I have been chasing a vibration in the steering wheel that I just can't pinpoint. It comes on at about 70mph.

The whole of the front suspension as been gone through. New upper shock mounts, powerflex upper and lower control arm bushings, lower ball joints, sway bar bushings, end links. Wheels have been checked for true and road force balanced. Tie rod ends are tight and there is not a bit of play in the bearings.

I'm starting to wonder if the brake rotor(s) might be out of balance. There is no pulsing in the pedal, so the run out must be ok but the vibration persists.

The rotors were replaced shortly after I got the car and the other fixes came later so I can't say for sure whether the vibration started with the new rotor.

I do see a mill mark on the right side where it was balanced but there is none on the left rotor.

Has anyone ever encountered an out of balance brake rotor? And where can you get one balanced?

 

Warped rotor would only cause vibration upon braking but not just driving along at 70mph. I would bet on bad tire or balancing if it comes on only at a certain speed.

 

Well, we will consider that all lug nuts of the same type are being used.

So, maybe a wheel weight came off?

Perhaps a friend can drive along side of you and check the movement of your wheels at 70mph?

Considering that a brake rotor is typically a solid mass of homogeneous metal, I would think that balancing a rotor would only require a very small amount of material to be removed, if any. If the rotors are vented, then maybe more material would be removed for balancing.

Oh, even though you checked the tie rods, could there be a little slack in the rack? That is, slop in the steering wheel to rack interface?

 

Balancing a disc rotor is an interesting thought. In all my years, I have changed a lot of brake discs, but never had one come back for being out of balance. Consider that the mass is very close to the hub, and rotates at fairly low speed compared to a tire. I would follow the idea that it is still a tire imbalance. It doesn't take much at 70. Oddly, I am actually fighting a slight tire imbalance at that same speed on my personal XK8. Glass smooth at 60, very noticeable at 70.

 

The problem is similar to what you describe, starts to come on about 65, peaks about 75 and then gets a little better at higher speeds but is still noticeable. This isn't a huge vibration but it's noticeable at speeds we often see out in the desert and my OCD will just have none of it.

I had not heard of balancing rotors either but I've been systematically trying/repairing things over the last year trying to isolate it and have basically run out of other things to try. Occam's razor and all that.

These are original 18" hydras, so I know they fit the hub properly, and the lug nuts are Jaguar ones, rattly caps and all.

Wheels and tires have been balanced numerous times, including road force balancing but the vibration persists.

Switched the tires L-R and also F-R but the vibration is still in the front. For the record, 9in on the front and 8in on the back looks a little silly but scientifically this was illuminating because the problem STAYED in the front so it can't be a wheel or tire.

The rotor seemed unlikely, but at 14" around and weighing 25lbs, it isn't exactly small, so it is at least plausible that it could be the cause.

In reading, I found that brake rotors are often balanced at the factory and in fact the right side does have a cut along the outer edge where it was milled, presumably for balance. Thing is, the left side has no such cut, which got me to wondering.

Maybe XKRacer or someone who has drilled or slotted their own rotors can comment whether it effects balance and how they went about re-balancing them?

I'll try calling some brake shops and see if they've ever gotten it done or maybe try a machine shop.

 

I'm willing to bet that you have a slightly bent wheel or two. Hunter road force balance will "pass" a wheel that has a slight bend, I know because it happened to me.

I don't know what size wheels you have, but if they are 18's it's likely and if you have 20's it's certain that your wheels are not "true" unless you have never hit any road imperfection, pothole, etc.

Have your tire guys remove the tires and observe the wheel alone spinning on the balance machine. You may see a slight "wobble" in the wheel by itself. The wobble may be side to side or in and out.

If this is the case, you can either replace the wheel or have it professionally repaired.

On my XJR, I had two bent rims when I bought the car. I bought two reconditioned rims to replace them and both of the initial replacements were slightly out of round. The Hunter machine said they were OK, but a visual observation and a cooperative tire tech revealed the out of round condition. I swapped the rims twice with the company I bought them from to get wheels that were "true."

I am very sensitive to any vibration in my cars, not OCD, but close, lol. My wife couldn't feel the vibration from the first set of replacement wheels, but I could. It only came on above 60 mph and was very slight.
Vector

 

I have been going through the same thing. Discount Tire did a road force balance and found that one of my tires,a Toyo that was on the car when I bought it, cannot be balanced, but the wheel is okay. Again, vibration becomes a problem around 70, falls of over 80.
The tires are fairly new so I'll go to a Toyo dealer and replace that one.

 

Interesting discussion. I have had a shake at 70 for years. I have had the wheels checked and rebalanced. When I got ht ecar, it had new Michelins that strted chnking tread and they shook like crazy. I threw them out and installed Sumitomos HTZII's. they were a lot better but still ahd the slight problem at 70. I took the car to a racing shop that had a Unte rroadforce balancer and a guy that knew how to use it. He said that the tires were bad. He could measure the sidewall resistance at four points around the wheel as the wheel turned and the tires had resistances that were too high and variable all around the tire. I replaced the tires and the problem is just about gone, but still have a slight twinge now and then. I replaced the rotors with new ones and that didn't change anything. The drilled rotors were a pricey check!

