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 |]

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 |]

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?

[gbrtng]

You still have an air bubble in the system somewhere if the pedal is not rock hard with
the booster depleted of vacuum. My preferred bleed sequence is RR. LR, RF, LF, and
I use the 2-man procedure.

What bleeding procedure and equipment did you use?

[| 1990 ZR-1 |]

You still have an air bubble in the system somewhere if the pedal is not rock hard with
the booster depleted of vacuum. My preferred bleed sequence is RR. LR, RF, LF, and
I use the 2-man procedure.

What bleeding procedure and equipment did you use?

I'm really hoping that's the case. I bled the right rear then left rear, then right front and left front. I had my wife pump the brake pedal twice and hold it while I opened and closed the bleeders all while topping off the reservoir with new fluid.

[mike100]

I had a little trouble with my rears not having much volume or squirt, but I think I just went over it about 3 times until they all had a strong flow of clean fluid. I think there was a little goo in the bleeder end.

[Aurora40]

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.

[gbrtng]

I'm really hoping that's the case. I bled the right rear then left rear, then right front and left front. I had my wife pump the brake pedal twice and hold it while I opened and closed the bleeders all while topping off the reservoir with new fluid.

Sounds like you got it right - the trick is to get the bleeder closed before wifey releases the pedal each and every time. BTW, the 90 ABS unit has no bleeder screws so if there is a bubble trapped there ??? what to do.

One other trick - I have the wife put her other big toe under the brake pedal so it does not go all the way to the floor. Somehow I feel better about not running the master cylinder plunger all the way to the end of its stroke.

[| 1990 ZR-1 |]

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.php?t=7466&highlight=soft+brakes

[| 1990 ZR-1 |]

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

How do I do that?

[| 1990 ZR-1 |]

Thanks for the feedback guys. I will try bleeding the brakes again this weekend. Hopefully that'sthe problem....
I went with a Valvoline DOT 3 & 4 Syntetic Brake Fluid. Any reason I should go with another brand?

[ittlfly]

How do I do that?

The short answer is, you don't . As I *recall* it used to take a dealer with a Tech 1 and / ABS cartridge used to cycle and purge the ABS unit. Maybe some one has come up with something else...

[mike100]

Thanks for the feedback guys. I will try bleeding the brakes again this weekend. Hopefully that'sthe problem....
I went with a Valvoline DOT 3 & 4 Syntetic Brake Fluid. Any reason I should go with another brand?

$6 parts store DOT3 until you get the kinks worked out. A good dot3 flush is cheap-you can bleed in some premium stuff right before you go to the track.

[gbrtng]

The short answer is, you don't . As I *recall* it used to take a dealer with a Tech 1 and / ABS cartridge used to cycle and purge the ABS unit. Maybe some one has come up with something else...

I looked thru the 91 FSM section 5 and there is no special method for bleeding the ABS modulator when hydraulic lines are disconnected during repair. Later model C4s have bleeder(s) on the modulator (I think) but I don't know when the change was made.

The FSM bleed sequence is RF, RR, LR, LF - not the sequence I mentioned earlier.

However --- there is a caution note in section 5E1 to never charge the battery with a quick charger with the negative battery cable connected. Failure to disconnect the negative cable could result in the BRAKE fuse to blow or serious damage to other electrical components. YIKES !!! How many AAA bozos know that requirement? How many ECMs have had their service life reduced by a quick charge? And who would look in section 5E1 for how to connect a quick charger? BEWARE ...

[gbmidyear66]

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.

I am just getting ready to do the same upgrade (Hawks, slotted rotors, braided lines....) to improve the mediocre braking on my 90. I hope your issue is as simple as residual air in the system.

Please post root cause (and your impressions on the new pads, etc) when you have it all resolved

Glenn

[Aurora40]

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.php?t=7466&highlight=soft+brakes
Ah, thanks for the reminder! I must have blocked that out... ;) I bled the calipers again, a few times actually. I believe that the brakes were as good as it gets at that point. Sometimes it would still have a long initial pedal, then the second application would be more normal. I believe that was due to the knockback of the pads, and the extra fluid volume it takes to move them vs the stockers (due to the increase in piston area).

