ZR1 Brake Problem

[carnold]

After acquiring a 90 ZR1 that sat for 7 years I put in new brake fluid by bleeding at each caliper. After driving for 10 or 15 minutes the brakes locked up and the brake pedal is very hard. I thought it was just the rears so I changed the rear calipers. The fronts are locking up and maybe still the rears after 10 minutes of driving. Once everything cools down everything works fine again. Any thoughts on the problem and a solution? Thanks Chuck

[jonszr1]

I'm not totally positive but I think some thing could be sticking on your power booster. Does the pedal stay down when this happens. hope that helps alittle . Congrats on getting that beast on the road again. Once you get her sorted you will find your stays this big . have a blast

[carnold]

Yes the pedal does stay down. The vacuum hose is clear but don't know anything about the internals of the booster. Problem corrects itself after everything sits for awhile. Where would you look to check further if it is a vacuum problem?

[jonszr1]

i'll pm you a ph to call he will know. have a great turkey day.

[petefias]

Originally Posted by carnold

Yes the pedal does stay down. The vacuum hose is clear but don't know anything about the internals of the booster. Problem corrects itself after everything sits for awhile. Where would you look to check further if it is a vacuum problem?

I wouldn't think it is a caliper (front or rear). I don't think the booster is servicable. I think it is unique to the Z and it is not cheap. After all these negatives, with the help of a service manual and the ZR1Net I'm sure it will get fixed.

I assume all wheels are "locked" when this happens. There is a bleed-off mechanism in the booster.

First I would eliminate the possibility of the pedal mechanism itself (start with the easy stuff). Second, eliminate the possibility of the handbrake assembly (although that wouldn't hang up the pedal).

I think this is a lesson to be learnt by others: don't let your Z ZZZ too much. The car is much happier when it is driven regularly. When I see 0 miles Z's available I get the urge to buy, but then I start thinking about all the problems that I would have to address that my car doesn't have.

[carnold]

The car belonged to a friend and I told him to not let it sit. So far replaced all injectors with RC, thermostat and fluids and still can't go anywhere. Think I will look at the master cylinder next. I am guessing the return is clogged.

[tomtom72]

My 90 was/is developing brake problems also. I experienced somewhat of a "lock up", actually more of a "drag" on the rears. I'm guessing you are sure it's all four and not the rears?

No insults implied or intended. The helm has a section for brake trouble shooting, it's a "look up" chart in the brake section. Humor me for a bit(I'm old & senile ). If you have a FSM look at the chart. On mine when the rears were "draging" the chart said do the parking brake & cable adjustment and brake pedal switch adjustment.

Brake pedal switch adj = pull up on the pedal & listen for a rachet sound...if there is a sound, pull up again & repeat gentle pull up till sound is no longer.

Parking brake & cable adj = pull up lever & release at least three times. When finished the lever should move up 3 to 5 notches w/61 lbs of force applied to it. That's it on the simple stuff, all of 10 mins.

When the pedal feels like a rock, do you get what you would consider acceptable stopping results? If not the symptom is pointing to a booster failure, maybe. The booster is unique to a Z, dual diaphram & NLA from GM. The repair kit is also NLA. Cardone & a couple of others make reman'ed units with a core exchange. If the master leaked fluid out the back seal for a long enough time you will most likely ruin an otherwise good booster. Fluid disolves the diaphrams as I've been told.

My car sat more than it was used before I bought(big mistake on my part). When I started using it and when I bleed clean fluid thru the system my master leaked into the booster. Look up at the top of the brake pedal & see if the push rod boot is wet. You will have to r&r the hush panel/knee bolster to really see the tops of the pedals. While you're ther look at the clutch push rod also & take note of any fluid. If ya have fluid on both plan on replacing both master cylinders....GM lists rebuild kits but the clutch one is BO'ed. Rock auto has the rebuild kit for the brake master....about $90 I think.

You can put a mity vac on the booster, suck about 10 to 13" & see if it holds. If it does then you're good....unless the master did leak. If it did it's only a matter of time.

One other thing....long shot unless you know for sure that someone didn't r&r'ed the booster + master...there is an adjustment on the push rod that comes out of the booster & hits the piston on the master. If it's too long it will close the "return" circuit in the master & keep hyd pres in the system causing a drag or lock up. Go to Classic Performance Products.com they have a Q & A section that I found useful...but I'm a novice so any info is useful to me!


Tom

[carnold]

Thanks Tom lots of good ideas I will keep checking and let you know the results.

[carnold]

Thanks everyone for all your advice. After changing rear calipers (thought initially) the rears were locking up but turned out to be all locking up and getting new brake lines turned out was master cylinder. Found a guy on ebay who sold me a NOS PBR for 99 dollars. Back on the road. Just got to put the CDM box in (ouch) and will be happy.