyway, pistons stay put when I push them back. More importantly after I apply the brake, the rotor is free to turn and the pads just touch rotor instead of binding.
Thank you for all of your help and suggestions.
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Wallace,
From your description it sounds more like the new seal around the brake piston was a bit too tight and therefore not allowing the piston to return to its rest position.
With you exercising the piston a couple of times, it caused the seal to loosen some of the grip on the piston and hence the easy return.
I have seen this happen a few times with rebuilt calipers and usually a bit of exercise relaxes the seals a bit.
Typically you do not need to bench bleed the calipers as long as you install them the right way - bleeder always at the top.
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It does appear that hysteresis may have contributed to the dragging brake. Good luck with the repair.
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An interesting thought. Maybe would be a good idea to exercise the pistons a few times before final installation. The front caliper on that side was also replaced and I didn't have any problems with that one. That caliper had a broken bleeder with a broken easy-out from the PO. No way to get that out!
Thanks for the help.
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Sometimes you can weld a nut over the broken bleeder screw by welding the open center of the nut to the broken bleeder and turn the nut and the bleeder comes out. Make sure you don't have rubber seals near the heat.
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This bleeder unfortunately broke off flush with the casting!!!! On the original caliper castings, the bleeder is in a 3/8" cavity. So this was way down in the cavity. If I ever have another (I hope I don't), I'll remember you clever trick.
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Ah the famous broken bleeder! This has happened to me before necessitating the purchase of a new caliper. I'm about to replace a rear rotor and pads on my pagoda and would like to also replace the rubber brake hose. The bleeder screw is not budging so I'm kind of hesitating to replace the hose. I might apply some heat to the bleeder and see what happens.
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Others might chime in who have done this sort of thing. I would use PB blaster several times first before applying heat. I once had to loosen the coolant elbow in the head. It wouldn't budge until a week's worth of PB blaster applications. Be patient. It will work eventually.
The old seals in the caliper as well as the brake fluid may not like the heat. I don't think the PB blaster (or any penetrate) would cause any damage to the brake system.
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The dragging rear brake and high temperature still persists but at this point, I don't know if it IS a problem.
In this process, I have learned something about the rear brakes. The rear pistons (on my 111 anyway) have have a spring loaded compensator that rides on a pin in the caliper bore. I found info about it in the BBB. It is to compensate for the rear rotor runout. The BBB mentions that the rear pistons require more air pressure to pop them out and that they are harder to move in their bores. The springs would also account for the pistons "springing" back when I pushed on them as stated earlier.
I did replace the brake hose and it wasn't a problem. I rebuilt the rear caliper anyway with new seals and dust seals. The pistons do seem to be a bit looser now than when I first received the new caliper. But after another test drive, the right rear brake was hotter (not as much so) than the other three. I removed the tire and spun the rotor and it was not as tight as before but more so than the fronts.
Is anybody familiar with this brake compensator feature? Does it just take some time to burn off some off the new pad before it loosens up? Or will it always be tighter and run hotter?
Anybody have experience with this?
Thanks for the help!
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Hello,
Keeping those little rubber caps on the end of the brake bleeders keeps droplets of road water from entering the bleeder and rusting the bleeder threads stuck.
As last resort tap on the end of the bleeder with a small hammer to loosen rusted threads after squirting it with penetrant. Make sure you tap straight on and not from the side or you will break it off !
I also like the heat method to get bleeders unstuck. Calipers are designed to handle a lot of heat so heating the bleeder is not an issue.
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An update to this thread. I am still having problems with the right rear brake getting hot, but have some new thoughts.
I replaced the new caliper with another brand new ATE caliper to eliminate the possibility of the caliper being bad. I noticed when I installed the new caliper, you have to be very careful to have the rotor centered in the caliper housing and secure. Because the rotor "floats" on the rear axle flange until the wheel is installed, the pistons positioning themselves for the first time can move the rotor out of center. The rotor has to be secured first. That was one problem.
I also found out that the caliper ONLY gets hotter than others when driving at high speeds for 20-30 min. or longer. The caliper will NOT get hotter just driving and braking on the city streets. The rotor itself is not that hot. My new theory is that the right axle bearing may be worn and causing the rotor to bind into one pad more than the other with load from the wheel. Because of the piston spring compensator's, the piston will not retract as easily. When I "centered" the rotor and bled the brakes, it was with the wheel off the ground. If the bearing is worn, a load would cause the rotor to shift. My axle has 140,000 miles on it.
