Tone

I'm in Moab, UT and cannot backup without the brakes locking up like it is sensing serious slipping or decending a steep hill. I can give it a lot of throttle and drag the tires backwards but I'm leary to do that repeatedly.

No codes. No event that caused it - just drove 1200 miles from Texas with a full load in the back. Have pulled fuses and relays related to ETS/BAS but with no help. Will even do it in neutral with the engine off but key on. 4Lo, same thing. Disconnected battery for 30 minutes and no change.

Any ideas? Posted on the 163 forum but no answers. Thanks.

MBTech21

Which brakes are locking up? Front, rear, all ? In Neutral with the key off, will it roll backwards?

Tone

ALL brakes lock up. In neutral, if you push or let it roll back, all of the brakes lock as well. On the trail today it would sometimes let me reverse a few feet and other times only a few inches before the calipers clamped down. Forward, everything works fine and it climbed a number of obstacles I never thought possible.

Tone

Now it appears to be isolated to the passenger side front tire. Still no codes - does it with ESP on or off, low or high range - way weird!

MBTech21

It's probably the ESP hydraulic unit/control unit-located under the washer bottle. We've seen this several times, where the RF(mostly), will burn the pads right off the car in about 2000 miles. The hydraulic unit has fixed it every time.

The first step would be relieving the hydraulic pressure and make sure the wheel turns then. The electronics aren't really effecting it- I think its some kind of check valve sticking in the valve body.

Tone

Thanks. Further testing shows that when I reverse w/o the brake pedal pushed, I can back normally but as soon as any pressure is on the pedal, the RF wheel locks up hard.

When you say relieving pressure, do you meen at the caliper or is their a bleedvalve on this hydraulic unit? It only seems to be when I am in reverse but I was going to drop that wheel off today anyway to see if there is anything visible. And my guess is, one can't simply backflush this system to clear it and that the part is insanely expensive? Wonder why no codes have been thrown.

Thanka again.

MBTech21

The caliper is easier to open- otherwise its the line at the unit. You could try flushing it, but I've never done it (liability and all!!). They aren't cheap, but I don't remember how much exactly.
Any I've seen have not thrown any codes, so its my thinking that is strictly a mechanical hanging up of the ESP 'hold' valve.

Tone

Thanks so much - I will try at the caliper and let you know. I really appriciate your time.

Tone

I was unable to pull the front wheels while there and noticed it was changing between left and right front. Got home yesterday and pulled the wheels and both front calipers were missing their lower bolts so when reversing, they would catch and sling up into the wheel. Not sure why they would lock at that point and why my buddies did not see them moving when I had them look several times. Replaced the bolts and all is fine except for a scratches on the edges of the rotors where the calipers rode. Thanks again for all the help.

MBTech21

That would do it- never thought to think about that!!

Quick note to all DIY guys and indys that read this forum- we put new bolts in the calipers when they are off for a reason (mostly the new loc-tite on the threads!). I'd like to say that it's the first time I've seen/heard of this..but it's not.