Rear spring replacement

For the M Powered Z3 derivatives

Moderator: Gazza

Post Reply
Thesurveyor
Joined: Tue 15 Oct, 2013 14:36
Posts: 119

  M roadster S50
Location: Kent

Rear spring replacement

Post by Thesurveyor » Thu 29 Sep, 2016 16:20

I have had the KW replacement suspension fitted to the M, and while all seemed well at first the new rear set up is knocking and making a real racket. The garage that fitted them have been good but they put it down to a lack of a top spring pad in the suspension kit (purpose made for my car!). They tried a gasket above the spring but its still bad. I did not get them to lower the ride height so that it is still standard and the front stainless struts are lovely. I still have the old rear springs and since I am going on a road trip next week...........they are going back on.

OK that was the background. The old springs have three pieces of rubber making up the pads. The bottom one is still on the car, the top one has the bump stop bit on it but what is the third? Anyone know? its a ring shape made of rubber the same diameter as the top of the upper pad and it has a sort of bulge that looks like its designed to hold the end of the coil spring. Its not shown on the real OEM diagram for my car so I'm puzzled as to where it was fitted?


DOH!!! A little more Googling revealed that my random spring pad is from the front not the rear! Who knew?
Anyway, has anyone else suffered form knocking noises with KW suspension? - any cures?

siwilson
Joined: Fri 19 Jun, 2009 10:54
Posts: 782

  M roadster S54
Location: Horley

Re: Rear spring replacement

Post by siwilson » Thu 29 Sep, 2016 21:16

No knocking on mine.

Do you have the short spring and the adjuster on the top like this? you can see the old upper spring pad now ion the bottom and no spring pad on the top. i have had this for a while and no issues at all.

Image
2001 M roadster S54 Laguna Seca Blue

Thesurveyor
Joined: Tue 15 Oct, 2013 14:36
Posts: 119

  M roadster S50
Location: Kent

Re: Rear spring replacement

Post by Thesurveyor » Thu 29 Sep, 2016 21:57

Thanks for the picture. It looks like yours has been lowered since there is more thread above the screw adjuster than I have. I don't know if it matters but the instructions that came with mine said to use the original bottom pad only. No bump stop apparently required.
I'm just confused. Your coils seem to be touching each other and I wondered if that rubbing action was causing the noise? However if you don't have any noise maybe that's not it at all. Still, I'm not using this set up to govern ride height so I've nothing to lose by changing back except perhaps the noise.

siwilson
Joined: Fri 19 Jun, 2009 10:54
Posts: 782

  M roadster S54
Location: Horley

Re: Rear spring replacement

Post by siwilson » Fri 30 Sep, 2016 12:59

Thesurveyor wrote:Thanks for the picture. It looks like yours has been lowered since there is more thread above the screw adjuster than I have. I don't know if it matters but the instructions that came with mine said to use the original bottom pad only. No bump stop apparently required.
I'm just confused. Your coils seem to be touching each other and I wondered if that rubbing action was causing the noise? However if you don't have any noise maybe that's not it at all. Still, I'm not using this set up to govern ride height so I've nothing to lose by changing back except perhaps the noise.
Mine is set about as high a ride height as you can get with the KW and this is still 20-25mm lower than stock. My instructions said to use the old upper pad on the bottom and not have a pad on the top. I have seen other people with the KW setup and theirs is the same as mine so this is the correct way. If you used the other pad then perhaps that is the issue. The pads can wear through and allow the spring to touch the mount which cant be good. You would also have no bump stop, which again would not be good.

The coils do bind when there is weight on. Even more when the car is on its wheels. I think in that picture I had lifted the rear axle to get the lower shock bolt in place.

You could swap to standard springs, but I don't think it will work out very well. The rear ride height will be quite a bit higher than the front inducing more rake than maybe good. The spring would also not be a good match to the shock. If you want to go down this route then I would dispense with the KW completely. The alternative would be to get some H&R or Eibach rear springs that are designed to lower without the adjuster. That way you could keep both original spring pads.
2001 M roadster S54 Laguna Seca Blue

Thesurveyor
Joined: Tue 15 Oct, 2013 14:36
Posts: 119

  M roadster S50
Location: Kent

Re: Rear spring replacement

Post by Thesurveyor » Fri 30 Sep, 2016 14:20

I hear what you say about the ride heights but mine really did not change after the install so hopefully putting the old ones back won't hike the back end up in the air.
My internet research indicates that so called "spring bind" is a significant problem with KW gear (wish Id known before) One possible cure (not really the right word) mooted is the use of short lengths of silicon tubing cut into a spiral and then bound around the coils that are rubbing/knocking. They will be the ones where the yellow paint has worn off! This can easily be done with the spring still in place so I'll try this first, then its new spring pads and back on with the old ones.
I really did not want adjustable suspension this much!

Thesurveyor
Joined: Tue 15 Oct, 2013 14:36
Posts: 119

  M roadster S50
Location: Kent

Re: Rear spring replacement

Post by Thesurveyor » Thu 06 Oct, 2016 08:08

For the sake of completeness and to help others that might find this thread in the future, I have now completely cured the knock from that back end of the car. I did this by.......putting the old springs back on. I can confirm that short lengths of 12mm aquarium pipe cut into a spiral and wrapped around the coils of the KW spring will stop the spring bind knocking and twanging but only at the expense of handling. The rear end felt very "floaty" and since this was obviously because the rubber was trapped between the coils I also thought it would quite quickly wear out/cut through. I took some out (used 50cm a side to begin with) from the centre coils leaving it at the top and bottom and that helped the handling and feel but reminded me of the harshness of the KW set up. A little (acceptable?) spring bind knock also crept back in.
Now I could probably have had the wheels on and off a dozen times more to find the "Goldilocks" amount and location of tube but I was fed up by now.
The cool looking stainless steel front strut is working well, no noise or hard ride, but other than being new the new springs were nothing but a pain. It is perhaps worth noting that I have to drive over a short rough track to get to my garage so cosmetically lowering the car was never an option for me, and this is not "race car" either.
Then the mechanic that looks after the car told me he ran KW front struts and rear shocks with standard rear springs on his hill climbing Z3 1.8 and that was it. I'd never done it before but the day before taking the car to Spain, I jacked it up and swapped the spings out.(The yellow KW springs are much, much easier to compress by hand than the standard ones.) The back end has risen a little, but it can only be the same as before this experiment begun, ie original BMW designed ride height.
So it's done, I'm in Spain now and the Z3M is behaving itself well. I will post further details of our road trip with pictures later.

Thesurveyor
Joined: Tue 15 Oct, 2013 14:36
Posts: 119

  M roadster S50
Location: Kent

Re: Rear spring replacement

Post by Thesurveyor » Fri 21 Oct, 2016 19:12

So, this is what my lovely (driven just 500 miles at this point) new spring looked like just before going off to Spain. Quite a marked difference to the KW picture posted earlier. No bump stop at the bottom and far less of the thread visible on the top adjuster. You would think that this would make my car lower but this was not the case.
The spring is not compressed at all in this picture, when it is the coils hit each other and that is why the plastic tube was applied. The other messy stuff is grease applied to try and silence the spring bind, but it didn't work. This tube arrangement works well enough but feels strange if you put too much on the coils.
I've just downloaded my pictures from my 1350 mile road trip on the original springs and will post them separately.

Image

Post Reply

Who is online

Users browsing this forum: No registered users and 2 guests