The other piece to this puzzle is the condition of the original caliper that had the outer piston extended and frozen with the dust seal cracked (see first post). That outer pad was very thin while the inner pad was thick. I wonder if a worn bearing could cause the rotor to shift causing a high load on one pad? This therefore would generate high heat and degrade the seal and finally seizing the piston.
I could sure use some advice with this one!
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Just a thought, Wallace.
Did you check the e-brake shoes while you had the caliper off?
On one of the UK Club members cars, the shoe linings had parted from the shoes and caused all sorts of noises and problems.
Naj
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Thanks Naj,
I did check the brake shoes and they looked OK. Without the pads in the caliper, the rotor can spin freely. When I apply the hand brake, the shoes lock the rotor. The rotor spins freely again when I release the brake. Strange why that one side is so hot. At its worst so far, I would guess that the RR caliper is around 170-180*F to the touch, while the other calipers are 110*F or so. Quite a difference. I can't hold my hand on the caliper for more than a half a second before it gets too hot.
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Is the rotor hot too?
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I check the calipers right after a drive so the wheel is on and the rotor is hard to access. But the wheel rim, rotor dust shield, axle housing and anything else I can feel are NOT hot. In fact, these parts are the same temperature as on the other side.
I can always tell when the caliper becomes hot during a drive, because the brake on that side will let out a slight squeak only just as I apply the brake. As I mentioned earlier, I replaced the caliper on the left rear side and have no issues. So at least I did that one correctly!
Keep the ideas coming.
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... If the bearing is worn, a load would cause the rotor to shift. My axle has 140,000 miles on it.
Hello Wallace,
Interesting problem indeed and I'm following this with interest.
One way to verify if the bearings are suspect/bad is to measure the amount of play in the rear hub with a dial gauge.
The process is similar to the one used to check the bearing play on the front hubs.
The other piece to this puzzle is the condition of the original caliper that had the outer piston extended and frozen with the dust seal cracked (see first post). That outer pad was very thin while the inner pad was thick. I wonder if a worn bearing could cause the rotor to shift causing a high load on one pad? This therefore would generate high heat and degrade the seal and finally seizing the piston.
It is possible...
Generally speaking, it is usually not the heat that seizes the piston, but rather the crap that enters when the dust seal is cooked/cracked. Moisture finds its way in the space under the dust seal and rust quickly develops in the space between the dust seal and the piston seal in the bore.
Also important is that the mating surface between the brake rotor and the hub is absolutely clean and free of corrosion/grime to ensure a perfect fit.
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Anyone know if there is a rule (of thumb ?) when the rear axle bearings should be repacked with grease?
Naj
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Naj,
I have been sifting through the literature I have and found nothing indicating when the grease in the rear hub should be replaced.
It's a different story for the front hubs though. According to the manual one should replace the grease in the metal dust caps every 20 000 km's (12 000 miles).
That's about 20 grammes of high temperature wheel bearing grease per cap (if filled to the line).
For the rear hubs you basically have to disassemble it (special tools required) to change the grease and that is quite a tedious job to do every 20 000 km's.
Thus it would be interesting to hear what other members have to say.
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Is it fair to assume the original grease should last the life of the bearing, perhaps 100,000+ miles?
Front bearings suffer much more stress due to steering forces and braking forces.
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Re: Lubrication of rear wheel bearings.
These bearings are lubed by the rear axle lubricant. Re-packing as in the case of front bearings is not necessary.
BBB recommends change rear axle housing oil every 12,000 miles.
Mait
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There is an oil seal between the rear axle oil and the bearing, this prevents the oil washing the bearing grease away!
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Larry is correct, there is an inner and outer oil seal fitted on the enclosed axle shaft and the bearing is indeed packed with high temperature bearing grease.
With reference to the rear bearings, the service manual states that the bearings should be rejected on principle (even if they appear serviceable) after 100 000 km as the duration of further serviceability is unknown.
I guess in practice it doesn't always work that way as the cost of replacement (in terms of time, effort and money) make many owners neglect that aspect.
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Thanks for the replies.
I was planning on rebuilding the axle in about 4-5 months and cleaning the entire rear under section including gas tank. That's a big project! I could wait until then, but I would like to see if I can find the cause to this problem first.
I think I will remove the wheel, pads again and see if the rotor is perfectly in-line. Maybe there is something causing the rotor to misalign when tightened down. I don't think the brake regulator in the rear could cause a problem side to side. I am pretty sure this has to do with the rotor alignment. Since the calipers have the piston springs to keep the pads snug on the rotor, I think this is the source of heat. Has anybody else ever seen the piston springs????
Maybe the rotor is warped????
