Car brakes

[Kickstart]

Hi

Any ideas on car brakes where the pedal slowly goes down (not to the floor, but say about 1/4 normal travel, 1/2 slowly going down and then 1/4 distance to the floor) without using any fluid? Only things I can think of would result in it using fluid except possibly ABS pump.

All the best

Keith
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[MarJay]

Brake balance valve? I had similar on my MX3, and although I didn't keep it for very long it had a similar issue. Looking at web forums they said it was the front/rear brake balance valve sticking in one position.
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[Teflon-Mike]

Whats the motor.
Be duel circuity, as like, so if compound master cylinder could be a seal, fluid passing from one circuit to the other. alterbnatively a failure in the bias or bias relief valve.
You say ABS, whats the arrangement?
Could be a sticking ABS relief valve, rather than the pump.
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[Kickstart]

Hi

Mmm, possible. With the bias valve stuck it almost blocking off the back it could take a while to push fluid to the back. But wouldn't expect it to take that much fluid. Would also expect it to take far longer to push the fluid forward to allow the same problem when trying the brakes again (same with a crushed brake line).

All the best

Keith
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[Kickstart]

Hi

Master cylinder seal failed and with 2 circuits does sound the most likely thinking about it.

Not my car so not got any details on the setup unfortunately.

All the best

Keith
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[Robby]

I'd go with master cyl failing in the middle too. When the brakes go like that it's almost always a master cylinder fault in some way.

[Kickstart]

Hi

Thinking about it I tend to agree.

Brakes feel like they do when you have a small leak in the system (except the pedal won't reach the floor), but it isn't using fluid.

All the best

Keith
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[weasley]

Possible leak in the vacuum assist cylinder?
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[Kickstart]

Hi

Vacuum leak would normally make the brakes harder rather than giving more travel. A fluid leak into the brake servo would result in fluid being used. The fluid level isn't going down which is the confusing bit.

Oddly just looked at another car of the same model and its brakes behave in the same way.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[weasley]

The reason I suggest the vacuum assist is that if you pump the brakes when the car is off, the pedal will go hard. Then put your foot on the brake and start the engine and the pedal will drop a little - sounds like the symptoms you describe is all!
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[Kickstart]

Hi

With the engine running it produces vacuum which operates the servo. Would need more vacuum rather than a leak.

All the best

Keith
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[mad4it028]

if it has drum brakes on the back re adjusting will bring pedel up but as its only creeping down ide sujest air in master cylinder if no leak but again if it has drums on rear the cylinder could be leaking dosnt have to be by much
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[mad4it028]

oh yes best way in my opinion to pin point a brake pedel problem on a car is this

clamp all 4 flexi hoses then with engine started pump pedel if its nice and hard this rules out master cylinder
then remove 1 clamp pump if this hard that caliper or cylinder is good refit and do same to next one untill you find where it goes soft

once found should be easy to sort why its soft could just need bleeding
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[Kickstart]

Hi

It has disks all round.

It doesn't feel like it needs bleeding. The brakes are not spongy. Stamp on them and the pedal stops rapidly. It just then slowly carries on going down.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[mad4it028]

clamp the flexis this will at least point you to the problem
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[Raffles]

[Kickstart]

[mad4it028]

ok dont listen to me a few small bubbles will cause a pedal to creep but you wont try it thats fine
once youve exhausted everything eles maybe you will try and you will see what i mean
also a perished flexi can do it too as well as a master cylinder by clamping the flexi you can at least confirm or discount the master cylinder instead of guessing
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always looking to buy bikes crashed ,unfinished projects,none runners pm me
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[mad4it028]

ok dont listen to me a few small bubbles will cause a pedal to creep but you wont try it thats fine
once youve exhausted everything eles maybe you will try and you will see what i mean
also a perished flexi can do it too as well as a master cylinder by clamping the flexi you can at least confirm or discount the master cylinder instead of guessing
____________________
always looking to buy bikes crashed ,unfinished projects,none runners pm me
currently riding kawasaki z1000 only bike ive ever loved

[Odie]

Moisture in the system?
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[Shaft]

Keith

You still haven't told us what the car is, that can make all the difference.
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[Teflon-Mike]

[Shaft]

[bootsbiker]

Keith

Is this right from the start of the journey or does it happen after a while. or heavy braking.. Does the car pull to 1 side when braking...??.
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[Nb]

What car is it since alot of cars now do this, old vectras brake pedals sink like that but they stop just before the floor.
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