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Discussion Starter #1
I'm working on a 1980 Z28 with stock brakes. His brake pedal was really mushy and the brakes were barely even working. Very scary. So I bled the brakes around and aroudn with no difference, also the first part of the travel of the pedal did almost nothing and the rear drums weren't adjusted properly and were barely moving. So I put a new master on and kept bleeding. Eventually I finicked with the rear drums and got them working. Finally I got a really stiff pedal with the car off(power brakes) So I figured everythign was good, but when I drove it again the pedal was still mushy and the brakes barely work.

I'm thinking that the front brakes are glazed over, partly from the rears not working and also possibly the rotors weren't turned last time the brakes were changed. So tomorrow I'm going to take some emerycloth and haze the pads and the rotors and see if that fixes it or at least makes it better.

Just thought I would check to see if anyone else has any ideas to try out if that doesn't work tomorrow.
 

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Glazing doesnt make a mushy pedal....there is a problem in the system somewhere.
Try clamping off each brake to idenfy which is at faullt by process of elimination. If u clamp hoses off one at a time and sudenly there is an improvement u have found the problem wheel
Dont assume that is the only wheel that is at fault, check the rest anyway.
You could also have a problem with the length of the activation rod in the power booster/master cylinder.
 

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A spongy pedal is due to air still in the system. Check for any fluid leaks at the wheel cylinders, bleeder screws, brake lines, etc. Pull the rear brake drums and inspect the rear brakes. Most likely there is a hydraulic leak causing air to get back into the system.
 

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Discussion Starter #5
I had the drums off and the rear wheel cylinders are not leaking. I am not getting any air out of the system. I have done the brake bleeding dance many other times. Its not just the glazing that makes it bad, its the lack of contact or grip between the pad and rotor. I am almost betting that he never turned the rotors last time he did the brake job, and second I think the front brakes had to work overtime which made the glazing even worse. The brakes are not seating when applied.

I know it sounds weird but I had a somewhat similar problem on my firebird. WHen I went to bleed my brand new system I kept getting a mushy pedal. I bled and bled but the pedal was still mushy. So I incidentally put some new hawk brake pads on it and took it for a quick drive and the pads bedded in and the pedal was instantly stiff! The stock GM pads that came with my C5 calipers weren't braking in properly. So who knows, but I will tomorrow
 

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Glazing causes a hard pedal, not a mushy one. It's the law.
The pedal travels the same distance, but you have to press really hard to get any reaction from the brakes.

A mushy, read "low spongy" pedal can be caused by excessive slave piston travel or air... basically either way it equals excessive master piston travel. Reasons for excessive piston travel are multiple, but glazing is not one of them.
I don't doubt that putting on new pads could fix a mushy pedal, I've seen it happen, but it is not from glazing.
 

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Discussion Starter #7
So how did the occurence happen with my car? Either way I could likely be wrong, but I think I will find the answer tomorrow hopefully
 

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Discussion Starter #8
also I'm curious as to why the pedal is so stiff when the motor is off, but when the assist comes on it gets sloppy. I would think that the master cylinder bore could be wrong, but usually that creates a low pedal but with a ton of bite. Also its the stock brake system with a stock replacement master cylinder. Also I have verified that the pushrod is correct. I will try bleeding it out one more time since the system has had time to sit over night
 

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I can't say exactly why it worked with your C5 brakes since i wasn't there, but if the pedal travel was too far, and new pads fixed it, it was NOT from glazed pads... maybe tapered pads, but not glazed.

Some excess piston travel can easily be covered up on power brakes without the booster involved.

First you need to use the hose pinch method mentioned to know if it's front or rear.
 

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I've had similar things happen on GM pickups. After changing the master cyl with somewhat erratic pedal height and numerous bleeding, we changed the proportioning valve and it solved it. Just something to consider.
David
 

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On the GM P/U, was it actually the RWAL valve? I've seen that more times than i can relate. It is right below the master. It bypasses fluid flow as if the rears were locked, but it does it all the time. It's common on 88+ GM P/U with rear ABS.
A normal prop valve has no capacity for bypassing fluid.
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Discussion Starter #12
Another thing is that I run race pads on my sportbike and when its cold the lever is mushy and pulls much farther than after you heat the brakes up. So I do think pads can affect pedal travel. I'm going to mess with it as I speak so I'll post back :)
 

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Discussion Starter #13
I inspected the front brakes today. The rotors were well worn but the pads were really thick, which leads me to believe that the pads were changed out and the rotors were never turned. I just had the guy buy new rotors and pads. I put them on and took the car out to bed the new pads in. After some heating of the brakes and cool down I took the car out again and I had good results!! The brake pedal got much firmer and the car actually stops and responds correctly and it got better and better the more I drove the car. So I was spot on in guessing that the front brakes were glazed over and creating a mushy pedal. This is the second time I have ran into this. I know the first time it happened on my car with the C5 brakes, the pads and rotors were brand new, that time it was just the crappy OEM pads that came restocked with the calipers and replacing them with good pads fixed it. So if someone is doing some searching down the road hopefully they will see this if they are chasing a problem.
 
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