Vibration Problems - Driving me nuts

[cykornr]

I have a 88 Turbo. The other day I replaced the front brakes, rebuild the calipers, replaced the rotors and of course replaced the pads.
Now when I brake, I have a vibration, in the steering wheel, in the front end, I can feel it in my seat. I don't see any shimmy in the steering wheel. There is no vib just rolling down the road at any speed.
I have taken apart the brake assy. 4 times, all looks OK, I checked the runout of the new rotors>.005 I bled the system 3 times , no air left.
The faster the speed the more pronounced the vib.
Anyone have any ideas?

Thanks

 

[Adjuster]

I'm dealing with the same problem. New brakes, and it vibrates under braking. Only thing I can think of is a warped rotor.

I noticed when I installed the brakes that the rotor dragged in places as it was turned. 5 thousands runout should not be a huge problem, but what was the runout of your old rotors? I think 0 is where it should be if you can get it.

I'm running fixed calipers now, and I think the floating ones should compensate for a slight warp of the rotors better, but still if they are brand new, they should be nice and flat with no runout. (5 thousands is going to be felt obviously.)

My other thought is the hub. The hubs on my car have never had anything done to them in about 170,000 miles of driving. They have also been subjected to some potholes and other road hazards over the years/miles.

Could a hub cause the runout problem? I've heard you can dis-assemble this hub and re-pack it with grease, and set the pre-load on the bearings. Never tried it however.

My brakes work awesome, but they do pulse, and it's very annoying. (I was hoping as the pads bedded in, and the rotors seasoned, it would go away, but no dice, it still pulses like crazy, and speed only adds to the feeling in the steering wheel.) The car does not pull to one side at all BTW.

 

[ddmcse]

new front struts took care of my braking vibration

 

[Adjuster]

My front struts are new. As are the ball joints. (It was totally smooth on the old brakes, same suspension and all other parameters except for the new brakes.)

 

[IJ.]

I always use a torque wrench on the lugs at 75 ft/lbs as with Mk3 Rotors they seem prone to warping if not done up evenly!
(Guys at the tire place look at me like I'm nuts when I won't let em use the rattle gun)

I still do it with my Mk4 rotors but it may not be needed but I guess it's good practice.

 

[mrnickleye]

My front struts are new. As are the ball joints. (It was totally smooth on the old brakes, same suspension and all other parameters except for the new brakes.)

You've already answered your own question....When a problem begins right after doing some work/changes....it must be that work is the problem.

I put new rotors and pads on my 89 n/a back in Jan. They were vibrating like yours, right away. I took the rotors back and swapped them for a new set (warranty), and there was NO MORE vibration. Now 8K miles later...still smooth braking. Take those rotors back and try a new set.

Also, MANY vibrations are cause by 'hot spots' in the rotor, and not necessarily any warpage. The pads grab the hot spot more than the normal area, thus creating a vibration at speed. We do brakes every day at my shop.

 

[Adjuster]

I agree the rotors are the culprit in this problem.

They are Wilwood rotors, and I need to talk to Precision brakes to see if they will warrenty them. (I have about 1500miles on them now, and they are not getting any better.)

Always use a tourqe wrench on the lug nuts. Every time. but I tourqe mine to 95lbs. Never had a problem. (I did have a flat fixed once where the guy used those tourqe rods... And had brake pulse vibration immediately. Went home and re-tourqed all my wheels, and could not loosen the lug nuts. Grabbed the 1/2" bar to get them loose, and two of the lug nuts fell off. I carefully drove the car back to the shop, and they ended up replacing every lug stud on my car as they ALL were streatched due to being tightend by the damn impact gun.

The other thing the tire dude did was jack up my car (A MK2 at the time.) by the front tow hook. It closed up the hood to fender gap completly while the car was in the air, and I was totally pissed at the guy. Grabbed the shop manager and showed him how my car was being twisted, and then the same butt nugget used the air gun to put the wheels back on. (I decided to have them all balanced and rotated while I was having one flat fixed. The gap was restored when the car was released, but my comments about where to jack up a car were completly ignored. (Untill I came back with the overtourqed lugs, then they were carefull with my car, and I watched everything they did closely to make sure they did not F up anything else.)

 

[cykornr]

You are right, I knew what I needed to do. I put the old rotors back on, no vibration. I replaced the rotors, it is about 80% better, but still shakeing. I'll be going back this afternoon.

Thanks for your support.

Rick

 

[bluemax]

So let me get this right,
You just changed brake pads and disc, and you didn't bed in the pads and disc?
So you probably drove a little and the vibration started to happen. And as you drive (and brake) more, its probably getting worse...............
Now you changed the rotors. You didn't bed in the new discs and you're getting a similar problem. Probably didn't start happening until after a few braking attempts.

Anytime you change pads or discs (especially the discs) you need to bed in the brakes.
http://www.stoptech.com/whitepapers/bedintheory.htm
Otherwise you can get an uneven transfer of brake pad material on the rotor face which causes vibration feeling when braking.

