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post #1 of (permalink) Old 06-29-2009, 09:17 PM Thread Starter
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Angry Warped Rotors???

Scout D44s.

Running CJ outers up front with CJ discs and Scout calipers. This is a relatively recent change when I installed high steer, but the same problem has persisted prior to this change (CJ calipers).

Running Suzuki discs with import calipers in the rear.

My front and rear rotors warp about once a year.... it actually probably averages out to slightly more often than that. I'm sick of it.

We are in and out of the water here on very hot days, but when we wheel, we rarely use any brakes and the speeds are low. Over the last three weeks, with very little off roading, the front rotors have warped very badly, to the point that I will need to have them turned/replaced before our annual trip to CO.

This winter I put new rotors and pads on the front. For reference, the Bash was the first time I drove with them for any length of time. And probably less than 1k miles since then.

Here's one thing that I think "could" be causing this. When I installed the DC-1 wheels I had to go to longer wheel studs front and rear. The new front studs don't press into the hub, but they are snug and the disc does not move around. In my time as a Jeep owner I have never re-turned the rotors after installing them on the hub... and I never had problems until about three years ago.

Now, I say that the longer, looser studs and not re-turning the rotor could cause this, but think about all of the front disc applications where the disc is held true by only the wheel and tire assembly. I am religious about torquing my wheels and keeping them in check. I just don't think it adds up.

How about this scenario? Could an out of balance rotating mass cause the discs to warp over a short time? I think my left front 35-12.50 is slightly out of balance, but I have no death wobble or vibration until I hit the brakes at speed. Or could I mostly be feeling the out of balance issue, and the rotors aren't as bad as I'm thinking? I can feel and start to see the out of balance issue at about 65mph plus.

The last time I took the fronts in, the guy turning them just shook his head when he gave them back stating they were BAD but he was able to clean them up.

I'm not as worried about the rears, I almost expect them to warp over time because they are not vented and they are subjected to repeated dunkings on hot days. I just hate the feeling of having the Jeep try to shake apart when I brake. Can't have that driving to and from the trails in CO in two weeks.

For the record, this is not death wobble. It doesn't change or get worse, its just shaking from the warped rotors.

Any ideas or input is appreciated. Let me have it.

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post #2 of (permalink) Old 06-30-2009, 05:53 AM
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If you don't have a dial indicator, get a cheap one. Harbor Freight has some with 1" travel for real cheap, and they're good enough to help with your problem. See how much your rotor is really warped, and also check the surface on the hub that the rotor and wheel attaches to. Maybe it's not flat. I wonder if there's something about the rotors you're getting that could make them prone to warping, like uneven thickness of metal between the friction surface and the cooling vents.

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post #3 of (permalink) Old 06-30-2009, 08:29 AM
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Quote:
Originally Posted by jdoggmoney View Post
Scout D44s.

Running CJ outers up front with CJ discs and Scout calipers. This is a relatively recent change when I installed high steer, but the same problem has persisted prior to this change (CJ calipers).

What exact rotors & calipers?

With CJ calipers you *could* be running mismatched caliper/rotor. Early style 1.125" wide "Big Brake" rotors (circa '77-'78 Scout/CJ) as opposed to the .875" late model rotors (which everyone ends up using because they cost 1/2 what the early rotor does ).

The symptoms I've seen from folks running a combo of early (wider) calipers on late (narrow) rotors is usually reduced braking performance since the pistons are nearing the end on their travel and never seem to clamp tight... this could cause some rotor overheating (like a sticky/dragging caliper) I guess?

My D30 disc conversion has some pics of the CORRECT Bendix calipers/casting#s for the early 1.125" rotors if needed for reference...

Caver Dave
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post #4 of (permalink) Old 06-30-2009, 09:23 AM Thread Starter
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Yeah Caver, I am running the thinner rotors with the Scout Calipers. I understand where you're coming from, but the new brake pads are half an inch (give or take a smidge) thick. I figure as long as I check the pads every few months and change them when they are about half life, the .25 inch difference in rotor thickness shouldn't have a negative effect. I observed absolutely no change in braking after the swap. Used disc brake grease during reassembly and the calipers are not hanging up/sticking. No pulling, excessive heat, dust or anything. Just a gradual warping that you can feel getting worse and worse over a relatively short period of time.

I only started using the Scout calipers last year. Could not use the CJ mounts/calipers with the GM knuckles and high steer. I had warping issues before the change to Scout calipers but went ahead and threw new rotors at it while I had it apart.

I will admit that I am using chain store rotors, but they are "made in the USA" per the label.

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post #5 of (permalink) Old 06-30-2009, 12:04 PM
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I'm not sure one can buy rotors that aren't made from recycled '57 Buicks; dashboard and all. I have seen rotors with hard spots right out of the box; then the next set be just fine. Sometimes nowdays the parts that say Made in USA just means the box was; not contents. If you find a brand that seems to be better let us know. I've warped them by plunging them in the drink;but they were rather hot. Like Jim Lou said,check with tool to be sure it's the rotors.
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post #6 of (permalink) Old 07-06-2009, 08:25 AM Thread Starter
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I do have a dial indicator. What is acceptable "runnout"? I'm getting some wierd numbers searching the next and I can't find the spec in manuals I have.

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post #7 of (permalink) Old 07-06-2009, 08:38 AM
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According to the '78 FSM, .005" is the maximum allowable runout. Variation in thickness, as measured in at least four places about an inch from the edge, must not be greater than .001".

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post #8 of (permalink) Old 07-06-2009, 10:57 PM Thread Starter
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Well something went haywire with the driver's side hub over the last thirty years. I had about .05 runout at the rotor and almost .07 at the edge of the hub!!! The passenger side rotor runout is about .02, but the hub looks good. I'll sweet talk the parts guy tomorrow and I already found a spare hub on the shelf in the garage.

At least now I know and I won't have to wrestle the Jeep to get it slowed and stopped on the mountain passes next week. And hopefully this solution will be more "long term" than the last three or four times.

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post #9 of (permalink) Old 07-07-2009, 05:54 AM
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It;'s odd that you have more runout at the hub than out on the rotor. The rotor must be warped opposite of the hub runout.

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post #10 of (permalink) Old 07-07-2009, 05:51 PM Thread Starter
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Nah, the rotor is only a few months old. I think it would continue to get worse rather quickly if not replaced.

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