combatdoc

From the top, I had the stock brake master cylinder rebuilt, I put C5 ZO6 brakes up front and have the stock brakes in the rear, I bled the abs block behind the drivers seat, went to each corner over and over, and still I have a sponge for a pedal, it gets stiff then as soon as I start the damn car it takes two pumps for the pedal to get hard again, now common sense tells me there is still air in the system, but I guess the booster could be leaking I don't hear anything in the car when pressing the pedal. Any help would be great, I am a little frustrated, some guys on the C4 general say they have to run tons of fluid through these cars to get them bled out! thanks Dan

mike100

I never had too much trouble bleeding a c4 (even with C5 brakes). Even though I have a tech1, I have never bled the ABS unit. Instead I have just cycled it by finding some loose gravel or water and making it modulate and cycle fluid internally. cycle the pump one way or another and re-bleed all four corners starting with the rear wheels first is what I would try.

The one thing that comes to mind is that you said you rebuilt the master cylinder...

mike100

Also bear in mind the C5 brake mounting hardware has a touch more slop in it than the original J55 setup. There is a little more take-up before the caliper squares up the pads and gets a firm pedal- most definitely not multiple pumps though.

-=Jeff=-

so on the two pumps is it firmer on the Second Pump (Push) of the pedal?This happened to me with my 89.. it was the master cylinder.. what year is your car? my guess is it is still the master but also depends how far it goes on pump one then on pump two of the pedal

WVZR-1

You replaced the master and it actually sounds like your describing a situation that would require the adjustment of the push-rod from the M/C to booster. To short I believe gives you the low pedal and if it were to long it wouldn't release when you let off of the pedal. I'd guess it just coincidental that you did the C5 brakes at the same time.

You had "your" M/C rebuilt? It's NOT one from the shelf?

The only part that is maybe a little confusing is you mention it takes a couple pumps to get "firm". Do you actually have what you'd consider adequate brakes on the first apply?

Mike's suggestion of the cycling of the ABS and a re-bleed sounds like a start! I never realized that the C5 had a "pause/take-up" issue but I've never had the conversion done either!

combatdoc

I sent the MC to A-1 Cardone in PA. It stops ok on the first pump but it feels like soft nthen I quick pump it then press and it feels firm, like I think it should, I guess. Something else I noticed today, I took the Z out to get some air and it felt like when I was at a stop and let off the brake almost felt like the brakes stuck alittle, car did not roll either way. I will pull the rear wheels off today re-bleed all all corners. If that doesn't work I guess I will send the MC back and have it done again.

combatdoc

Is anyone doing any sort of MC upgrades?

FU

I saw a post by POWERBRAKEBOB on the registry forum. He is involved with hydroboost brakes. And he posted about a upgraded MC that the company was working on. Here is his post. I'm looking forward on seeing this project. He's also working on a clutch master upgrade. Should prove very interesting.

"I do HYDROBOOST conversions, and can build for the C-4's. With a HYDROBOOST booster, I run a c0ommon 1" master, even one from a C-5 can be used. Gives outstanding braking performance, AND a firmer pedal "

combatdoc

my car is a 1992 fyi

erikszr1

I think you still have air in the system. im also going with the idea that your master cylinder is 100%. if its not then you have to start over with that. I know its a pain in the a$$.

Dominic Sorresso

The C6Z front calipers take a bit of bleeding to get right. They have two bleeders on each caliper, one per side. If it takes two pumps, you still have air in there. Have you tried using a Mighty Vac or Powr Bleeder?

combatdoc

yea, but not a good one, I am going to order one this week!

POWERBRAKEBOB

Yes! I am installing a Hydroboost unit on my car. At 255,000 miles all is getting tired. My friends at Baer brakes got into the business by making a bracket to install C-4 calipers on Camaros. They ended up actually reducing the piston area and had a smaller pad. I normally use a 1.125" master on cars. Because the C-4 calipers are so small, I have to downsize, even with a Hydroboost to 1" on Baer braked Camaros. I have rebuilt the C-4 masters, and they, for the price, are cheap, almost Volkswagen type, being from Australia. The ZR-1 booster is a dual diaphragm unit, vastly superior to the plastic booster on the std Corvette. I actually make those to upgrade std Corvettes. BUT they have a small bolt pattern which requires the Australian master. The Australian master is only a 7/8" diameter. The C-5 calipers needed the larger 1 inch master and a dual dia booster to operate. It's like using a 7/8" VW master on your bigger brakes. No good. The 1" master use the std GM bolt pattern of 3 3/8" spread. We can use any piston size. I like the HYDROBOOST because it runs off of the p/s pump, and needs no vacuum. With the secondaries blocked open the vacuum is lowered.
Usually, if you open the bleeder, loosen the m/c cap, it will just gravity bleed, unless the bleeder is not at the top.
The C-5 caliper set WITH a HYDROBOOST would be the Ultimate braking system for even a 200mph Supercar.
I plan to move the battery back, remove the vacuum booster, drop the computer into the battery well, run that huge harness UNDER the Hydroboost, use the 1" master, remove that joke of a 11/16" clutch master, and set up a 3/4" master. That will give a clean clutch release. Third gear has always been difficult to get in, which of course denies power shifting, and is hard on synchros. I will also have a new piston kit for the clutch slave cylinder.

POWERBRAKEBOB

I'm trying to see how I can post a photo. I don't see the button for that.