Possibly some re-shimming of the calipers to get them more perfectly centered would have helped that, I dunno.

However, on your car, there is no reason it shouldn't feel as good or better than before you messed with it. Air in the line sounds like the most likely culprit.

Also, can you explain your bleed procedure in more detail? Did you open the bleed screw, have your wife pump the pedal twice, then close it? That's sort of how it reads.

Also, FYI, if you went to braided lines, watch the rear line. They don't have an angled exit from the caliper, and thus sit a lot closer to the edge of the rear wheel. Mine would tap-tap-tap on the wheel weight, until I loosely zip-tied it out of the way.

I have to say, on the brakes, I wish I had just stopped after putting on HPS pads. That was more than good enough, and completely headache-free. I am trying to remember that lesson on the V, and resist the urge to upgrade to the 15" 6-pots from the new one...

[Aurora40]

Also, you could probably cycle the fluid in the ABS module by hammering the brakes in the rain. I never did anything to specifically bleed it.

[tomtom72]

Just a fwiw on the early ABS modules w/out a bleeder if you work on the system and then bleed, no air went into the ABS nodule. If you didn't get all the air out, and then activated the ABS system then you could get air in the ABS module, maybe. Depends where the trapped air is in the system.

The Tech1A + the ABS software will cycle the ABS, and using a pressure bleeder you can bleed the entire system at one sitting.

Or, you can get the air out manually, take a test ride and stomp the brakes to activate the ABS a few times and then redo the bleed. I do believe that when the ABS does a self test it only cycles the valves using the solenoids and no fluid is moved thru the system so if you had any air left from manual bleeding it would not necessarily get into the ABS module. This is how Jeff explained it in one of his posts if I remember right.

another fwiw, if you work alone the speed bleeders are worth the trouble to install. The one caveat is that you can not ignore the sealant on the threads, as it will wear out with use & leak air. I did minor work on my brakes and it took forever for me to get the air out working alone. The speed bleeders helped but still it took a few sessions to get it right. My next thought would be to use my Phoenix gun to do a reverse bleed as it would proly be quicker & more effective as far as working alone would be concerned.

:o I just figured to toss this out for your consideration as I found this system to be more troublesome to work on than my 72's brakes with respect to bleeding manually. I think it's the extra length to the brake lines due to the ABS plumbing. :o

:cheers:
Tom

[| 1990 ZR-1 |]

I am just getting ready to do the same upgrade (Hawks, slotted rotors, braided lines....) to improve the mediocre braking on my 90. I hope your issue is as simple as residual air in the system.

Please post root cause (and your impressions on the new pads, etc) when you have it all resolved

Glenn
Will do Glenn. The Pads seem to get better and better as I put more miles on them. I really feel that i still have air trapped in and am hoping to get it all resolved this week end with another bleed session. I'll keep everyone posted.

[| 1990 ZR-1 |]

Ah, thanks for the reminder! I must have blocked that out... ;) I bled the calipers again, a few times actually. I believe that the brakes were as good as it gets at that point. Sometimes it would still have a long initial pedal, then the second application would be more normal. I believe that was due to the knockback of the pads, and the extra fluid volume it takes to move them vs the stockers (due to the increase in piston area).

Possibly some re-shimming of the calipers to get them more perfectly centered would have helped that, I dunno.

However, on your car, there is no reason it shouldn't feel as good or better than before you messed with it. Air in the line sounds like the most likely culprit.

Also, can you explain your bleed procedure in more detail? Did you open the bleed screw, have your wife pump the pedal twice, then close it? That's sort of how it reads.

Also, FYI, if you went to braided lines, watch the rear line. They don't have an angled exit from the caliper, and thus sit a lot closer to the edge of the rear wheel. Mine would tap-tap-tap on the wheel weight, until I loosely zip-tied it out of the way.

