on a 07 coopers, I just replace the front pads and rotor..

The left front caliper is not retracting fully (~ 1/16th"). When I remove the caliper, I can fully retract it.. there are no signs of rust. the boot looks fine.

I can manually retract the caliper but when the brake pedal is depressed, once again, the caliper stops about 1/16 from retracting fully.

The pedal seems soft as well.. I can pump and get a firm pedal, but it will not hold. It slowly goes down.

Have tried gravity bleed and it is all clear fluid. Could there be air trapped some where? if air is the problem

Does the master cylinder need to be bleed also? if so, how?

thanks

 

see

 

Are you saying that you can not push the caliper piston all the way in to give you enough clearance to install new pads?
What are you measuring when you report ~1/16th of clearance?

You should not need to push the cylinder all the way into the piston. In fact, doing so only risks damaging the the rubber dusty boot. Retract it just enough to allow new/thicker pads to clear the rotor. Then you are done.


Sounds like you still have air in the lines.
If your car has a manual tranny, you can also bleed the air out at the slave cylinder in addition to the 4 brake calipers.
I never had to touch the master cylinder in 20+ years of bleeding brakes. YMMV.

Pressure bleeding is easiest and most reliable, by far.
I've had a kit that I have been using on all by bimmers for 15+ years. The brake fluid reservoir cap thread is identical on the MINIs, so any BMW kit will do. Turner sells one: http://www.turnermotorsport.com/p-28...pean-cars.aspx

Don't forget to buy 2 cans of fluid.
You will likely need only 1, but if that's all you have on hand Murphy's law guarantees you will need the 2nd can.

HTH,
a

 

Thank you for the replies..

The caliper installs fine with the new pads..

When I use the brake, the caliper does not retract fully.. the left front pads is somewhat stuck to the rotor. I can turn the wheel by hand, but just barely. the other side is fine..

I think when I was gravity bleeding, I neglected the reservoir a bit too long and got some air thru, before adding new fluid. mini brake fluid reservoir is, well very mini!!! and it was the left F caliper when this happened.. so there is very likely air in there.. I used a 'suction' brake pump. it helped a bit. will look into pressure unit. thank you.

 

Air in the brake line, or lack thereof, would have no impact on the brake pad and caliper piston retracting and allowing the wheel to free ride.

What you are describing could be due to either the caliper sticking, or caliper guides worn/bent and not allowing the caliper assemble to 'float' back after the brake line pressure is removed.
The former would require a rebuild - a much easier process than it sounds. If it goes there, you will be replacing the outer rubber dust boot around the caliper piston, and the 1 or 2 rubber o-rings around the caliper that prevent the brake fluid from escaping when the piston is moving. If the outer dust boot is damaged or askew, you are likely looking at a rebuilt.

The other possibility is that he caliper guide pins are either bent, caked in dirt, or rusted. In that case, the inner pad (facing the caliper) is applying excessive pressure to the rotor while the caliper carrier is not sliding evenly to allow the outer pad to apply equal pressure to the other side of the rotor. To diagnose: inspect in/out-board pads for equal wear, and replace/lube the pins.

Hope the explanation makes sense.

a

P.S.: Now the brake pedal sinking to the floor - that's classical air in the lines. Get a proper pressure bleeder and re-bleed your fluid.

 

Thank you for the suggestions..

The dust boot is fine, so as the piston. That leaves me the wiper(?) rubbers.

Once I get the air issue resolved, will check on those..

Just wasn't sure if air might get trapped inside the master?

the pressure fluid replacement is the way to go.. thanks again.

 

Check your pads for correct installation,the inner and outer pads are slightly different [pin location] and will drag on the rotor if installed incorrectly.