Front Calipers Sticking - after pad/rotor change

[Osameshar]

Hi,

Running into some strange issues after attempting a brake pad/rotor change and have completely ran out of ideas, hoping someone can help. Here is the situation. 2000 540i 6speed.

1. Trifecta lights, shipped module out for repair by module master.
2. New pads and rotors installed.
3. Drive around the block, when pressing clutch in can tell the some of the brakes are engaged.
4. Jack the car up, and the front wheels are locked tight. rear are fine.
5. Caliper release pressure when bleeding at the caliper.
6. Replace brake hoses on the front brakes and bleed
7. Drive the car again, and the calipers lock up again.
8. Remove the master cylinder from the car entirely should be no pressure in the lines.
9. Calipers are still locked up until we release pressure from the bleed screw. Only have to crack one bleed screw to release both wheels

At this point, we are out of ideas. Current theories are, something in the abs module is holding pressure between it and the front brakes with no pressure on the master cylinder side. Calipers are mildly frozen and dont release normally. We have test driven with the abs completely disconnected after a recommendation from module master tech. Same result.

Thank you for your time, let me know if i can give more information.

[Nfs021]

How many miles on the car? Also how is the condition of the brake booster? They are known for sucking up water and going bad if the drainage holes beneath them aren't kept clean causing all sorts of problems. Did you replace the master cylinder or just disconnect it? If your car has really high miles, they probably both need replacing.

One other thing, were the calipers rebuilt recently? The pistons in both could've been pushed back in wrong causing the problem. Granted that's unlikely, but still possible.

[Osameshar]

Around 90k miles on the car. Removed the booster fully from the car and the cylinder from it. Attempted to replace the master cylinder but the replacement part had some screwed up threads on it. So ended up just putting the old master back in there. No rebuilt calipers, just originals. Thanks for the reply.

[JimLev]

Caliper pressure is released thru the ABS module, you need to investigate why it isn’t releasing, clogged solenoid inside the module??

3172720A-8166-473D-8AED-F08959217EE9.jpeg

[Nfs021]

Yeah I suggest you try and find another ABS module to test. Maybe borrow or get one from a local junk yard car. If it works, then you solved the problem. Keep us posted.

[SW530]

Any chance you damaged the anti lock sensors?

[CPHES]

And this was not an issue before?

[Chedley]

Sounds like a locked ABS problem, or as simple as air introduced in the ABS lines while working on the brakes; pretty common issue.

This problem did not happen before you worked on the brakes system , yes ?
Do you have access to a BMW scanner - such as INPA - that can read ABS module errors ? Can you list those error codes necessarily left by the trifecta lights ? That would tell us what is going on.
My bet is on air in the ABS lines…, nothing wrong with the ABS module.

[Chedley]

I would add : Do NOT drive the car with a disabled ABS and risk of locking calipers. That can be very dangerous…

[KeysCoupe]

I think the problem is strictly in the calipers themselves. You replaced the pads, meaning you had to push the pistons back into the caliper housing. The pistons are binding in their “new” location. They have corrosion or crud built up outside the range where the pistons have been operating up to the pad change, which makes them stick in their new retracted position.
I’ve run into this same issue at least 4 times over the years. The solution is to dismantle the calipers, thoroughly clean, and reassemble with new seals and boots, provided the pistons clean up perfectly. You will need to pop the pistons out carefully with compressed air, if your lucky. Otherwise, install new or rebuilt calipers.
-Donny

[Osameshar]

Issue did not occur before changing the pads/rotors. Although trifecta lights had been on for many months at that point, only drive the car once a week maybe. I personally don't think there would have been air introduced to the ABS module, as this issue was occurring before removing any hoses.

Thanks for posting that diagram. Replacing the calipers was my next move probably. Or take it to the dealer at this point lol.

[Chedley]

Man, do not go to the "stealer" aka dealer on this one. They will milk your wallet dry...lol..

Buy a rebuilt calipers from a reputable BMW parts site, they will take your old calipers as "core" and give you some $$ credits. Install them and that is that. That is much better and cheaper than trying to rebuild them yourself.
Then still, do the ABS bleeding, then bleeding/flushing/replacing of the brake fluid from the brakes lines and master cylinder..