I have to say, on the brakes, I wish I had just stopped after putting on HPS pads. That was more than good enough, and completely headache-free. I am trying to remember that lesson on the V, and resist the urge to upgrade to the 15" 6-pots from the new one...


Bob, I would have her pump 2-3 times and hold the pedal in, than i would unscrew the bleeder to let the fluid out, and than would screw the bleeder back in not to let air back into the system, only then she would release the pedal and would pump again.

[Aurora40]

Bob, I would have her pump 2-3 times and hold the pedal in, than i would unscrew the bleeder to let the fluid out, and than would screw the bleeder back in not to let air back into the system, only then she would release the pedal and would pump again.

You definitely have air in there, then. You can not release the pedal while the bleeder is open, or it will suck tons of air back in.

You need to open the bleeder, press the pedal down and hold it, tighten the bleeder, then release the pedal. Repeat until air stops coming out (And watch the reservoir doesn't run out).

[Scrrem]

I am not a big fan of the two person method, but have used in the past. I just got done removing all four calipers to clean them up and hit them with some caliper paint (I know...cheap a$$). When re-installing I used a hand vacum pump at the bleeder screws and it took about half a resevoir of fluid before I felt comfortable that all the air was out. I drove the car last Sunday and the brakes felt great.
Rich

[batchman]

I've been fighting this same issue for a couple seasons. Have run probably a gallon of fluid through and had best result with the bleed order in the FSM.

Fresh hubs help as they always have play and as mentioned pad knockback is a contributor.

I think I'm going to try a Camaro master cylinder to get the 1" piston. But I misplaced the drawing I did for making an adapter... Gotta go through it again. These brakes are killing me on the track, never thought I'd get out of a Mustang and miss the brakes. Same caliper too!

Best,
- Jeff

[| 1990 ZR-1 |]

The brakes are a secondary priorety now. If the plenum pull goes well this weekend, I'll bleed the breaks again per FSM instructions and will post the results.

[Rex Ruby]

Dark brown gunk came out with little rust pieces especailly out of the front calipers.

I'd take apart the front calipers to inspect the inside condition then rebuild or replace as indicated.

Or, you can get the air out manually, take a test ride and stomp the brakes to activate the ABS a few times and then redo the bleed.

I was going to suggest this. Find an area that has some gravel and hit the brakes hard to activate the ABS.

I had a soft pedal after some brake work, activated the ABS, rebleed, was 100% better then.

[| 1990 ZR-1 |]

Quick update. I had a chance to bleed the brakes over the weekend, and I definitely saw air bubbles come out. The brakes feel much better now, I also belive the brakes are still not broken in all the way since I have both new pads and rotors. The pedal feel gets better each day as I put more miles on them. Hoping in another couple of hundred miles they will be perfect.

[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.

[Paul Workman]

Speaking of breaking in brakes, etc, here is some info worth a read (http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml). The break-in discussion I find to be valuable - used successfully on 3 different cars since reading this, and it seems to work quite well. Just sayin.

:cheers:

P.

[| 1990 ZR-1 |]

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.

The rotors are brand new Centric Premium rotors. They have a what looks like fine lines in a dimond patern on the surface of the rotor. I went through the proper bedding procdure of the pads when I first installed them, and put about 150 miles since, but I can still see that dimond patern. I'm guessing it'll take another 100-200 miles to get that smooth surfaces at which point I should have an even better grip.

[mike100]

Sounds like you are on the right track. Once bled properly etc, you will notice gradual improvement with the pad bite. Mine really started working better after I did several 110-115 mph to 20 mph stops. The rotor has a bit of a purple darkish hue, but the crosshatch lines from the machining are almost gone. I have 1000 miles on the brake job now and it will lock up and work the ABS easily.

I used a wagner street pad, so they wouldn't be too rough on the rotors, but even 'soft' pads need a good bed-in.

ON EDIT: (I have the C5 front brake conversion using oem A-Mold wheels)