New Brakes....No Stopping Power....help please

[| 1990 ZR-1 |]

I just finished a full brake overhaul with new rotors, new Hawk HPS Pads, braided stainless steel brake lines, and flushed the fluid with Synthetic fluid. Dark brown gunk came out with little rust pieces especailly out of the front calipers. I did go through two botlles of fluid just to make sure all the crap was out. I managed to get air into the master cylinder, which I bench bled the get the air out of it nad properly bled all four corners again (RR, RL, FR, FL). I also went through the proper procedure of bedding the pads, but after all this, I still have a somewhat soft pedal feel with long travel. I'm not really sure if this how the brakes on the ZR-1 suppose to perform since it's my first corvette, but they feel unsafe. The car brakes and stops, but does so with a huge effort, and the ABS does not kick in. It feels like the brakes do not match the power of the car. I' afraid to accelarate too fast in trafic in case I have to stop suddenly. I try to keep a safer distnace than normal so I don't rear end any one. It just doesn't seem normal. My only conclussion is there's either something wrong with the master cylinder or the brake booster, or both. How would I check if either one or both are bad?? They seem to be verry expensive to replace. There's no air hissing sound coming out of the brake booster.Does that mean it's okay? is there anything else I need to check?

Thanks in advance guys!

On a side note, I also finished installing the FX3 suspenssion and it works flawlessly!!

[mike100]

You probably still have air in the system, but even if you do get a hard pedal when you pump the brakes a couple of times, I'd say maybe you just need to put 30 or 40 miles on those pads because they will be terrible until they really bed in (depending on compound).

Not sure how to diagnose your vacuum booster. My non-ZR-1 95 coupe had terrible power boost, but my 91 ZR-1 with the double diaphragm brake booster is twice as good.

try to bleed the rears again...that firmed up my pedal (which was crap when I acquired the car).

ON EDIT: I now have brand new C5 calipers on my fronts with a lot more pad area, but even my stock J55 calipers were good enough to lock up the brakes a couple of times once fully bled.

[Aurora40]

You can lock the tires and no ABS? Or you can't lock the tires?

[| 1990 ZR-1 |]

Originally Posted by Aurora40

You can lock the tires and no ABS? Or you can't lock the tires?

Hey Bob,

The pedal is pressed all the way down, but there's not enough braking power to lock the tires for the ABS to kick in.

[| 1990 ZR-1 |]

Originally Posted by Aurora40

You can lock the tires and no ABS? Or you can't lock the tires?

Bob, I found a similar post by you in 2009, but you never posted your resolution. How did you end up fixing your issue if you still remember?

[Aurora40]

Originally Posted by | 1990 ZR-1 |

Bob, I found a similar post by you in 2009, but you never posted your resolution. How did you end up fixing your issue if you still remember?

Can you post a link? I don't recall having that problem. The biggie I had was installing Baer 6-pot calipers, the OEM banjo bolt was too long and was pressing the piston out. I couldn't get the car to *not* brake, they dragged really badly. Baer sent me a shorter bolt.

I did have a longer pedal after that. The DRM brake spring helped, but there's no getting around the larger piston displacement. They weren't scary, though.

Hmm, well one time they were scary at the dragstrip (braking from 115, they'd give out by around 80), but that was due to the sissy ceramic pads Baer included. A swap to Hawk's cured that.

It does sound like you have air in your lines, though. Also, supposedly it's not a good idea to press the pedal to bleed, as you can move the pedal through longer travel than it experiences normally, and can jack up seals. I dunno how true that is. I use a Mityvac to bleed brakes, and then gravity bleed to get any air that was sucked in around the bleed screw.

[BlackWidow#2]

Did you bleed the ABS unit? You have air somewhere in the system I would bet.

[| 1990 ZR-1 |]

Originally Posted by BlackWidow#2

Did you bleed the ABS unit? You have air somewhere in the system I would bet.

How do I do that?

[POWERBRAKEBOB]

The booster has one steel rod pushing against another, It can't collapse inside. You said new rotors, not remachined? Coarse cut on a remachined rotor will not stop. the surface looks like a phonograph record, and only rubs on the high spots. No good. Also check for any interference between the pad and the caliper piston boot. ANYTHING jacking the piston away from the pad will push the piston in. Loose wheel bearing will cause th erotor to sit at an angle pushing in th epistons. Oher than that, open the bleeders one at a time and let it gravity bleed, with the caps OFF.
We also build a ZR-1 style DUAL Diaphragm booster to fit non ZR-1 vettes. The stopping power is incredible.

[| 1990 ZR-1 |]

Originally Posted by Aurora40

Can you post a link? I don't recall having that problem. The biggie I had was installing Baer 6-pot calipers, the OEM banjo bolt was too long and was pressing the piston out. I couldn't get the car to *not* brake, they dragged really badly. Baer sent me a shorter bolt.

I did have a longer pedal after that. The DRM brake spring helped, but there's no getting around the larger piston displacement. They weren't scary, though.

Hmm, well one time they were scary at the dragstrip (braking from 115, they'd give out by around 80), but that was due to the sissy ceramic pads Baer included. A swap to Hawk's cured that.

It does sound like you have air in your lines, though. Also, supposedly it's not a good idea to press the pedal to bleed, as you can move the pedal through longer travel than it experiences normally, and can jack up seals. I dunno how true that is. I use a Mityvac to bleed brakes, and then gravity bleed to get any air that was sucked in around the bleed screw.

Here you go Bob. If you remember, I'd love to know how you fixed your problem sine mine sounds awfully similar to yours.

http://www.zr1.net/forum/showthread....ht=soft+brakes