It can happen to anyone, I guess. Snow, ice, or just rain, plus too much throttle at the wrong time can send the back end of the car sliding sideways. If the slide is forcibly stopped by a curb or such - boom - your trailing arm is probably bent. Probably your wheel, too, and possibly your subframe as well if the hit was hard enough.

Here's my resulting mess:


You can see where the back of the tire was rubbing against the inner fender and gas tank after the hit. Check out the lower shock mount.

Luckily I happened to mention my bent arm to Lee Rector at Black Forest Werkshop, and he suggested I check the subframe. Otherwise I wouldn't have thought of it. He suggested I look for cracked or peeling paint on the inside curve of the subframe. I was skeptical because of all the undercoating and gunk under there, but I took a good, hard look. Sure enough, I found one little spot next to the driveshaft surround, on the front side of the frame, where it looked like the undercoating was cracked and peeling a bit.

I needed something more definitive before I went looking for a replacement frame, and I settled on the distance between the car's body and a tab that's welded to the subframe on the front on the passenger side.




The distance was barely the width of a screwdriver tip. When I went to the junkyard for the trailing arm, I watched them remove it from the car, and I got a look at what this distance should be. It was obviously much bigger. I ended up getting a replacement frame through eBay.

Here's some side-by-side comparisons. The replacement (black) frame is taller, because the curvature has not been flattened like mine was:


Likewise, the old frame is wider due to being flattened:


Here you can see how much the arm was bent. The left side half-shaft is straight from the diff to the hub, the right side is not:


The above pic also let's you see how a blow to the trailing arm can flatten the subframe. Imagine grabbing a miniature version with both hands at the ends, and using your thumbs to press in the middle. That's essentially what happened when I hit the curb.

Here's what the gap from the tab to the body should look like - more than the width of 2 screwdriver tips:


Here's some shots of the replacement subframe going back in, just for fun:

Erwin 89 750iL Lowered (a little)

Engine / Driveline Wolf chips 19 lb, 4-hole (Design 3) fuel injectors PowerFlow Intake Air Filters Royal Purple 20W-50 Custom Cold Air Boxes 3.64 LSD w/Royal Purple gear lube Royal Purple trans fluid Interior Phone removed, replaced with cut-to-length dash wood trim on hinge E38 Shifter Knob, Console Plate, and Boot M-Tech 2 M-technic Steering Wheel - air bag deleted E38 Self-Dimming Mirror Audio BMW Business CD Player "CD43" Head Unit Refurbished factory amp w/equalizer Bass blockers (300hz/4ohm) on stock front kick panel speakers Rear deck speakers: Alpine SPS-13C2 5.25" 2 way 175 Watt with bass blockers Subwoofers: 2 JBL GTO804 8" 4-ohm subs Subwoofer install: custom sealed enclosure mounted behind ski bag opening Subwoofer amp: Alpine MRP-M450 400w MONO CD changer relocated to driver's door bottom pocket actuated by bio- mechanical arm controlled by semi-intelligent nut behind the wheel Suspension H&R Lowering Springs (1/2 coil removed from fronts) Koni adjustable front shocks Stock rear shocks (self leveling) Racing Dynamics Stress Bar Stock front sway bar Dinan rear sway bar - 21mm M5 aluminum lower control arms Front tires: 245-40-18 Goodyear Eagle F1 GS-D3 on 8.5" EuroTech rims Rear tires: 275-40-18 Michelin Pilot Sport PS1 on 9.5" EuroTech rims Exterior 25% Side tint 5% Rear tint BMW Mud flaps - rears trimmed to tire width Rear fender lips rolled Smoked side markers (after pic taken) Euro Smiley Headlights (after pic taken) Zymol wax Way too many paint chips touched up Brakes Front Rotors: 850CSi, 324 X 30 mm, cross-drilled and slotted Rear Rotors: stock size, cross-drilled and slotted Pads: Hawk Performance Ceramic (may switch to HPS) Stainless steel lines Racing Blue brake fluid

• Bent trailing arm? Check your subframe (pic) - erwin 2008-05-13 23:16:05 (181 views)
  • Re: Bent trailing arm? Check your subframe - my406cid 2008-05-15 10:49:32 (40 views)
    • Which job in particular? - erwin 2008-05-15 20:07:07 (45 views)
  • Thanks for sharing this rather difficult fix - Patrick C 88 750 160K 2008-05-14 23:53:05 (42 views)
    • Repairs can snowball if you let them - where to draw the line? (url) - erwin 2008-05-15 11:18:19 (96 views)
      • My wife would find other things for me to do so I would be away again ;-( (nt) - rv8flyboy 2008-05-15 12:06:21 (39 views)
  • Yes, another photo goof (pic) - erwin 2008-05-14 00:26:21 (112 views)
  • What's wrong with this picture? (pic) - erwin 2008-05-13 23:29:06 (114 views)
    • Great work. (nt) - alv12 2008-05-30 00:44:55 (21 views)
    • You can always cut the bolts into pieces. Dremel is you friend ;-) (nt) - Johan750 2008-05-14 11:03:34 (42 views)