Severe Vibration When Breaking Options

[Windriderusa]

I have a 1991 Previa AWD that has a very bad shake in the front end when I put the brakes on, especially when going down hill. When I put the brakes on hard the shaking stops. Sometimes when I brake it doesn't shake at all. I have new brakes all the way around, new calipers in the front, the rotors have been replaced and the front end has been looked at as well. I have replaced the master cylinder and the ABS pump. I also have unplugged the ABS system with no difference----It still shakes. I thought maybe the mounts were bad so I replaced the transmission mounts and looked at the engine mounts. I also held the wheel and shook it back and forth to see if the bearings were loose. They seem fine too. I am going crazy. Any suggestions?

[Stillin Saigon®]

I still believe it's your brake rotors. If you have driven the van through water on an Interstate, the rotors are warm to hot and when hitting a puddle of water...even though they're new, they can warp. The other way a brake rotor can warp is by someone running the lug nuts down with an Impact Wrench. Lug nuts now have to be tightened to a certain amount of torque measured in foot-pounds. If you "zap" a wheel onto your van, this can also warp a rotor for my impact wrench goes to about 185, foot pounds of torque whereas my lug nuts only take between 86 ft lbs (on my BMW) to 95 ft-lbs on my Grand Cherokee Laredo TSI with the huge off-road wheels or tires.

Have someone check the "run out" of your rotors or some places turn rotors cheaply if you pull them off yourself. To determine which rotors are causing this, go down a road with little traffic on it and then pull up on the Emergency Brake. If the van shudders, then it appears to be your rear rotors, if hitting the brake pedal causes the steering wheel to shake and vibrate, then it most certainly is your front rotors. Also the lack of Caliper grease can cause a new caliper to stick on the trusted caliper mount. Check all the brake pads to see if an inside or outside brake pad is wearing more than the others and there's your problem.

I Hope This Helps,

~Stillin~

"Still Living on the Right Side of Dirt..." (IMG:style_emoticons/default/harhar.gif)