I get a vibration/pulsing when braking - feels like coming from rear. Could it be the ABS speed sensor?

1992 F-250 4x4

 

have your rotors turned and if that doesnt cure it turn the drums. my truk was doin the same thing till i turned the rotors now it brakes smooth as new.

 

If the rotors need turning, you'll feel the vibration through the wheel and generally not much through the pedal or vehicle, if at all. The ABS will pulsate the pedal.

The speed sensor is just a magnet, it's pretty simplistic and virtually never "breaks".

 

no no no i completly disagree with that. if the rotors r really out like mine were it will shake the truck bad. the pedal didnt pulsate as bad as the truk shook. most of the time cars just pulsate the pedal when the rotors have too much lateral runout, but trucks can shake like you wouldnt believe. when slowing down from about 45, it was like the truck was trying to shake u out of it. turned my rotors and problem 100% went away. agree the abs sensor wont make this happen.

 

on my 1994 f150 i got a vibration that seemed to shake the whole truck when stoping from 40 mph or more, it was really bad above 60. it ended up being the tires not being balanced right, i found this out when i put my other set of rims on and the vibration went away

 

Rear brakes out of adjustment. Hear any metal on metal rattles coming from the rear while driving?

 

Rear brakes being out of adjustment will never cause a pulsation. If it only happens while you're braking, it's warped steel. If it happens all the time, it's out of balance tires.

It's easy to tell if it coming from the front or the back. If you feel it in the steering wheel, it's the fronts. If you feel it in the brake pedal, it's the rears.

 

If the rotors are warped, the steering wheel will shake back and forth as you hit the brakes. That's the caliper wobbling back and forth and translating through the steering. That is a well known characteristic. If your truck was shaking that bad when you hit the brakes, then you had more of a problem then just typical front rotor warpage.

The pedal should not pulsate if just the rotors are warped and that is the only problem present. If the brake pedal pulsates, thats likely ABS kicking in when it's not suppose to, indicating a potential problem with the ABS system or it's sensors. I have never heard of a pulsating pedal due to just rotor warpage. Keep in mind the brakes are hydaulically activated, so mechanical movement is not translated through the rotors to the brake pedal. If your rotors were warped enough to shake the truck while braking, your steering wheel would be going nuts.

A shaking of the whole truck while braking could be rear drum warpage, andym stated that.

It would be wheel/tire balancing if the truck vibrated at certain speeds, not just only braking, just like andym said. Check into rear drum warpage like he said also, that could be what it is. He's always got good advice.

Just to throw out there, my buddy's maxima shakes the wheel really bad because his rotors are terribly warped, but I can't feel a thing in the passanger seat.

 

I have the same problem on my 99 f150 4x4. There is a bad shaking of the whole truck only when I brake. It gets worse the more I slow down. I have replaced tires all around, replaced front ball joints, cleaned and replaced rotors on front only and had it aligned. Nothing seemed to help. I had an auto parts store guy drive it and he said it feels like the ABS is trying to kick in early or whenever I am braking. Has anyone heard of this and what is next? If it is ABS, what is wrong? I have no warning lights for the ABS system on the dash. I am running out of options. The truck has 105000 miles on it.

 

ok if i had more problems than warped rotors, then how come the problem completely 100% stopped when i turned the rotors and did nothing else? one of the first things u learn as a professional brake mechanic is pulsating pedal is caused by thickness variation of the rotors caused by lateral brake runout that wears the rotor unevenly.the caliper piston is bieng pushed back and forth by the runout, pulsating the fluid in the hyd line back to the pedal. if u have really bad thickness variation, its enough to shake the truck like crazy.if the abs is activating, its a different type of pulsing. a lot of newer vehicles have problems with rust and corrosion forming under the wheel speed sensor where it mounts, causing the speed sensor to lose its proper gap with the cogged sensor ring and it tells the abs computor in effect that wheel is locked, so it pulsates the fluid pressure in an attempt to " unlock" that wheel when u hit the brakes. just some thoughts from an ase master certified mechanic with 2 years of college and years of experiance.

 

Cut for brevity. This fellow knows what he's talking about - good info.

 

You could pull the abs fuse to rule that out.
You could brake using the only the e-brake and diagnose it to the front or the rear.

 

I have no idea...but the calipers and brake pads were dealt with, as well as removing the rotor and disassembling the hub/wheel bearings.

Could be something in conjunction with that, I duno...just discussing other possible events.

I have had situations where I could of sworn changing XX part fixed a problem when it was actually something else, that you find out later on...

I could be wrong, thats a given, but I am explaining what I've found through my experiences.

 

installed new rotors - no more vibration!

 

[QUOTE=Popa Tim
You could brake using the only the e-brake [/QUOTE]

Oh dear god if yuo do that make it slow and hold that handle. I did that in a old ranger that I got for free no bed or hood or right quarter panel just it ran and it was fun we pulled the ebrake at like 45 and it spun out and almost rolled.