Bushing pre-load question - reassembling rear suspension

[Casa de Mesa]

I'm getting ready to reassemble my rear suspension. I opted to put in the subframe first, then bolt everything to it piece-by-piece.

My question is, where there are rubber isolated bushings in places like inner control arms pivot points, can I "fake" the ride height by jacking up the unladen suspension to the point of my ride height and torquing the pivot point down? See below pics, I circled the lowers in the one pic because of the adjustable TMS arms, but the uppers are even trickier to reach while on the ground.

My possibly flawed logic: I know my axle center to fender arch measurement, why can't I just "set the ride height" without springs in the rear, torque it down now and move on with the rest of reassembly? I would think the forces that you're trying to eliminate are the twisting forces on the suspension bushing that is torqued at full droop, but spends its life in a much different spot. I would not think that it's a weight-on-bushing pre-load you're trying to avoid, but locking that bushing down in a different place than the control arm typically sits.


Here is how the cars sits right now:

[Ramps]

I think your logic is sound, this is exactly what I was planning to do when i do this job next year. I’d love to see more opinions from others who have done it.

[duracellttu]

I set the rear end down on ramps before torquing down the inner control arm and camber arm bolts.

[dilmorecg]

I have not done this on my e46 but have on my previous 135i front control arms. I did what you are suggesting...jack up the hub to where it sits normally and torque down. You are doing exactly the same thing as setting it down and torquing it in terms of bushing positioning.

You just don't want the bushing to be twisted as its normal position or it will wear way faster.

[SteelGreyM]

You will need an alignment after this anyways. Get as close as you can to ride height when torquing and take your car to the alignment shop right after. be sure to mention it to them and you should be alright

[Casa de Mesa]

Thanks for all the great replies. I think I will go forward with my plan - jack the suspension up to ride height, torque it down, install diff, install springs, put car on ground and align it.

Thanks!

[oceansize]

Interesting approach. I completed my sub-frame bushing refresh a few weeks ago and never really considered not doing all the work on the ground. I had a three dollies from HF that I could wheel the unit around in and do all the work off the car. Out of curiosity what made you take this approach?

I went with the monoballs for the ARCAs and RTABs to eliminate the preload crap.

[Casa de Mesa]

Interesting approach. I completed my sub-frame bushing refresh a few weeks ago and never really considered not doing all the work on the ground. I had a three dollies from HF that I could wheel the unit around in and do all the work off the car. Out of curiosity what made you take this approach?

I went with the monoballs for the ARCAs and RTABs to eliminate the preload crap.

This is the first time I've gone this far into the rear suspension of an M3. I dropped the entire rear suspension as a unit. When looking at the subframe bolts as I took it out, then realizing I was going to have to align about 150 pounds of stuff to those bolts when reinstalling, I wanted to see how the subframe aligned to the chassis without a ton of weight hanging off of it. Did it have any movement/play side to side, did I need to square it to the chassis (the front right bushing hole is elongated, as you know, so I wasn't totally sure), what did the clearances look like, etc. I just figured I could check each piece for fitment one-by-one while bolting everything up.

I too went to a completely solid and/or monoball setup. The only rubber bushing in the suspension arms are the ones I circles/highlighted in my original post. I replaced the rubber bushings in the uppers with a Turner monoball.

I know NVH will go up, but I don't care.

[Rich022]

Yes that method will work. Also do the same for the rear sway bar and while you're there and everything is torqued down, I would mark every bolt with a white paint pen. Sometimes things have a way of magically loosening. Another bit of advice, be careful and take your time getting the rear diff bolt in (the 150ish? ft/lb one). The diff is iron and the threads easily strip. Asks me how i know.

[Casa de Mesa]

Yes that method will work. Also do the same for the rear sway bar and while you're there and everything is torqued down, I would mark every bolt with a white paint pen. Sometimes things have a way of magically loosening. Another bit of advice, be careful and take your time getting the rear diff bolt in (the 150ish? ft/lb one). The diff is iron and the threads easily strip. Asks me how i know.

Thanks for the tip on the diff bolt. Yikes, that would suck.

I've marked every bolt I've torqued down so far like this one. Also, I did all the diff seals and marked every bolt on it too. Taking my time with this project so I was worried about forgetting to torque something down.

[nogoodname]

I just reinforced my subframe. On rebuild, I installed everything and then torqued it all in its “neutral” position. I’ve always done it like this and will continue it.

i used a deadman post while on the lift. Best I could do.

[eacmen]

I'm getting ready to reassemble my rear suspension. I opted to put in the subframe first, then bolt everything to it piece-by-piece.

My question is, where there are rubber isolated bushings in places like inner control arms pivot points, can I "fake" the ride height by jacking up the unladen suspension to the point of my ride height and torquing the pivot point down? See below pics, I circled the lowers in the one pic because of the adjustable TMS arms, but the uppers are even trickier to reach while on the ground.

My possibly flawed logic: I know my axle center to fender arch measurement, why can't I just "set the ride height" without springs in the rear, torque it down now and move on with the rest of reassembly? I would think the forces that you're trying to eliminate are the twisting forces on the suspension bushing that is torqued at full droop, but spends its life in a much different spot. I would not think that it's a weight-on-bushing pre-load you're trying to avoid, but locking that bushing down in a different place than the control arm typically sits.


Here is how the cars sits right now:

Checking in as I am going through this right now. Did this method work for you?

Is bushing preload also a concern for the outer ball joints? Or just the rubber bushings?

[Tbonem3]

Pre-load is only for rubber or something like the swaybar arm that, while metal, still bends (spring steel)

[George Hill]

That is how I have been doing it for years, never seen an issue. Ride height is ride height.

[Casa de Mesa]

Checking in as I am going through this right now. Did this method work for you?

Is bushing preload also a concern for the outer ball joints? Or just the rubber bushings?

Yep, it worked really well. I was overthinking it when I posted that. As George Hill said, ride height is ride height. I set mine without springs in place, super easy to do.