seamus2154

Art was involved along w/ two other regional reps that all came down. They definitely ordered the rotors to themselves first as there was a delay and then sent to us. They told my manager they wanted to verify they were perfect to rule out the rotors if it continued. I assume because there were problem rotors put out and as you said pulling off the shelf was the same as what you may have already had. The rotors were the problem because all they did after all that work and months of nonsense I drove home first shot for the first time since new with no vibrating.

Reciprocal

Here's the latest:

Rotors mounted.

LF lateral runout 0.000 inch
LF radial runout 0.018 inch
LF balance 5.0 grams

RF lateral runout 0.000 inch
RF radial runout 0.018 inch
RF balance 16.0 grams

mirage2991

i can tell you it is the 1/4 oz that is the problem.

Reciprocal

Hey Mirage, is there a particular reason in your opinion why 1/4 oz at the rotor takes on more significance than 1/4 oz anywhere else, for example the wheel?

Correct me if I'm off base, but a road force balance is accurate to a tolerance of 1/4 to 1/2 oz, which I think is where they call it good. Is that not correct? In other words, the machine display readout precision is .25, so if the tire balances to .24, it displays zeros.

mirage2991

take off a 1/4 oz at the wheel and you will get a vibration. GM wants 10lb or less for RF on the zr1, and you are correct, some of those machines are loosly calibrated, because they do not take the time to calibrate them often. That is also why gm uses cut to weight weights at the factory.

mirage2991

look at it this way: centrifugal force from 1/4 oz at 15" or 19" is close enough that it would give you a vibration (6lb vs 8lb). You also have a very small sidewall on a runflat tire (very little flex if any ) so it should translate into less force being absorbed by the tire. in essence the tire does not absorb as much of the inbalance than say a truck tire. 1/4 oz of might not be noticeable on a truck or familly sedan but in theory would be on any low profile tires.
I am sure there is much more to it, but in my mind this all translate to a car that is very picky when it comes down to tire balancing.
What would be interesting is to see how well balanced a set of steel z06 rotors are.
It is worth noting that as the rotor evaporates inside out, you could be chassing the problem for ever with a rotor going in and out of balance (i am speculating).

Kristobias

I have a GT3 RS with PCCB. No issues at all and I would think Brembo is the supplier as well. Weird. I hope this gets resolved for you soon.

Reciprocal

Here's the latest:

Got the call from Discount Tire that the replacement Michelin came in for the out of round tire Ed Bozarth Chevrolet condemned last week. Discount wanted to have a look at the tire before replacing it, no big surprise but they say the tire is good, no problem at all on their road force machine and that Michelin would not replace this tire under warranty. They had me come back to see this for myself on the Hunter road force machine which I appreciated, and I honestly didn't see a problem with it either.

So I took the tire back home and carefully mounted them both on the ZR1. I indexed the lightest part of the wheel/tire combo 180 degrees from the lightest part of the rotor. This point on the rotor has a paint mark on the hub, and is engraved with the weight needed to balance the rotor to 1 gram, by Denver Balancing. I used a scale to trim and weigh the weights to be applied, 13.7 gram for the right side, 4.3 gram for the left, which I then carefully installed on the i.d. of each wheel directly under the rotor and aligned with the painted mark.

Next I took the ZR1 out on the test section of the interstate, 75 to 85 mph.

Forum participation...what do you think was the outcome of the test drive?

A.) No vibration.
B.) Vibration same as before.
C.) Some vibration, but reduced intensity.

AORoads

No idea. Wild guess is B. You did all that at home? wow.

But, there's a test section of interstate?

seamus2154

Well??? I say A. And indexing to fix a rotor issue will just cause you heartache when you get a flat or new tires and have to start all over again. With my new rotors which are apparently perfect I have had the tires off several times for cleaning wheel wells and rims...(yes I am OCD, it ain;t easy) and just put back on and no issues now for 2 years,

Reciprocal

As seamus predicted, yes the answer is A, no vibration.

