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Hi,

Thought I should report some quite unusual brake problems I have been having with a VE Valiant I am trying to get back on the road, as it may help somebody else. I am a newbie here so apologies if it is a really well known problem, but I could not find it after surfing many forums.

Problem:
No matter how much I bled the brakes, you had to double-pump the pedal after which the pedal felt good, i.e. did not feel as if air in the system, it felt as if a brake shoe or pad had retracted too far.

Previously had replaced entire brake system, new remote servo, recon master cylinder, new slave cylinders at rear and rebuilt front calipers with new seals and pistons.

I then scoured the forums. Did the usual suggested things; Took master cylinder off and bench bled it, Adjusted rear brake shoes up until just rubbing the drums, bled brakes several times again. No improvement.

So, problem was something was not close enough to a brake disc (rotor) or drum so had to double pump pedal to push it closer, after which brakes would work fine.

Tried adjusting rear shoes til locked against drums - problem still remained.
Tried PTFE tape around threads of bleed screws, so air did not get sucked in past the threads, then quasi-vacuum bled brakes using gentle suction and a syringe (some people swear by this method) - still no better.

So, it must be the front calipers retracting too far, strange and rare as that may seem. The pistons are supposed to retract by the flex of the square section piston seal as it springs back, they are not sucked back as you might imagine when you release the brake pedal. Therefore caliper pistons should not retract too far (unless wheel bearings loose and rotor is wavering left and right as it turns).
However, on an obscure Porsche forum I found that in some cases they can on 924's, especially if the calipers have just been rebuilt, which mine have. Nobody knows why in the technical sense, but it has been reported.

SOLUTION:
Measure thickness of disc (rotor). Take caliper off, leave hoses connected. Put something flat between the brake pads that is about 3 mm THINNER than thickness of the brake disc. Compress brake pedal to push the pistons out a few mm more than they were before, past the (new) seals. Gently retract pads just a tiny bit while at same time trying to get caliper to slide back on over the brake disc (rotor), tapping it with soft hammer if necessary, being careful not to damage the pads. The aim is to get the caliper back on and bolted back up with the pads actually slightly gripping the disc, even with no pressure on brake pedal.

RESULT: Brake pedal works perfectly after about 1 inch of travel. Apparently (on Porsches anyway) if you drive the car around for a while this also solves the problem as it just goes away as the seals bed in in some way. My problem was I could not drive it around without it passing a road legality test, and it would not pass if brake pedal had to be double-pumped to make it work.

I have seen on some forums people have suggested "blocking" the brake pedal, i.e. jamming it down under pressure then leaving it for 2 days to solve similar problems to "remove air". Cannot see how that would remove any air but can see how it might allow pistons to gradually creep out past the seals in situation I had above.

Best wishes

John
 

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I don't see that you replaced your caliper guide pins, John. Perhaps they have a flat spot on them, not allowing the caliper to fully slide back and forth. Did you replace them or not? If so, I have no other suggestions other than to make sure you lube the guide pins too.
 
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