Normal for DeDion to contact chassis rails?

[KnifeySpoony]

Another build question on my 420R. The rear suspension is completely assembled now. Is it normal for the DeDion tube to contact the angled chassis rails (the ones that run parallel and behind the A frame) when in full droop? I would have thought the dampers would limit the travel, but when resting the car on jackstands on the chassis (ie suspension unloaded), the tube droops and contacts the chassis. Seems like a bad setup...

[Croc]

Never had that happen on my cars.  I agree with you that something sounds wrong.  

[sf4018]

I have about a 1/2" gap between bottom of dedion tube and chassis frame when on stands. Maybe send some pics?

[JohnCh]

Pics will help.  Also, paging @Pokey to the thread.  He was very meticulous in his recent build and may be able to comment on the amount of clearance or any installation issues that could potentially minimize that gap.

 

-John

[Pokey]

I can do like sf4018 and jack up the rear to see what clearances look like now, but otherwise I'm not going to be much help.  I assembled the rear suspension with the DeDeon supported, leaving roughly a one inch gap in the area where I think KnifeySpoony has contact.

 

@KnifeySpoony, suggest adding a photo or two loaded and unloaded so those of us with the same or similar car can compare.

 

 

[yogi]

Here's what mine looks like unloaded. It's close, but not touching. This is a new build but it's spent a week or two on its wheels.

 

 

[KnifeySpoony]

Ok here are some pics. It's hitting on the right side of the big triangular thing that hangs off the bottom of the dedion tube. Left side is clear. You can see in the pics. You can also see that looking at each end of the dedion (near the ears), where it hangs over the side chassis rails, the clearance is about equal. This suggests that the right side is not just hanging lower, which was my initial thought. I thought maybe the right sided damper was too long, but this doesn't seem to be the case. It almost seems like the diagonal chassis tube is too high or something.

[JohnCh]

If I understand you description and the photos, one of the downward facing rectangular section's sloping sides hits the adjacent tube, but the other does not, yet the De Dion tube is equidistant above the chassis on either end.  Is that correct?  I am not familiar with the De Dion, so am probably way off here, but is it possible that the De Dion tube isn't centered within the chassis? 

 

-John

[KnifeySpoony]

Yes indeed that does seem to be the case. The dedion is centered via the Aframe - there are spacer washers used to get the dedion ends equidistant from the side chassis rails, which was done (to a closer tolerance than the manual specs). I could shift some washers around to try to center it within those diagonal members instead of centering it on the side rails. However, there's only about 3mm clearance on the good side, so the gap would be incredibly small; I can't see how it still wouldn't be likely to hit with dynamic movement involved.

[sf4018]

Long shot but do the top and bottom of the dampers have the spacers like in the pic below between the bolt and damper hole?

[yogi]

46 minutes ago, KnifeySpoony said:

Yes indeed that does seem to be the case. The dedion is centered via the Aframe - there are spacer washers used to get the dedion ends equidistant from the side chassis rails, which was done (to a closer tolerance than the manual specs). I could shift some washers around to try to center it within those diagonal members instead of centering it on the side rails. However, there's only about 3mm clearance on the good side, so the gap would be incredibly small; I can't see how it still wouldn't be likely to hit with dynamic movement involved.

 

The gap between the outer frame rail and your tube look fairly close to mine ± a few mm, perhaps it is just a bit of centering. I haven't found the frame to be very precise overall so I'd think a mm here or there is within tolerance. Once loaded the gap will of course increase (~1–1.5"), so unless you're going airborne on a regular basis I wouldn't think it'd be an issue. Then again, I'm new to this whole 7 thing.

[KnifeySpoony]

I have spacer bushes in the top damper holes but they look different. 

 

I have an email off to Caterham to see what they say. I just measured by dedion centering based on the side longitudinal rails (as the build manual indicates), and i am within .5mm left to right. So some misalignment elsewhere is causing this it seems.

[sf4018]

Those spacers were missing from the bags I got in the original shipment, I installed without them not knowing I needed them as the build manual doesn’t show them...here’s the page of the build manual with no spacer, and a photo of the bottom of the damper with the spacers...the top may be different.

 

[JohnCh]

That looks like a spherical mount vs. a rubber bush mount shown in the manual.  Is that a difference in the various Sport/Track/Race suspension options?

 

-John

[yogi]

Yeah that looks like the race spec damper: https://caterhamparts.co.uk/dampers/2670-rear-spring-damper-race-threaded.html 

[Pokey]

@KnifeySpoony, just asking because it is something I might have done and we are spitballing, but did you use the upper or lower radius arm mount point on the chassis?  If there is an issue here it may not be with the DeDeon being too low but too far back, and I'm not sure if Caterham uses the same radius arm for the S and R.

[KnifeySpoony]

I have the watts linkage, so the front watts link bar goes in the upper hole.  

[sf4018]

Maybe try loosening the top and bottom bolts of the dampers a couple of turns and push up the dedion and see if there’s any play. Can’t imagine the rear subframe is bent up, that would have to be some major force to do that.

[Pokey]

@KnifeySpoony, just asking because it is something I might have done and we are spitballing, but did you use the upper or lower radius arm mount point on the chassis?  If there is an issue here it may not be with the DeDeon being too low but too far back, and I'm not sure if Caterham uses the same radius arm for the S and R.

 

I don't have the Watts.  Does it have forward/aft adjustability such that you can move the DeDeon forward to create clearance?

 

[KnifeySpoony]

Yes i could shift the watts linkage, but that would just tilt the de Dion fore or aft (since it will rotate about the connection to the a frame). Tilting it forward would also bring it down which would worsen clearance. Tilting it back raises it but also pushes it back into the narrower "v" of the chassis rails.