Mechanics

CHEVROLET LUMINA GREASE PROBLEM

1998 Chevrolet Lumina • 150,000 miles

I have a 1998 chevy lumina my wife blew a tire out and somehow messed up 2 lugs so had to change them out so had to take brake caliper loose 2 do so repaired it but now I cant get the air out of the brake line it just wnt bleed off its the front left side we loosen the the bleeder then push the pedal to the floor tighten bleeder back up let off pedal wait 15 seconds and repeat over and over with no success its driving me insane im about to go crush it for junk metal lmao HELP!
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Guest
April 11, 2013.




You have to put some punctuation in that huge sentence so it will make sense. What I was able to figure out is you can't get a wheel to bleed and your car is suffering from do-it-yourselfer-itis. First of all, the previous person who replaced the lug nuts did not use a click-type torque wrench to set them to the proper tightness. There are four reasons every manufacturer lists that value. Every shop has a huge wall chart listing every car model with its lug nut torque specs. A mechanic caught not using a torque wrench can expect one verbal warning. The second time he will be fired. It's that big a deal. The damage was done the last time the wheel was removed but it shows up when you need to remove the nuts the next time.

Second, why did you disconnect the flex hose from the caliper? That is not necessary to replace anything except one of those two parts. There would have been no need to bleed anything. This entire procedure would have taken a professional 15 - 20 minutes.

Third, all professionals know to never ever push the brake pedal to the floor. Doing so will usually damage the master cylinder. Crud and corrosion build up in the bottom halves of the two bores where the pistons don't normally travel. Running the pedal all the way down runs the lip seals over that crud and can tear them. That damage may not show up for a few days. It will result in a low or slowly sinking brake pedal.

Fourth, GM master cylinders have an internal valve that trips when there is unequal pressure in the two hydraulic circuits. That prevents fluid loss when there's a leak and it is why you can't get any fluid to bleed from the caliper. The only way to unseat that valve is to open the bleeder screw for the left front caliper or the right rear brake and give is short quick burst of compressed air. The goal is to push the brake fluid back only a few inches. You don't want to push air all the way back to the master cylinder because it will be just that much harder to bleed it all out again. Once the valve is centered just let that line gravity-bleed. Professionals rarely use a helper to push the brake pedal. If no fluid comes out loosen the cap on the reservoir to prevent vacuum from building up and impeding fluid flow. When the air bubbles stop coming out, snug the bleeder screw, stroke the brake pedal a couple of inches a few times to push the piston out of the caliper. Any remaining air bubbles will wash into the caliper. Open the bleeder screw once more for a few seconds to expel those bubbles.

Check the wheel for signs of roughness or other damage to the friction surface that holds the lug nuts tight. If there is damage the wheel must be replaced. Grease on the studs is another concern. If the studs have an anodized coating no grease of any kind must be used. That coating is typically found on import cars and is a lubricating and rust-preventive coating. Some greases will eat that coating away. If you have steel studs a very light coating of grease is okay but only on the threads. If a mechanic uses a little grease he will not use an air impact wrench to run the lug nuts on. The centrifugal force can cause that grease to build up and whip around onto the friction surfaces where it will cause the nuts to work loose repeatedly. Anti-seize compound must never be used with lug nuts. If that was ever found on any car my students had to scrub it completely off, then check for damage.

Some other things to watch out for are rust between the rotor and hub and handling of the rubber flex hoses. Calipers must never be allowed to hang by the hoses. That will often tear the inner liner resulting in a restriction that prevents the caliper from releasing. It is a common cause of dragging and overheating brakes

There are access holes in the hub where water can splash through creating raised spots of rust buildup on the mounting surface of the rotor. Rattling in the area while doing other repair procedures can break that rust and scale loose and it can get wedged between the hub and rotor. Removing the rotor and reinstalling it in a different orientation will put that raised spot of rust between the two parts also. That will make the rotor and wheel wobble. That's a common source of steering wheel shimmy after brake or tire service.

Caradiodoc
Apr 11, 2013.


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