Front end shake at 45mph E24 M6

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Ethanh100
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Front end shake at 45mph E24 M6

Post by Ethanh100 »

Hello,
I have an '87 M6 that has had an issue where it had a front end shake that could also be felt in the steering wheel when braking around 45mph and higher. Pretty mild shake nothing crazy, I assumed it was just warped rotors but wasnt anything bad so didnt look into it yet.

However the other day I was driving it and I was getting a pretty violent shake in the front end that I could also feel in the steering wheel. However this time it wasnt under breaking it was just when I was going at around 45-52 pretty specifically. Any faster or slower it would go away. Under heavy acceleration I didnt notice it, maybe just because I was going trough that speed range so quickly I couldnt feel it. But just cruising at that speed was unbearable. Getting on the brakes didnt really change it, just slowed me down to the point where it stopped shaking.

I drove and parked it a few times and was still happening, but then all of the sudden one time I drove it, it was no longer shaking violently, just a little bit under breaking like before.

I did some reading and think that it might be that the break caliper piston is getting stuck, which is causing warping in the rotors. This made sense to me because if its stuck its causing the rotor to warp, and maybe the reason why it was shaking when not even breaking was because the caliper was stuck and hitting that warped rotor. What do you guys think? Should I replace my rotors and take apart the caliper and see if it fixes it? or does it sound like something else? Thanks!!
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Re: Front end shake at 45mph E24 M6

Post by bpoliakoff »

Warped rotors will only cause shaking under braking. First check tire balance. Then start checking suspension components.
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Re: Front end shake at 45mph E24 M6

Post by Pod »

If you have non-standard wheels, check the bores. If you need spigot rings and do not have them, this could be a cause of the problem.
plip1953
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Re: Front end shake at 45mph E24 M6

Post by plip1953 »

Simplest thing to check first is swapping out front wheels - fronts to backs would do. Does the shaking stop or at least reduce?

Or maybe even before that, because it's so simple, is to check for any obvious play in the front bearings - wheels off the ground and grab top and bottom (not sides) and rock to and fro.

Worn bushes would most certainly not help the situation.

And I'd be a bit surprised if it's a sticking caliper, although not difficult to check.
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Dimi555
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Re: Front end shake at 45mph E24 M6

Post by Dimi555 »

I just had the same thing happen today on the interstate at ~80 mph. Shaking pretty violently and loss of power. I passed through a toll booth at pretty low speed, and then when I accelerated again, it just stopped and proceeded to run fine all the way home. I am confused. Will it come back? What would cause this?
plip1953
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Re: Front end shake at 45mph E24 M6

Post by plip1953 »

For the shaking to be present at all there must be some form of imbalance that can then become accentuated if the frequency of the vibration coincides with the natural resonance frequency of the rotating assembly (someone feel free to correct the wording of my technical description - it was a long time ago that I was in a physics classroom!).

That imbalance might be temporary (eg on a track it's quite normal for tyres to attract discarded rubber from other cars and that can a vibration until it self cleans), but more likely on a road car is where a balance weight has detached itself or a tyre has started to deform.

As suggested in earlier posts, switching tyres back to front is a simple and often very effective way to pinpoint the cause, but beyond that you might need to check for play in bearing and bushes ie anything that might allow a vibration to start and then become accentuated due to the resonance effect.
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Re: Front end shake at 45mph E24 M6

Post by Da_Hose »

Wacky as it sounds, wheel nut torque affects wobble on an M6. I tightened to 95 ft/lb once because that is what my local wheel shop said their book showed. Research revealed that original torque was rated at 75 ft/lb, then later upgraded to 85 ft/lb, and now shown (in BMW references) as 95 ft/lb. I re-mounted using 85 ft/lb and my wobble went away. I tightened back to 95, and the wobble came back.

What this suggests to me, is that the hubs flex under high torque, which induces the wobble. At 85 ft/lb you are still plenty tight, and at 75 ft/lb it would still be secure, but warrant periodic checks. I suggest tinkering with wheel torque, and see if you have the same experience I did.

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Re: Front end shake at 45mph E24 M6

Post by plip1953 »

Da_Hose wrote: Thu Jan 14, 2021 7:35 pm Wacky as it sounds, wheel nut torque affects wobble on an M6. I tightened to 95 ft/lb once because that is what my local wheel shop said their book showed. Research revealed that original torque was rated at 75 ft/lb, then later upgraded to 85 ft/lb, and now shown (in BMW references) as 95 ft/lb. I re-mounted using 85 ft/lb and my wobble went away. I tightened back to 95, and the wobble came back.

What this suggests to me, is that the hubs flex under high torque, which induces the wobble. At 85 ft/lb you are still plenty tight, and at 75 ft/lb it would still be secure, but warrant periodic checks. I suggest tinkering with wheel torque, and see if you have the same experience I did.

Jose
I really don't think it anything to do with the differing torque values

Of course it's entirely possible that the hub face is warped, a bearing is worn, or that the mating faces between hub and disc and disc and wheel aren't perfectly clean. But simply applying torque ranging between 75 and 95 lbs/ft will not induce or remove wobble.
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Re: Front end shake at 45mph E24 M6

Post by Da_Hose »

I know what I know plip. Torque values made a difference in my case, and the problem/solution was/is repeatable.

The only thing I haven't done yet is replace the front hubs.

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Re: Front end shake at 45mph E24 M6

Post by plip1953 »

Da_Hose wrote: Fri Jan 15, 2021 4:34 pm I know what I know plip. Torque values made a difference in my case, and the problem/solution was/is repeatable.

The only thing I haven't done yet is replace the front hubs.

