Hello,

I am having a weird issue with our 2010 GLK 350.

About two years ago we had the front PS caliper lock up on us while driving.

We brought it to our local shop - and decided - well it is probably time for a full brake job anyways (100,000 km) given it had smoked the pads and rotor on the PS side. They believed it to be a failed hose.

Had new rotors, pads, calipers, and hoses installed, on bith sides of the front. Everything was great. For 12 months and 2 weeks.

Drive to work and notice a smell.. touch the front PS rim and was hot, others are not. Drive it home 10hrs later (15 min drive) and rim is smoking hot. Original shop couldn’t get us in for a few weeks - so went to an alternative shop.

Again, front PS calliper is dragging and stuck. The shop tried cleaning the slides etc - no luck - replace calliper. Everything works great.

12 months plus a day - get home from work and smell brake smoke. Touch the front PS rim - it’s hot - others are ice cold (Canada in December) I already had an appointment the next day at my original shop for motor mount replacement- let them know what I suspected for them to troubleshoot.

Shop troubleshoots - yes brake is dragging - so they clean it, check the slides - everything seems normal and good - test it - brake is dragging - only worse now.

Shop is in agreement that one failure okay - that can happen - second one, on the same side.. same timespan - that is suspicious

I had the brake fluid changed out when I had the rear brakes done like 8 months ago.

Shop is doing more digging, but suspects it may be something to do with the ABS/TCS

In all cases where it has happened - there has been no brake issues leading up to the failure, no stuttering, vehicle pull , no poor mileage. First and second time began while driving uphill.

i can’t fathom a brake caliper failing after 25,000km.. twice on one side, while the other side is completely fine.

Thoughts?

 

I'm with you - can't imagine two bad brake calipers. Could be a flakey master brake cylinder but due to the intermittent nature I'd be more inclined to go with an ABS/TCS fault or a fault with the system that lightly applies the pads against the discs to dry them off when they get wet (assuming your GLK has that).

 

I bet you have a solenoid sticking in your ABS module.
You say it began while driving uphill. Were you stopped on the hill? The ABS module will hold the brakes on hills so you don't roll back, so a failure in the ABS module in this scenario would make sense imo.

 

Could also be a fault in the 4matic. thinks the wheel is slipping and applying brakes.

 

Thank you for the reply - the first time we were not stopped, it was a long hill on the highway - but I was slowing down to take an exit lane

 

Would that be like an issue with the wheel speed sensor?

 

I think so . Just strange it does not happen more, but electrical faults come and go. Dealer is expensive but several Mercedes garages in BC

 

When it initially stuck and overheated debris was made from the excessive heat, it probably was not flushed properly or enough. To flush it the Abs has to be manually opened with a scanner or the old fluid stays inside it. You say someone cleaned the calipers. It should have been replaced . I would flush the brakes properly with 1/2-3/4 gallon of new fluid and examine the old fluid for debris . There is probably junk in the oil clogging up things. Maybe the mechanics never triggered the abs to open. Once I paid for a flush, and by chance I got it on a lift and nothing was even touched. the Bleaders were covered in rust! I went Back to the mechanic and got it done. It’s hard to trust people.

 

What do you mean by "caliper locked up on us while driving".
Have they checked the wheel bearing and/or play in the axle? If there is a play, it will generate heat. You would likely have other symptoms but this whole situation is weird to begin with.
Failed hose will not cause a locked up caliper. If hose fails (i.e. raptures/leaks) you would lose pressure and use of brakes (pedal to the floor situation).
In your first case it's possible that piston in the caliper seized (with salt moisture and time it's not uncommon) so the pad wasn't releasing fully.
As far as "brake dragging" how do they figure that out? Btw, benz pads are notorious for leaving deposits on the rotors causing vibration and need for rotor replacement. MB pads for GLK are junk.

I find it hard to believe that TC would be applying brakes without causing a TC light on the dash.
Wheel speed sensor is very basic technology and if it doesn't work you would have error codes.

I think its likely something mechanical or improper pad installation.

 

Good points above about Adaptive Brake technology which preloads brakes and does brake drying. Maybe there are some unintended consequences or pressure going to that one particular wheel.
Somebody should diagnose the ABS module and activation. Might need a mechanic with proper software and troubleshooting steps.

 

A brake hose that has failed internally can cause a caliper to not fully release or even lock up a caliper. When a brake hose fails internally it can create a tiny one-way "flap" that allows brake fluid pressure to be applied to the caliper but not fully allow the pressure to be released. In this situation there is no fluid leak or loss of pressure.

 

When a caliper sticks , for whatever reason or defect, (mine stuck passenger side ) the temp could reach 1000f and vaporize the brake fluid and melt the hoses and contaminate the fluid with debris. It probably was not cleaned and flushed properly. Plus did you follow recommended brake fluid flushing? With ABS opened? I think it’s every 40000 miles. Flush it properly this time. Yes problems may come back from junk in the system and lack of proper maintenance, and the defect that messed up the caliper .

 

Is there source for this theory?

 

Did your hoses actually melt from the heat? Brake system is designed for pretty high heat. I would expect mb pads melt before any hoses are affected.

I agree that proper regular flushing is necessary given dot4 brake fluid but junk from failed caliper doesn't travel up and down. Unless you are pushing fluid backwards it doesn't circulate all the ways around. So even simple bleed would remove that.

 

It's factual, rather than a theory. I've personally experienced it on a Renault, years ago.

https://www.vehicleservicepros.com/s...alve-imbalance


"Symptoms of an imploded brake hose occur when the inner nitrile tube of the brake hose ruptures. Using vice grips to crimp off a brake hose when changing calipers is a bad practice since, many times, it will break the inner nitrile tube, setting the stage for a hose rupture and implosion. Some manufacturers clamp the brake hose to the fender wall. Over time, there is a warring effect between the point where the hose is held tight in the clamp and where it flexes. Over time, the inner tube will rupture again, setting the stage for an implosion of the inner tube.

Once the tube rupture occurs, and the brakes are applied, the brake fluid is pushed past the rupture, actuating the caliper. However, when you release the brake, the implosion acts like a one-way valve, not allowing the fluid to find its way back to the master cylinder or the caliper to release. This has all the indications of a stuck slide or frozen piston, but it is only the hose that needs replacement. It is a hard lesson to learn when the car comes back with the same symptoms after replacing all the brake hardware, (i.e., rotor calipers and brakes)."

 

Interesting. Thanks for posting. By "theory" I meant what theory behind issue in this thread.
When changing rotors I treat calipers and brake lines very carefully. Now I know why.
Crimping hose line during caliper change - wow do mechanics really do that? That's idiotic.