Pulsating brakes

L

Lyle Wiese

Member
73 1010 2wd t'all. Oem disc/drum.

A new rambleall problem.

When coming to a stop, the brakes seem to be pulsating like the rotors are warped. I put an indicator on the rotors a few minutes ago and they show less than .010 warpage. I fully expected the indicator needle to go crazy with how the beast stops. The calipers were replaced when I put this rig back on the road a while back. The system was bled recently when I replaced the front brake hoses.

I was hoping for just a quick trip to clackamas auto parts to get the rotors turned.

What am I missing?

Lyle
 
As you know, there were two different caliper systems used on those rigs in the beginning as the disc brake system option was implemented.

One caliper designed used the two threaded "pins" that the caliper slides/floats on. The other caliper slides across the mounting bracket itself and is retained with those funkee anti-rattle springs and clips.

I'm suggesting that at least one of the calipers is not "sliding" now when the caliper is pressurized. It's simply hanging/cocking on either the slider pins or the bracket, depending upon which system you have (I don't remember even though we've discussed this before). This is a very common occurrence and is easy to rectify.

What is possibly happening is that because one or both calipers are not moving smoothly, under light-to-medium braking, the caliper simply "deflects" instead of being able to slide freely. Since it can't generate full contact, then the pads kinda "chatter" which feels just like a warped rotor at the pedal.

The fix...pull either the pins and polish/lubricate with a high temp silicone grease made for that purpose (clean the bore of the caliper also which slides on the pin), or...pull the keepers and springs out and polish/clean the brackets and caliper contact points and also smear the mating surfaces with silicone grease.

I bet this came on all of a sudden after the rig has not been driven in several days??
 
michael mayben said:
as you know, there were two different caliper systems used on those rigs in the beginning as the disc brake system option was implemented.

One caliper designed used the two threaded "pins" that the caliper slides/floats on. The other caliper slides across the mounting bracket itself and is retained with those funkee anti-rattle springs and clips.

I'm suggesting that at least one of the calipers is not "sliding" now when the caliper is pressurized. It's simply hanging/cocking on either the slider pins or the bracket, depending upon which system you have (I don't remember even though we've discussed this before). This is a very common occurrence and is easy to rectify.

What is possibly happening is that because one or both calipers are not moving smoothly, under light-to-medium braking, the caliper simply "deflects" instead of being able to slide freely. Since it can't generate full contact, then the pads kinda "chatter" which feels just like a warped rotor at the pedal.

The fix...pull either the pins and polish/lubricate with a high temp silicone grease made for that purpose (clean the bore of the caliper also which slides on the pin), or...pull the keepers and springs out and polish/clean the brackets and caliper contact points and also smear the mating surfaces with silicone grease.

I bet this came on all of a sudden after the rig has not been driven in several days??
Click to expand...

Yeah, I don't remember which calipers I have either. Funny, just looked at them today, but I was looking for a warped rotor, not a problem caliper. Something to do with tunnel vision.

I will take them apart tomorrow and clean/lube them. Your description, Mike, of the warped rotor feel is right on. I meant to ask you about this last weekend.

Thanks,

lyle
 
This afternoon, I took the calipers apart and lubed up the threaded "pins" and all the metal to metal surfaces the calipers "slide" on. The plating on the pins is still shiny and the rubber bushings the pins go through are all in good shape. Took it for a test ride up and down the street. A hard stop will practially put the r'all on it's nose. A nice easy stop, which is where I was having the pulsating issue, seems to be fixed.

I should clarify; it wasn't a pulsation in the brake pedal, it actually felt like the brakes were "grabbing" and then releasing. Not a real grab, but more like the pedal was being pushed and released.

I inspected the pads for uneven wear and everything looked flat and parallel to the metallic backing of the pad.

I think/hope it's fixed.

Lyle
 
It's fixed!

The "pin" brake set I believe were sourced from delco/moraine. The slider set were kelsey hayes.

I didn't realize they used both vendors back when we juju'd about the brake hoses! If we'd though of that, the delco brakes would have been the deciding factor on "which" hoses ya needed.

Anytime a "floating" caliper set is serviced, the points of contact (either type) must be lubricated. If the calipers were slightly binding (I call that situation..."stiction") when they needed to move ever so slightly, then what you described is exactly right!

Good work!
 
michael mayben said:
it's fixed!

The "pin" brake set I believe were sourced from delco/moraine. The slider set were kelsey hayes.

I didn't realize they used both vendors back when we juju'd about the brake hoses! If we'd though of that, the delco brakes would have been the deciding factor on "which" hoses ya needed.

Anytime a "floating" caliper set is serviced, the points of contact (either type) must be lubricated. If the calipers were slightly binding (I call that situation..."stiction") when they needed to move ever so slightly, then what you described is exactly right!

Good work!
Click to expand...

Well, actually this issue was not fixed. The pulsating issue continued on. It only stopped like it should when I stopped hard. The other day at the Binder Bee I had 6 folks in the rig, (you know who you are) and at one of the stops, I was standing on the brake pedal. (nobody in the rig knew it.) I also noticed a hissing sound with the pedal to the floor. I vacuumed tested the booster and found it would lose vacuum when the pedal was pressed to the floor.

When I installed the new booster I discovered the push rod on the front on the booster was about 1/4" short of where it was supposed to be. In other words, the booster was bottoming out and losing vacuum before the master cylinder was fully actuated. Now with a new and properly adjusted booster, I can almost stand the rig on its' nose. I think it's fixed this time, but I will drive it to the meeting tomorrow before I say for sure.

Lyle
 
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