Rear damper piston/rod nut tightening question

[Bolin]

Hi all

When trasferring the mounting plate, washers and bumpstop/gaiter from an old rear damper to a new one, should the nut that holds these parts to the piston/rod be done up so that these bits are held firmly in place on the piston/rod?

The torque setting is 30nm, I don't have the necessary special socket but can tell that it is definitely more than 30nm of effort to tighten the nut down far enough to get the mounting etc to be held against the shoulder on the piston/rod and not be loose.

The photos in Haynes suggest that the nut should be further down the piston/rod than the point where 30nm is exceeded. Unfortunately I didn't look closely at the old one before dismantling (classic mistake, bah).

I am using a new genuine damper and nut.

Can anybody advise?

Thanks, Bolin.

[KWIL]

RAVE says fit bump stop and dust cover to damper, washer, upper mounting and washer to damper ensuring correct orientation of washer, fit new nut and tighten to 30Nm.

[Bolin]

Thanks Ken - the same as Haynes then.

The problem is that this leaves the piston rod able to move up and down the mounting when assembled, and the old one wasn't like this - unless it was rusted up solid when it shouldn't have been, but the only part that appeared to have rusted in place was the rubber bumpstop, and I cannot see the rest of it rusting solid due to the clearances and the forces in that area.

So perhaps the shoulder is at a different point on the new damper - but I would have to remove and dismantle the new one to check.

I decided to tighten the mounting etc using a standard flange nut and threadlock, rather than the special ovoidal nut which really didn't want to go on far at all without needing a lot of force (certainly no where near as far as shown by the thread sticking out in the Haynes photos). I don't think the new nuts are the problem, as I tried the old nut and it was the same.

By following the instructions, I am sure that the piston/rod would be able to move when going over bumps and produce a 'clonk' - it just seemed obvious that this shouldn't be loose.

[KWIL]

Is the new one an XPart Rover 75 spare part?

[rich17865]

I would make sure that it is tightened so that the piston does not move up and down in the mounting, as that is how my originals were when they were removed.

Just another point to note, I am pretty sure if memory serves me right, there is a metal insert in the mounting which will not allow you to crush the mounting anyway, the only problem I can see with over tightening the nut is stripped threads.

[T-Cut]

Originally Posted by Bolin

I decided to tighten the mounting etc using a standard flange nut and threadlock, rather than the special ovoidal nut which really didn't want to go on far at all without needing a lot of force

That's the root of the problem IMO. The 'ovoidal' nut is presumably a self-locking system, where part of the nut is compressed around the thread. It's seems clear that the nuts require more torque to run them along the thread than the torqued up setting. Wrong nuts for the job basically.

You did the right thing in swapping them to a better nut. A Nyloc type may have done better, but in any case the torque setting isn't that critical where the nut meets an abutment. You can't over-compress the rubber washers anyway.

TC

[Bolin]

Originally Posted by KWIL

Is the new one an XPart Rover 75 spare part?

Yes, a brand new genuine damper from Rimmers - but doesn't appear to be made by Delphi, who made the original fitted by the factory at build. It is unbranded and has visual differences.

So I was using new genuine damper and new genuine nut, but it was no where near holding the mounting tight with just 30nm applied.

Originally Posted by rich17865

I would make sure that it is tightened so that the piston does not move up and down in the mounting, as that is how my originals were when they were removed.

Ah, thank you, good My orginals were not loose, they could have been seized with rust but I doubt it as I reasoned above.

Originally Posted by rich17865

the only problem I can see with over tightening the nut is stripped threads.

Well, the new nut did start to damage to damage the thread. I then tried the old nut, but it needed such huge force that the allan key started rounding out in the centre of the piston/rod. So I cut it off with an angle grinder to avoid any more damage to the allen key hole, and used a die to recover the thread.

Originally Posted by T-Cut

That's the root of the problem IMO. The 'ovoidal' nut is presumably a self-locking system, where part of the nut is compressed around the thread. It's seems clear that the nuts require more torque to run them along the thread than the torqued up setting. Wrong nuts for the job basically.

More torque than advised by haynes, and with my experience of trying the old nut, more torque is needed than the allen key hole can take!

This is the nut in question, you can see the ovoid at the top:
http://www.rimmerbros.co.uk/Item--i-ERR597

Originally Posted by T-Cut

You did the right thing in swapping them to a better nut. A Nyloc type may have done better, but in any case the torque setting isn't that critical where the nut meets an abutment. You can't over-compress the rubber washers anyway.

Thanks, glad you agree with my approach.

Interestingly, when I did the other side (3 months ago as I did one side just before the car went off the road for 3 months), the damper came with a nyloc for a 17mm spanner, as opposed to the 15mm ovoidial nut that is on the parts list and on the old damper - so I used the nyloc, assuming there had been a change in specification required. I subsequently asked Rimmers about this, and they said the damper should not have come with a nut, and that I should have used the one in the parts list (same as original). The second damper (a replacement for a faulty new one, so probably from a different batch) did not come with a nut.

The main point is that if I used the 'correct' nut and the torque setting in Haynes (or just as tight as I could try before the allen key hole rounds) then the mounting would not abut against the shoulder, nor the rubbers be compressed at all, and would be totally loose.

But I don't think this problem could just be due to a difference in the position of the shoulder on the piston/rod as the photos in Haynes show an original damper but with more thread above the nut than I could get to show when using the 'correct' nut.

The only possibility I can now think of is that the new Genuine damper, made by somebody other than Delphi, isn't compatible with the ovoidial nut, whereas the original Delphi ones were - the new one appeared to have an ordinary-looking M10x1.25 thread, I haven't looked at the old one yet but cannot directly compare the two now without taking a damper off the car (which I'd rather not do).

All in all it is confusing but it looks like I have taken the right approach in getting the mounting tight on the piston/rod so hopefully I can leave it.