This section contains information on special Front Suspension conditions and diagnosis.

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750I Thrust Arm Bushings

Front Wheel Bearing Diagnosis

Vibration

Front shock replacement on 83-87 6 series

750I Thrust Arm Bushing Installation - "Steven C. Morey"

By popular request, here's a synopsis on installing the heavier 750il thrust arm bushings:

First, the reason that these are needed is simply that the original design is simply too light to "snub" the tremendous forces applied (especially when braking) on the relatively heavy 6 series cars. This is exacerbated by the use over the years of larger and heavier tires wheels with a bushing design from an earlier time that was intended for a lighter 6 with smaller tires wheels. Even so, the original bushing was marginal even for the original 6 series. Although I have not seen a TSB on it, it is my understanding that BMW is now recommending the 750il bushing for all 6 series.

I don't want to elaborate on the fine points of thrust arm removal, this is readily available info. in the Haynes, Chilton, Bentley manuals for the 5 series (which, if you don't know already, is what your 6 body sits on - either the E-12 or E-28 depending on year model). Before you put your car up on four (that's *four*) jack stands, get a huge set of channel locks (the ones that are about 22" long) which you can use to squeeze assorted ball joints while you are under your car to check for play. New thrust arm bushings won't overcome other worn components vice versa.

The 750il bushing is considerably wider than stock (giving more support) and is "denser" rubber. It also has a partial urethane core so they is less rubber "thickness", which imparts a *slightly* stiffer feel. There are some after-market companies that make polyurethane core "performance" bushings that I personally think are counter to what we all love about the BMW feel - that firm yet nicely "damped" feel that filters out high frequency vibrations through the use of rubber. You can buy the 750il bushings pre-milled to fit the 6 series from Dinan for about $180 pair or you can just get the stock 750il bushing and save a bunch by milling it yourself (instructions to follow). I mail - ordered mine from Rod Sydney at Dealer Marketing (I'm sure most of you know him) for about $60 pair.

Whether you are removing the entire thrust arm in order to install the bushing in a press (my preferred technique) or simply dropping the bushing end and using a special tool to do it in the car, get the bushing end out of the chassis mount. Measure the width of the mount opening and the outside width of the stock bushing. They should be pretty close to the same although on mine the bushing was very slightly (.015") narrower. Now, crawl out from under the car and measure the width of the 750il bushing at both the outside (widest point) as well as the "barrel" that houses the rubber. You will find that the barrel is a little narrower than the opening width of the chassis mount (about 0.06"). The objective is to mill equal amounts from either side of the bushing ends until the outside dimension is a *slight* interference fit into the chassis mount. This will still allow the steel barrel to float inside the mount and not make contact with the chassis, thus maintaining the rubber - isolated, damped feel. IOW, when you are finished milling the outside dimension from end to end will still be more than the barrel.

O.K., having said all that, how do you mill the bushing? Simple, really. First, if you just happen to have a nice Bridgeport milling machine in your garage, go for it (you don't need me to tell you how!). If not, you will simply need some kind of power sander, either belt or disc (orbital would take years to remove enough material). If you have a table saw you can install a sanding disc in it and raise it high enough to clear the OD of the bushing. I used a hand held belt sander, turned it upside down (belt face up), clamped it so it couldn't walk away, and locked the power trigger in the ON position. This in effect gave me a stationary sander so that all I had to hold was the bushing. Now simply grind away the soft alloy urethane ends a little at a time, alternating sides. If bushing gets a little too warm, set it aside and work on the other one (you are installing pairs, aren't you?). Don't get too uptight about this, its not that critical. Just check each side frequently for measurement and squareness. I did it all by hand with no problems. If you hate "free-handing" then the table saw cum stationary disc sander will allow you to stabilize the bushing and even use your sliding miter guide to hold it square.

Press bushings back into thrust arms, bolt up to car. Don't forget to *not* tighten the thru-bolt until the weight of the car is on it. BTW, since there is not enough room to do this properly with the car on the ground (i.e. with a torque wrench!). I do it by placing my floor jack under the hub and jacking up each side individually until the car *just* begins to rise off of the jackstand (hopefully you are doing all this with both front wheels removed!). This compresses the strut from the weight of the car to almost exactly the standard ride height, now torque the thru-bolt, unload that side, move to other side of car, repeat.

