Discussion
I have just had the front brake pads, discs and calipers changed but the brakes still feels spongy. When I push the pedal it travels almost to the floor before I feel the brakes are working. The system has been bled wwhich I am thinking discounts air in the system, could it be the master cylinder needs replacing?
New discs and pads will take a couple of hundred miles of gentle driving to bed in and all other things being equal your pedal feel should return to normal after that. Until then expect a softer pedal and reduced braking effort - you'll have to press a bit harder to get the same braking effect.
Was the entire system bled or just the front calipers? There's always the chance some air may remain or has been introduced via the master cylinder if the brakes were not bled carefully and slowly.
With the engine off pump the brake pedal several times to exhaust the vacuum in the servo. Then with your foot just resting on the pedal start the engine. You should feel the pedal drop slightly as the vacuum builds back in the servo then it should firm up again in that slightly lower position.
Next pump the pedal up and down several times. It shouldn't feel soggy or mushy although with modern ABS systems brake pedal feel is pretty horrible at the best of times - nowhere near as good as it used to be. If it's springy or you hear a squelching sound when you pump than that's usually trapped air.
Hold firm steady pressure on the brake pedal again with the engine running. If it slowly sinks down to the floor then either the master cylinder is f
ked or you've got a leak.
I'd bleed the entire system first of all right through, starting at the rear using clean fluid from a new container. You'll need between 1.0 to 1.5 litres to do the job properly. Treat yourself to a Gunsons Eazibleed if you're diy-ing - that's the pressure resevior thingy that works off the spare tyre. Works a treat and makes one man brake bleeding so easy.
Was the entire system bled or just the front calipers? There's always the chance some air may remain or has been introduced via the master cylinder if the brakes were not bled carefully and slowly.
With the engine off pump the brake pedal several times to exhaust the vacuum in the servo. Then with your foot just resting on the pedal start the engine. You should feel the pedal drop slightly as the vacuum builds back in the servo then it should firm up again in that slightly lower position.
Next pump the pedal up and down several times. It shouldn't feel soggy or mushy although with modern ABS systems brake pedal feel is pretty horrible at the best of times - nowhere near as good as it used to be. If it's springy or you hear a squelching sound when you pump than that's usually trapped air.
Hold firm steady pressure on the brake pedal again with the engine running. If it slowly sinks down to the floor then either the master cylinder is f
ked or you've got a leak.I'd bleed the entire system first of all right through, starting at the rear using clean fluid from a new container. You'll need between 1.0 to 1.5 litres to do the job properly. Treat yourself to a Gunsons Eazibleed if you're diy-ing - that's the pressure resevior thingy that works off the spare tyre. Works a treat and makes one man brake bleeding so easy.
Edited by Jaguar steve on Friday 29th October 14:34
Edited by Jaguar steve on Friday 29th October 14:35
Jaguar steve said:
New discs and pads will take a couple of hundred miles of gentle driving to bed in and all other things being equal your pedal feel should return to normal after that. Until then expect a softer pedal and reduced braking effort - you'll have to press a bit harder to get the same braking effect.
Was the entire system bled or just the front calipers? There's always the chance some air may remain or has been introduced via the master cylinder if the brakes were not bled carefully and slowly.
With the engine off pump the brake pedal several times to exhaust the vacuum in the servo. Then with your foot just resting on the pedal start the engine. You should feel the pedal drop slightly as the vacuum builds back in the servo then it should firm up again in that slightly lower position.
Next pump the pedal up and down several times. It shouldn't feel soggy or mushy although with modern ABS systems brake pedal feel is pretty horrible at the best of times - nowhere near as good as it used to be. If it's springy or you hear a squelching sound when you pump than that's usually trapped air.
Hold firm steady pressure on the brake pedal again with the engine running. If it slowly sinks down to the floor then either the master cylinder is fked or you've got a leak.
I'd bleed the entire system first of all right through, starting at the rear using clean fluid from a new container. You'll need between 1.0 to 1.5 litres to do the job properly. Treat yourself to a Gunsons Eazibleed if you're diy-ing - that's the pressure resevior thingy that works off the spare tyre. Works a treat and makes one man brake bleeding so easy.
I did have a soft pedal and some vibration on braking before changing the discs, pads and calipers but hoped that changing these would do the trick. I have been to my mechanic today and we re-bled the whole system but no air came out. Was the entire system bled or just the front calipers? There's always the chance some air may remain or has been introduced via the master cylinder if the brakes were not bled carefully and slowly.
With the engine off pump the brake pedal several times to exhaust the vacuum in the servo. Then with your foot just resting on the pedal start the engine. You should feel the pedal drop slightly as the vacuum builds back in the servo then it should firm up again in that slightly lower position.
Next pump the pedal up and down several times. It shouldn't feel soggy or mushy although with modern ABS systems brake pedal feel is pretty horrible at the best of times - nowhere near as good as it used to be. If it's springy or you hear a squelching sound when you pump than that's usually trapped air.