Jose
I accept that in your case it made a difference, but it wouldn't have been simply because of the differing applied torques.
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Re: Front end shake at 45mph E24 M6

Post by emac »

I have found older BMW's are very sensitive to tire balance and many shops just dont take the time to balance as well as they could. As others have noted suspension components need to be checked. Tires can get flat spotted if they sit for a long time and may need time to warm up to get better. Sometimes the quality of the tire just isnt good. Also, make sure they mount the tire properly (red/yellow dots). Red dot I think goes opposite the valve stem for best balance. It can be frustrating. I typically just take the wheels to the tire shop to mount the tires and I put them on. I just dont trust those guys to use a torque wrench. Over/uneven torquing will warp rotors.

If it makes you feel any better I just had brand new Pilot sports mounted on brand new wheels and they drove fine the first outing. After sitting for a month, they now have a wobble at about 50mph! I will probably just bring them back to check the balance as I have never had an issue on this car.
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Re: Front end shake at 45mph E24 M6

Post by clipper47 »

I have been dealing with this same problem for several years. When I first bought the car I installed new Michelin tires and replaced the upper thrust arm bushings and followed the Bentley pre load instructions.The shake began after the first winter storage at about 100km. The car sits for 6 months of the year so I suspect the tires had developed flat spots that wont correct. Have done the front to back tire change, had the tires road forced balanced and have installed Moosehead Engineering spherical upper thrust arm bushings and it still has a shake but now at a higher speeds that the car rarely sees so I am leaving it for now. In winter I pump the tires up to maximum pressure and the problem hasn't gotten worse. The tires are now eight years old.
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Re: Front end shake at 45mph E24 M6

Post by Jlc »

Have you thought of leaving the car on jackstands to take the weight of the tires? I had my e21 in storage for a year due to a job transfer and luckily no serious flat spots but the parkbrake had been set and it froze/rusted to the drum.
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Re: Front end shake at 45mph E24 M6

Post by clipper47 »

Jlc wrote: Thu Jan 21, 2021 4:50 pm Have you thought of leaving the car on jackstands to take the weight of the tires? I had my e21 in storage for a year due to a job transfer and luckily no serious flat spots but the parkbrake had been set and it froze/rusted to the drum.
I have but I have also heard that it is not a good idea as the suspension is stessed if it is hanging.
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Re: Front end shake at 45mph E24 M6

Post by plip1953 »

clipper47 wrote: Thu Jan 21, 2021 11:56 pm
Jlc wrote: Thu Jan 21, 2021 4:50 pm Have you thought of leaving the car on jackstands to take the weight of the tires? I had my e21 in storage for a year due to a job transfer and luckily no serious flat spots but the parkbrake had been set and it froze/rusted to the drum.
I have but I have also heard that it is not a good idea as the suspension is stressed if it is hanging.
I agree with you on this, although I have had my car up in the air for a relatively extended period without any apparent detriment.

More generally I have practised pumping the tyres up, which has definitely worked, although latterly I store the car an a second set of wheels/tyres that I know I'll never want to use on the road. I also keep my main set of wheels/tyres stored upright in a relatively cool and dark place, but where temps would be very unlikely to drop below freezing.
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Re: Front end shake at 45mph E24 M6

Post by Jlc »

clipper47 wrote: Thu Jan 21, 2021 11:56 pm
Jlc wrote: Thu Jan 21, 2021 4:50 pm Have you thought of leaving the car on jackstands to take the weight of the tires? I had my e21 in storage for a year due to a job transfer and luckily no serious flat spots but the parkbrake had been set and it froze/rusted to the drum.
I have but I have also heard that it is not a good idea as the suspension is stessed if it is hanging.
Good point. Perhapsusing jackstands on suspension points would help with that concern? I have never needed to do that so I really don't know for sure the best answer.
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Re: Front end shake at 45mph E24 M6

Post by clipper47 »

Jlc wrote: Fri Jan 22, 2021 3:46 pm
clipper47 wrote: Thu Jan 21, 2021 11:56 pm
Jlc wrote: Thu Jan 21, 2021 4:50 pm Have you thought of leaving the car on jackstands to take the weight of the tires? I had my e21 in storage for a year due to a job transfer and luckily no serious flat spots but the parkbrake had been set and it froze/rusted to the drum.
I have but I have also heard that it is not a good idea as the suspension is stessed if it is hanging.
Good point. Perhapsusing jackstands on suspension points would help with that concern? I have never needed to do that so I really don't know for sure the best answer.
It is a bummer having to store a car for 6 months. Without salt on the roads I would drive the car year around. I have been putting the car on a set of those wheeled dollies which have a contour similar to the tires so it does help if not eliminate the flat spotting.
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Re: Front end shake at 45mph E24 M6

Post by Jlc »

I have visions of a set of four vehicle supports consisting of 3/4 plywood base with a 3/4 ply riser drilled for the e24 bolt patten used to hold it up with the wheels removed. I mean, I've used a 2x4 over the fenders and a J hook to lift a VW Rabbit engine to replace a clutch. I've lived in GA too long....
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Re: Front end shake at 45mph E24 M6

Post by emac »

To reinforce what Pod posted. I recently purchased some style 5 wheels from BMW. They were originally for an e39. The e39 has a 74.1mm bore and the e24 and most other BMW's had a 72.56mm bore. They have a slight wobble, so I am installing hubcentric rings and that should fix it. I didnt realize this until today.
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Re: Front end shake at 45mph E24 M6

Post by Pod »

If the rings are made of aluminium, put a smear of grease on them to avoid galvanic corrosion, otherwise you may have difficulty removing the wheels in the future 😉
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Re: Front end shake at 45mph E24 M6

Post by mark22 »

Took me FOREVER to figure this out on my car. Check for a seized brake caliper. This was surprisingly elusive. I waited 6 months for a new calipers from Germany.
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