My M6 had slight braking shimmy prior to this. After checking my rotors (which did have slight run-out) I decided to install the heavier bushings first. Total shimmy elimination. For those of you who have a lot of shimmy, check your rotor run-out, you may need both.

The beauty of the heavy bushing is that they will hold your struts in a more stable position and not allow the rotors to "oscillate" (which begins to amplify and creates even more run-out and rotor warpage). Future rotors will be less apt to warp. Kiss your shimmy goodbye!

Happy thrusting,

Front Wheel Bearing Diagnosis

Front Wheel Bearing Diagnosis.....hom_lanihau@juno.com (Norman S. Hom)

The front wheel bearings when they go bad they will make a god awful loud humming noise. What is happening is ( the 1983 to 1989 hubs and bearings are suppose to be not serviceable -can't re-grease them - more later on this) over time the bearings start to burn by grinding into the metal ball bearings or bearing race (believe this is the correct term). Thus the noise, as there is no lubrication. I don't think you need to check for play in the wheel/ bearing as by this time the humming or buzzing noise will be very loud and if you do not attend to this you will also have a rhythmic thumping sound as the vehicle is moving. The faster you go the more rhythmic and faster the thump. As they say don't ask how I know. At least I did not burn out the wheel bearings on a BMW (over 25 years ago on my mother's buick I learned about bearing rhythm).

Regarding the not serviceable part -

I replaced one front hub in my 1985 318i which is similar to the 633, only smaller. The new sealed hub (French or Italian made) had inner and outer bearings which easily popped out of the hub which had to be greased prior to installing. The old hub was similar in that the inner and outer bearing also easily popped out of the hub. Based on the ease of the bearings coming out of the hub, one could take the hub off with a gear puller to re-pack the bearings. I would suggest you get a new backing dust shield (cheap) for the hub if you are replacing the hub and possibly even if just re-packing the bearing . The shield was in the way when I had to pull the race from the spindle. I bent the dust shield on the 318i to get it out of the way to get my gear puller on the race. The cost of hubs from Bavarian Autosport runs about $75 non ABS and about $100 for ABS for the 1983 to 1989 Six(s), so it may or may not be cost effective to re-pack bearings depending on your time and $s. For the fortunate ones that have pre-1983 Sixes, re-pack those wheel bearings routinely.

If you ignore the humming and get to the rhythmic thump, be prepared to replace the spindles which I am sure run into some big dollars. Bottom line, re-pack bearings every 50,000 to 75,000 or replace the bearing at the first sound of the odd humming sound. You may first think the humming is coming from the trans or even like a rear-end growl.

To check if the wheel bearing is doing the humming, jack the car up and when you rotate the wheel compare the sound of a normal rotating wheel versus the suspected humming one. The bad bearing will be noticeably louder and not rotate as freely as it rotates. You may even hear the grinding of the grit and crud that has made its way into the bearings.

Vibration - Mike Gordon <mikego@Attachmate.com>

Suspension problems that can cause excessive vibration:

1) Worn bushings on the upper control arms--very likely! The stock bushings wear out due to the forces that they are subjected to. A popular upgrade is to use milled 750iL bushings.
2) Worn ball joints on the upper and lower control arms
3) Loose wheel bearings--There would probably be a lot of noise associated with this.
4) Worn tie rod ends or idler arm bushing can cause the steering to vibrate and wander
5) Lack of hub inserts in aftermarket wheels with an incorrect hub size since E24 wheels are hubcentric.
6) Certain tires may be prone to shimmy on certain road surfaces.

> Driveline problems that can cause vibrations:

1) Worn u-joints
2) Worn center support bearing--this will cause a thump-thump by the shifter during spirited acceleration from a dead stop. Very likely!
3) Cracked or worn guibos--These can cause driveline vibration.
4) Tranny rubber mounts--check these as they are cheap and usually need replacing.
5) Diff rubber mount--can cause the diff to contact the trunk when accelerating/decelerating at highway speeds--sounds like someone inside the trunk is trying to beat their way out!
6) Rear subframe bushings--can allow the subframe to twist and contact the frame.

