Re: Help! Possible front control arm bushing failure

There are control arm bushings and thrust arm bushings in the E39 M5 front suspension. The control arms are perpendicular to the centerline of the car, and (together with the strut & its upper mounting) determine lateral location of each front wheel. The thrust arms extend towards the rear of the car, are longer, and attach to the body under the rear wheel well liner more or less lined up with the inner surface of the wheel well. This bushing locates the front wheels fore and aft, and mainly takes braking reaction loads. Note that the thrust arms are in the front on 6 cylinder E39s.

The symptoms you describe are more typical of a failed thrust arm bushing (wheel shake/shimmy while driving and especially when braking, something loose in the front end). This bushing has a lot of void space (air) and is of a "webbed" design, for maximum isolation from road shocks. It is also a common failure item for the past few series of BMW 5 & 7-series cars. This bushing can be purchased individually and is pressed into the thrust arm. Depending on the shop, the thrust arm may not need to be removed from the car (a PITA) to replace the bushing.

The control arm bushing is solid rubber, MUCH stiffer, and basically controls toe in the front. Failure of this bushing is less common, and in a severe bushing failure the car becomes undriveable - poor directional stability, heavy steering wheel pull, audible scuffing of the front tires, and the DSC light will go on & off. Replacement of this bushing requires replacement of the complete control arm assembly, per BMW.

I know about the above because I replaced the stock bushings on my car with PowerFlex aftermarket bushings. The control arm bushings used a too-soft polyurethane and failed catastrophically in less than one day at the track (the fix was to reinstall the stock control arm bushings). PowerFlex has now redesigned this bushing and provided me with a set of parts of the new design, but I have not yet installed them. They look very substantially stiffer. as they need to be. A solid ball joint as used in the M3 rear suspension would probably be even better. The PowerFlex thrust arm bushings have worked well without any problems. These are solid polyurethane and have no void area.

If you do not have any toe-out symptoms when driving (just vibration under breaking plus some knocking noise), I would not be afraid to drive the car to a nearby service facility. Condition of the front wheel bearings should be checked as well, as a failing bearing could produce some brake vibration and noise when the car is moving. Any competent shop can make this repair, and the thrust arm bushing does not affect wheel alignment (toe) either.

Regards, Dick Roberts

 

Re: Help! Possible front control arm bushing failure

The symptoms you describe are more typical of a failed thrust arm bushing (wheel shake/shimmy while driving and especially when braking, something loose in the front end).

If you do not have any toe-out symptoms when driving (just vibration under breaking plus some knocking noise), I would not be afraid to drive the car to a nearby service facility. Condition of the front wheel bearings should be checked as well, as a failing bearing could produce some brake vibration and noise when the car is moving. Any competent shop can make this repair, and the thrust arm bushing does not affect wheel alignment (toe) either.

Thanks for taking the time to share your thoughtful response, Dick! Without fail, I learn something new each and every time I read one of your posts.

I did confuse the thrust arm and control arm in my original post. Thanks for setting me straight! :1:

In the meantime, I spoke with my trusted SA and he concluded the same thing as you. As such, he also told me that a flat-bed was unnecessary, and he carved out an 0745 appointment for me tomorrow so I can drive on in (and get a BMW loaner---what a guy!).

I have and will continue to track this car, so do you think a PowerFlex replacement of just the front thrust arm bushings would make sense? It sounds like the OE control arm bushings are a bit more sturdy.

I'll also suggest a looksie at the wheel bearings, as I'm simply amazed that they've lasted as long as they have, what with my 'adventurous' use and the potential added load of a BBK. I may just replace those as a preventive measure.

-Dave

 

Re: Help! Possible front control arm bushing failure

Regarding the uprated front bushes, they were on the car when I bought it and do not offer any harsh or noise problems they are evidently simply a little taughter.


I actually had the dealer replace a front tie rod under warranty as I have a light vibration problem under braking....

The steering and light vibration has improved but not gone away. I have swapped back to 18's to eliminate wheels, will go for a trip tonight to see if that has changed things. Then it's possibly the discs themselves, AP can regrind the faces and have said that is is unusual but not unheard of for minor runout problems under very hard use (I have been quite kind to them !) and at .0006 " out they would reface them.

The dealer says that the suspension is now perfect with no problems anywhere else ?

W'ell see !

 

Well, it turns out the flatbed was necessary....

As I pulled out of my parking garage, the clunk quickly escalated to a metal and mechanical 'explosion' of sorts nearly every time I touched the brake pedal. There was a metal-on-metal grinding that I could feel through the wheel, almost as though my brake pads were down to the backers (they aren't). Even that behavior was intermittent.

So I limped back to my parking space and called the towing company. Since a tow last nite would have incurred overnight storage fees, I opted to wait until this morning and had them come flatbed my baby away.