Hold firm steady pressure on the brake pedal again with the engine running. If it slowly sinks down to the floor then either the master cylinder is f
ked or you've got a leak.I'd bleed the entire system first of all right through, starting at the rear using clean fluid from a new container. You'll need between 1.0 to 1.5 litres to do the job properly. Treat yourself to a Gunsons Eazibleed if you're diy-ing - that's the pressure resevior thingy that works off the spare tyre. Works a treat and makes one man brake bleeding so easy.
Edited by Jaguar steve on Friday 29th October 14:34
Edited by Jaguar steve on Friday 29th October 14:35
We have deduced that it must be the master cylinder. I managed to pick up a cheap second hand one from ebay so going to try this first and see if it cures the problem.
Thanks for all the advice!
My mechanic and I have just fitted a second hand brake master cylinder as my one was a little spongy. However having bled the system there are no brakes whatsoever. He has over 30 years Jaguar experience and I worked with him on this. We can't understand what the problem is. The fluid level dropped in the reservoir when we bled the system so fluid must be getting through. Any ideas?
S6 Devil said:
My mechanic and I have just fitted a second hand brake master cylinder as my one was a little spongy. However having bled the system there are no brakes whatsoever. He has over 30 years Jaguar experience and I worked with him on this. We can't understand what the problem is. The fluid level dropped in the reservoir when we bled the system so fluid must be getting through. Any ideas?
Perhaps the SH one is fked. Your original problem sounds like air in the system not the master cyl.jagracer said:
S6 Devil said:
My mechanic and I have just fitted a second hand brake master cylinder as my one was a little spongy. However having bled the system there are no brakes whatsoever. He has over 30 years Jaguar experience and I worked with him on this. We can't understand what the problem is. The fluid level dropped in the reservoir when we bled the system so fluid must be getting through. Any ideas?
Perhaps the SH one is fked. Your original problem sounds like air in the system not the master cyl.
More than likley - sounds to me like the OP has made things worse by fitting an unknown master cylinder to a system that already had problems - I'm surprised any professional mechanic would even consider fitting secondhand parts to a customers' brake system 'tho. The only suggestion I can make now is to refit the original master cylinder, bleed the entire system right through again then follow the diagnostic steps I posted earlier.
Jaguar steve said:
jagracer said:
S6 Devil said:
My mechanic and I have just fitted a second hand brake master cylinder as my one was a little spongy. However having bled the system there are no brakes whatsoever. He has over 30 years Jaguar experience and I worked with him on this. We can't understand what the problem is. The fluid level dropped in the reservoir when we bled the system so fluid must be getting through. Any ideas?
Perhaps the SH one is fked. Your original problem sounds like air in the system not the master cyl. More than likley - sounds to me like the OP has made things worse by fitting an unknown master cylinder to a system that already had problems - I'm surprised any professional mechanic would even consider fitting secondhand parts to a customers' brake system 'tho. The only suggestion I can make now is to refit the original master cylinder, bleed the entire system right through again then follow the diagnostic steps I posted earlier.
We will refit the old one and follow jaguarsteve's advice.
Edited by S6 Devil on Saturday 27th November 16:32
S6 Devil said:
Incidentally, what would be the symptoms of a failed brake master cylinder?
With the system bled correctly and the engine running apply steady pressure to the brake pedal. If the pedal slowly sinks to the floor - maybe over several minutes - then that proves some fluid is leaking past the internal seals inside the master cylinder instead of all of it pressurising the brake system. You'll probrably find that lightish pressure on the pedal will show this particular fault better than a heavy push. Master cylinder failure often has nothing more than subtle symptoms so it's important to keep steady pressure up and repeat the test several times before you condem the master cylinder 'tho as a couple of quick dabs on the pedal can feel OK and send you off looking somewhere else for the fault. Try comparing the pedal feel on the same test with another car to see if there's anything you can learn from that too.
Check the rear of the cylinder and the servo for any signs of leaking fluid too. It's possible - though not likley that's where some of your missing fluid has gone.
Jaguar steve said:
S6 Devil said:
Incidentally, what would be the symptoms of a failed brake master cylinder?
With the system bled correctly and the engine running apply steady pressure to the brake pedal. If the pedal slowly sinks to the floor - maybe over several minutes - then that proves some fluid is leaking past the internal seals inside the master cylinder instead of all of it pressurising the brake system. You'll probrably find that lightish pressure on the pedal will show this particular fault better than a heavy push. Master cylinder failure often has nothing more than subtle symptoms so it's important to keep steady pressure up and repeat the test several times before you condem the master cylinder 'tho as a couple of quick dabs on the pedal can feel OK and send you off looking somewhere else for the fault. Try comparing the pedal feel on the same test with another car to see if there's anything you can learn from that too.
Thanks Steve, I will get on to it on Monday!
Check the rear of the cylinder and the servo for any signs of leaking fluid too. It's possible - though not likley that's where some of your missing fluid has gone.
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