Would the REAL springs please step forward?!

[notakit]

I'm suspecting I have the wrong length rear coils. While building my own car very close to original 1960 specs and have been unable to get an acceptable answer on rear damper dimensions. I have received all four "series II" dampers and springs from Caterham USA but something isn't adding up with the rear springs.

 

With mere 75lb spring weights, the rear dampers will only compress 1/4" from full extension with the combined driver/passenger/full tank/spare tire load. This can't be right. Caterham lists series II and III dampers separately from I's which concurs with most photos and drawings that show I's required longer springs for a damper mounted forward/below center or the rear axle. Series II and III's appear to have the damper mounted centered above the rear axle which should require a shorter spring.

 

Even if the same damper could be used for both positions (below and above axle center) I do not understand how the same length and strength spring could possibly work. Caterham lists the same spring for all three series. What am I missing here, my mind?

 

If anyone has real information or at least an accurate guess that points me in the right direction It would be most appreciated!

[Ian7]

Is it possible you have a huge amount of friction in the suspension bushings that is acting to help hold up the load?

 

When I first built my Caterham, the bushings were so tight when installed I couldn't stroke the A-arm arc by hand....

[notakit]

There is virtually no friction at all. One of the few things I've changed from original design is a five-link suspension with rod end bearings. The only friction would be the damper's valving which I have adjusted to the minimum settings. You can compress the dampers (sans the springs) with your hands. With the springs installed and the spring perch at it's longest adjustment, the rear end of the car is up in the air.

[cs3tcr]

Mike,

I take it your building the rear suspension in the style of the Series 1, but with a panhard bar instead of the triangulated trailing arm?

 

One thing to do would be confirm the spring rates, or at least get a good estimate of what they are. I put a piece of round stock in a vice, placed the spring on the vice over the round stock, then put some weights on and measured the deflection. Its a very rough measurement, but it confirmed that i had 90 lb/in springs on my car (eleven replica, which is very very close to Seven S1 rear suspension). And, with two of us in the car etc, they do compress a fair amount.

 

Other than that, like its been mentioned check for anything binding.

 

Failing that, you might want to contact Mike Brotherwood, he helped me out with my Eleven issues, and is very knowledgeable on Seven S1 stuff.

[notakit]

Thanks cs3tcr! You're right about the rear end; the only thing series I about it is its the same live axle. "Five link" (two pairs of control arms per side and a panhard rod) eliminates the twisting of the original and is a bit lighter. I'll give Mike Brotherwood a hollar next week.

 

I didn't have ideal weights for testing in my vise so I used a bathroom scale on the drill-press, then pulled the chuck down till the spring was an inch shorter. I took the scale's compression into account as well. Spring rates look correct but way too long. If I cut them down the spring rate goes way up. Custom springs may be my only option.