Can't decide if rotors are warped or not

[Ghostrider]

This is starting to drive me nuts. I did the front brakes 10,000 miles ago with Brenbo rotors and Toyota pads. Lately I am getting some vibration while stopping but very intermitant. I cannot decide if it is the rotors or just bad roads. It seems to show up more from 65-0 than from 45-0. Other than pulling everything apart and measuring with a micrometer I am open to suggestions.

 

[Victor]

Does your steering wheel shake side to side during braking? When you replaced your rotors, did you clean the hub 100% prior to putting the new rotor on? If you wanted to check, if you have access to a dial guage indicator you can do a rotor runout check. If there's runout, check the hub surface and make sure it's clean then proceed to machine if needed.

 

[(4)runnin'it]

i had the same thing happening to me, it is aweful! mine would do it at 35-0 so i knew something was wrong, so i took it gateway tires and they turned my roters for 75 bucks.

 

[Stick Figure]

hubs can be slightly warped as well... some shops will use a brake lathe that cuts the rotors while bolted on the car to accommodate for this.

 

[Ghostrider]

Id it is the hub would it be intermitant or constant? Also why show up after 10000 miles?

 

[johnny c]

Just wondering, are your rear brakes out of adjustment? This will cause added strain on your fronts, causing overheating in relatively normal situations.

 

[Keros]

It's almost next to impossible to warp rotors that have been bedded properly... did you bed the brakes when you first installed them?

Most people I know don't even know what bedding brakes is or why one would do it...

It's very hard to warp a peice of cast iron without breaking it... most rotors will crack long before they warp. All the stuff people blame on warped rotors, 99 times in 100, is hot spots on the rotor surface. Further explained; brakes work by both mechanical friction and the forming and breaking of molecular bonds between pad material on the surface of the rotor and pad material in the pad... thus, pad material is deposited on the rotor's surface to allow the exchange of pad material between the rotor and the pad. 'Bedding' the rotor is getting a nice even distribution of pad material over the rotor's surface... if it's not done properly or at all, it's not hard to cook the pad onto the rotor's surface (causing one spot of the rotor to get hotter than the rest, called glazing) , in severe cases requiring an air chisle and alot of profanity to get seperated. Glazed spots on rotors build up pad material differently than the rest of the rotor, causing a high spot on the rotor, and thus, vibrations under braking.

In the end though, turning the rotors is the only permenent solution. You could sand-paper down the braking surface of the rotor and it may provide temporary relief, but it's likely to return in a while if the glazing was more than superficial.

Are your rotors glazed? A glazing is a spot on the rotor that is a nice outline of the pad... if you can see a glazed spot, that's where the trouble will begin. If the rotor surface is clean and has no blemishes, chances are the problem is somewhere else: the hub may be bent due to overtorquing lug nuts, or there may be rust buildup or dirt between the hub and rotor... unequally or improperly torqued lug nuts can also cause a rotor to not spin true. Improper torque sequence... ect. The list goes on.

It's possible to have a bad glazing on a rotor and it never give you trouble... there's alot of variables.

 

[Ghostrider]

Yes I did the bed them in by doing a series of hard stops that were described in the Brembo instructions. I am thinking of pulling my old Toyota rotors off the shelf and getting them turned and seeing what will happen if I put them back on. Also I always use a torque wrench on the lugnuts.

 

[uscgretired]

I am having a similiar problem with my 98 4Runner. Had new pads and rotors turned about 12 months ago. Vibration problem is back. It was the second time the rotors had been turned. Got an estimate of $445.00 at a local Mieneke Brake Shop to replace the rotors and install new pads. Only good part is that they are guranteed for life. Of course, I don't want the same problem to resurface every 6 months and have to deal with taking it back to have it repaired. I asked the brake guy if I could provide my own rotors and he got offended, telling me that it was like buying a chicken and taking it to a restaurant to have them cook it. I tried to explain to him that it wasn't about money but about fixing the problem and not having it reappear in six months. Anway, he finally gave me a price for both ways. Big problem is, I know they won't guarantee it for life because I didn't use there rotors. I can see it coming.

Didn't mean to hijack the thread, but had a similiar problem with my brakes and rotors.

 

[Ghostrider]

From reading threads on another forum I think I am going to try a quick fix of cross rotating the tires. I took my old OEM rotors in today and had them turned so that will be the next step.

 

[Keros]

Do you have access to a dial indicator and a magnetic stand to test the runout of the rotor and the hub? If you do, test the both and see how they fare (if you haven't already).

If you bedded the brakes in, it's pretty hard to get a highspot or warp them... Not impossible, but difficult and if you're always careful with a torque wrench putting lugs on, that rules out that problem.

The only other things I can think of to look at: Are the pads worn square and even? If they're not, a piston could be stuck and causing the brakes to overheat. Does the rotor spin freely after the brakes are applied then released? If not, the master cylinder could be to blame. I don't think the 3rd gen 4runner has slide pins to lubricate...

I'm curious as to the theory behind cross rotating the tires, can you link the thread it's discussed in?

Good luck, I hope this doesn't break your bank Ghostrider.

 

[Ghostrider]

The 4Runner has been well maintained and the problem is intermittant which hopefully rules out master cylinders. Cross rotating the tires was mentioned on another forum - the theory is that a bad front tire could cause the vibration and you move it to another location. The tires have 40K on them so a bad belt could be the cause but I doubt it since it should show up at other times than braking. The pads are OEM Toyotas with only 10K on them. I haven't pulled the wheels yet to see what the calipers look like but I do bleed the brakes every year just because it's cheap and easy to do.