Braking system failure????

Ben.Kitcher · Mar 15th, 2008, 22:33

Hi,
I have a 1990 760 sedan (Auto) and am experiencing servere brake system problems. Can anyone throw some light on the problem?
When in slow moving trafic (20mph) the brakes overheat and sieze up after about 5 mins, when allowed to cool down for about 40 mins they release but the brake peddle goes to the floor, if left for a further 2 hours the brakes come back to normal. i have changed all the calipers twice now and have bled the system thoughly. it has passed the braking test for the MOT.

Any Ideas

craig8661 · Mar 15th, 2008, 22:45

sounds as if it could be the servo applying the brakes but dont hold me to it as could be very wrong was the calipers free moving

Glen Morangie · Mar 15th, 2008, 22:54

Quote:

Originally Posted by craig8661

sounds as if it could be the servo applying the brakes but dont hold me to it as could be very wrong was the calipers free moving

That's about all I could think of which would affect all of the calipers - could the pedal not be returning fully sometimes, light pressure on it will activate the servo which then increases the pressure.

Sometimes the pivot for the pedal wears out.

Ben.Kitcher · Mar 15th, 2008, 22:54

Fairly free moving, but due to the heat the piston dust boots had disintergrated.
I have just been offered from a scap merchant friend of mine 2 newish front calipers + discs, 2 used rear calipers + Discs, master cylinder + servo, all for £40 if i remove before monday as car is being crushed

Glen Morangie · Mar 15th, 2008, 22:57

Quote:

Originally Posted by Ben.Kitcher

as car is being crushed

Hmmm............. a lot of them are doing that!

Ben.Kitcher · Mar 15th, 2008, 23:04

A real shame i couldnt get to it before the fork lift otherwise would have brought the whole car!!!!

craig8661 · Mar 15th, 2008, 23:05

yer even our local scrappy dont keep them now any car before 1998 straight on lorry and crushed he allways keeps a eye out for volvos for me tho i even missed a herse of him once and i would have brought it
other thing dont the servos have a spring that retuns the pedel to top could be spring gone in it

Ben.Kitcher · Mar 15th, 2008, 23:09

Cheers i'll check it out.

shrewsbury_sam · Mar 16th, 2008, 03:00

sounds like your master cylinder is faulty and is making the brakes stick on

turboboy · Mar 16th, 2008, 08:19

Would agree that most likely cause is either faulty master cylinder or servo.

Are you losing any brake fluid?

Once took a servo off and found that it was completely full of brake fluid because of an internal leak.

Mar 15th, 2008, 22:33	#1
Ben.Kitcher Comfortably Numb Last Online: Jul 23rd, 2008 19:16 Join Date: Feb 2008 Location: Southampton	Braking system failure???? Hi, I have a 1990 760 sedan (Auto) and am experiencing servere brake system problems. Can anyone throw some light on the problem? When in slow moving trafic (20mph) the brakes overheat and sieze up after about 5 mins, when allowed to cool down for about 40 mins they release but the brake peddle goes to the floor, if left for a further 2 hours the brakes come back to normal. i have changed all the calipers twice now and have bled the system thoughly. it has passed the braking test for the MOT. Any Ideas

Mar 15th, 2008, 22:45	#2
craig8661 Master Member Last Online: Oct 29th, 2018 11:16 Join Date: Apr 2007 Location: Chesterfield View Photos By: craig8661	sounds as if it could be the servo applying the brakes but dont hold me to it as could be very wrong was the calipers free moving __________________ i kno im a dirty beastie sadley no longer rest in peace in volvo heaven NOTICE OF DISCLAIMER any information i give is soley on my own findings and mess ups

Mar 15th, 2008, 23:05	#7
craig8661 Master Member Last Online: Oct 29th, 2018 11:16 Join Date: Apr 2007 Location: Chesterfield View Photos By: craig8661	yer even our local scrappy dont keep them now any car before 1998 straight on lorry and crushed he allways keeps a eye out for volvos for me tho i even missed a herse of him once and i would have brought it other thing dont the servos have a spring that retuns the pedel to top could be spring gone in it __________________ i kno im a dirty beastie sadley no longer rest in peace in volvo heaven NOTICE OF DISCLAIMER any information i give is soley on my own findings and mess ups

Mar 16th, 2008, 08:19	#10
turboboy Master Member Last Online: Dec 15th, 2023 08:44 Join Date: Dec 2003 Location: Twickenham	Brakes sticking on Would agree that most likely cause is either faulty master cylinder or servo. Are you losing any brake fluid? Once took a servo off and found that it was completely full of brake fluid because of an internal leak. __________________ Turboboy Current: 1998 Volvo V70 2.3 T5 Auto. Previous: 2000 Volvo V40 T4; 1981/2 265 (x2); 1988 740 Turbo Estate.

Mar 15th, 2008, 22:54	#4
Ben.Kitcher Comfortably Numb Last Online: Jul 23rd, 2008 19:16 Join Date: Feb 2008 Location: Southampton	Fairly free moving, but due to the heat the piston dust boots had disintergrated. I have just been offered from a scap merchant friend of mine 2 newish front calipers + discs, 2 used rear calipers + Discs, master cylinder + servo, all for £40 if i remove before monday as car is being crushed

Mar 15th, 2008, 23:04	#6
Ben.Kitcher Comfortably Numb Last Online: Jul 23rd, 2008 19:16 Join Date: Feb 2008 Location: Southampton	A real shame i couldnt get to it before the fork lift otherwise would have brought the whole car!!!!

Mar 15th, 2008, 23:09	#8
Ben.Kitcher Comfortably Numb Last Online: Jul 23rd, 2008 19:16 Join Date: Feb 2008 Location: Southampton	Cheers i'll check it out.

Mar 16th, 2008, 03:00	#9
shrewsbury_sam Junior Member Last Online: Jan 29th, 2009 17:50 Join Date: Mar 2008 Location: shrewsbury	sounds like your master cylinder is faulty and is making the brakes stick on

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