Torque for shocks

[4380r]

What is the correct torque for the rear damper mounting bolts?

[EuropaTC]

On the TC;

Upper bolts, 40 ft/lbs
Lower bolts, 55 ft/lbs (which includes the lower link to the transmission as well as dampers)

I've included the relevant pdf pages for torque settings in case you guys work in these new-fangled kilo-thingies.....   

Brian

[Grumblebuns]

I'm trying to figure out how to torque the lower link to transmission bolt and nut. You can't get a socket on either end so I'm thinking of using a crowsfoot on the nut. Anyone have any other ideas.

Joji Tokumoto
Fallbrook, Ca   

[EuropaTC]

I've got to be honest Joji, I can't ever recall using a torque wrench on the suspension apart from one time I did the front trunnions to get a feel for what it was supposed to be. I do use the settings when I'm assembling an engine & gearbox (things that whizz around and can explode on me    ) but for everything else I just go by feel. 

The one you've mentioned is difficult to get at but I'm sure you could get a reading with an extension and a crowsfoot on the nut. I wouldn't have a clue as to how accurate it was though, so I'd just go with new nylocs, weight the car to get the suspension in the right plane and then "tight" would do for me 

Brian

[BDA]

A torque wrench is required for the front suspension because the bushing acts as part of the spring (weird, isn't it?). The front suspension is supposed to be torqued at ride height.

[Roger]

A torque wrench is required for the front suspension because the bushing acts as part of the spring (weird, isn't it?). The front suspension is supposed to be torqued at ride height.

True, but what has the torque on the nut got to do with the spring rate of the bushes? Tight is tight.

[BDA]

I really don't know why we are supposed to do it. This is one of those things I pretty much take on faith. It is different from every other car I've worked on and spelled out specifically in the workshop manual so I figure it must have some importance!

Now with polyurethane bushings for the front suspension, it seems to make less sense (unless polyurethane bushings defeat some important benefit of the original design - seems HIGHLY unlikely).

[Grumblebuns]

I really don't know why we are supposed to do it. This is one of those things I pretty much take on faith. It is different from every other car I've worked on and spelled out specifically in the workshop manual so I figure it must have some importance!

Now with polyurethane bushings for the front suspension, it seems to make less sense (unless polyurethane bushings defeat some important benefit of the original design - seems HIGHLY unlikely).

If my understanding of the front suspension bushings is correct, the rubber part is bonded to the inner and outer sleeves. Once pressed into the control arms the bushing is locked into place and should not move within the outer sleeve of the control arm. With the car at normal ride height and the bushings at their relaxed state, the control arm bolts are torqued down so the inner bushing sleeve is now locked. Any up and down movement of the suspension causes the rubber bushing to twist and flex as part of the overall suspension design. As Roger states, tight is tight. As long as the tightness of the nut and bolt keeps the inner sleeve of the bushing from rotating, the suspension is working as design. But then I'm probably wrong on all of this.

I have never installed PU bushings and I don't understand how PU bushings work.

I finished tightening up the lower links yesterday. I could not get a crowsfoot on either inboard nut. On the left hand side, I could get a socket on the bolt head so used that to torque the lower link. On the right hand side, had to go by "feel". One of these days, I'll have to fab a special tool for this application.

Joji Tokumoto
Fallbrook, Ca

 

[EuropaTC]

I think your explanation & understanding of how these bushes work is spot on Joji, and I've assumed front & rear have the same operation.

Personally I think it has less to do with a contribution to the suspension springing than preserving the life of the bushes. If you think about it although twisting a rubber layer will require some force, compared with the 100lb (or whatever rated) metal spring and damper resistance above it, it's going to be relatively minor.

From what I've seen of the plastic bushes, they seem to have the center metal tube as a tight, but not bonded fit in the nylon/polythene/whatever.  So in theory I'd guess they make zero contribution to the springing, but have the advantage that you could possibly tighten them in any position and they'd just slip as the suspension moved ?

Brian

[BDA]

I think you're right. As I thought about it more, it may have something to do with the stress on the rubber in the bushing. If you tighten the bolt at full droop, when it goes into full bump, it may put too much stress on the rubber and reduce the life of the bushings, but at right height, the total angular displacement is reduced.

Tight is tight, of course. Often torque values are specified to give some people guide lines, not for actual requirements. I'm on a Mercedes Benz forum and people want to know what the torque value is for spark plugs!!

Ok, I've evolved. 

As I was typing this, EuropaTC posted his comments. We are in agreement! 

[jbcollier]

Yes:

Rubber boned bushings with the suspension loaded at working height so there is no undue stress due to excessive twisting.

PU bushings are not bonded and can be tightened up at any position.