High frequency vibration after replacing rotors and sway bar bushings
 

Hi,

after replacing the front rotors including brake pads and the sway bar bushings I feel a subtle high frequency vibration in the foot well. It is a very light vibration, the kind that tickles you feet very subtly but annoyingly for long distance drive. However the vibration is not felt on the gear shifter. What can be the cause?

Thanks,
texholdem

Do you feel it in the brake pedal?

The vibration on the right foot (gas/brake pedal) is less than on the left foot, which has full contact to the floor.

He means do you feel the vibration when hitting the brake or while driving (no brakes)?

I think that wheel bearings need adjustment after replacing rotors, but i am not sure of that..

when hitting the brake pedal I actually don't feel the vibration because the muscle force applied overtoned the feeling of tickling. On the gas pedal the tickling of the right foot is less than on the left foot.

The vibration seems to spread thru the base plate of the foot well and partly over to the pedals.

Does it do it out of gear? Does it do it in gear while stopped? What speed ranges does it occur in and does the intensity/frequency of the vibration increase with engine and/or road speed?

the vibration is there both when in and out of gear. it is very light, almost unperceivable and seems not to increase much with speed. Maybe the new rotors need some time to adjust.

I would suspect wheel bearing.

Texholdem, were the replacement rotors genuine MB rotors or aftermarket? It's possible one (or both) of the new front rotors is out of balance, or slightly warped. A runout check with a dial indicator will show if the rotors are warped.

Replacing front rotors should not affect the wheel bearings. If the wheel bearings were OK before the recent work they should be the same now.

talked to my "indy". He also thinks that the rotors, which are aftermarket parts, are not well-balanced.

Lesson learnt about non-MB parts. Thanks for all inputs!

Some of the veterans can confirm or deny this ......

But when you change rotors, front wheel bearings will need to be adjusted/ tightened..if not it will vibrate.....I am sure I read this a number of times on this forum the others...

Edit: if Fredman says no, then forget about it, he is one of the experts !!!:)

So it only happens while moving, then?

yes, my guess is now narrowed down to the new rotors. Thanks!

New rotors being warped is nothing new; they should have been checked for run-out...

You can also rotate yout tires and if there is a change in the feel of the vibration, then it would point to tires being out of balance.

also could try cleaning/wire brushing the bearing hubs where the rotors mount ~~~ dirt/rust underneath won't allow the rotor to sit flush and cause a vibration

It has also been done prior to mounting the new rotors.

Thanks, I am going to give it a try.

well, here's something...you mentioned that put new sway bar bushings in? Did you properly lubricate and pre-load these bushings? That could cause this...

actually, the more I examine this thread, the more it seems that it's the sway bar bushings, as you been in there anyway...I'd look there first...I've seen this before in other German automobiles...these bushings are very tempermental to install....they do alot of work and don't like to be screwed with....if you do it incorrectly (the replacement) it will come back and raise some hell...if it were something like the brakes it would become more than apparent by now, same with wheel lugs and rim balancing and stuff like that there...no, this sounds like sway bar stuff to me...good luck

I agree with above. Most of the components, wheel/tire, bearings, rotors are more inclined to have a lower frequency.

We put dish washer soap on the bushings. What means pre-loading the bushings?

Yes, it was a hard job to mount the bushings and the sway bar. We did the best we could, maybe not good enough. I gonna check it. Thanks for the info.

Is it possible your work has caused a transmission fluid hose to come in contact with the chassis or the bar you just worked on?

I don't think so but gonna have a look. Thanks!

pre-loading
 

pre-loading is simply installing the part, you did OK with the soap initially, but that stuff dries out quickly, there is special stuff, but, anyway, preloading is installing the part while jacked up, of course, but not actually
torqing the fasteners to spec until after the car has been lowered off the jacks and all of the weight is on the suspension...that allows the bushings to seat in the proper fashion. If you lock the bushing/carriers into place without the proper stress you could experience what you mention. Your new bushings are fighting to situate themselves...Leads to premature wear as well....

How do one get under the car and torque the fasteners "after the car has been lowered off the jacks and all of the weight is on the suspension"? Even when the car was on 4 jacks and all wheels were off, there was barely enough room to operate.

yes....see? this is why everyone is not a mechanic, the important thing is, if you can conceptualize the issue the solution should appear shortly...good luck....

pre-loading
 

Ask any decent Mercedes or any mechanic about pre-loading.....here's how I do it....I simply put the wheels back on and lower the car down onto a bunch of 4X4's while keeping some jack assistance..the lowering of the car onto its' haunches is sufficient..it allows everything to sit nice like. Then I go in and ratchet everything up...then you lift back up...remove the 4X4s or whatever, with the tires still on, lower the car via the jacks to the point where you can make sure the lugs are still tightened properly..if so (as it should be) drop the car and you should be good to go...there must enough room under there to do these things...are you sure your jacking the car up high enough?

some good news; I thought I'd go with the easiest fix first. I checked my manual on the torque specifications and it says 80 ft.lb , meaning the wheels were a bit overtightened by 15 ft.lb. I bought a heavy torque wrench and retorqued them to specs. Voila, the vibration is gone!

It's surprising that just 15 ft pounds made a difference but it did.

Thanks for all inputs, I keep them all in mind for future reference.

that is smart, my simple mind did not figure it out :), just got stuck with the image of the car lowered meaning 4 wheels on the ground :)