And he is right, if the wheel is taken off the car, the balancing weight has to be realigned with the painted mark on the rotor, so I am in no way making the case that this is an acceptable fix. On the contrary if anything, it supports the premise that the rotors are the source of the vibration. The fact that GM has awareness of the issue to be replacing rotors for some while giving others a hard time is, as I stated in the opening post, DISGUSTING.

Since there were 2 operations performed on my ZR1 after it was returned to me by Purifoy, road force balancing and off-the-car balancing of the rotors by Denver Balancing, it's fair to question why I reject a conclusion that the road force balance had the larger role in correcting the vibration. The reasons are these:

1.) I didn't observe significant runout in the tire or rims when spun on the car. The tire out-of-roundness that Ed Bozarth Chevrolet noted was not observed by me or Discount Tire when they spun it on their Hunter Road Force balancer.

2.) The Hunter Road Force machine uses (2) arm mounted sensors to measure wheel runout, one for the i.d. of the rim to measure radial runout, one for the outside of the rim to measure lateral runout. From these two sensors coupled with the load force drum, a calculation is made that permits match mounting the high part of the tire to the low part of the rim. Thereafter, the balancing is just a conventional dynamic balance.

The problem with this for the ZR1 Speedline wheels is that the outside part of the rim (decorative side) is not machined flat to facilitate a lateral runout measurement, but rather has a taper cast into it. It's virtually impossible for the operator to get a repeatable lateral runout measurement. Yet...you can see easily that the tire itself has negligible out of roundness. I believe that the Michelin Pilot Sport ZP is made to a high standard of roundness that isn't much improved by match mounting to the rims. The lateral runout measurement only makes sense on the Hunter Road Force machine with these Speedline wheels when you can measure the lateral runout of the rim without a tire on it, from the inside edge of the bead. Nobody dismounted a tire to do that, and likely never will.

3.) It seems likely that all that has occurred in doing these multiple tire/wheel balances is a redo of what was probably already acceptable tire/wheel balance.

mirage2991

what you have done was outlined in the sticky, I believe Aston does this for their DB9 with the ccb's.
now if we could only get those damn bolt-on weights that some rotors come with it wouldn't be a big deal!

cflm3

Despite multiple attempts at wheel balance, wheel hub bearing change, new tires, road force balance, different wheels I had the same 75 mph vibration. Even through dealing with art Spong, I had to replace the rotors myself (I paid for this), which improved the problem. Art Spong passed this issue to the district manager at gm who I have not heard from. Do others in the forum think I should buy another gm product?

K B Vettin

if you don't have these weights on your front rotors this is the fix to the vibration. my first zr1 didn't have them and i had a vibration at 75+MPH and my new ZR1 has these weights and i have zero vibration. i just drove home from TX and most parts of the 10 west i was cruising at 85 or 88 mph. this was GM's fix and i would demand they install the weights or put on new rotors with the weights. you all paid the same for your 09, 10, & 11 ZR1's as the 12's and 13's which came with these weights.

mirage2991

not all new rotors come with the weights... mine didn't... but still had a little bit of vibs though now it is mostly gone 95% of the time.

GM did not handle this well at all, should have been a letter going out to all owners experiencing the issue and if balancing did not fix it new rotors ordered with no BS or persuasion from the owner to the dealer to go do so... not on 125k car... .

Reciprocal

I do not.

Reciprocal

Not only not handled well, but still not acknowledging the issue which tells you they think they are doing the right thing to this day.

OnPoint

Chevy Customer Service here on the forum (Sarah. . . Kelly. . . .anyone),

When is GM sending new replacement rotors to OP?

Reciprocal

OnPoint, that is kind of you to suggest but at this point, my problem is solved no thanks to GM, its dealers or reps.

If GM Customer service wants to help, I'd be more grateful to see them take care of the OTHER owners who don't have the resources, patience or skill to do GM's job for them. They shouldn't have too!

If they'll pay for your rotors, or reimburse the other guy cflm3 who bought wheels and rotors on his own, I'll make a donation to St. Judes, (which I will do anyway because I want to.)

GM step up to the plate!

K B Vettin

That's why I would request rotors with the weights. You don't have them and you say you vibrations. I just drove 1400 over the weekend 90% on freeways going 80+ mph and I had zero vibrations. Not even a hint of vibrations.