So I went and bought a used M3 in August. 48K miles on the clock, lease return. Did my usual drive-it-like-it's-stolen-test-drive followed immediately by inspection of the engine bay and underside of the car. Engine is clean as a whistle, underside is dry as a bone, and short of pulling plugs, my estimation is perfect mechanical condition of the drivetrain. Tires are the window to the suspension, and these were almost brand new, so not much luck getting a good reading if there was anything wrong. Tough break for me, as it turns out.
After 2 weeks of driving (yes indeed, 2 WEEKS), i notice the rear tires are almost toast. Yikers! Could be 3 things:
1. I drive too fast - very true, but 2 weeks... gawdaaaaam!
2. Alignment sucks - most likely
3. Tires too soft (Michelin Pilot Sports)- also likely, but 2 weeks??? gawwdaaaaam!
After 4 weeks total, rears are done. Fronts still lookin' new. Now I drive a lot. Probably 2000 miles a month, easy. But gawwdammm!
I decide to eliminate the possibility of numbers 2 and 3 above at the same time by getting two new BFG Comp T/A KDW's and an alignment. I'm not one to give a damn about having mismatched pairs front to back... just as long as they are a matched set on the front or rear. We can probably start a new topic on this by itself. In fact, some tire wisdom topics might be nice too. But first things first.
Alignment shop found a bent right rear lower control arm. Mighty bent as it turns out. Looks like the car had been towed in another life, and not by a flat bed tow truck. Bastards! There were marks on both lower control arms where the tow truck apparatus had lifted the car, but only the right side bent for whatever reason.
If you ever have your E46 towed, make sure to insist on a flat bed truck!And so begins the lower control arm saga...
After some lengthy web surfing sessions, I decide to get some Turner Motorsport lower control arms (
http://www.turnermotorsport.com/html/detail.asp?PRODUCT_ID=TSU9940001). Others I considered: UUC (almost got these), Rogue Engineering, OEs, Ground Control, Bavarian Autosport
The setting for this wonderful R&R is in my garage, on my back, with the rear of the car jacked and supported nicely by 3 ton jackstands. An initial inspection reveals that the instructions were not kidding about having to remove the three bolts holding the differential to the subframe. There isn't a chance on earth you will ever get the 4 inch long inner control arm bolts out without moving the differential back outta the way. Also, the left side is partially obscured by the exhaust. So I will start with the right!
Supporting the differential with my floorjack, I pull out the single large front bolt and two smaller rear bolts and the differential is free. It moves nicely back and forth, and quite a bit side to side as there is play in the driveshaft and both halfshafts. This is different than the 330, BTW, as there are two FRONT bolts and one REAR bolt on the 330. My bentley manual only had shots of the 330 diff, so I mention this because I was confused for a while (and just a little nervous about using the torque specs!)
The right side control arm swap is sickeningly easy. I get the inner bolt in and torque it to spec. Now for the left. After struggling for a while by simply repositioning the diff, it is clear there is no way it will work unless more things get removed. So far, rear wheels, all splash shields in the rear, the rear v-brace, and the rear sway bar are all off. I now disconnect the muffler from the exhasut pipe, and the two exhaust pipe supports along the middle of the car and let the exhaust pipes hang down. With this setup, the diff moves JUST enough to make it tempting to think you can still accomplish this without removing the differential completely. The bolt is now about 3/8's of an inch from coming out, but not budging. After some more time spent repositioning and wiggling and tugging, I get the idea to just try unscrewing it out the rest of the way. Two minutes later I'm hoping this trick will now work for putting it back in. It does. But only after a half hour of blood, sweat, and tears - quite analogously foreshadowing my impending doom, much like the defunct rock/jazz band of the late 60's, early 70's.
Torque the inner bolt to spec, attach both outers, and begin the reassembly. Everything is going smashingly well until it's time to put the differential back. I jack up the diff with the floor jack, and start the front bolt by hand. I put it about
half way in. Pay particular heed to this advice! Had I threaded this bad boy
ALL the way in, my story would be ending shortly with "and I finished torquing everything back to spec, and everyone lived happily ever after." As it turns out, during my wiggling and repositioning of the differential in order to get the rear bolts in, the front bolt skipped a thread. I did not know this, of course, and I torqued the rears to spec and went back to the front already anticipating my first drive... Front bolt doesn't budge. I put a breaker bar on it and it moves... barely. YIKES... to the tenth power!
Right now I think: bolt is bent, or skipped a thread. Pause here for a moment of silence... now... scream F U C #!!!!
With the breaker bar still attached, I start to move it back and forth, little by little. Visions of a snapped bolt head are dancing in my head, so the movements are REALLY small! I put some penetrating oil on the bolt. Little by little I work the bolt in a bit, then out a bit. Each time going a little further than the last time. After careful work for what seemed like hours, the bolt is freed amongst a puff of metal thread shavings. Inspection of the bolt shows it is perfectly straight... but the threads are not happy. I clean out the hole completely and my worst fears are realized. The threads on my M14 bolt hole in my $2K differential are hosed! Panic, fear, despair... yah, they are all friends of mine right now.
After an hour of agony... a flash of hope. Somewhere from the annals of automotive literature consumed during my auto shop years, comes a memory of something called Helicoils. Five questions a minutes begin springing out of my head... can it be repaired, do they make metric helicoils, how long are the coils, how long is my bolt, how deep is the hole, will it still support the same size bolt, will it be strong enough, what do these coils look like... then the ultimate question... do I have to take out the differential? OMG... I have to take out the differential. More silence.... and yes... another scream. Sigh.
The car sits for weeks while research takes place. The wife is not happy, but appeased with chocolates. Research complete, parts ordered, more chocolates, parts arrive, back to work!
To remove a diff from an E46, you must disconnect the drive shaft and both half shafts. The good news is, I already had practice removing all the other stuff that has to come out or get loosened. Bad news, I had already put them back and torqued them because I thought I was done four weeks ago. One additional note... in order to get to all of the driveshaft bolts, the alluminum heatshield needs to come out too. One additional, additional note... yah, now that stoopid inner control arm bolt is TOTALLY accessible. Grrrrrr.
Diff's out, plop it on my bench. For helicoil repair of an M14 bolt, you must first bore the original hole with a 9/16ths inch drill (yes, a
standard drill size as opposed to metric, I thought that was weird too!). Clean it out real good with a final magnet pass to make sure all shards are out. (VERY CAREFULLY) Tap the hole with the helicoil-sized tap. Clean it out again with a final magnet pass. This bolt hole is ~40mm deep. Each helicoil insert I got is ~20mm in their unpositioned state. As you thread it in, it probably grows to about 25mm. Screw the first one in. When it hits the bottom, I reach in with some long nose pliers and break off the installation tang. This leaves about 15mm of my bolt hole un-helicoiled. I put a couple drops of red loctite on the exposed 15mm of thread in the bolt hole and begin threading in the second coil. Once butted completely up to the first one, I break off the installation tang and stare at the 10mm or so of helicoil haning out of my differential. Hmmm... what to do...
With dremel tool in hand and saw disk attachment fitted, I carefully choose where to cut and saw off all exposed coils. And now the moment of truth... I take the brand new ($6 !!!) BMW sourced M14 bolt and thread it all the way in by hand. WHEWWWW!
Unlike my Blood, Sweat, and Tears band counterparts, this story does have a happy ending. The differential goes back in, my front bolt gets torqued to its otherworldly 128 ft/lb torque spec, and one month and many chocolates after beginning my control arm install, my M3 is back on the road with new rear control arms. And now, three months and 6000 miles later I am happy to report that my tires look excellent, and my fix seems to have worked.
