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front brake calipers locking up

08-29-2004, 04:31 PM
Looking for some ideas. Fairly recently acquired 1992 525i, 101,000 miles. Love the car and driving feel, don't mind putting the effort in but do not know where to start. She needed some work including both upper and lower control arm bushings. Replaced those over the last couple of weekends. This week the front brake calipers are locking up adding significant drag to the car, overheating the front brakes, smells and feels hot. Rear brakes appear to be fine. Seller had replaced brakes within the last 5,000 miles. I thought maybe he did not 'grease' the caliper guide pins and components, so I tried that and all was well for a few miles then back to the same locking brake calipers.

Is this brake caliper, brake cylinder, master cylinder or ABS related? Do I need to bleed the system? I cannot not imagine how but could replacing any of the front suspension components have had anything to do with this? I read on one thread about an interconnection (power assist) provided by the power steering pump and that 'over filling' the PS resevoir could cause such a problem. I did add fluid to the resevoir recently but the level is between the marks on the cap dip stick.

If caliper, or cylinder related is this DYI? How about the ABS? I have been looking for some good links to address this problem and repair procedures but no luck as yet.

Thanks in advance.

John Q

08-29-2004, 09:50 PM
Hi John Q, hope I can help you a little. Here's what my 'Diagnostic Dartboard' come up with [ I wasn't blindfolded this time ].
1] the power steering/hydro boost idea isn't your problem and, hopefully you misunderstood one of those threads.
a] your car has a vacuum booster.
b] no problem in a hydro boost system would cause this situation.
c] the ABS can't can't hold residual pressure in the lines.
d] there are sometimes exceptions to every law [just kidding, mostly]
2] unlikely you could have done anything during the suspension repair to cause the problem unless you somehow twisted the caliper hoses.
3] your problem is unusual on an E34 but not uncommon on E30's [same caliper mounting design]
4] I think you were very close to solving it. Remove those 7mm allen head bolts that hold the caliper to the brackets, this time cleaning off all the rubber residue from the bushings they ride in and relube them with a silicone grease ['sil-glyde' comes to mind]. This 'mechancial' seizing or binding of the calipers is the cause of more brake problems than many think and the fix is so simple [ and cheap! ]. Give the car another good test drive and see how they are.
5] If the dragging persists and do take the time to jack it up and know which wheel[s] are effected, crack open the bleeder screw. If pressure is relieved and the wheel suddenly spins freely, the problem is hydraulic and there'll be a few more steps. IF the wheel still drags badly, the caliper piston/seal is sticking and the best course is a quality rebuilt unit[s].
6] so far all of this is experienced do-it yourself stuff I'm sure you can handle. The brake bleeding is easiest done by two people depending on your equipment.

BEST TO YOU and 'will be waiting a future post from you..........jeff b.

08-30-2004, 08:13 AM
Jeff B,

Thanks for the quality input. Really love this bimmer and have high hopes of getting it back to what it should be. One of the things I love so much is that it has rekindled my interest in automotive repairs, long lost on modern American vehicles - guess it goes back to my youth as a VW nut. Anyway I have to think it is something simple.

But in follow up why would both front calipers be experiencing similar problems concurrently? I could understand a single caliper - but both?

I cleaned and lubed the guide pins and other caliper sliding surfaces on both front calipers but did not think to clean and lube the bushings themselves while I had them in my hand - doh! I will give it a go this evening and have the caliper re-build kits handy. I will post the result - (with hopefully a happy ending).

Oh one more thing, if the above does not work and I crack the bleeder valve and the wheels spin freely are the additional hydraulic repair steps still DYI?

Thanks again.

John Q

08-30-2004, 06:45 PM
Hey John, no it's not common to see both calipers develope this 'sticking problem at once and yes, the further steps can be 'experienced diy', but it will be important to be ready to jack it up as soon as you complete your R/T to isolate any possible further conditions as these problems can be 'fleating' ones, disappearing after a cool down, etc... jeff b.

08-30-2004, 08:52 PM
Jeff B,

Just dropped the car from the jacks after the R/T, cleaned up and came in to get some dinner and saw your post.

