Car moving under braking

[will950]

Hi PH,

Slightly puzzled by my wife’s CMax (2014 2.0 diesel power shift auto). It started pulling hard to the right under braking. I could feel the front offside wheel was hot compared to the nearside wheel when I pulled over. I had this investigated and a sticky piston in the caliper was identified on the front offside wheel. We had the caliper replaced, as well as new front discs and pads and brake fluid. I’ve also had the wheel alignment checked and adjusted. The front tyres are a matched pair of Avon AS7’s and the pressures are regularly checked.

The work we’ve had done has helped a lot but there is still a pull under braking and I’m a bit lost for where to look next. It’s not as severe as it was but it is noticeable. I did some test emergency stops and it stops fine, there is an initial pull to the right but the car comes to a stop well. Id be grateful for any pointers!

Thanks!

[ARH]

well there are a few things that would cause this, brakes not working the same on each side, this could be a bleeding issue, the new caliper not being the correct one fitted.

It could be a suspension or steering joint failing.

It could be a wheel bearing.

It could also be badly executed repairs or alignment, do not dismiss this as parts can be faulty or mechanics can make mistakes as we all do.

[fooman]

I'd put money on sticky piston on left caliper, but could be any of above

[RizzoTheRat]

Is the wheel still warm? I had what the garage thought was a sticky piston and replaced the calliper which solved it for a while but it happened again. It turned out the lining of one of the brake lines degrading leaving sludge in the brake fluid which stopped a calliper from releasing properly.

[E-bmw]

fooman said:

I'd put money on sticky piston on left caliper,

^^^^ Wot 'e said.

To be clear lift the front end & rotate each wheel, I'll bet the front left sticks.

The way it exhibits itself on a car is as follows.

Assume the (worst case is easier to explain) front left is seized and the pads are off the disc.

Driving along is fine, and when you brake the front right works & pulls the car to the right.

Assume the (other worst case) front left is seized & the pads are on the disc.

Driving along the car pulls to the left, when braking the car either straightens up or now pulls to the right.

I believe they partially mis-diagnosed your original issue & you didn't need a new calliper at all, all you needed was for both callipers to be serviced but garages don't like doing this as it takes more of their time & makes a bill look harder to swallow as there are no parts on the bill.