98 lumina vibration problem

My wife has been complaining about her lumina vibrating excessivly. After much work and troubleshooting, I have come to the conclusion that this only happens wen the car has been drive awhile or the brakes have been used extensively from speeds above 50 mph. The more the brakes are used the worse the vibration gets. The whole car shudders under braking and when driving, large vibrations can be felt in floorboards. After dirving the car awhile the vibrations go away unless the brakes are used again. When driving in town a slower speeds care performs flawlessly. Any Ideas.

You have a dragging issue with the brakes, probably a defective caliper or brake hose. The more you use them, the hotter the rotor gets from the drag, and the more warped it becomes. you can feel it even when not braking because the brakes aren't fully releasing.

I have replaced hoses,calipers and turned the rotors. Still the same problem but do suspect problem to be in front brakes

Things to check: Bent/stuck caliper slide, brake pad not properly seated (easy to do on these!), residual pressure at master cylinder/booster (rare) If you just turned rotors that had been warped before, they will warp very readily on these. They dont have the meat that the old ones did. I gave up on turning rotors on customer's FWD cars, they are so cheap that if there was any doubt, I just replaced them.

two other things to check, lug nut torque and the brake hoses. Uneven lug nut torque can cause a contorting of the rotor as they heat up due to uneven clamping force of the lugs, which will cause the worsening pulsation as you use the brakes more. A bad brake hose will act like a valve, not allowing the fluid to return upstream and the caliper won't retract. The more you use the brakes, the more the fluid heats up, which in turn makes the hose softer and magnifies the problem. check the hoses for cracks and/or soft spots, and replace any that are questionable. Then re-torque the wheels to proper spec (100 ft/lbs) and see if that cures your problem. Good luck.

Good one, I forgot about the torque. I haven't checked mine since the new tires were mounted.

Replaced all hoses yesterday. I dorve the car for about an hour on back roads and tried to duplicate the problem. Car acted as it should - no vibration or shaking. Just got a call from the wife and she said the car was doing it again. It must be something in the way she drives the car that I can't duplicate.

Replaced all hoses yesterday. I dorve the car for about an hour on back roads and tried to duplicate the problem. Car acted as it should - no vibration or shaking. Just got a call from the wife and she said the car was doing it again. It must be something in the way she drives the car that I can't duplicate.

She's not a "two footed" driver, is she? I'd have customers come back with burnt linings and/or shuddering problems, and after the first fix, I'd start to wonder. When I'd ask them if someone was riding the brake, they'd swear up and down that they weren't. Then I'd show them the pedal pad wear on the left side of the brake pedal. There's no way to do that with your right foot. Busted a few brake ridin' wives that way.:lol2:

Seriously, though, I've found that my wife makes long, drawn out stops, with light to moderate pedal pressure, where I make quick, decisive stops with heavy pedal usage. The former method (common to women drivers, too) can really heat up hardware.

she doesn't drive with left foot on the brake. Talked to her later when she got to work. Said traffic was stopped on the highway this morning for a while for an accident. After getting by accident, the car was fine the rest of the way - appox 10 miles.

followed my wife home from work while ago. noticed that when she reaches about 25 to 30 MPH that the brake lights come on. stay on unitl she has to stop. after proceeding lights come back on when she reaches speed. Say she hears the shift solonoid actuating when she is dirving. Something is lightly apply the brake when she gets up to speed. She doesn't use her left foot on the brake at all. Any Ideas?????

You might be dealing with the rare "residual pressure'" problem I mentioned earlier. On some cars, a slight adjustment of the push rod in the booster will cure it (usually only happens on Fords, in my experience though). Make sure there is nothing interfering with the pedal or rod under the dash. That is very unusual, but not unheard of. Make sure the master cylinder is firmly bolted to the booster, and the booster is firm to the firewall. You dont have some floor mat rolling up do you? My wife thought the clutch was going out on her Mustang, turned out she was shoving the mat up under the clutch pedal in a wad, making it stop before disengaging. I can't wait to see what Richtazz has to say about this. I know he'll come up with something I didn't know/think of. Take the mat out, then follow her around. Floor mats cause some strange issues at times. But the shift lock should be inop once the car is in gear, so I'm guessing there is something else happening. In some rare cases, the brake light/shift lock/cruise cancel switch can "ride" the brake slightly, if misadjusted. I'm gonna say look at that first.

I'm wondering, the more I think about it, if the contacts in the brake light switch have disintegrated somehow, allowing the switch plunger to stick out and get stuck holding the pedal just a bit at times. Would explain the brake heating, and the lights/shiftlock strangeness.

That's gotta be it. I can think of nothing else that would explain the symptoms. Push the pedal down, and push the plunger on the switch a few times, I bet it is sticking. If it "notches" at all when you try to push it in or feels rough, you've found the problem.

but would that explain the speed thing. why would the brake lights be off until she reaches a certain speed? The reason I had to follow her home form work yesteday was that I had to replace the battery. IT was dead when she tried to leave work. Brake lights were on all day.

Probably has to do with the vacuum level in the booster as you accelerate, changing feedback on pedal effort. You don't feel the difference, but if the switch is barely getting stuck enough to hold the pedal, it makes a difference to it.

Just looked under the dash. At 6'2' not easy to do but found the fiberboard kick panel under the dash had fallen off of the stud that keeps the firewall end from dropping down. Ths would hold the brake pedal enough to keep the lights on when the engine was running. Would not do it unless the engine was running. Too much force required when engine not running.. I guess she would kick it out of the way when comming to a stop and It would drop back down as she drove. I don't know if this would apply enough pressure on the pedal to keep the pads in enough contact with the rotors to heat them up enough to cause the vibration. I will have to let the wife drive it to see. It won't do it with me.

Just looked under the dash. At 6'2' not easy to do but found the fiberboard kick panel under the dash had fallen off of the stud that keeps the firewall end from dropping down. Ths would hold the brake pedal enough to keep the lights on when the engine was running. Would not do it unless the engine was running. Too much force required when engine not running.. I guess she would kick it out of the way when comming to a stop and It would drop back down as she drove. I don't know if this would apply enough pressure on the pedal to keep the pads in enough contact with the rotors to heat them up enough to cause the vibration. I will have to let the wife drive it to see. It won't do it with me.

If the brake lights stuck on, you have to replace or adjust that switch, anyway. I gaurantee that's the brake dragging cause too.

Just looked under the dash. At 6'2' not easy to do but found the fiberboard kick panel under the dash had fallen off of the stud that keeps the firewall end from dropping down. Ths would hold the brake pedal enough to keep the lights on when the engine was running. Would not do it unless the engine was running. Too much force required when engine not running.. I guess she would kick it out of the way when comming to a stop and It would drop back down as she drove. I don't know if this would apply enough pressure on the pedal to keep the pads in enough contact with the rotors to heat them up enough to cause the vibration. I will have to let the wife drive it to see. It won't do it with me.

You've found it! That makes sense to me. With power brakes, it doesn't take much effort at all to ride the brakes a little. I still don't know why the shiftlock would be engaging, unless the switch is coming apart.

I think the shiftlock solonoid is activated every time the brake is pushed. It has done that as long as I have had the car. You have to push the brake to get the thing out of park. I sure hope this is it.

thanks for the help

it's possible that the check valve for the brake booster is leaking, or the booster itself is bad causing the plunger to sink over time, which would allow the brake pedal to move just enough to turn the brake lights on. There should be a return spring on the brake pedal which keeps this from happening, which may have broken or become weak. While driving, the pedal sinks and lightly engages the brakes, which casues the brake lights to come on and the brakes to get hot, causing the vibration.