Before I did any work this evening I tried turning the wheels the pressure had relieved somewhat since parking yesterday and I could at least rotate the wheels but still too much effort. Cleaned up the guide pins and bushings and re-lubed - wheels turned about 1.25 revolutions with a strong spin - still not great but better - no luck after the first push of the brake pedal though, same old major resistance to rotation. So I tried step two and cracked the bleeder valves - no great pressure or burp of BF - wheels still do not want to turn easily. Took it out for a test drive to see if the action would 'loosen anything up'. Put her up on the jacks upon return and feel that the problem is about the same as before and definitely front end oriented.

Based upon your earlier e-mail at this point I am thinking the caliper pistons are sticking. Sound reasonable? I had to order the re-build kits so I cannot mess with this until tomorrow evening.

Still curious about both front calipers experiencing problems at the same time. The only common thread that I can think of that may have occurred - I have never (and I mean never) hit a car with as much force as I did removing the ball joints at the upper and lower control arm replacement - maybe I just knocked some grit loose in the piston sleeve and started my problems?

Thanks again for the input,

John Q

08-31-2004, 07:43 PM
Hello again John Q, well, here are some further thoughts since it's really, really difficult to diagnose some problems from 2,000 miles. I've tried but just can't get the feel of how 'hard' it is to spin your wheels. You may have fixed the problem and heres why.....these style calipers does really 'release' or feel 'free' like some other designs. Fixed calipers rely on the piston seals only to 'retract' the pads along with the very slight axial run-out of the wheel hub to 'bump' them away from the disc. With your style of 'floating' caliper, 'fixed' in the flexible rubber bushings the 'bumping' away doesn't happen as readily as the bushings absorb most of this movment. On E34's, E32's and some others, that 1.0 to 1.5 free revolutions is actually pretty good! If after pumping the pedal a couple of times you can get 1/2 a spin of the wheel, I 'm think'n your ok! These rotors are terrible for warping and if you do have a problem you'd feel it in the steering wheel fairly quickly, but again, I can't feel the drag from here.
By the by, I know what you mean about the 'pickel-fork' surgery, I fortunately possess the seperating tools for the joints. I DOUBT HOWEVER if you caused any disruptions as you suspect AND before your dive into rebuilding the calipers [which take a bit some finesse to install the dust boots and could create a new problem] I recommend you drive it a few days, see how it feels. On a level surface, coasting to a stop in neutral, better yet a very slight incline up, as long as the car doesn't seem to 'grab' when the wheels stop turning or on a suitable incline begins to roll back a bit, I think your good...Keep in touch........jeff b.....

08-31-2004, 11:05 PM
Jeff B,

I'm in the deep end and treading water okay at the moment.

The wheel spin I achieved was only after immediate work on the guide pins but there was zero spin after depressing the pedal and the wheels would actually only rotate with considerable effort. I can feel the drag on test-drives, wheels still heat up and gas mileage is way down. Tried the neutral coast as well and can definitely feel the resistance.

Kits in hand. Calipers are off and pistons almost out. I will need a little air to finish the job, but that is tomorrow. I cannot yet see in the caliper cylinders yet but the piston extensions so far show enough crud to think I am on the right track. I doubt her previous owners ever flushed the brake fluid.

Thanks for the input, I know it is hard to diagnose from a distance but do appreciate the sounding board and advice. I hope to have her back on the road tomorrow night. I will post you with the results.

John Q

09-04-2004, 09:53 AM
Just thought I would post the outcome in case it may help others in the future.

It was the calipers, they were really (and I mean really!) stuck or frozen. I made some mistakes in my repair efforts that made the job more difficult than it had to be.

I originally struggled with my diagnosis, trying to make sure I had checked all of the "simpler" repair options before diving into the rebuilding of the calipers. Once I convinced myself that this was the direction I needed to go, I pulled both calipers from the car to work erect at the workbench - I could not move, let alone remove, the pistons! This cost me hours of effort and trips back and forth to the tool store, as I thought, “it cannot be this hard”. I then tried the air pressure option – no luck even at 85 psi. Stumped I took a break and contemplated my future as a home BMW techie.

