Centring the Dedion following diff swap

[CtrMint]

Hey All,
I am encountering difficulties with centring the Dedion on my 620R  after completing my diff change. In the process of swapping the diff, I removed the A-frame and roll bar, followed by the ears, hubs, and shafts as a single unit,   I intentionally left the Watts linkage and Radius arm untouched.  Once the diff install was complete I reverse the process to reinstall.

Upon reinstalling all components and conducting a thorough sanity check on the Dedion, I noticed a bias towards one side. I made sure to reinstall the A-Frame spacers in their original positions, and I've even experimented with various spacer combinations, but the lateral balance remains largely unaffected. I am contemplating whether the combination of the Radius arm, Watts linkage, and suspension struts might be restricting the Dedion's lateral movement.

Should I be doing the centring process without those attached?  If they are to blame, surely once reattached the offset will return... 🤔..

Any recommendations would be very much appreciated. 

Thank you

[CtrMint]

Started to figure this out, though maybe a Seven suspension expert can offer a view as to what’s happening.

My 620R was corner weighted, and so there is a difference in the spring platforms changing the droop in the strut when the chassis is support on axle stands.   If I lift the side which is lower by say placing a trolley jack under the brake disc, it takes up the slack and moves the Dedion laterally as well.  I guess there is some form on moment at play within the axle.  

I need to place the spacers as they came off, to fully test, but the above seems to the explanation as to why I’ve been struggling to centre the tube. 

[Geoff Brown]

I had the same struggle after refitting my BMW Diff. In the end I fitted the A Frame with the Watts Linkage disconnected.

When coming to refit the Watts Linkage there was a slight bias to one side. If I recall with my car it was the n/s.  It could have been the o/s but I had connected that side up first with ease.

I slackened off the n/s lower damper mount bolt to afford some 'give' in the system then with a jack & some grunting managed to align all the linkage attachments. Do not slacken off the lower damper mount bot too much as this will also cause problems when tightening which could result in a crossed thread.

As you have surmised this 'offset' is due to the damper platforms being adjusted creating an unequal dimension affecting the way the De dion sits.

Edited January 29 by Geoff Brown

[Gridgway]

I don't understand why spring platform adjustments affect droop.  Isn't droop just defined by the open length of the damper?

[paul richards]

5 hours ago, Gridgway said:

I don't understand why spring platform adjustments affect droop.  Isn't droop just defined by the open length of the damper?

That’s correct. 

[Gridgway]

On 28/01/2024 at 10:11, CtrMint said:

Started to figure this out, though maybe a Seven suspension expert can offer a view as to what’s happening.

My 620R was corner weighted, and so there is a difference in the spring platforms changing the droop in the strut when the chassis is support on axle stands.   If I lift the side which is lower by say placing a trolley jack under the brake disc, it takes up the slack and moves the Dedion laterally as well.  I guess there is some form on moment at play within the axle.  

I need to place the spacers as they came off, to fully test, but the above seems to the explanation as to why I’ve been struggling to centre the tube. 

This doesn't seem right to me.  If at full droop the DD tube is at different heights each end in relation to the chassis then that's a damper problem.  May not be a biggie, but not one I'd want on my car!  If the DD then moves laterally, then there is play in the system.  Either the A-frame is moving or the A-frame to DD mount has play.  Neither are correct and certainly not desirable.

[paul richards]

Lateral movement is controlled by the A frame. If there is lateral movement then something is wrong. Is there play in the bushes or insufficient spacing washers?