Ok guys, I'm trying to figure out exactly what the deal is with this car. So far, its a 1987 iroc, originally front disc(duh) rear iron disc (delco moraine). The car had been updated with 1LE spec parts up front, and 93-97 camaro brakes (same as 89-up) rear aluminum discs. new flexible lines, but original hard lines. I basically flushed out the entire system before reinstalling everything.

the system was also gravity bled, that is, load the system, crack the valves on the calipers, and wait for the fluid to run clean.

I used the part number listed in the 1LE threads for the correct proportioning valve, along with a rebuilt master cylinder for the disc/drum car. I've also replaced the booster with a low mile orginal 85 or 86 unit.

the problem that I have had and still have is the brakes work, and seem pretty good, but the inital hit is soft, and the pedal gets hard, and its difficult to lock up the tires. I know it is not 'recommended' by all of our internet buddies, but the bottom line is that they should have the capability to be locked at full force.

now, it may be that I'm not really leaning on them really hard. I can say that I am using more force than I normally would have to on every other car I've driven, so it seems wrong.

I'm not sure how much manifold vaccuum I have, but its a zz-4 cammed 350, still TPI. It feels kind of like when you have no vaccumm on the reservior, like stopping a car that isn't running, but only at the very end of the braking event.

the wierd part is that everything peice of the system, except for the hard lines, was replaced, and this sympton had been in the car since I got it, original 350, new 350 cammed, and now new brake system.

I guess it also needs to be said that I really haven't gotten a chance to beat the car up much, I've only driven it a few times, but try and more or less bed the pads when I do drive it.(firm 60-0 stops)

so what you guys think?

 

The initial soft pedal feel is normal and is due to the design of the master cylinder where the initial travel causes excess fluid back up into the reservior.

Doesn't sound like you have air in the pipes, as the pedal is getting hard before the endstop. However I'm not sure your method of bleeding the brakes is quite right. I've always used someone pushing the pedal when doing it. If you can then I'd repeat with the 2 man method to force out any bubbles.

Depending on the type of pads it may take a while to properly bed in.

Not sure how much better the 1LE is over standard, but I certainly couldn't lock J65 4 wheel disc brakes without bending the pedal....

Sounds like you need to have a look at the vacumn that you're getting, and make sure the pipe is in good condition?

Si.

 

I agree 100% with every point IROC -si has made above. He's pretty much completely covered every possible issue and it does appear to be multiple issues.

It never hurts to buy an inexpensive auxillery vacuum canister and install it in line to increase quanity at lowend with that cam. I have heard of other people with lower yet still not dangerous vacumm readings with that cam, but a added reservoir would give more reserve and completely eliminate any potential problem. This however would be the LAST thing I try in the list above. Break the pads in better, and most importantly first off make sure you pressure bleed those lines (I am betting this is your biggest problem.)

 

cool, sounds alot like what I was thinking.

I will try and check out bleeding those bad boys again, and get a vaccuum guage on the thing to see whats happening during the braking event with engine vaccuum.. this is a MAF set-up, otherwise, I coulda probably just watched the MAP readings.

thanks again for the help! anybody else that chimes in, thanks too!

 

Bingo!
Rebuilt master cylinders have about a 50% failure rate and a failed unit will exhibit the symptoms you describe, get a new one. Throwing on a 20-year-old booster (no matter how low it's mileage) cannot be helping.