350i long brake pedal travel after rear calliper rebuild
Discussion
It's been quite a while since I've posted here, good to see a few old names still are around.
I had to rebuild my rear callipers last week as they were sticking on, fitting stainless pistons and new seals.
Since the rebuild I've had a long pedal that always pumps up on the second press. I have pressure bleed the system umpteen times and the master cylinder is relatively new.
Today I finally realised what I think is happening. The pistons in the rear callipers appear to be springing back into their bores leaving the pads loose. When I first press the pedal the free play is taken up, the second press gives me a nice pedal with normal travel. This happens with the car stationary. I removed the reservoir cap thinking that it might be causing a vacuum?? Clutching at straws I know, but I am totally out of ideas.
Could it just be the new seals flexing, any suggestions much appreciated.
Danny
I had to rebuild my rear callipers last week as they were sticking on, fitting stainless pistons and new seals.
Since the rebuild I've had a long pedal that always pumps up on the second press. I have pressure bleed the system umpteen times and the master cylinder is relatively new.
Today I finally realised what I think is happening. The pistons in the rear callipers appear to be springing back into their bores leaving the pads loose. When I first press the pedal the free play is taken up, the second press gives me a nice pedal with normal travel. This happens with the car stationary. I removed the reservoir cap thinking that it might be causing a vacuum?? Clutching at straws I know, but I am totally out of ideas.
Could it just be the new seals flexing, any suggestions much appreciated.
Danny
Danny
I had a similar problem when I dropped mine out on the Gredge. Turned out to be air in the system (i think it was caught in the so called brake bias box and the rear calipers) I actually power bled mine 6 times and then the manual way before it all firmed up. On the bright side I know that all the fluid was new!
I had a similar problem when I dropped mine out on the Gredge. Turned out to be air in the system (i think it was caught in the so called brake bias box and the rear calipers) I actually power bled mine 6 times and then the manual way before it all firmed up. On the bright side I know that all the fluid was new!
When mine was like this, it was air getting into the master, a new once cured it.
I know you say you have a new one on there but maybe it's faulty.
If you think the pads are "springing back" then try slipping a sheet of paper between pad and disk, press the pedal, and see how long it takes before you can pull it out easily.
I know you say you have a new one on there but maybe it's faulty.
If you think the pads are "springing back" then try slipping a sheet of paper between pad and disk, press the pedal, and see how long it takes before you can pull it out easily.
adam quantrill said:
If you think the pads are "springing back" then try slipping a sheet of paper between pad and disk, press the pedal, and see how long it takes before you can pull it out easily.
The pads have sprung back by the time I get out the drivers seat and back under the car to check, so it only takes a few seconds.Danny Hoffman said:
Jack Valiant said:
Turned out to be air in the system
I can't understand why air in the system would suck the pistons back into the callipersFluid is "solid" it cannot compress like air.
I suggest you bleed manually...open...down...close... up, put a decent few CCs through it.
Give the fronts a quick bleed too, no substitute for decent brakes!
Danny Hoffman said:
Jack Valiant said:
Air can be compressed and then returns to normal once the pressure is released
Beat me to it :-)
So the air would expand and push the pads against the disks, but that is the opposite of what's happening?Beat me to it :-)
On release of the pedal the air in the system would return to atmospheric.
Trust us
...bleed them manually....open down etc Don't forget you are bleeding four cylinders from one nipple, you need to push a decent amount of fluid thru
Edited by jeff m2 on Monday 23 May 23:56
TVRleigh_BBWR said:
the pressure bleeders can help a lot with this make sure you use max recommended pressure, or even a few PSI over.
Well I've been using the car quite a lot over the last week or so and the brakes had virtually returned to normal.Either new seals have lost their springiness (my theory) or any trapped air has found it's way up to the master cylinder.
I decided today to give them one more bleed with the pressure bleeder.
My pressure bleeder says 20psi maximum. So I tried it at 25psi.
I couldn't see any air coming out when I bleed it.
Just I was getting out from under the car the cap blew off the master cylinder spraying brake fluid everywhere.
Lesson learnt, don't use more pressure than the instructions say
Yep don't exceed maximum pressure as it won't do the seals in the master cylinder a lot of good either 
Westfield rear brakes are famous for rear caliper issues and we used to end up taking them off and making sure the bleed was at the top as when fitted on the car the bleed nipple is too low and traps air in the top half of the caliper/s
We used to take then off and clamp a piece if hardwood and them bleed them.
Some folks also used to leave a length of wood holding down the brake pedal overnight and swore that it did the trick..
Westfield rear brakes are famous for rear caliper issues and we used to end up taking them off and making sure the bleed was at the top as when fitted on the car the bleed nipple is too low and traps air in the top half of the caliper/s
We used to take then off and clamp a piece if hardwood and them bleed them.
Some folks also used to leave a length of wood holding down the brake pedal overnight and swore that it did the trick..
perksy said:
Westfield rear brakes are famous for rear caliper issues and we used to end up taking them off and making sure the bleed was at the top as when fitted on the car the bleed nipple is too low and traps air in the top half of the caliper/s
We used to take then off and clamp a piece if hardwood and them bleed them.
You might be on to something here, I had the car parked forwards on my sloping drive and increased the angle further by jacking up the rear of the car. Maybe this was enough to stop the bleed nipple being at the top of the calliperWe used to take then off and clamp a piece if hardwood and them bleed them.
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