P J Moran

I've been chasing this problem for some time, now. There seems to be a bit too much pedal travel, but the brakes basically work. However, at the bottom of normal travel, I can push a little harder and the pedal will give and bottom out. There's some give at the bottom that limits how much pedal pressure I can apply before bottoming out. It's like I'm up against some kind of rubber stop because it does spring back (the pedal doesn' stay down under normal pressure).

To fix this, I flushed the system. I ran nearly two quarts of new fluid through to make sure all old fluid and air was expelled. This had virtually no effect.

Next, I made a couple of plugs for the MC out of lines robbed from a junker. Plugging the front port (rear brakes) had no effect. However plugging the rear port (front brakes) had a huge effect! Far less pedal travel and no mushy bottom.

This tells me that the problem is in the front system. The only culprit I can suspect is the hose(s), but they look perfectly ok. They would explain the mushy bottom, but not the pedal travel.

Plugging the ports and getting a high, hard pedal rules out the MC, doesn't it? Could the proportioning valve be malfunctioning somehow? Please offer suggestions. This is unsafe and is driving me crazy. Thanks.

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'87 IROC 5.7l TPI - original owner!

stingerssx

Did you swap to rear discs? I did and I need to change the combination valve to a proportioning valve. If this is not your problem, then try changing to an adjustable aftermarket prop. valve like from Wilwood, or Summit. then you can adjust the rate of the rear only. The front is straight from the MC to the calipers. That should help.

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'82 Firebird, dead stock, 9 bolt disc rear, over 200,000 miles and still going strong, more to come...
http://www.spinfrenzy.com/stingerssx...easures.html#4

RB83L69

Sounds like air in the master cylinder.

The fitting for the line isn't at the highest point of the actual cylinder in the master cyl when it's installed; so you can bleed gallons of fluid through it and still not expel all the air. The only way to get it full of fluid is to "bench bleed" the MC. Chilton's and Haynes and all those will tell you how to do it.

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"So many Mustangs, so little time..."

P J Moran

I thought that the reason for bench bleeding was to keep from having to purge air in the MC all the way through the brake lines. Besides, when you bench bleed, don't you simply run a hose from the outlet port back into the reservoir and pump it until all the air is out? You're still working at the same point. What am I missing, here?



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'87 IROC 5.7l TPI - original owner!

Jza

The point is, air bubbles in the fluid go *up* and you're trying to bleed it through a point very low in the car.