Finally I recalled a thread posting that suggested the use of the cars hydraulics to remove the pistons. So back to the car and on the brake lines the calipers went – not necessary to actually reinstall the calipers in their mounting bracket, just reconnect the hydraulic lines – support the calipers as needed to avoid stress on the brake line. (Recall that I had started this procedure much earlier in the process to push the pistons most of the way out and stopped to move to the workbench…) Check the fluid level in the brake reservoir – keep an eye on this. Several pumps of the brake pedal and the right caliper popped its piston. This will be a messy procedure as the fluid will spew under pressure once the piston pops, a few disposable aluminum roaster drip pans and wrapping the calipers in some ‘disposable rags’ kept this to an acceptable mess.

Ahh success at last… or so I thought, I again remove both calipers to the workbench rebuild the right one (remember only one popped completely out) and mechanically try to remove the piston from the left caliper – without any luck! So back on the brake lines the calipers went only I was able to completely reinstall the right side – prep for the mess – a few pumps of the brake pedal and the left piston pops right out. Unbelievably simple but I made it more difficult in not knowing the simplicity and in my efforts to get to work at the bench too soon.

Oh… the things I noticed as wrong included – nothing real obvious, dark brake fluid indicating contamination, some ‘minor’ corrosion on the pistons, and rolled seal rings. I believe the rings to be the root of the problem although I am not sure how or why it would have happened and still curious as to why both at the same time.

A good clean up of the pistons and caliper cylinders, reinstall the seal ring and lube all with “sil-glide” and I am ready to reinstall the pistons - right!! I was not prepared for the resistance to reinsert the pistons. It took a makeshift drift (ratchet extension with socket sized to fit inside the brake piton and some ‘gentle’ taps with the 3# sledge. Once the pistons were 75% inserted I could basically move them by hand – ahh success at last. Only one thing left to do – install the dust boots.

Jeff B was right I was not prepared for this effort either. I really struggled with the first one trying to tuck the dust boot into the cylinder receiver channel / groove. The trick was to push the piston all the way in – then the dust boot receiver grooves on the piston and the cylinder will be aligned allowing the room to slip the boot right on – use of the sil-glide to lube the boot and receiver grooves was helpful. Complete the caliper reinstallation, coerce the wife to help with the brake bleeding, then back on the road – all working as it should with the Ultimate Driving Machine.


Moral: Patience, do one caliper at a time, use the cars hydraulics to push the pistons out, clean and lube all parts thoroughly, expect more resistance due to BMW close tolerances, push the pistons in all the way to install the new dust boots, make sure there are no left over parts, enjoy the ride.

Specialty tool help – small size “tail pipe expansion” tool fits inside the piston to aid in gripping the piston - loaner tool from Autozone.

Thanks again for the input throughout Jeff B.

John Q

04-08-2009, 11:08 AM
Hello there. I have a E28 535i 1986 with the same problem. It have the hydraulic booster and the right caliper locks-up to the point it stops the car. You mentioned that if the wheel spins free when loosening the bleeder is a hydraulic problem and some more could be done. What else could be done? Can you tell me what shoud I check next? Thank you very much.

02-27-2010, 11:52 PM
God bless this conversation a couple years ago, I was able to fix my car with this topic. I have a 1999 Mustang GT v-8 and the front right wheel froze up shortly after the left front wheel froze up. It ended up being both calipers the square seal inside the calipers was bad. i was able to go 75 mph with my brakes locking up but the steering wheel shaked violently which made me think it was tie rods. After i got out the car both rims were super hot. and the brakes smelt like burnt toast. i jacked the car up and wasn't able to turn the 2 front wheels by hand. of course the engine is a lot stronger then my hands.

so yeah i took my car to the mechanics and he was able to check from the master cylinder by cracking the lines open and the response the wheels gave him like weather they were able to move or not. it told him the master cylinder wasn't bad then he went and opened the lines on the frame. he thought it could be the brake hoses but it turned out being the calipers. The lines were delivering brake fluid like it was supposed to.:runaround:

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