Front shock replacement on 83-87 6 series "Gene M."

Bentley's indicates that in order to replace the front shocks it is necessary to remove the entire strut assembly from the car. This is actually not necessary on the 6 series with its wider fender wells and front shock replacement can therefore be done without having to separate any of the ball joints. This write up is a brief summary of this procedure. Bentley's or the shop manual should be used to get full details on this job.

Special tools needed is a set of spring compressors, a large pipe wrench or equivalent. An air impact wrench will also make this job a lot easier--without one, you will be in for a heavy duty workout. Most of these nuts and bolts are on very tight.

Jack up the front wheel and use a jack stand so that your jack can later be used to jack up and down the strut/rotor assembly.

Remove the front wheel.

Remove the two 19mm bolts holding on the brake caliper and use a stiff wire to tie the caliper out of the way (you will need to slip the brake hose from the holder on the strut but you do not need to disconnect the brake hose--be careful not to overstress the brake hose). You will probably need to use a large blade screwdriver to push back the brake pads to clear them over the brake rotor edge. On the driver's side you will need to disconnect the brake lining sensor wire.

Remove the 17mm nut holding the top of the sway bar link to the strut. You will need a thin 17mm open end wrench to hold the back side--it will slip in between the dust boot and the strut. Jack up the strut/rotor assembly enough to allow the removal of the top sway bar link bolt from the strut assembly.

Remove the 19mm nut and bolt holding the lower control arm bushing. Jack up the rotor until the bolt can be easily removed. Disoldge the bushing end from the subframe. Leave the jack in place for the next step.

Remove the three 13mm nuts on top of the strut tower. Now gradually lower the jack while guiding the strut assembly and springs down the fender. The top of the strut assembly should be able to be worked down to clear the wheel well, but you may have to put on the spring compressors to slightly compress the springs (maybe just 1/2") to get it to clear. The passenger side on my 83 633 cleared with no problem but the driver's side required the use of the spring compressors. You may want to tape the edge of your fender to protect the paint.

Once the top of the strut assembly have cleared the wheel well and has been swung out, you will now need to compress the springs until the spring is no longer exerting pressure on the ends. (Be careful with the spring compressors especially since the strut assembly can flop around) You may want to place a block of wood under the rotor for support.

Remove the cover on the top strut bearings and there will be a 17mm nut down inside. An air wrench with a 17mm thin wall socket will spin this right out, but if you don't have an air wrench, you will need to use some vise grips to keep the shock shaft from turning while you remove this nut. You can also put an 8mm 1/4" socket on the end of the shock shaft, then put the 17mm 1/2" socket over the nut, then put a 1/4" ratchet with a small extension through the hole in the 17mm socket to hold the shaft end, and finally a vise grip on the side of the 17mm socket to turn the nut (this method helps on reassembly so that you are not gouging your new shock shafts (just the outside of your socket).

The strut bearing mount can now be removed. Be careful to keep track of the washers so that they can be assembled in the same order. This is a good time to lubricate the upper strut bearings by removing the dust cover on the bottom and injecting grease up through the bearings.

Lift off the springs and slide off the rubber cushion and its sleeve.

Next you will need to remove the brass colored collar that holds the shock inside the strut. I don't know if there is a special tool for this, I have always used a large pipe wrench because this thing is on very tight and a lot of leverage is needed to get it off. You may want to put a block of wood under your rotor, reinstall the lower control arm bushing end, and have someone hold the strut while you loosen, and later retighten this collar (it needs to be tight or it can back out like it did on my 320i and 733). If you are switching from conventional shocks to gas shocks, you will need to remove the oil from inside the strut. I used the leg off of some blue jeans to do this.

On re-assembly, make sure your springs are seated properly on both ends before you start loosening up the spring compressors. Use the jack under the rotor to raise the strut into position to line up the 3 upper strut bearing bolts and to allow the lower control arm bushing and the top bolt on the sway bar link to easily be lined up. I do not retighten the lower control arm nut until I have reinstalled the wheel and lowered the car (I'm not sure if the lower control arm bushing is like the upper control arm bushing where the weight must be applied before tightening). Remember to use new bolts, nuts or Loctite where called for and proper tightening torque on re-assembly.