 

I could understand the shake in the wheel not being any different when swapping the tires L-R but when I moved the rear wheels to the front? That one has me scratching my head. I suppose it's possible that I have bad tires on both ends but it seems unlikely.

The engineer part of me just wants to know where it's coming from and it's become a matter of principle now. No mere machine is going to defeat me!

I'm going to call some auto machine shops that can balance flywheels and pressure plates and the like so see if they can check a rotor.

Surely it will cost less to check than than to buy a new tire(s) as an experiment.

 

I notice my P Zero's tend to vibrate until they warm up in the morning then they smooth out. Only thing I didn't see that you fixed on the front end is the hub bearings. Wouldn't hurt to jack up the car and pry like you do to check ball joints to check them. If I recall correctly the inner tend to wear out before the outer bearing.

 

I have not had an out of balance rotor in 50 years. Any rotor manufacturer not balancing them would be out of business pretty quick! No one could use their product. The last set I got for the XKR were balanced by machining recesses into the outer edges of the rotor. If you saw this machining on any one of them, you can bet they all were on the machine. I suggest finding a Hunter Roadforce system and get the readouts on the hysteresis of the tires. They read out in ranges from 0-40 or so at each quadrant. The higher the number, the worse the tire. Mine were in the 28,35,38,28 range..bad tires. The XKR tires are staggered so they can't be moved from front to rear. It was intereseting that the wider rears were not bad, the narrower fronts were the problem. Part of the problem might have been improper storage at Tire Rack. When I got the fronts, they had obvious indentations in them where they probably sat on a sharp edge like an angle. When I rolled the new tires, they would thump on these indentations. I should have rejected them. The rears did not come like this.

 

I had an internal belt issue in a tire do something similar...Have you tried swapping rears and fronts to see what changes? Even on my bikes, where the weight of the brake disc is more of the rotating mass by proportion I have never given a thought to brake disc balance. Can't wait for you to post up what the solution was!
-t

 

I found a local automotive machine shop that does balancing work on flywheels, pressure plates and that sort of thing. It was an old school place, the kind where the walls are covered with pictures of all the race cars they have run over the years, dating back to the 70s. Chevys, Dodges, and even a Healey 3000 among them.

In talking to the guy, he said that out of balance brake rotors are reasonably common, and he even gets the occasional brand new vehicles from the local Ford and Chevy dealers. Usually it's the big trucks and Suburbans that have trouble.

Since this was a test as much as anything, he said he would balance them with clay first so he could weigh it and we'd know how far out they were.

The next day I get a call that they are done and he gives me the rundown:
LF = 2g
RF = 16g
LR = 50g
RR = 21g

If those numbers look big it's because they are HUGE! 3 out of 4 rotors were outside what you might call acceptable, and one was off by almost 2oz.

That's crazy. So crazy he didn't believe it was right and had one of his assistants tear down the setup and re-do it to confirm the result.

He ground them around the hub area to get them in balance and I happily paid the man the $200. The picture is of the 50g one before painting.



I shot some new paint on them last night, let them dry and put them back on this morning.

After a test run I can confirm that the vibration is gone. There is no discernible shake at any speed up to about 100mph so I'm going to call it fixed. Finally!

Through all this I learned a couple of things.

1) I won't trust that a brake rotor is in balance ever again. Next time I do a brake job I'll just take the new rotors and have the balance checked. I was lulled into complacency when I saw the mill marks on them from the factory, but not again!

2) Centrics doesn't have the greatest quality control. Their machining seems fine and they run true but were WAY out of balance.


I won't go so far as to say that others should avoid Centrics because even including what I paid to have them balanced they are still 1/3 the cost of an OEM Brembo part.

At this point, I wouldn't trust a rotor to be balanced no matter what the price was and would get a real Brembo one checked, just the same.

 

A few rears back there were shops that touted wheel balancing "on the car". I haven't heard much about this technique in recent years, perhaps as a result of computerised wheel balancing machines being so good.

Of course, one could not depend on a balanced wheel after a rotation but the "on the car" technique would certainly compensate for unbalanced brake rotors.

 

Just a ditto from Edd China on wheeler dealers ( the XK8 episode ).

He said when fitting new discs, make sure you clean any rust off the hub so that the disk ( rotor ) seats properly on the hub.

I guess the faster you go, having it not quite seated flush can create an out of balance centrifugal force, even if the disk is balanced.

I fitted my new discs without cleaning the hub, but since the car has hardly moved since fitting them i don't know if it's ok or not.

They are coming off again so i can clean up the mating surface on the hub.

 

Well color me incredulous. Glad you got the problem solved. Will keep the notion that rotors need balancing as well in my head.

 

Would you be willing to share the name of this place? I too am in Phoenix and am fighting a similar if not the same issue.

Thanks!

 

King Balancing in Glendale
Home Page

 

Thank you for sharing.

I've been having the same exact issue that you had for months, I figured it was just the cheap pair of used tires I slapped on the front.

Looks like I'm going to tear these rotors off and have them looked over.

 

Awesome! Thanks!