Luckily, I have an extra eyebolt to allow for winching and cinching from both ends (prevents operators from attempting to place those evil hooks on some fragile aluminum suspension bits).

I'm now thinking that it may be a wheel bearing issue, b/c I cannot think what else would cause that horrid grinding noise.

I'll update when I find out.

-Dave

 

Re: Help! Possible front control arm bushing failure

Good luck and fingers crossed it's not too expensive :byebye:

 

Re: Well, it turns out the flatbed was necessary....

Dave,

I have the same symptoms, braking at 45-60 MPH range. No vibrations at other speeds. No grinding sound either. Car just turned over 60k miles.

Please keep us posted on the remedy and tge cost.

Thanks.

CP

 

Re: Help! Possible front control arm bushing failure

Well just taken the car out os 18's ..........

The symptoms are the same (A little blunted by the 18's vs 19's) I really don't think it's my brakes which means some suspension bushes. The dealer replaced the fron tie rod and that has improved things and the front feels sharper as well as much reduced vibration under light braking.

Does any one have any pictures o see which bushes are potentially to blame, I would really like to tighten things up there. Not sure which bushes have been replaced, any threads that have some piccies so I can undertand which ones to replace and the poly bush options ?

Tks:wroom: :wroom: :wroom:

 

Re: Well, it turns out the flatbed was necessary....

Dave,

I have the same symptoms, braking at 45-60 MPH range. No vibrations at other speeds. No grinding sound either.
CP

I had the same symptoms last year. Thrust arm bushings replaced. No problem since. I ignore the question why bushings would wear out in 25000 miles and keep on driving. :M5eyes:
Regards,
Jerry

 

Re: Well, it turns out the flatbed was necessary....

I had the same symptoms last year. Thrust arm bushings replaced. No problem since. I ignore the question why bushings would wear out in 25000 miles and keep on driving. :M5eyes:
Regards,
Jerry

Jerry,

Thanks for the confirmation. I'm sure yours was under warranty right? I wonder how much that would cost?

Thanks.

CP

 

Mea culpa time...

Good luck and fingers crossed it's not too expensive :byebye:

I've got good news and bad news.

Good news: $200 all-up, including the flat-bed trip to the dealer. Flat-bed operator was an enthusiast, and brought along wooden planks to allow easing my lowered Beast up onto the platform without scraping her chin.

Bad news: this was not a thrust arm bushing failure, or even a front wheel bearing failure. It was the operator (me) being all too impressed with my skills as a diagnostician.

Let this be a lesson to others: nothing beats a thorough first-hand inspection of the area of the vehicle in question.

When I first felt the slight shimmy under braking, I knew warping and pad deposition were non-issues, and I recalled threads on the board related to OE bushing failures.

When I heard slight 'clunking' under pressure, it confirmed my hypothesis that the thrust arm bushings were the culprit, since those load up under braking.

NOT!

What happened is this: the caliper bolt on my front-right StopTech big brake kit had backed itself all the way out, and the caliper was affixed by one lone, loose bolt. Hence the clanking, and occasional grinding noise. DOH! Insufficient torque applied by owner/operator/tech the last time I swapped my track pads for street. Idiot!!

For those of you familiar with the StopTechs, their first-generation model requires you to remove one of the (factory) caliper mounting bolts, and loosen the other, so the caliper can pivot up to allow the removal of the brake pads. The tiny bridge bolts that lock the pads in their slots cannot be backed out without pivoting the caliper, as they intersect with one of the suspension components.

Thanks to feedback from Dave Zeckhausen, StopTech redesigned the bridge bolt design so the bolts now remove from the outside, and clearance is not an issue.

Without having the proper tools at the track, I did not torque those bolts sufficiently and one worked its way free. My bad. Too smart for my own britches.

Glad I never left my office parking lot last night!

-Dave

 

Re: Help! Possible front control arm bushing failure

Dave:

I also have the early design StopTech brakes in the front. I became aware of the bridge bolt issue, and the redesign after purchasing the BBK but before installing it (it gets mighty cold in the winter in Chicago). StopTech offered to sell me new calipers, but no other fix or exchange was in the cards from StopTech. I ended up reversing the lower bridge bolts on each side, to match the factory fix. This meant machining some threaded inserts to fit on the inside into the former recess for the allen bolt head, and carefully drilling out the threads on the outside and counter-boring to provide clearance for the bolt head. This fix works great, and has been no trouble for several years of use - including quite a few pad swaps for the track. Since I am fairly anal about these things, I drilled the reversed bolts for safety wire to make sure they never back out into the wheel. Pulling the calipers to change pads is a major PITA, particularly once the discs become worn.

Glad it was nothing more serious.

