12 replies to this topic

[Seanyboi6]

Hi

Very rarley but randomly i press the pedal on my brakes and it goes really soft and the brakes barely work. The pedal doesnt spring back up

But drive on a little bit and next time i try too use them they are back to normal.

This is dangerous as you can imagine.

The Brake fluid resovoir is full and the calipers are on the right way, (Bleed nipples to top)

Any ideas?

[RobWill116]

Could be a little bit of air left in the system. Try bleeding the system with the correct sequence for you master cylinder and see if it still does it.

[coopdog]

Does the brakes work if you pump them?
If so check the wheel bearings

[Seanyboi6]

once the pedal has gone soft i was pumping it back and forth (having too lift it back up with my foot) but still had no joy.

Drove down the road abit and it was hard and working fine again

[Alex_B]

Sounds dangerous, PLEASE DONT DRIVE IT ,till its fixed, and yeah get some fresh fluid and bleed the system, look for leaks and if there is a leak replace whats leaking,

[Seanyboi6]

whats the basic procedure for bleeding system?

[coopdog]

Sounds weird :/

[DannyTip]

Sounds like a problem with the master cylinder if the pedal doesn't return. The master cylinder may be letting fluid past the seals therefore not doing its job.

[davej]

Have you checked the pistons in the caliper are not sticking and are returning once you take your foot off the pedal?

[Seanyboi6]

I dont think its the pistons sticking because the brakes arnt sticking on, no resistance at all on the car and i wouldn't of thought the cylinder seals have gone as the brake fluid resovoir level hasn't moved

[pdaykin]

If you havent touched the system and the reservoir is full (i.e not leaking), it doesnt sound like bleeding is going to be the answer.

I had a similar problem when the tapered washer started to fail on the hub.

[Seanyboi6]

its only happened twice in about 4 hours of driving, the rest of the time the brakes are fine, pedal nice and hard, then the odd time i press the pedal and it is really soft n brakes barley work with my foot pinned too the floor n the pedal doesnt return, then it goes back too normal

[tiger99]

When did you last change the brake fluid? One symptom could well be of boiling fluid, although it would not explain everything.

You also most definitely have a defective pedal to master cylinder linkage, or faulty master cylinder, or both, if the pedal is not returning, which is the definitive clue to where at least one problem must lie. Is the large and very important pedal return spring intact? Is, and it is very important, the master cylinder pushrod returning fully every single time? Is it slack when the pedal returns? (If it remains tight, the master cylinder may need shimming.) Is something down there jamming in some way? Has the clevis pin fallen out?

Sorry, but it is going to mean contortions in the footwell, most inaccessible part of the car, to sort this one out. You may want to raise the car very high, on the edge of a loading bay for example, and stand outside with the door open, or take the driver's seat out, put down something soft, and lie on your back, to get to the pedal mechanism and clevis pin.

Edited by tiger99, 19 July 2012 - 04:06 PM.