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MG MGF Technical - Tightening Lower Nuts on dampers ??

I fitted my four dampers with poly bushes to the car at the weekend no problems - all except, how the f*&@ do I torque the lower nuts to 45Nm ??

Looking at the workshop manual and Tims guide on Robs site - they all say that these have to be torqued with the car lowered. But I can't reach them :¬(

What would the effect be if I tightened them with the car raised ??

Colin

You torque up the bolts whilst the car is jacked and the wheel is still off.....

17mm socket and (I think) a 10mm on the other side. You may need a long extension to give yourself enough room to move.

I may have a pic somewhere.....
tim woolcott

Rover MGF Manual actually says that you should fit wheels etc, drop the car and THEN torque to 45Nm, which is a pain, but can actally be done if you have a long extension as Tim says. Even better, if you can get the car on a ramp.

You have to get the tracking reset anyway, so while it's up on the ramp, get the torque reset as well.

Tony
Tony

Just a thought - can the car be lowered down onto an axle stand positioned under the lower suspension arm? That way the suspension would be compressed as it would be with the road wheel in place, but with much better access to the lower damper bolt?
Rob Bell

Ahh, that sounds a good idea Rob !!

Tried the Ramp idea but would need to remove bumpers to get up them - so not too keen to do that.

As an aside, what is the reasoning behind needing the weight applied ??
Colin

As an aside, what is the reasoning behind needing the weight applied ??

As I see it the reason to apply weight to the suspension it in order to tighen the head bolt correctly ie squishing the bush on the head of the shock. I really can't see the need to lower the car to tighten the bottom bolt.....

Anyone else have any ideas....?
tim woolcott

Exactly, this is where I was coming from Tim.

Once I found that I couldn't reach the lower nuts - I jacked up the car and torqued them all with the wheel removed. Now, I'm quite happy to redo it all if there is a pressing reason - but couldn't figure one out myself :¬/

Question is, is it safe? And can I now go and get my tracking done?

Colin

If the bush is torqued up when the vehicle is not at its standard height, once the vehicle returns to the standard height the bush will be forced to twist. This means it is not operating as it was designed and will affect the performance and the durability, as it will always be trying to return to the position it was when it was made and subsequently putting unwanted loads into the suspension. I found when I changed my dampers that having the rear subframe on axle stands and using the trolley jack under the rear hub to compress the suspension until it was approx the correct height, measuring the centre of the hub to the wheel arch and torqued them up then. Not sure health and safety would agree but it worked for me!
R Baker

I think that the answer to that is the way that the bushes are compressed and distorted when placed under a load. A rubber bush will 'squish outward' when compressed. What this means is if the bolt is torqued whilst there is no load on the bush, it will be relatively over-torqued when the bush is under load because of that 'squish' factor...

Hope you are all impressed by my use of sophisticated engineering jargon! ;o) LOL

Since poly bushes don't distort quite so much, this is probably not quite so relevant as it is to rubber, but probably pays to do things 'by the book' :o)
Rob Bell

The reason for compressing the suspension - i assume would be this:

If you tighten the lower arm in the "drooped" position, the bush will be effectively locked in that position, so that when the car is lowerered back to the ground , and the suspension compresses, there will be approx 30 degrees (or whatever)of preload on the bush. When the suspension in further compressed during use, there will be a further shear force on the bush, which will inevitably lead to early failure.
Took me a while to work this out when replacing lower arm bushes on a parental Austin Maxi many years ago - Bush life was down to around 5000 miles before i sussed it..

Hope this makes sense

regards

mike

mike

I think that I prefer Richard's and Mike's explanations to mine! LOL

Nice one chaps :o)
Rob Bell

I was about to do the same....replace damper bushes.

Are we confusing damper bushes with lower arm bushes here?? Why do you need to reset the tracking for replacement of shock absorber bushes?? These should have no effect on suspension geometry.
Phil Stafford

Just replaced my damper bushes too and didn't (couldn't) tighten up the lower bolts when the car was down.

I understand that you probably put some torque on the bushes when you tighten them before you lower the car.

But first of all :
there is a little tube that you have to put inside the lower bush. If i remember correctly, that tube was a little longer or same lenght as the bush. So if you tighten the bolt you actually press on the tube and not on the bush so the torque should be very minimal.
Second :
you have to put grease between the damper and the bush and between the bush and that tube. If there would be some torque and the grease lowering the friction, couldn't it be that after some time and vibrations of driving the car, the bush would settle to a 'torque free' position ?

just my 2 cents...

I think from the moment you change something to the suspension (damper or lower arm bushes) it is advisable to chech the geometry, it can't hurt...and it is cheaper then replacing 2 front tyres some 2000km later.
Geert

To expand on Geert's comment and my own thinking:

I still have a problem with this theory..... Sounds quite convincing for the original rubber bushes but the new poly bushes have a stainless steel hollow spindle which will offer little or no rotational resistance when vertical load is applied. The bolt is acting as a pivot joint and should rotate.

So I think that when installing OE shocks and bushes torquing when loaded would be a good idea but for replacement poly bushes this really isn't going to make any difference.

There we are my tuppence worth too.

Tim
tim woolcott

I replaced my shock absorber bushes about two years ago AND I torqued them whilst on stands with the wheels off - so far nothing has dropped off nor has it thrown me int a wall or the Armco etc and it been round the Nürburgring a few times since.

Ted
Ted Newman

Tim

"but the new poly bushes have a stainless steel hollow spindle which will offer little or no rotational resistance when vertical load is applied. The bolt is acting as a pivot joint and should rotate."

Damn good point!!! I was assuming the spindle was bonded to the bush.

Mike

mike

Thank you all, gentlemen, for your erudite opinions.

I'm gonna go on the basis that the 'squishing' factor is reduced for poly bushes, and if Ted's has survived another trip to the Ring this year - then that's good enough for me :¬)

Time to go and get the geometry done.

Thanks again,
Col

Colin

This thread was discussed between 29/09/2003 and 30/09/2003

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