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If the pushrod or the booster rod are too tight fluid pressure will build up in the lines and cause the calipers to seize. The master cylinder has to return fully to relieve this pressure. The fact that the rears are the only ones that lock might indicate that you aren't quite balanced (front to rear) yet. Do you also have the stock rear prop valve in line? I needed both after trying with just a Wilwood adjustable valve, the rears still locked up first. No residual valves are needed on disks unless the master cylinder is below the calipers, as in some street rods and race applications.

HTH,
Mike
 

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Originally posted by Kaiser Bill:
<STRONG>SpaceGhost,
Are you saying that since my Front/Rear Bias is off,thats why the rears are locking first?
I should say "seizing" I guess.
I can get all 4 whls to skid on pavement,but the rears do lock first on gravel or dirt.

I'll try backing off on the pushrod somemore,but I already have an airgap with the pedal released,should'nt this be enough? <IMG SRC="smilies/confused.gif" border="0"></STRONG>
First off I understood your original post to say that you had removed the residual valve. Some masters have this in the outlet and others have a bushing (fitting) that contains the residual valve and it also reduces the line size to 10mm x 1mm. The symptoms you are describing are exactly that of a drum brake residual valve that is still in the circuit. I would first off make sure that this is removed! Not doubting you, just worthy of note.

Based on that, what I was hoping to convey was that the rear are siezing "first" as a result of the front/rear bias or lack of enough proportioning. I'm only guessing that if you could continue to drive the fronts would be locking up shortly thereafter. Might be able to confirm this with the front jacked up to see if the fronts are dragging. The bias is not the cause of the seizing, just the reason the backs are most obvious.

There is an adjustable rod that is part of the booster that may be too tight. Assuming you have backed the pedal pushrod out until there is play or daylight you need to seperate the booster and master and back that one off also. A clue will be if the master starts to seperate when you back the bolts off like it under compression. Maybe you could drive it until the backs seize and then loosen the master bolts and see if they free up? Then adjust the rod in until there is some play.

As far as the backs seizing first, I had to install a stock prop valve and an adjustable one to get the bias balanced. The test is best done on loose gravel or downhill where you can watch that the rears don't lock up first. On a dry street at 30 mph with 35" tires it is difficult to be certain what's happening.

I had read all kinds of posts about going to rear and 4 wheel disks before I started on mine. Since I had manual, single circuit drums all around (68) I did not have a stock prop valve and most of the posts were about converting a disk front Cruiser to 4 wheel disks. These all had the stock prop valve and I "now" assume that everyone just added the adjustable valve. I also have seen and read of people that leave the residual valve in and don't report any trouble with it. Seems that different combinations give different results under different types of use.

Hope this set you free!
Mike
 
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