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Steering vibration; something to add

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peterpilot
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Steering vibration; something to add

Post by peterpilot » Fri May 25, 2012 8:34 pm

Of all the posts I have read on this, our website, I do not recall it being mentioned that anyone has has had the experience of brake discs/rotors being out of balance and causing vibration or steering wobble.
Well, hopefully this can be of some use to anyone still having this problem.
I recently fitted a new set of drilled Discs/Rotors to my '85 euro 6 here in South Africa. I obtained them on Ebay from California.
I immediately got a steering vibration/wobble between 90 and 100kph (50-60 mph) and to confirm my suspicions, I first went and had my wheels balanced. (Applying the brakes had no effect.)
After the balance the problem remained. The discs were out of balance!
I then took off the first wheel, removed the caliper and was happy to find that the wheel bearings and grease seal were free enough to statically find the heavy side if the disc and balance it within a very close tolerance by grinding material away as the factory does. (I used my little angle grinder with a cutting disc.)
The second front disc seemed pretty much in balanced.
After reassembly, the problem had almost disappeared.

I have since used an aircraft wheel static-balancing rig, found the other disc to be a little out as well and removed a little more material from the first disc. I did a test drive today and I'm happy to report that the problem has completely disappeared. Better than before I replaced the discs, so the old ones were probably very slightly out too.

So guys, before spending lots of cash on expensive replacements, be sure to first fit Hub-centric rings if your rims are not standard and rings are required (you cannot rely on the wheel bolts to centralize the wheel accurately, check that your wheels/tyres are straight, round and balanced, your discs/rotors are equal thickness all the way round (check with a micrometer) and......Yes..Balanced!!! I would not have believed it would have made such a difference.

If you have ticked off these items, only then look at Steering Box mounting, Idler Arm bushes, Track rod and all steering related ball joints, Control Arm Bushes/joints (inboard and outboard) and upper strut mountings/bearings.
To make up a cheap balancing rig, I would suggest buying a second hand front strut from any 5/6/7 series remove the grease seal, wash out the wheel bearings, and lightly oil them before reassembly. (Do what you wish with the strut and how you make a suitable stand.)
The rear discs, if not ventilated, should not be out of balance as the complete disc and hand brake drum are machined. Ventilated discs/rotors have the rough casting vents between the two sides which is where the imbalance occurs.
I hope this will assist someone.
1981 635 CSI Euro Manual
1985 635 CSI Euro Manual
1998 540 I Steptronic
2004 K1200 RS

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Masked Man
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Post by Masked Man » Fri May 25, 2012 11:51 pm

Thank you, Peter!

I haven't experienced this problem but having another arrow in the quiver as one hunts down front end vibrations is always desirable.

Keep the shiny side up

Phillip

PS Welcome back!
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AusE24
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Post by AusE24 » Sat May 26, 2012 12:53 am

Good Article.

I was a BMW tech in the 90's and had to deal with the balance issue in 6 series and E28 5 series cars regularly. We off car balance the wheels and then "Finish" balanced them on the car to resolve the issue

Other than this, Split Compression Bushes, Then worn drag link and insufficient steering box preload, Or all above were the culprits.

Regards

Greg

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peterpilot
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Steering Vibration

Post by peterpilot » Sat May 26, 2012 6:17 am

Hi Greg,
Thanks. Yes, I had an E28 (528) in the 90's and almost got rid of it before it got stolen. This problem really spoiled a beautiful car.
In hindsight, I had after-marked rims on, no hub Rings. I changed a suspicious Disk, replaced control arm bushes Track Rod (Drag Link), Idler Arm Bushes, Bla Bla Bla. Never got rid of it completely. A real Bugger!

An E12 before that and my '81 6 (which I still have), have nothing like this, even without hub-centric rings, correct steering box pre-load etc. Pity that a suspension upgrade would have this problem.
I must say, for experimental reasons, I have been tempted, and may still try fitting a VW Combi (80'style) Steering Damper to the drag link. It could have positive results for those still frustrated. I'm sure it would help reduce the steering feedback that these cars do suffer over undulated, rough surfaces. It seems that when it a certain frequency is reached, it becomes sensitive. Maybe even a mass balance on the Drag link could change this??
I always preach; "check the simple, cheap stuff before diving in and spending money and getting involved in big, complicated jobs".
I don't always practice what I preach though, after 50 years of playing with cars and bikes.
Take care,
Peter
1981 635 CSI Euro Manual
1985 635 CSI Euro Manual
1998 540 I Steptronic
2004 K1200 RS

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sharkfan
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Re: Steering Vibration

Post by sharkfan » Sat May 26, 2012 8:21 am

peterpilot wrote: I always preach; "check the simple, cheap stuff before diving in and spending money and getting involved in big, complicated jobs".
I can echo this. I recently fitted some E39 wheels to my E34 with the correct hubcentric rings in plastic and correctly torqued down; some miles later some vibration started but on taking the wheels off to re-check their balance I discovered the wheel nuts weren't fully torqued up.

