brakes pulsating

[KillerGmcTruck1988]

1988 GMC K1500 4x4, had front and rear brakes fully replaced in 2018-2019, mileage on new brakes about 5-6k miles..

Took front brakes apart and everything looks good and so does rear, but getting nasty brake pulsating in brake pedal, anything eles i should look for?

 

[GrimsterGMC]

1988 GMC K1500 4x4, had front and rear brakes fully replaced in 2018-2019, mileage on new brakes about 5-6k miles..

Took front brakes apart and everything looks good and so does rear, but getting nasty brake pulsating in brake pedal, anything eles i should look for?

Check the discs for run out, I have been through 3 set of discs in the 8 years (100k miles) I have owned my truck. For some reason they don't wear evenly all the way around, so they get thinner in some places and that results in the pulsating brakes. You can have them skimmed but there is only enough material to do it once before having to replace them altogether.

 

[1998_K1500_Sub]

Check the discs for run out

That's where I would start. I often check runout when installing new rotors. Check both sides (inboard and outboard) of each rotor, note any high and low spots. For specs, see attached .pdf.

If you get numbers out of spec, remove the rotor and re-mount it on the hub (e.g., 180deg) and measure again.

As usual, make sure the hub surfaces are smooth / clean, ditto for the hat in the rotor. Any rust should be removed (I use either a needle scaler, or a chisel with just enough tap from a hammer to knock the rust off).

Check the brake rotor thickness as well (see attached). Even a few thousandths variation in thickness can cause a LOT of pulsation.

Check your hubs for runout as well, as bearing wear may allow the hubs (and thus rotors) to run askew, even if the rotors are true.

Make sure the pistons move in/out smoothly in the caliper bore w/o bind, so that a pad / the pads aren't dragging on the rotor.

I can't help but wonder if bad ball joints / tie rods / worn rubber bushings might allow play in the front suspension that might manifest as a pulsation or wobble during braking. Hopefully others will comment.

 

[KillerGmcTruck1988]

That's where I would start. I often check runout when installing new rotors. Check both sides (inboard and outboard) of each rotor, note any high and low spots. For specs, see attached .pdf.

If you get numbers out of spec, remove the rotor and re-mount it on the hub (e.g., 180deg) and measure again.

As usual, make sure the hub surfaces are smooth / clean, ditto for the hat in the rotor. Any rust should be removed (I use either a needle scaler, or a chisel with just enough tap from a hammer to knock the rust off).

Check the brake rotor thickness as well (see attached). Even a few thousandths variation in thickness can cause a LOT of pulsation.

Check your hubs for runout as well, as bearing wear may allow the hubs (and thus rotors) to run askew, even if the rotors are true.

Make sure the pistons move in/out smoothly in the caliper bore w/o bind, so that a pad / the pads aren't dragging on the rotor.

I can't help but wonder if bad ball joints / tie rods / worn rubber bushings might allow play in the front suspension that might manifest as a pulsation or wobble during braking. Hopefully others will comment.

well i guess ill just try a new set of rotors tomorrow since they aint too much, and to add the balljoints,tierods,pitman arm,idler arm,wheel bearings, ect. all were replaced last year. went back out tonight and saw on one of drums didnt look too right inside, ill post a pic tomorrow

 

[Schurkey]

Use the park brake at moderate speed. If the truck shudders, the problem is with the rear drums.

If it doesn't, the problem is more likely front brakes.

Yes, rotor warpage is likely...but why are you having repeat problems?

DO THE REAR BRAKES WORK? Sometimes the front brakes overheat/overworked because the rear brakes don't function at all. Plugged rear brake hose is a possibility, as are problems in the ABS unit.

Just to ask the question...your brake pedal pulsation isn't a result of over-active ABS operation...right?

 

[KillerGmcTruck1988]

didn't get a chance yet to tear back into the truck this morning, but took the truck to the store today, noticed when coming to a quick fast stop 35mphish seems there is no pulsation in the pedal, now slowly braking coming to a stop is bad pulsation in the pedal

 

[texas tough]

air in the system can cause pulsating as well.. any brake or ABS lights on?

 

[Pinger]

Just to ask the question...your brake pedal pulsation isn't a result of over-active ABS operation...right?

Same question from me. Noting that depending on how sensitive the system is, slight discrepancies in tyre rolling diameter can trigger ABS. Mismatched wear eg, worn tyres with others being new, or wrong pressures can be enough.
By what I've just read in post 6, I'd look for a front tyre to be behaving as if it had a larger diameter than the rears. Or rear behaving as though smaller.

 

[KillerGmcTruck1988]

air in the system can cause pulsating as well.. any brake or ABS lights on?

no lights on, guess I'll bleed the system and go from there

 

[KillerGmcTruck1988]

Same question from me. Noting that depending on how sensitive the system is, slight discrepancies in tyre rolling diameter can trigger ABS. Mismatched wear eg, worn tyres with others being new, or wrong pressures can be enough.
By what I've just read in post 6, I'd look for a front tyre to be behaving as if it had a larger diameter than the rears. Or rear behaving as though smaller.

and to add I did just get new tires a week ago, and this problem started when it had my old set of tires.