How much movement in front disc is acceptable, if any?

[D911SC]

I am putting my suspension and brakes back together and for the most of it everything is going together nicely. One issue I have (maybe) is the front right disc. When I fit the disc/hub I am getting about 2mm of movement, almost as if the disc is warped.

The disc is new, new bearings, and hub has been blasted clean. My local mechanic did the bearing for me, he's a Porsche specialist so I expect the bearings are done right.

I have tried various torque amounts on the nut although I know that it needs to be 'just' tight or else there's too much resistance on the bearings. This seems to make no difference. It appares to be seated correctly.

The race that is fitted on the spindle appears good.

When I fit the caliper and pads the disc binds too much for my liking - due to the movement.

Any advice on how to tackle this?

Thanks.
Darren

[ivangene]

2mm!!!
0.02mm would be ok.. NOT 2 MM!!

have you tried it without the brake caliper in place...sometimes a stuck piston will cause the rotor to act funny...see if removing the caliper gives you a good rotor alignment without movement - that will issolate if its brake or wheel bearing to start looking at more closely

[D911SC]

Thanks. The movement is is there without the caliper fitted. Maybe 2mm is an overestimate but it's definitely very obvious when spinning the disc.

[ivangene]

so when spinning it has latteral movement (in and out)?

I would guess the race is not fully seated - you said they are new? remove it and check the inner race to see if its resting against the shoulder of the hub (may have to remove all the grease)

[D911SC]

Thanks again. I'll try this and report back tomorrow. You're right in that the movement is in a lateral direction.

Everything in the hub is new. The race on the spindle is not new and I didn't remove it when repainting the struts. I masked it and the spindle.

[steve911T]

I know this would be a real PIA, but you could swap it to the other side to see if it is warped out of the box or is a bearing/spindle problem. I think that I would take it off and take it to a machine shop just to see if the rotor was true, first. Good luck. Steve

[JP911]

What brake setup is on your car (and what year is the car)?

[ivangene]

JA, I dont have race on the spindle... only in the hub

I think its an 83 per the sig

[johnsjmc]

I suspect the new disc itself isn,t seated square on the old hub. Dirt or rust will keep the disc from seating when the discs are changed.If I recall there are 4 bolts which draw the disc to the hub . I would remove the disc and wire brush the hub face and mounting area and try mounting again. Tighten the bolts only a turn at a time in a cross pattern

[Trackrash]

IIRC the allowance is .008" run-out. When I replaced my front disks one had a noticeable wobble. I used my dial indicator and it was about .005" out so I used it.
When driving the braking is very smooth, no noticeable vibration.

+1 on removing the disk from the hub and cleaning the surface well.

See if you can borrow a dial indicator and check where the problem is, either the hub or the disk.

[Flieger]

Is this runout or just slop like a floating rotor?

[KTL]

When you remove the disc from the hub (5 bolts inside the hub "eyes") and clean it, reorient/clock it on the hub. Clocking it can sometimes make quite a big difference.

[D911SC]

Originally Posted by Flieger

Is this runout or just slop like a floating rotor?

If I understand correctly it's runout. There is no slop or free play at the rotor.

I'll set up some sort of gauge that will help me determine if it's the rotor or the hub. If it's the rotor I'll try clocking it.

Thanks for all the feedback so far. I'll do some more work on it and write back.

[D911SC]

I've had another look and I'm pretty sure the hub/bearings are the cause, not the rotor. There is a slight movement at the hub when it spins but it's most obvious at the end of the rotor (presumably because of the distance from the centre point).

I removed the hub/rotor and the sealing ring shown in the below pic seems slightly off alignment, only by a small amount. It is not perfectly flush all around the hub body. I marked where it was raised (hard to see but you can feel it with your finger) and re-fitted. I thought the greatest point of lateral movement would be at my mark but it was 180 degrees out. In the pic you can't see that it's not flush but I have marked an arrow to the ring I am talking about.

I also ran my finger in and around all the bearings and in between contact points but couldn't feel anything that might be causing an obstruction.

Also I have uploaded a video here to show the runout: YouTube - Front rotor runout

Thanks again for taking the time to help me with this.

[KTL]

That's not necessarily disc-to-rotor alignment. I say try the other rotor on the hub, else that looks like a crooked bearing race to me. With all due respect to your mechanic, it's easy to cock a race in a front hub. Especially if somebody prior to him didn't do a proper job of removing or installing the bearing races.

I don't believe the seal is a contributor to the problem. The lips have enough compliance and the rotor/hub has enough inertia to overcome any slight misalignment with the seal. Simply put, it looks flush enough to me.

Thanks for posting the video because it's very telling.

[D911SC]

Thanks Kevin,

I'll take the hub/rotor back to the mechanic and get him to have a look.

Darren

[johnsjmc]

Looking at your video and pic I still think the disc isn,t seated squarely.This is easy to do and happens often. Undo the 5 bolts and clock the disc.

[H-viken]

Originally Posted by johnsjmc

Looking at your video and pic I still think the disc isn,t seated squarely.This is easy to do and happens often. Undo the 5 bolts and clock the disc.

By "clocking" do you mean "rotate the disc and fasten it in a different location"?

The reason I'm asking is that I'm experiencing almost the identical problem. My guess is that the hub is not seated properly with the rotor. Tomorrow I'll take it apart, clean, and reassemble it.

[johnsjmc]

Yes remove and rotate and fasten in another location. Tighten the bolts a little at a time in a criss cross pattern

[D911SC]

I'll be trying this over the weekend and will write back with the results.

Any advice on much to rotate? 1 bolt hole? 90 degrees? 180 degrees?

Darren