I can only put this down to some small very small compression of the hubcentric rings causing the torque-loading of the wheel nuts to eventually loosen just a little. So after torqueing it all up again it drives beautifully and I now have a reminder in my diary to re-torque again in a week or so.

HTH

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Re: Steering vibration; something to add

Post by PTFunk » Sat May 26, 2012 11:01 pm

peterpilot wrote:After the balance the problem remained. The discs were out of balance!
I then took off the first wheel, removed the caliper and was happy to find that the wheel bearings and grease seal were free enough to statically find the heavy side if the disc and balance it within a very close tolerance by grinding material away as the factory does. (I used my little angle grinder with a cutting disc.)
Thanks for your detailed analysis and solution of this problem! Just so I understand 100%, you ground material off the edges of the rotors until you couldn't perceive any weight bias, when starting from various positions?

I guess I'm naive enough to have thought that modern brake rotors shouldn't have uneven weight distribution, even if they're cross-drilled. Or if they are indeed a bit out of balance, the effect shouldn't be felt at the steering wheel. Then again, the moment of inertia of iron rotors spinning at 60 mph might contribute a lot to the total wheel MoI of rotor + rim + tire.

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PTFunk
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Post by PTFunk » Sat May 26, 2012 11:05 pm

AusE24 wrote:Good Article.

I was a BMW tech in the 90's and had to deal with the balance issue in 6 series and E28 5 series cars regularly. We off car balance the wheels and then "Finish" balanced them on the car to resolve the issue
Greg - could you give a bit more detail as to how you "finish" balanced the wheels once re-mounted? If/when I bring my car to the tire shop and ask them to do this, I'd like to give the impression I have a minor clue about how such things are done. :wink: Perhaps they'll still give me a sidelong glance and tell me to go chill in the waiting room until they're done.

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peterpilot
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Balancing Rotors

Post by peterpilot » Sun May 27, 2012 8:59 pm

Hi PT.
You may notice on some factory Rotors on various cars, BMW for instance, that they grind away material between the two halves, so to speak of the ventilated rotors (front). If you can imagine the overall width/thickness of the rotor being say 1", the grinding wheel or cutter is only 3/4" wide. Therefore the outer edges of the rotor are not ground down and therefore the removed material is not seen from either side of the rotor.

I have also seen in the past, on some vehicles that even thick spring steel clips are pushed on to the vanes which work as balance weights.
Just be sure that if you make a static balancing rig, the bearings must be super free, with minimal friction.

The rig the aircraft guys use have very small 1" OD ball bearings supporting each end of the balancing shaft. The smaller the bearing the better.
As I said in a previous post. if you are using and old strut with the stub axle and hub on it, remove the grease seal/s to get rid of that friction, wash out the bearings and lube them with light oil. that should work as long as the bearings are not shot.

If it is the older strut with taper roller bearings, it is probably easier as you can pre-load the bearings to your satisfaction.
Once again, in the old days, on-car balancing was quite popular, but nowadays the off-car balancing machines are so good that they get the wheels pretty much perfect, so to request on-car balancing thereafter would raise a few eyebrows.

Some may ask, "the rotors were balanced by the factory, so how can the go out?" If they were in fact totally in balance and they did not require material to be removed then this will probably not apply. But, if a substantial amount of material, (say 50 grams) had to be removed to get the rotor in balance and the complete rotor weighed 5kg when new, after many miles of braking, the rotor gets thinner and therefore lighter, (say 4.8kg), then the original material removed is a larger percentage of the total weight of the rotor now. So it is no longer perfectly in balance.

So for those of you who have front end shimmy problems, and especially those who have bought new rotors, as I did, from a non-BMW dealer, do yourselves a favor and make sure the rotors/discs are balanced.
I have been through the exercise this past week and the problem has completely gone. I am totally convinced that this is causing a few people serious headaches, not to mention big bucks.
I discovered this totally by chance when I fitted the new rotors to a car with no shimmy problems. It was blatantly clear what the problem was as the steering wobble was serious, and only between 90 and 100kph.

If anyone needs to see a picture of a rotor with the aforementioned material removed, I will gladly remove a front wheel and take a pic.
Good Luck,
Peter
1981 635 CSI Euro Manual
1985 635 CSI Euro Manual
1998 540 I Steptronic
2004 K1200 RS

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Post by gaspump » Tue May 29, 2012 2:09 am

Good info on your problem. I just fitted a set of 17x8 Style 32's on my 1985 635. Without the lug nuts on, the wheel does not wobble at all on the hub. It's a very tight fit. I get a little vibration around 50 MPH, but I'm not driving it long distance now because I'm getting my driveshaft fixed in 2 weeks,(another stroy). Think I need hub rings on these wheels?

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Post by Griffter » Tue May 29, 2012 5:36 am

If they are e39 fitment (which I think the 17s are) then yes you need hub centric rings.
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Post by Spencer1 » Tue Oct 09, 2012 12:43 pm

Griffter wrote:If they are e39 fitment (which I think the 17s are) then yes you need hub centric rings.
I think you have problem in your steering wheels rod which control the front wheels you should check that all the barring and the hydraulic system. I think you should also check your front wheels alignment because they can also become a reason for this problem.

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