brake problems

[bumpinkicker04]

I have an 01 mercury mountaineer 5.0 AWD with disc brakes all around. About a month ago the steering wheel would shudder and shake when I hit the brakes. So I replaced the front rotors and pads and then last week replaced the rear rotors and pads. And the shudder is still there. The thing I have noticed is that if I hit the brakes really hard then the next couple of applications are firm with no shake and then the shake comes back. Could it be the calipers? And if that is a possibility, how do I test them? Master cylinder? Air in the lines? I am stumped and I don't want to take it to the shop and get ripped off. Thanks in advance for any advice.

[Johnny Mullet]

I wonder if you have a bent hub? Sometimes a mechanic will beat a stubborn rotor to the point that the hub will bend slightly.

[bumpinkicker04]

Originally Posted by Johnny Mullet

I wonder if you have a bent hub? Sometimes a mechanic will beat a stubborn rotor to the point that the hub will bend slightly.

But wouldn't there be a vibration or something at all times? thanks

[j_w_spence]

Had the same problem. Mine went away when I turned the rotors. May have a bad (new) rotor. Has your gas milage gone down? I ask this because I think the brake booster actuation valve in my booster is staying slightly engaged and dragging the brakes. (My rotors rewarped in about 2 months) My brakes seemed to stay engaged for a moment on the freeway one day after I released the pedal. Could yours be dragging and rewarped the rotors? My family owned 2 auto repair facilities and I was a mechanic for about 8 years and this problem is stumping me too.....just wanted to give you some avenues of thought. Hope this helps.

[bumpinkicker04]

Originally Posted by j_w_spence

Had the same problem. Mine went away when I turned the rotors. May have a bad (new) rotor. Has your gas milage gone down? I ask this because I think the brake booster actuation valve in my booster is staying slightly engaged and dragging the brakes. (My rotors rewarped in about 2 months) My brakes seemed to stay engaged for a moment on the freeway one day after I released the pedal. Could yours be dragging and rewarped the rotors? My family owned 2 auto repair facilities and I was a mechanic for about 8 years and this problem is stumping me too.....just wanted to give you some avenues of thought. Hope this helps.

Thanks for the reply but I finally fixed it. Wanna know how? Traded it in on an 05. LOL I ended up replacing all 4 rotors and pads and the front and rear brake hardware.

[shorod]

I suppose it's kind of OBE for this thread now, but maybe for future reference....

I too used to work for my parent's shop. We received new rotors that were warped numerous times. It got to the point where we would take 0.002 inch off each rotor surface before installing the new rotors to make sure they were true. If it took more than that to get them true, they were sent back and exchanged for another one. Yes, you may have received warped new rotors.

As for j_w_spence's issue with the brakes staying applied, have you replaced or checked the brake hoses? You may have a hose or more that has collapsed internally. The power brakes exert enough force to push fluid to the calipers, but the calipers struggle to release because the collapsed hose restricts the flow, causing the calipers to drag.

You can check for this by attempting to compress the brake calipers with the bleeder screw closed. If it is difficult, but compresses easily once the bleeder is opened, collapsed brake hoses is a likely culprit. Of course, if the booster is failing to release pressure (which I've never experienced happening) then you would have similar symptoms. You could further check the hoses by disconnecting them from the hardline and seeing if the caliper with closed bleeder was difficult to compress with only the rubber hose installed.

-Rod

[j_w_spence]

Thanks Rod.....you jogged my memories of my wrench pulling days! Very valid point....Another reason that suggested booster....I visited my brother in CO. at 8000 feet and there were times my truck wouldn't stop at all! Less vacuum at altitude so it kinda sent me in the direction of the booster. A restricted brake line would also cause the vehicle to "pull" once the brakes were released.....can't see both hoses restricted the same....thought maybe I had some debris in the proportioning valve that might act like a "check" in some situations....I'll post how I resolve this issue....thanks for the help!