Regards, Dick Roberts

 

Re: Help! Possible front control arm bushing failure

Spent about 2 hours last night searching the web to uncover piccies of the e39 M5 front suspension so I can see what's what ! Can anyone help with piccies ?

Tks

 

Re: Help! Possible front control arm bushing failure

Spent about 2 hours last night searching the web to uncover piccies of the e39 M5 front suspension so I can see what's what ! Can anyone help with piccies ?

Sure. The two lower control arms are pictured below:

Front lower control arm = "Wishbone"​

Rear lower control arm = "Traction Strut"​

And here is a photo I took while upgrading my front swaybar. I've labeled the various bits and pieces that were discussed in this thread, including the missing bolt from Teutonaddict's car which caused his symptoms.

 

Re: Help! Possible front control arm bushing failure

Great explanation Dick...and pics Dave!

Thanks for sharing! Rick

 

Re: Help! Possible front control arm bushing failure

Hi - give me a call on 07765 408118 I think I may have a solution for

 

Re: Help! Possible front control arm bushing failure

THANKS CHAPS :15: :15: :byebye:

 

Re: Help! Possible front control arm bushing failure

I am planning n having a look under the car on Sunday (I think I can get it on a ramp) I will also take some piccies of the suspension and the Eibach coilovers

 

Re: Help! Possible front control arm bushing failure

I had a quick look under the car today, I have the powerflex bushes on the traction strut only, the other arms are stock

Still no nearer finding what is causing the vibration under braking, it is more shimmer than strong vibration. The BMW garage checked all links when tehy replaced the centre steering joint and said all was ok, they also dialled up the runout on the discs which were 'perfect' so they said...

NOt sure where to look next !................:sad1:

When the roll bars are uprated next weekend I will ask the garage to take off the links and look at bushes and ball joints on each strut.

Is the lower control arm 'wishbone' bushes worth upgrading do you think ? Are the current powerflex bushes for this arm now OK ?

 

Re: Help! Possible front control arm bushing failure

Hi Carrera 2 RS

It is me this time, My work mates had posted my number, so i'm sorry that I couldn't help at the time.

My bro in law works at Porshce GB in Theale and one of his colleuges is X-BMW and sh*t hot on "M" Beemers.

I have just been out with my brother in law and he said that if you want them to check over your car`they could give it a good check over and if you still have the Extended BMW Warranty they will alsol "advise" you on what to say when you take it into the dealer*

(*When i took my '99 with 60K into the local BMW dealer with a small oil leak from the LHS where-ever. They "advised" me to mention that my battery light has been flashing on and off. Three days later 1new Alternator, 2X VANOS units, New Rear Suspension Bushes etc etc) I paid for an Oil Change and Loan Car for 3 days £300 The total bill for the car and 3 days labour £2300)

If i can help out please do give me a call that number was correct!!!!

My bro in law also said if you ever need anything sorted out on the RS let him know, Put it this way if I didn't have kids i would be driving a 911 but for the servicing costs of an Audi S3/Golf R32 (Affordable to say the least)

Simon

 

Re: Help! Possible front control arm bushing failure

Simon,

Thanks, I'll give you a call 2moro !

The car is on extended warranty,I think it might actually be the discs, I went out with a race engineer today and he saud it feels like the front discs, AP's are evidently prone to this when using new discs and new pads. Something to do with two smooth surfaces causing polishing and heat spots, on race cars they only ever use new pads or new discs never both.....

It's still causing unpleasant but not dreadful vibration........

 

Re: Well, it turns out the flatbed was necessary....

Jerry,

Thanks for the confirmation. I'm sure yours was under warranty right? I wonder how much that would cost?

Thanks.

CP

CP
Either under warranty or maintenance, I didn't ask. I can dig out the receipt if it makes a difference.
Regards,
Jerry

 

Re: Well, it turns out the flatbed was necessary....

CP
Either under warranty or maintenance, I didn't ask. I can dig out the receipt if it makes a difference.
Regards,
Jerry

Jerry,

No need to spend time on my behalf. I'm at 60,075 miles, it will be my nickle regardless.

Thanks though.

CP

 

Re: Well, it turns out the flatbed was necessary....

Luckily, I have an extra eyebolt to allow for winching and cinching from both ends (prevents operators from attempting to place those evil hooks on some fragile aluminum suspension bits).
-Dave

FYI, as I understand it, the eyebolts should ONLY be used for actual towing (ie with a strap to another car) or winching the car up onto a flatbed. They should NOT be used for strapping down the car since the points they attach to are not designed for downward or sideways forces.
The proper tie-down points as I understand it are accessed by removing the four jack pads under the rocker panels and there should be points appropriate for tie-downs there.

 

hey carrera

did you find out what was the problem eventualy??