You can rework the disc by lightly sanding the friction face of the disc to remove the transfer material (you can't see the transfer material). Use a sanding agent that is compatable with steel (not recommended to use aluminum oxide sand paper as you might get dissimilar metal corrosion). Then properly bed in the disc and pads.

If this doesn't work, then get new rotors and bed them in.

 

[mrnickleye]

That's interesting reading , bluemax. I think there out to be a section (header) called "Links of Interest" so we all can easily get to these kind of important items.

 

[IJ.]

I worked in the brake industry as a kid and we had a late Friday afternoon customer in for pads and discs, the boss sent her out without giving us the time to properly bed the pads in.

She was in a hurry in rush hour traffic and I'm guessing was hard on the brakes and of course they hot spotted boiled the resin in the pads to the surface then the next time traffic stopped bonded the pads to the rotors!
(4 cyl Capri so not enough power to break em free)

We had to arrange a flatbed tow truck to bring the car back to the shop and then had to use an air chisel to free the pads then replace everything!

 

[bluemax]

IJ, she really got them hot.
I think normally, you just get uneven deposit of brake material on the rotor face. And as time goes on, the material builds up more in the high spots than the other areas, thus you get chatter when you brake.

This is in the SM information section, CKanderson submitted it:
Titled : StopTech's list of brake system myths
http://www.supramania.com/forums/showthread.php?t=18

Apparently discs are never really warped. It just needs to be bedded in properly.
And if you really heat your brakes up in a panic stop, or pulling a load and brake hard, never leave your foot on the brake when stopped. When the pads are real hot, they stick to the disc and deposit more material when they brake loose. So you end up with an uneven foot print of the pad on the disc.

 

[flubyux2]

the problem is that the runout or TV in the rotor is too much. you can feel a varation as small as 0.001", considering you said there was 0.005" of runout, the problem is in the rotor or that something is stuck between the rotor and the hub.

The driver can feel a 0.0004" deposit or TV on the disc. 0.001" is annoying. More than that becomes a real pain. When deposit are present, by having isolated regions that are proud of the surface and running much hotter than their neighbors, cementite inevitably forms and the local wear characteristics change which results in ever increasing TV and roughness.

from stoptech.com

 

[bluemax]

Calipers hare self centering on the disc. So if the rotor is warped, the caliper will just float and not cause vibration.
But if you have a thickness variation, you get more pad pressure in the thicker region, the friction changes, so you get a local area on the disc where you get more braking.

Cementite is a state of the disc material. It apparently has higher friction and is much harder than the normal. So you get more pad material transfer at the cementite locations on the disc. This leads to increased local build up of the pad transfer material.

 

[Adjuster]

You guys, the rotor was dragging BEFORE I even drove them. (Just installed the rotor,caliper and pads, and then the wheel, and rotated the wheel, and noticed that it was smooth and free on one side, but on the other would catch as it went around.)

I then pulled the wheel, and re-tourqed the rotor/hat to make sure I had not caused a warped condition somehow. No change.

Checked the bolts holding the caliper, and the spacers? Nope, not a problem there either. Pads are fine. Everything looks fine, nothing is out of order, but the rotor was dragging.

Now, I thought since these rotors are zinc coated, possibly the coating was thicker on one part than the other? Also Precision noted that the brakes would not work right untill the zinc was worn off on the swept area, and the rotors seasoned by heating and cooling.

Before everything was installed, I coated the pads on the side facing the pistons with thermal barrier. (To limit heat transfer to the calipers/pistons and brake fluid) I'm pretty sure that the brake guys are going to say that's my problem, but I think the 6 pistons would equalize any pressure being put on the pads backing plate no matter what is coating it. (It came with some paint or powdercoating anyway. The Wilwood pads are made by Raybestos.)

If the rotor was coated with zinc that was not evenly applied, and then that caused the pad to deposit material in a uneven manner, it would make sense that the rotors are pulsing.

I only have about 1000 miles at the most on these brakes, I think I'm going to see if Precision will do anything about this. (I doubt it, but it will not hurt to see what they suggest.) Or I'm going to have to pay to turn these rotors and clean up the swept area before the pads wear anymore. (I don't intend to replace the pads, they are brand new.) I was hoping not to disturb the zinc coating outside of the swept area to limit rust, but if they are turned, it is going to make a mess of that idea. (And I'd want a nice crosshatch pattern on the rotors to re-bed the pads to the re-faced rotors, so that's going to scratch up the rotors too.)

Nothing custom is ever easy. LOL

 

[bluemax]

The discs were zinc coated. Probably to keep them shinny looking.


That may be your problem. But I would not think so. Electroplating is usually very even over a surface. You might get some thinning, but it would be gradual. I don't know about zinc, but cadmium plating is only a few tenths of thousands of a inch thick anyway.
You can dress up the friction face of the rotors to remove the zinc and pad transfer material by using abrasive paper to polish the disc. You only have to do the friction surface. That way the other areas will stay looking good and not rust. I would mask the areas outside the friction surface.
This should solve your problem.
You don't have to turn the rotors.