brake vibration

[cogs]

hi, new here: 1994explorer; when i brake, i am seriously vibrated until i stop, and near the end of the stop, the abs turns on and grabs. what i've done about it:
on driver's side front wheel: replaced three rotors; changed caliper and brake hose; changed a few brake pads and sliding pins; new races and bearings (plenty of grease); bled brakes and filled reservior; cleaned abs connectors and sensor.
symptoms: on the driver's side, the inside pad worn and the backside of the rotor scratched where it meets the pad. the passenger front tire is worn a little on the inside. i cleaned off the sensor to the abs, so that's why it activates now. the front end doesn't vibrate until i brake.
what i think it is, and please tell me what you think it is: something is bent, such as the spindle on which the rotor bearings run, or whatever connects to that spindle. i think this because my father who gave me the truck says he vaguely remembers that side getting hit (or not). thank you for your input. cogs

 

[IZwack]

Disable the ABS (pull its fuse or disconnect the ABS module's wiring harness) and see if it makes any difference.

 

[JohnJ]

For the brakes to produce a pulsation type vibration (vibration at wheel speed, not ABS type vibration which occurs at a steady speed regardless of how fast you're going) the problem must be either directly or indirectly caused by a rotating part which means that a spindle isn't likely to be your problem. Overtightened wheel bearings or a brake rotor with an out-of-plane or inconsistent thickness would be much more likely. You can check for out-of-plane (lateral runout) using a dial indicator or thickness variations using a micrometer.

If you've replaced both front rotors and the problem returned immediately then I would be more inclined to suspect overtightened front wheel bearings or out of round rear drums. If you spin a rear wheel you should be able to hear any out-of-round condition bad enough to shake the steering wheel without using a gauge. If overtightened wheel bearings are the problem, search this forum for proper tightening instructions.

If you find that the problem is with the front rotors and new ones just keep going bad, look for something that could cause them to overheat and be sure that you aren't overtightening your lug nuts. As far as looking for overheating goes, drive around a bit, then jack up the front wheel and see if one of them feels hot or is hard to turn. You should be looking for a mechanical problem (pads fit too tight or caliper dragging) or a hydraulic problem (brake line or hose clogged, twisted banjo bolt at caliper to hose connection, bad master cylinder, overlong master cylinder pushrod). If it drags, try opening the bleeder valve. If opening the bleeder valve releives the drag, it's hydraulic otherwise mechanical.

If your problem is not this wheel-speed related pulsation but is the steady buzzing vibration of erroneous ABS activation your problem is either with a wheel speed sensor (or reluctor) or normal response to a lockup condition which might be a fluid leak onto a drum or rotor or a bad tire or mismatched tire.

 

[cogs]

speaking of wheel bearings, what tightness, like, how much to turn the nut that holds the rotor on? and, on the inside bearing, what else can you do, but put the plate on? i ask this, cause i believe, as you said, something is causing misaligned rotation of the rotor. also, when i said spindle, i didn't know what to call the axle that the rotor rides on. btw thank you.

 

[JohnJ]

To the best of my knowledge, the thing you call a spindle is actually called a spindle and does not spin. I can't think of any way it could be responsible for your brake problem.

Also, when you need a specific piece of Explorer related information, it can be very quick and easy to use feature at the top of this forum. I can bring you to posts such as this in a matter of seconds.

 

[cogs]

continued troubleshooting:
torqued both front wheels' nut to specs.
passenger side front: rotor dragging with caliper on. abs sensor full of steel splinters. reluctor has line where sensor rides. cleaned off sensor. bent backing plate away from rotor. the back brake pad was a little thin, and cracked a little. needed to mention that master cylinder was replaced awhile ago.
test drove, and rotor still pulses (a little smoother). in reverse, i can feel it grab also. disconnected the fuses to abs, and the pulsing continues. have not tried to loosen caliper nut to see if it's a hydraulic problem. i will try that later. please respond if this narrows it down for you?

 

[JohnJ]

continued troubleshooting:
torqued both front wheels' nut to specs.
passenger side front: rotor dragging with caliper on. abs sensor full of steel splinters. reluctor has line where sensor rides. cleaned off sensor. bent backing plate away from rotor. the back brake pad was a little thin, and cracked a little. needed to mention that master cylinder was replaced awhile ago.
test drove, and rotor still pulses (a little smoother). in reverse, i can feel it grab also. disconnected the fuses to abs, and the pulsing continues. have not tried to loosen caliper nut to see if it's a hydraulic problem. i will try that later. please respond if this narrows it down for you?

So then if follows that your dragging is overheating the rotor and the damaged rotor is causing the pulsation. Once you open the bleeder you'll know if it's hydraulic (usually the hose) or mechanical (usually the caliper but sometimes the pads). Once you get the dragging fixed you can turn or replace the rotor and you'll be all fixed up.:roll:

 

[cogs]

johnj, i cannot thank you enough for pointing me in the right direction.
the stress caused by this to me and my wife while being jarred every
breaking was quite annoying after some time. plus, knowing the danger of
a bad breaking system. i think you're right, cause a mechanic said my rotor
was warped, and replaced it. the trouble disappeared somewhat, then returned later.
i will replace the caliper, pads, and rotor, and post back here. god bless til then. cogs

 

[JohnJ]

Before you replace the caliper you might want to open the bleeder to make sure opening the bleeder doesn't release the drag. If that does release it you need a hose and not a caliper.

Also, replacing one caliper can sometimes lead to unequal braking (left/right imbalance) so if you do need to replace the caliper it's good to consider replacing the pair if they're not too expensive.

 

[cogs]

hey, finally spent some money on parts. replaced passenger brake hose, rotor, and pads on both sides. vibration disappeared completely. i want to get my hopes up, but waiting to see if rotor warps. if it doesn't, it was the hose i replaced. if it does, probably needs another caliper, or last resort, adjust the master cylinder(new). so right now, the hose fixed it. thanks to all.