Tools/torque specs for rear shock replacement

[narhay]

I'm going to be attempting to change the rear shock mounts (RSM) and rear shocks on my 1998 Z3 2.8i. I have a few hand tools and a lot of bicycle-specific tools, but I was going to buy some new car-specific tools for the job. I figure I spend some $ on tools and save the $150 I was quoted to replace them. Does anyone know what the bolt torques should be?

- Torque wrench. What torque rating am I looking for here to attach the RSM and the shock to the RSM?
- Jack stands
- Wheel blocks/chocks
- Sockets (sizes?)

Anything else I am missing/flaws in my plan? I was going to use my scissor jack to put the car on the jack stands and use the scissor jack to lift the lower mounting point/bolt for the shock up to the RSM.

- - - Updated - - -

Found some info online.

17 Ft-Lbs
204 In-Lbs
23.05 N-m
Connects: Damper Mounting Plate To Body
Note: REAR Upper Mount Nuts


74 Ft-Lbs
888 In-Lbs
100.33 N-m
Connects: Damper/Shock Absorber To Trailing Arm
Note: REAR Lower Mounting Bolt


10 Ft-Lbs
120 In-Lbs
13.56 N-m
Connects: Damper/Shock Absorber To Damper Mounting Plate
Note: REAR Damper Shaft Nut

Seems like all the mounting points. Am I missing something? Looks like I'll need the larger and smaller range torque wrench to do this job and others.

[gmushial]

Maybe I'm misremembering, but I think before you torque the bottom bolts, you want the car with the suspension loaded - I've always done Z shocks with the rear wheels on ramps - that way it's always safe (no jack stands to fall over - the concern here is that you're going to be torqueing over 80ftlb to get the old bolts loose and 80 to put them back on - if that force is upward no problem, but if rear or forward, then one might just have a car come down on you :-( x100), and the suspension is already loaded, so nothing special to do w/re such.

[Vintage42]

... I think before you torque the bottom bolts, you want the car with the suspension loaded...

Yes, that is the instruction in the Bentley Manual: "Tighten the lower bolt to its final torque once the car is on the ground... in normal loaded position." For the right shock, it helps if the spare tire is not in the carrier. Otherwise it is hard to get a big torque wrench on the bolt, there is little room to turn it, and hard to apply any muscle to it. The 74 ft-lbs feels like it will pull the bolt out of the trailing arm, and I prefer 65 ft-lbs.
For the OP, some shocks have bolt bushings that are centered and some are not. If the bushing is not centered, the larger space goes on the trailing arm side, not the bolt head side.

[ptimko]

Does anyone know why they suggest torquing the lower bolt while the suspension is loaded?

Paul

[BenFenner]

When the lower bolt is torqued down, it clamps the innner metal sleeve, preventing movement of this sleeve. The outer bushing sleeve is also locked in place, being pressed into the lower shock hole. This means that any rotation that bushing encounters will take place in the rubber bushing itself, as the rubber is bonded to both the inner and outer metal sleeves of the bushing.
So, if you're following along, the rubber will twist one way when the suspension compresses, and twist the other way when the suspension extends. To try to make sure the bushing doesn't twist too far in one direction or the other, and to limit the built-in suspension bind, it is recommended to tighten down that bushing while the car is loaded (suspension at the middle of travel). This allows the same twisting of the rubber in either direction (during compression and extension).
If you tighten the bushing at full droop, the bushing will twist in one direction when the car is loaded, and then twist even more in that same direction when encountering a bump in the road. The life of the bushing will suffer, and the bind you experience on compression will be greater.

[rf900rkw]

Suspension components swing in an arc. This puts a twist in the rubber bushings. If you torque at full droop, you lock the bushing sleeve in this position and the rubber will be under a constant torsional twist; a shear load. Premature failure is the result.

[gmushial]

And until the rubber does fail, you're building a bias into the suspension, ie, whereas a normal suspension is homeostatic towards its loaded, at rest position, with bushing locked into the full drop position, with the torque now built into / "trapped" in the bushing, you'd have a (piece of the) suspension constantly fighting to return to the full drop position... the amount of force (until it shears) in the rubber can be nontrivial, resulting in a "peculiar" behaving suspension.

[BenFenner]

The above is one type of "suspension bind" or part of a "binding suspension" and was included in my explanation above.

[BimmerBreaker]

A local Z3 member (and forum member esses) reports a slight "loose" or "wandering" feeling in his rear suspension, particularly on highway on/offramps over bumps. All the rubber bushings and suspension components are new but it still exhibits this problem. I'm wondering if it could it be related to the possibility that the bushings were maybe torqued in the unloaded position? I imagine whoever installed them did it right, but what is the possibility that IF the bushings were installed unloaded, it would cause symptoms as described above?

[Vintage42]

A local Z3 member (and forum member esses) reports a slight "loose" or "wandering" feeling in his rear suspension, particularly on highway on/offramps over bumps. All the rubber bushings and suspension components are new but it still exhibits this problem. I'm wondering if it could it be related to the possibility that the bushings were maybe torqued in the unloaded position?... IF the bushings were installed unloaded, it would cause symptoms as described above?

I don't see how the thin little shock bushing rubber isolators could have any effect on the handling of the rear suspension.
I don't even know if tightening when loaded on the ground is for the benefit of the rubber bushing isolators. I had thought it was for proper stress on the bolts and their threads in the the trailing arms.
But my car does have the symptoms as described above. Especially when a sharp S curve has a high rise in the middle. I enter steering one way, then with the suspension unloaded, I steer the other way and land compressing the suspension. I can feel the car move to the other side of the suspension as it accepts the new direction.
I think this is due to the soft stock rubber rear subframe bushings allowing sideways movement in the rear suspension.

[esses]

I don't see how the thin little shock bushing rubber isolators could have any effect on the handling of the rear suspension.
I don't even know if tightening when loaded on the ground is for the benefit of the rubber bushing isolators. I had thought it was for proper stress on the bolts and their threads in the the trailing arms.
But my car does have the symptoms as described above. Especially when a sharp S curve has a high rise in the middle. I enter steering one way, then with the suspension unloaded, I steer the other way and land compressing the suspension. I can feel the car move to the other side of the suspension as it accepts the new direction.
I think this is due to the soft stock rubber rear subframe bushings allowing sideways movement in the rear suspension.

That's definitely one thing I haven't looked at. My IE Subframe bushings have about 35k miles on them. It's possible something went wrong there.... I first focused on new suspension.. that wasn't it. I looked at the diff mount. Looks good. I'm considering rear swaybar link/mounts. I hadn't considered subframe bushings.