Rear Suspension Rebuild
Aug 8, 2010
The rear suspension has been torn down and I've cleaned and painted most of the parts. Now it's time to put 'em all back together and bolt 'em back to the car.
I dunno, I've heard people say this is an "easy" project. "Yeah, the whole thing just drops right out and you can do it all right there. No problem." Maybe. The "whole thing" definitely "drops right out," and that was fairly easy. But to tear it all apart, clean, and rebuild took quite a while. What was supposed to be a winter project in the basement dragged on through the early summer.
Anyway, let's put it all back together.
Subframe mounts weren't terribly expensive, so I just bought whole new ones. There's no way to replace their bushings anyway; repair is by replacement. Here, I've put in red urethane inserts meant to stiffen the mounts by filling the gaps in their bushings.
The old bolts were well rusted, presumably sped-on by different metals touching. Easy replacement from Lowes and bolt-on install.
Rebuilding the half-shaft CV joints is a little project of its own. I'll link again to this post at my2002tii, which covers it well. Here's some high-points and a few things to note:
With the half-shafts themselves newly-painted with POR-15, I bought a CV joint replacement kit. It comes with new rubber boots, clamps, and moly grease. First step is to put the new boot on the shaft, then place this washer over the splines.
Now for the dirty part. Squeeze moly grease into the bearings, with lots of paper towels on hand.
Tap the CV joint onto the splines of the shaft and fit the circlip in place. These bearings are over-full, as some grease squeezed out when I placed the cover on.
The cover is press-fit over the end of the CV joint with some gentle tapping. The next step is frustrating (and greasy; I didn't get pictures) and that is to get the rubber boot in place on the CV joint. I used a flathead screwdriver to stretch it over the lip. After that, all that's left is to put the clamps in place to hold the boot on. And to do the whole process three more times. . . .
The parts pile slowly gets smaller.
Moving on, let's put new bearings in the trailing arms. Here's the order that parts will go in. A seal on either side, two bearings, with a central cylindrical spacer.
According to the Haynes Manual and this diagram provided by BMW 2002 FAQ user c.d.iesel, the inboard and outboard bearings must be spaced 64 mm apart. Most pictures and diagrams I've found show a cylindrical spacer like above along with a circular shim of whatever thickness is needed to bring the spacing to 64 mm. Well, when I took everything apart, there was no shim. That worried me, so I dry assembled the bearings here and measured their spacing. Turns out that my cylindrical spacer by itself gives a 64 mm spacing, so no shim was needed.
After packing the bearings with new grease, I used a bearing/race tapper to push in the bearing and then the dustcap. It takes some pounding, but they go in.
With one bearing and seal in place, I flipped the trailing arm over and started the other side. The spacer cylinder goes in, and grease is packed around it. The Haynes Manual says to put 35 grams of grease in, but damned if I'm measuring out grease by weight. I packed in as much as I could, figuring there's plenty of air bubbles in there for expansion when everything heats up under use. If I end up with brake drums full of grease later on, I'll know I put too much in.
Here's the bearing/race setter. It has heads of various diameters, and you can choose the head that matches the diameter of the bearings you're tapping into place. I've heard of people using a socket instead, but this was cheap and worked perfectly. In the background is the white plastic bearing-filler that hooks up to a grease gun to quickly and evenly pack grease into the bearings prior to inserting them into the trailing arm.
With the bearings in place, the stub axle slides through them with some gentle taps of the rubber mallet.
The brake backing plate gets bolted on. Note that left and right are different: the parking brake hole faces the front of the car. Then the hub slides onto the stub axle splines. It's held on by that large castelated "Jesus nut", so called because of the 200+ ft/lbs of torque it takes and the fact that it holds the wheel on the car. I'll torque it down later when the transmission and parking brake can hold everything still. Until then, I put a zip-tie in place to remind me that it hasn't been torqued.
After fitting the trailing arms with new urethane bushings (which press in easily because they're spilt down the middle), it's time to fit the trailing arms onto the subframe itself. It took some serious rubber mallet banging to get them on, but they fit. If you're going to weld the trailing arms to box them like tii ones, a jig would definitely be required. Otherwise the heat will deform them too much to refit.
