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Jensen front suspension like Zephyr


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I'm rebuilding a 1938 Jensen car with independent front suspension by twin tranverse leaf springs (see pic). I have taken these springs off and find that they are of slightly different tension. The top spring is less tensioned than the bottom spring, so it sits a little wider when removed from the car. I would like to rebuild these springs but do not know if the two springs should be set the same, or whether there is any good engineering reason why they should be set differently, and if so, by how much? There is no surviving data on the original set-up. The springs are constructed the same, as far as I can see, with 8 leaves each. There is no greasing facility on the springs. I understand the Zephyrs have a similar set-up, so can anyone offer any suggestions about this one?

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The Lincoln Zephyrs only had a single transverse spring up front, with around 14 (I think) leaves, so it is much different than what you have there. The only advice I can give you is to contact Eaton Detroit Spring. Supposedly, they have over 23K blueprints, so you might get lucky:

http://www.eatonsprings.com/

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It would seem that the connection at the spindle mount would force both springs to work in unison reguardless of any variation in spring rate. I wonder what provision has been made for camber/caster adjustments? There appears to be some kind of shackle set up on the upper connection and how is the spring hung at the lower connection? An interesting suspension.

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I'm not sure how it works either. Here is another pic of the spindle from the front of the car. At the rear the wooden beam is serving to join the two wheels as a steering arm lock. The mounting point on the upper spindle is for the shock absorber arm. I can't see any obvious camber/castor adjustments.

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Here's a pic of the two springs laid on top of each other to show the difference in curvature. In the pic, the top spring is the top spring from the first pic showing the suspension in situ. You can see that it is a little stiffer than the lower spring. I don't know if this is correct as is, or whether the two springs should be identical, or whether the difference can be put down to aging over the past 65 years.

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<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Here's a pic of the two springs laid on top of each other to show the difference in curvature. In the pic, the top spring is the top spring from the first pic showing the suspension in situ. You can see that it is a little stiffer than the lower spring. I don't know if this is correct as is, or whether the two springs should be identical, or whether the difference can be put down to aging over the past 65 years. </div></div>

I'm certainly no expert on the Jensen, but I am pretty certain that the two springs were originally arched differently, just as you see on the car now. This suspension is essentially the same as what is called "Tojeiro Suspension" as was used on Fiat 500/800 cars, and on AC sports cars in the 50's, including the first Shelby Cobra's.

The shallow arched bottom spring acts as the lower A-arm, the tighter arched upper spring serves the purpose of an upper A-Arm. Almost all A-arm suspension setups are done "SLA", or short-long arm, with the upper A-Arm shorter than the lower, for providing some alteration of camber as the body of the car rolls side-to-side in curves and turns. I'd not alter that one bit. As this is a Jensen, and as such, a British-built car, perhaps some searching for Jensen website (and there are several!), is in order here, I believe. I know I've seen several, with technical areas, and if you can find one, I think a post or email might well give you the information you are looking for.

Good luck in your search!

Art

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Thanks Art - useful insight. I will try the sites of the other cars you mention as I'm pretty sure there isn't anything on Jensen sites. You mention the shallow-arched bottom spring but the way the springs came off the car, it is the upper spring which seems to be the flatter one. Am I reading this wrong or do you mean that the flatter spring should be on the bottom?

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I'm guessing here but it looks like some adjustments could be made. The camber could be "equalized" by moving the upper spring side to side. The caster could be adjusted and set by moving the upper spring for and aft. The spring pivots at the spindle are probably pretty rigid but some movement seems possible? Is the upper or lower spring mounted to the frame with any shims? Moving the mounting surface of the upper and lower spring closer or further apart could effect a small change in the camber. It would be interesting to find out what the alignment recommendations were on these cars when they were built.

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