(Problem solved - thx for the help) Way off topic - Help with Chevy Cav brakes

[Casper4104]

This is way off topic, but there's some REALLY knowledgable people here and maybe somebody has a Cav as a toad.

Help with Chevy Cavalier brakes please.

'96 Cav W/anti-lock brakes, 4-cyl, 5-speed.  145K miles.

Daughter had to quickstop and the pedal just went soft on her.  Couldn't stop and bumped the SUV in front of her.  Puddle of brake fluid was found under the car, and the master cylinder was empty after the incident.  Everbody's Ok.

Towed the car home (ain't Good Sams great!) and got the front wheels up – refilled the master cylinder.  Wife pumped brakes several times but couldn't get any pedal.  Both front rotors not braking, could turn rotors by hand with pedal all the way down.  Couldn't find where the fluid loss came from.  That's where I'm at right now.

I'll attack the car this weekend.  Will try to bleed air from system with front bleeders, then put front wheels back on and jack up rear and check back there for leaks or anything amiss.  Chilton book says these brakes are diagonally linked, so I was surprised when both front brakes were non-op.

Any first guesses?  Anything Cavalier brakes are notorious for?  Help!

Thanks,

Casper4104

[Busted Knuckle]

Casper from what you describe first things I'd look at are the master cylinder or the power booster! Let us know what ya find, an we'll go from there! BK 

[Sammy]

Casper, I'd jack up the car, support it with proper jackstands,remove all 4 wheels and start inspecting all brake lines,wheel cylinders(if you have drum brakes at the rear axle) brake calipers and brake hoses.If you don't see anything wet, fill the master cylinder and try to bleed the brakes again.You must start at the wheel furthest from the master cylinder - the r/rear-when bleeding hydraulic brakes. The brake system is now airbound and will take some pumping and bleeding to get the air out. Once you get most of the air out, fluid will start to flow again, then you will hopefully find your leak.
Good luck with your repair. 
Sammy 

[Casper4104]

Thanks for the tips Bryce and Sammy - I'll work the bleeding as Sammy recommends.

Since both front wheels quit working, I'm with Bryce and thinking Master Cylinder.  It seems that if I blew (for example) the right rear wheel cylinder, that should take out the right rear and the left front, but the other 2 wheels should still work.  Wierd.

Anybody know a definitive test for a master cylinder other than "Pull the lines loose-put your thumb over the holes & pump"?

Thanks,

Casper

[RJ]

Casper -

Might try this - it's simple, before disconnecting anything:  Take off the cap to the master cylinder and make sure the fluid's at the full mark.  Then have your helper slowly step on the brake pedal while you watch the fluid reservoir.  If the master's failed internally, the fluid will sort of look like it's boiling while the pedal's being pushed.

Well, at least that's one check we used to do back in the old days before Anti-Lock brakes.

My (now sold) '91 Dodge Caravan had a pump inside the master cylinder that was integrated into the anti-lock braking mechanism somehow.  Maybe the Chevy's got something similar and it's failed?

FWIW & HTH. . .

[wrench]

 Here the procedure as per  DA-BOOK!!

Manual Bleeding 1. Remove master cylinder reservoir cover, then fill reservoir as necessary. 2. Attach one end of a clear plastic hose to rear bleeder valve of the brake control assembly, then put opposite end of the hose into a clean container. 3. While depressing brake pedal, slowly open bleeder valve, until fluid begins to flow. 4. Close valve and release brake pedal, then repeat procedure for front bleeder valve. 5. Ensure master cylinder is full, then raise and support vehicle. 6. Bleed wheel cylinders and calipers using the following sequence: a. Right rear. b. Left rear. c. Right front. d. Left front. 7. Lower vehicle and check fluid level in reservoir, fill as necessary. 8. Turn on ignition and note pedal travel and feel as follows: a. If pedal feels firm and constant, start the engine and recheck pedal travel. If pedal still feels firm and constant, continue procedure. b. If pedal feels soft or has excessive travel either initially or after engine is started, repeat bleeding procedure. 9. Road test vehicle, make several normal stops from a moderate speed, then make one or two ABS stops at approximately 50 mph. 10. Ensure pedal is still firm and constant.

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         wrench

[wrench]

  You won't be able to find the leak if not properly bleeded because not enough pressure with air remaining in the system.  Check the hose for small crack, & under the dash where the rod goes in the M. cylinder if it's wet.
                 wrench

[jaybe_2]

I am pretty sure you will find a leak when you get the fluid flowing! But if you want to test the master take the lines off the master and plug them, you should have a rock hard pedal if you do that. You can get brake line plugs at the auto parts stores. Good luck

[Casper4104]

Here's what happened.

These cars have diagonally linked brakes.  RR-LF and LR-RF.  Well when I started bleeding I found that there was a problem in the line and the LR was getting no fluid - and probably hadn't been for some time.

The master cylinder failed, blowing an O-ring or seal in the part of the cylinder that feeds the LF-RR wheels, so they got no pressure.  With the LR not working, that left just the lonely RF braking.  I would assume that the ABS kicked in to keep the RF from skidding - which left my baby girl with no brakes at all.

Diagnosed & fixed, including new lines to the LR.  Thanks for the help fellers.

Casper

[Jeremy]

I almost suggested a blown master cylinder 'o' ring originally, as the problem had occured after a heavy brake application. The reason I didn't say anything was that I couldn't figure out where the oil puddle had come from; the master cylinder 'o' rings I am thinking of are internal seals, so the failure I was suspecting would have given all the symptons except the external oil leak. I also know very little about ABS systems so wasn't sure of myself there either. So, out of interest, how exactly had the oil escaped?

Jeremy

[Casper4104]

The 2 chambers in the master cylinder feed 2 inlets in the ABS module, which then bleeds off pressure from the 4 lines to the individual wheels as necessary to prevent skidding.  O-ring blew out where the fluid goes from the master cylinder to the ABS module, dumping it on the ground.

I probably just needed to replace that O-ring, but for $47.99 I went ahead and replaced the MC - which came with all new O-rings for everything.  I had already bought the part, and already had the whole works apart,,,

Thanks,

Casper

[Jeremy]

Ok, thanks. The 'o' rings I was thinking of were the ones that seal the piston inside the master cylinder, thus allowing it to push the oil. I once blew one of those on my Range Rover, with all the same symptons you describe except the oil leak

Thanks

Jere,y