Front End Vibration/Pulsating When Brakes Applied

Hello All,

I apologize for the long post.

1998 GMC 3500, 6.5TD, Crew Cab, 4x4, Dually
Currently 128407 Odometer miles

When applying brakes, I feel a pulsation, I think it is from the right front.  Also, the steering wheel pulsates back and forth to the right about an inch when brakes are applied.  When stopping hard from high speed it is a very strong vibration and hard pull to the right.  When going slow with light brake pedal pressure, you can really feel the pulsation, but there is not as much pull to the right.  The truck was originally purchased to tow a horse trailer, but has seen very little towing or carrying of heavy loads.  Many of it’s miles were accumulated running the kid’s up and down the turnpike to ice hockey games.

I first looked in the engine bay, under the truck, and all around for any leaks, but I found none.  I checked the brake fluid in the master cylinder, it was full and the fluid was clean.  I also checked the power steering fluid, it was a little low, but after topping it off, and driving the truck several more times for a pretty good amount of miles, the pulsing was still happening.  So next, I pulled both front wheels to see what I could find.  As someone else had suggested, I checked the rubber brake hoses for deterioration but found them to be in great shape.  Both sets of pads have plenty of material on them, in fact they look almost new.  Also, the rotors are not heavily scored, or marked in any way.  But, I could not get a good measurement of the thickness of the rotors because I don’t have the proper tool, i.e., a brake indicator.  I was however able to get what I think were good measurements of the run-out of each rotor.  I mounted an electronic indicator using a “Flexbar Mighty Mag” magnetic base attached to the calipers.  I then turned each rotor by hand and watched the indicator for the amount of deflection throughout a complete circle, I did this several times with each rotor to make sure I was getting the same readings consistently.  I was only able to check the outside surface of each rotor, I was not able to get to the inside surfaces.  I have an authentic set of GM 1998 C/K Truck Service Manuals.  The manuals state a maximum run-out of rotors at 0.08mm.  My measurements were 0.1016mm of run-out for the right front rotor, and 0.1143mm of run-out for the left front rotor.  If my measurements were correct, than both rotors are out of spec – IF I’m correct.  I don’t understand how both could be out of spec at the same time, and the left is further out of spec, but it does not pull to the left it pulls to the right?  Also, when I turned both of the rotors by hand, I could feel and hear the pads and rotor make contact for about a fifth of the rotation.  The contact was in the same locations that measured out of spec for run-out.    

Fun Facts:  just 3619 miles ago the rear drums and pads were replaced by the dealership, and just 3707 miles ago the front rotors were turned by the dealership, and 9851 miles ago new front calipers and pads were installed by a local garage, and 34872 miles ago the local garage replaced both rotors and deglazed the pads.

So, what do you guys think?  What should I do?  

Should I buy new rotors, and/or new pads, or find someone to turn the rotors?  With my constant problems with vibrations and pulsations, should I buy a higher grade rotor and pads?  If so, what would you recommend?

Thank you for the help!


Chip  

i am going through the same thing with my truck.  
that is a heavy truck i would put on new rotors and pads as they are cheap.
i paid 90.00 for 2 rotors and 45.00 for premium pads.
when you turn rotors they warp faster(thinner). pads glaze over.  

the pulsing is the brakes and warped rotor interaction, replace them and it'll go away. don't use original type pads but semi-ceramic bonded style and brakes will last  indefinitely; they are incredibly powerful when right.  

Quick question, when were your wheels rotated last, and did this problem seem to appear after or before the rotation?

My thoughts...(in addition to what was already mentioned previously)...

First...the hard pulling to the right can be from the slide pins not being lubricated.  The pins usually are not replaced often (if ever) and most people overlook properly lubricating them when replacing pads/rotors/calipers.  You should remove the pins and lube the outside, and the bore they slide in.  Then work the caliper on the pins back and forth to make sure it moves rather freely.

Second, the pulsation can be from the same problem I listed above.  Furthermore, your run-out reading doesn't mean a lot (to me) if you used a flexible shaft to mount the dial indicator.  Ideally, you would measure the run-out of the rotor on the machine used to turn the rotor, and before doing so take off any corrosion around the inside diameter of the rotor mounting hub/hat.  I'd also remove any/all corrosion on the mounting surfaces of the rotor.

Third, the pulsation can also be from an out of balance wheel/tire/brake assembly.  Truck tires and wheels are large, and if uneven wearing occurs from improper installation or a poor alignment it will throw off the balance.  Decelerating the wheel/tire emphasizes this imbalance thru the pedal/steering wheel.  Plus, if the tires/wheels/rotors have mud/dirt/rocks in/on them it will also throw off the balance.  And again, don't forget to clean off any corrosion from the wheel mounting surface and all lug nut holes.  I'd also say clean off any contamination of the lugs and make sure to use a torque wrench when installing the wheels to the proper torque (if your rotors turn out to not be warped).  Though these trucks of ours are tougher, they're still susceptible to warping rotors if installed improperly.