Mounting Ireland Engineering's rear swaybar is notoriously hard, and here's why. The urethane bushings that it comes with are just slightly too large to fit their mount. Some people trim them, or use sandpaper to grind the flat side down a hair. I just used brute force, which was only really feasible because the whole thing's on the floor and not under the car. I used a C-clamp to pull the mount into place and a drift to manhandle the holes into position while I threaded the first screw. It was hard work.
Notice how much the urethane bushing bulges once mounted. Of course I forgot to grease the bushings before mounting them, but there's no way in hell I'm taking them off and doing this again. So the rear end might squeak a little. Whatever.
This cold steel wedge thingie worked great to spread the Aluminum mount just enough to let it slide along the swaybar. A flathead screwdriver would work, too.
Bolted up, now it's time for the other side.
I busted out a ruler and measured the amount of overhang to make sure the swaybar mount on this side was at the same position on the bar as the other side's mount. By adjusting the position of the mount, the bar's length — and thus stiffness, shorter is stiffer — is highly customizable.
The whole thing's almost too heavy and awkward for one person to move, so I moved it outside, closer to the car. I plopped the differential on but left its four bolts loose. There's a little fore-aft play that'll allow the diff's input shaft to meet the driveshaft flatly. I'll tighten the diff down on the frame after the whole thing's back on the car.
The half-shafts go in. 24 bolts in all.
The only problem with reattaching the CV joints was the boot clamps getting in the way. But loosening and spinning them worked. New nyloc nuts were cheaply sourced from Lowes.
No more big pieces to attach means all the banging and clanking is done. So now's a good time to put the delicate brake cylinders and hard brake lines back on. I should probably replace all these, but, eh, they've been working fine.
Before the whole assembly can be raised back onto the car, the differential hanger needs to be mounted. It has two rubber bushings, which I pulled because they were cracked. After painting the hanger, I went to put new urethane bushings into it. Turns out the original rubber bushings had metal rings surrounding them, and they were still pressed into the hanger.
Jeff Ireland (from whom I bought the urethane bushings) suggested using a hacksaw to cut the metal rings. You could certainly use a press, but cutting the rings and banging and pulling on them a lot worked. Here's one, cut and torn, coming out.
Now that the new urethane bushings are in it, the diff hanger goes back on the car, with that bottom lip pointing rearward. (Yeah, I painted the whole underside of the car with POR-15. I bought a gallon of the stuff, so why not?)
Balancing the whole rear end assembly on a floor jack, up it goes. The subframe mounts bolt up, as do their front-pointing connections.
As it goes up, the new shocks need to be guided into place. They came with new bolts and bushings for mounting to their perches in the trunk.
Slight digression: each of the rear springs has an upper and lower spacer/pad. This pic shows both top and bottom spring pads, which are different. I found my old ones fit Ireland's springs perfectly. They'll want to pop off as you raise the rear end back onto the car. Quick trick to avoid that in the next caption. . . .
Three things to note here: 1) Ireland's rear springs are short enough that they won't mount both above and below until the car is lowered. 2) The trick to keeping the pads on the ends of the springs is plastic zip ties. I snipped off the extra length and left them there, but purists could snip them entirely and pull them out once the car's on the ground. 3) Make sure that notch in the bottom spring pad lines up with its corresponding hump on the spring's lower perch
Since the diff was still loosely bolted, a little shove pushed it up against the driveshaft. Four bolts with new nyloc nuts bolt 'em together, then it's time to tighten down the diff to the subframe and bolt it to the diff hanger out back.
I won't go over reconnecting the rear brakes or rebuilding the drums. I've covered some of it before, and while it's kind of a pain in the ass, it's also pretty straightforward.
But that's it! Pull out the jackstands, drop the jack, and it's done. Here's the new stance:
Stock suspension in the front and Ireland Stage 2 Sport springs with Bilstein Sport shocks in the rear. The change in the rear end's ride height with these new, shorter springs almost nil. I think that's because the old, original springs were tired and sagging. Plus, the back might drop a little as the springs settle in. Here's a picture, soon after it was dropped and prior to driving the car.
Something else observant readers might notice is that I didn't mention the exhaust. This whole process was predicated by disconnecting the exhaust at the downpipe up front. I just wasn't in the mood to put it back on, and the rear hanger was gone anyway, replaced by a wire clothes hanger. Besides, the car sounds pretty badass with no muffler.
And anyway, the most-pressing concern now obviously is to replace those stock, worn out front springs and shocks!