Brake bleeding problem - '98 Impreza WRX
 

Brake bleeding problem - '98 Impreza WRX

Changed calipers to reconditioned 4 pots but the O/S won't bleed. After several attempts using different methods we decided to start looking in different places.

Pumping by foot - no fluid.
Vac pump on brake end - no fluid.
Old caliper - no fluid.
With the bleed nipple off - no fluid.
With the bleed nipple out - no fluid.
With braided line off caliper - no fluid.
With hard line disconnected from braided line - no fluid.

Tried cycling ABS pump using diagnosis plug but this makes no change to any of the above.

Removed braided line from caliper and hard line from ABS pump, submerged one end in brake fluid and used vac pump on the other end - fluid passes through fine - line is not blocked.

With hard line removed from ABS pump and pedal pushed there is a small squirt of fluid but nothing substantial.

With hard line removed from master cylinder definite fluid movement.

ALL OTHER BRAKES BLEED (albiet diagonal rear NS was a pain, it did bleed).

Essentially only two things left... replace master cylinder and/or replace ABS pump. I don't think the MC would be at fault as other brakes are bleedable... and I don't know the ins/outs of an ABS pump to say whether this strange situation could be caused by internal failure?

Tracing the lines I see that the front brakes get fluid from inside the ABS pump... Surely this is at fault here?

Help?

To add to this - All of the above methods/tests have been performed countless times in different orders to no avail.

The calipers are the right way around (nippled ARE at the top) - even though we've ruled out caliper problem I thought this was worth mentioning here.

Can't remove the MC->ABS line to temporarily bypass and test as this is seized on currently. Again, the rear NS did bleed so suspect internal problem anyway.

No fluid seems to be leaking as levels have not changed.

There is no brake pedal feel whatsoever... doesn't feel completely dead but there is no pressure, no brakes. Even pumping several times on a closed system makes no difference to pedal feel.

When you took the old calipers off did you just push the pads back or did you have the nipples open.

I wasn't there when the caliper was initially replaced, I came along afterwards to try and resolve the bleeding problem... with no luck :(

HOWEVER, from what I understand the old rubber line was clamped before being removed from the caliper and once the new caliper was bolted in, unclamped (The braided line was fitted later on to rule out brake line problems).

Out of interest, what difference would your methods have made?

If the pads were pushed back without the bleed nipple being open and before the clamp was put on it is possible to affect the seals in the abs or master cylinder but as you say the master cylinder is ok.

Couldn't have collapsed the rubber line, blocking it, by clamping, could it?

This was one of the initial thoughts, hence why this was replaced with a braided line (nice upgrade at the same time...).

OK, maybe dislodged a bit of rubber from inside the line, it's causing a block elsewhere?

Line has been checked between caliper and ABS pump, all clear.

Problem resolved - New master cylinder.

Can't explain why the NS rear would bleed when the OS front wouldn't... but fitting new master cylinder resulted in almost instant bleeding from all four corners and consistently hard pedal.

So there.. if anyone else experiences this - your MC seals are gone!