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...I don't think the brake regulator in the rear could cause a problem side to side...
Highly unlikely to be the cause of your problem.
I still would check the brake rotor and the hub with a dial gauge to check for any deviation.
If I remember correctly, one also need to check if the brake rotor itself is centered in the caliper.
Can't for the life of me remember where I read that in the manual at the moment, but will look for it and report back.
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Hi,
Interesting problem. I second checking the runout of the rotor on the axle then I would check the runout of the axle flange itself. if the axle flange is bent from a previous accident or curbstrike it will cause even a new rotor to "Wobble" more than is acceptable.
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Are you aware that there is a locating stud for the rear disc/drum on the halfshaft flange.
The hub only fits in one position. Usually if the hub is tightened in
the wrong position the stud just pushes back through the flange but maybe
in your case it did not.
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I looked for a locating stud but never found one. The rotor without the wheel bolts or pads will spin freely. The other side was the same way and I am not having problems there. However, maybe the stud is sticking through just enough to cause problems.
I don't much like the thought of the axle being bent!!!! BUt a good idea nonetheless.
Hopefully I can pull the wheel off tonight and do some investigation.
Great ideas. Its always easier to find something when you know what you are looking for.
Thanks!
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There definitely isn't a locating stud on my axle flange nor is there a place for one. After removing the wheel, I found the rotor alignment to be slightly more inboard in the caliper. I couldn't find any obvious warpage with the rotor using a straight edge.
The end play on the right axle flange is about 1.5mm (.060"). The run out is 2mm (.008"). I looked in the BBB and I found a spec for the shaft run out which is .12mm (.0047"). I could not find a spec for the shaft end play. It looks like the run out is only slightly out of spec but the end play seems excessive.
The new rotor arrived and I will put that on and see what the run out is. What is the spec for the rear rotor run out?
Any thoughts?
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Hello Wallace,
The runout for the brake disk is measured on the outer edge (dial gauge mounted perpendicular) and would be 0.12 mm for the front and 0.15 mm for the rear (maximum).
That end play does sound excessive indeed. Bearings towards the end of their life perhaps?
The specifications I have for the rear axle flange is as follows:
a) maximum permissible vertical runout on centre alignment with shaft installed is 0.12 mm
b) maximum permissible lateral runout of flange is 0.12 mm
Hope this helps.
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The spring type pistons in the caliper may lead to higher pad pressure but I doubt it's causing your disc to run hot. Any lateral deflection on the rotor or the axle shaft would normally move the pads back and should prevent any heating problems.
In most cases, one pad having more wear than the other is usually a stuck piston. I can't imagine it being a wheel bearing. Spinning the wheel while lifted should tell you if the bearing is bad just by the amount of noise you hear. You could also put the car on a lift and use a mechanics stethoscope to listen for any unusual noises.
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The problem is temporarily solved!!!! The right axle shaft flange had a lateral (wobble) run out of .008-.010" as measured at the edge on the face with a Starret dial. The end play is exactly .046". The rotor had a run out of .012". To me, both of those dimensions are excessive. I installed the new rotor on the flange and secured it. When the axle was pushed in, the rotor was about a 1/32" away from touching the inboard caliper casting. With the axle pulled out to the end play range, the rotor was just about centered.
I had already moved the pistons back in their bores. I held the rotor in the centered postion and applied the brakes to reset the pistons in that spot. When I turned the left tire, the rotor and pads made a shh...shh...shh sound from the rotor run out. I decided to again reset the pistons directly on the spot where the pad didn't make contact with the rotor. After doing that, the rotor/padnoise was almost consistent all the way around!!!!
After doing a quick blast down the highway, both calipers were the same temperature. Normally the right one would very hot at this point. So, this is a temporary fix and will only be permanent when I rebuild the rear axle.
If this would have happened on the front, I don't think that the heat generated would have been as severe. The spring loaded pistons in the rear not only keep the pads snug on the rotor, but also a stronger force is required to push them back.
Thanks to everybody for their suggestions as they were extremely helpful. Oh well, I have more fish to fry.
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I had a similar problem a while back. This was with a standard caliper. I had a hot running problem as well but this was caused by a defective caliper. The casting was a bit too thick or something like that and we had to put a washer behind the caliper to [position correctly;y.
I changed axles last week to the LSD and I had the exact same problem with a completely different unit. The caliper works fine but is clearly no to spec.
LDS really makes the car pull hard. I can definitely feel the difference and the front of the car lifts more under hard throttle. Should be fun when the roads clear up.
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The problem is temporarily solved!!!!...
Glad you got it sorted Wallace.