Thread: Spongy brake pedal

Originally Posted by snowbound

I just renewed my hydraulic clutch. Bleeding pain in the Slave Cylinder

Reverse bleeding works well on the clutch.
.

Originally Posted by BathurstTom

Too wet to get much done so I took the calipers off and brought them home. New pistons and seals installed. Will fit them when I go up next time...


Tom.

Did you check the pad slides for wear, as had two calipers wear to the extent the pad drops & sit on rotor. One was 12 monthes after rebuild & onces prior.

Sent from my GT-N8020 using AULRO mobile app

The pads are nearly new - though they are aged, there is plenty of meat on them. Once I sort the main problem out they will be replaced though.

Cheers,
Tom.

Bench bleeding master cylinder.

[ame=http://www.youtube.com/watch?v=kEPXgDGU6_0]How to - Bench Bleed a Brake Master Cylinder - YouTube[/ame]

At one point the operator mentioned that damage can occur if the plunger is pushed in too far.
.

I have been busy looking at the pro's and con's of pressure bleeding as compared with vacuum bleeding.

Now I'm under the impression that vacuum bleeding is more likely to dislodge a trapped air bubble.

.

Ok, I spent 4 days trying to solve the problem again. Fitted the reconditioned calipers. Pressure bled the system. I bled over a litre through each of the calipers and no improvement (and no air bubbles visible). Scratched my head and made up a hot wire to run the ABS pump and each of the valves in the module for multiple three to four seconds burst. Got a fair bit of air out of the front d/s caliper. Aha! Thought I had the problem solved! But no improvement.

I fitted a new booster for lack of other ideas as one of the causes of a sinking pedal is a faulty valve in the booster (see page 602 of the rave manual). No improvement.


My only idea now is that perhaps the brake line from the the master cylinder rear (primary circuit) to the abs module or the line from the abs module to the Proportioning valve may be blocked. This may explain why the system seems so slow to bleed. With the pressure bleed system at 20lbs'sq inch it does little more than dribble out.

When reversing the vehicle, the brakes are very effective - which I would think indicates that the secondary circuit is working. It has a very spongy pedal and minimal braking power going forward.

I think that perhaps if the line from the master cylinder rear is blocked, the system would still bleed, albeit slowly, through the secondary circuit. This would fit in with the symptoms. It is just unfortunate that I was already 80k's towards home (and not enough time to go back) when I thought of this possible cure.

Will be too busy to go back for at least a month, so the saga continues.


Cheers,
Tom.

maybe the brake calipers are upside down?

Nope, the calipers are right way up. Thanks for the suggestion though. I'm searching for ideas...

Tom.