Brake Pull After Calliper Rebuild

[m4tti]

I've recently rebuilt my AP CP 6600 callipers. Annoyingly having put everything back together the car pulls to the left under braking. Ive bled the system several times and have examined the rear drivers side calliper and it seems to be working perfectly.

The only thing I can see when testing the calliper with the pads removed is that the upper piston of the inner half of the drivers side front calliper is slightly lazy. It also takes a fair amount of effort to push it back in but it does go in. It also will come out a decent way when all of the other pistons are held in place.

Thee doesn't seem to be any air left in the calliper as fluid does come out if I release the bleed nipple.

Theres some sample pics below. Not really sure where to go with this now, whether to pull the drivers side calliper apart again or work that upper piston.

Drivers side calliper inner half - The upper piston looks slightly lazy in comparison to the lower


Drivers side calliper outer half - This looks far more balanced


Passenger side calliper outer half



Passenger side calliper inner half

Edited by m4tti on Sunday 23 April 12:46

[m4tti]

paintman said:

You say you recently rebuilt the calipers. What did you actually do?

The calipers were stripped to the bodies, soda blasted, new seals, new link pipes and bleed nipples.

[m4tti]

Nothing else has been changed.

I think the pistons upper to lower vary as the lower are larger diameter.

[m4tti]

paintman said:

Is there any valving in the system that in the event of a hose or pipe failure would cause the system to only operate partially which has been upset by the bleeding?

And has everything been connected up correctly?

Edited by paintman on Sunday 23 April 19:47

It's a tvr so has about as much intelligence as a potatoe

[m4tti]

I used a vacuum bleeder on these so I don't think there'll be any issue in the master cylinder area.

I've just spoken to the guys that I've bought all the parts from, BG developments.

Essentially the pistons will come out at different rates. The fact the bottoms come out before the tops is pure chance and on the test rig they can come out in any order. The important thing is the pistons do come out and aren't seized into the bore.

One thing they've suggested is I remove the rattle clips to make sure the pads are seating correctly. So I will be doing that.

The other small issue is i didn't label the pads on removal so can't gaurantee they went back exactly the same as they came out. BG have provided me a method of measuring the taper on the pad to return them to the caliper in a uniform fashion.

Ive also measured the disc temp after driving and all discs have a similar temp within one degree...

[m4tti]

E-bmw said:

Good point, with mine using certain pads I actually used a grinder to take the edges off just to make sure they were slightly loose & therefore moved correctly.

Also a good point, with mine, there was a very slight machining error that meant for the first few hundred miles one pad was basically slightly un-square & would take longer to bed in and become fully effective.

That too may be a good call. The pads are snug and I've replaced the wear plates. It's possible as they warm up the simply can't move easily in the carrier.