[Nfs021]

Chedley is right. The dealer will absolutely rape your wallet. If you go with new calipers, here are ATE calipers at FCP for great deal. Can find cheaper rebuilds. But with FCP, you are covered by lifetime warranty. Screenshot_20220904-173931_Chrome.jpg

[Osameshar]

Caliper pressure is released thru the ABS module, you need to investigate why it isn’t releasing, clogged solenoid inside the module??

I believe you were on the money here. I had it towed to a shop, and this is what they determined. Quoted replacement for hydraulic unit at $4400. Obviously not going to pay that... guess I may try to source one from a junkyard or get a second quote.

[Chedley]

By "hydraulic unit" you mean the ABS module , yes ?
If so, it usually logs an error code if it is malfunctioning. Did the shop tell you what is the error code ? Or how did they determine that it is bad ??

Anyway, if so, you can always buy a used unit at the junkyard or the bay-site for less than $100 sometimes. That would be probably your best bet instead of getting a new one or going thru rebuilding. As to removing and installing it, it is pretty straightforward. Check the DIY's.

[Osameshar]

By "hydraulic unit" you mean the ABS module , yes ?
If so, it usually logs an error code if it is malfunctioning. Did the shop tell you what is the error code ? Or how did they determine that it is bad ??

Anyway, if so, you can always buy a used unit at the junkyard or the bay-site for less than $100 sometimes. That would be probably your best bet instead of getting a new one or going thru rebuilding. As to removing and installing it, it is pretty straightforward. Check the DIY's.

I'm not sure of the exact terminology but, the pump piece that the electronic ABS module attaches to. Waiting on the documentation, will hopefully know more tomorrow. Only tricky part I've seen is the bleeding process after installing a new one.

[StephenVA]

HOW TO BLEED BMW E39 BRAKES (and any other BMW model during these years)

Brake bleeding procedure (DIY anal version)
1. Suck all old fluid from master cyl reservoir
2. Top off brake fluid DOT 3/4 (Do NOT use cheap store brands) (Preference: Valvoline Synthetic DOT 4)
3. Pressurize system to 15-20 PSI using tool of your choice (Example: https://www.ecstuning.com/b-motive-p...eder/motivepb/)
4. Plug in scanner/test unit and select brake bleed for ABS (Tool example: Foxwell 510/530)
5. Move to RR, open caliper bleed screw with hose to catch bottle
6. Flow until bubbles stop (make sure fluid in Reservoir stays more than 1/2 full
7. Turn on ABS cycle purge, flow until no bubbles, then pump pedal 5 X
8. Turn on ABS cycle purge once again Bubbles? Flow until clear
9. Tap/hit Caliper with rubber mallet
10. Flow until clear
Move to LR, RF, then LF repeating steps 5-10
I personally do a final go around after all are clear to be safe.
11. Road test making sure ABS gets activated on loose road surface No need for stomp and lock on Hwy.
12. Final re-bleed to confirm all is well

Pedal should be normal at this point. If not look for master Cyl, vacuum line check valve, or power booster failure. On X5 4.8is there is a vacuum pump on the Right front cam that leaks and will fail sooner or later. On this fail, pedal is perfect until engine start, then it drops off.

Can you short cut this process and come out OK? Y/N

If all you are doing is a bi-annual bleed out and you have no pedal pump up (NO AIR trapped in lines). Your brake fluid flush is really simple, skip steps 7, 8, 9, and 12.

To the OE Poster: Your ABS is NOT releasing pressure in the front lines. See post #4 as Jim noted ABS block solenoids locked for whatever reason. Have you ever cycled them with a BMW specific code tool/lap top with the BMW software?

No? Then try that step FIRST.

Helpful?

Valvoline Synthetic DOT 4 Brake Fluid (32 oz.)

See attachments
* Mike Miller BMW CCA Tech Writer
* TIS (BMW Tech Manual)

[Osameshar]

Just to close the entire loop on this thread in case someone is searching for a similar issue. Ended up buying a used hydraulic unit, replaced the unit and bled the system. Car functions normally again.

[StephenVA]

Congrats and thanks for the follow through. It is appreciated.

there are lots of interest in the tech world on brake fluid contamination causing abs failures. They all point at Euro applications. I personally believe the the recommendation of bi-annual brake fluid changes on daily drivers as insurance to side step down stream issues. Every time I see an image from a lack of maintenance car brake caliper piston, there are pock marks on the pistons from the moisture that boils and re settles on the bottom half.
the shops around me seem to get quite a few in especially newer models than ours.