Using Chevette Springs to Re-gain Original Ride Height

[Oiluj]

Interesting and useful discussion. Thanks John & Jon for the info!

[jmortensen]

You have that right. Mine were valved for the unsprung weight on both sides, the idea being that the wheel will stay in contact with the ground over rough surfaces because the rebound damping isn't preventing the tire from coming down and following the contours of the road. I had a mountain bike set up like this, and it tracked great on some really rough downhill single track stuff, but it was very uncomfortable to ride, especially when jumped. It was actually painful on the hands. I increased the rebound and it's more comfortable but doesn't track as well. On the car I talked to a shock guy and he suggested this setup. My car being a dedicated racer and all, I decided to give it a shot. I already have second thoughts about it because I actually started autoxing a Miata in the meantime, and one of the local autoxes where most of the SCCA events take place is VERY bumpy. I think once you hit some critical amount of bumpiness it not only gets uncomfortable, but the sprung weight starts to move so much that you lose whatever traction you would have gained otherwise. I do think this idea works on relatively smooth road courses, and I've found examples of older BMW touring cars in Germany valved the same way (it worked out to 90/90 instead of my 100/100 once you took the motion ratio into account).

Edited January 8, 2013 by jmortensen

[LeonV]

You have that right. Mine were valved for the unsprung weight on both sides, the idea being that the wheel will stay in contact with the ground over rough surfaces because the rebound damping isn't preventing the tire from coming down and following the contours of the road. I had a mountain bike set up like this, and it tracked great on some really rough downhill single track stuff, but it was very uncomfortable to ride, especially when jumped. It was actually painful on the hands. I increased the rebound and it's more comfortable but doesn't track as well. On the car I talked to a shock guy and he suggested this setup. My car being a dedicated racer and all, I decided to give it a shot. I already have second thoughts about it because I actually started autoxing a Miata in the meantime, and one of the local autoxes where most of the SCCA events take place is VERY bumpy. I think once you hit some critical amount of bumpiness it not only gets uncomfortable, but the sprung weight starts to move so much that you lose whatever traction you would have gained otherwise. I do think this idea works on relatively smooth road courses, and I've found examples of older BMW touring cars in Germany valved the same way (it worked out to 90/90 instead of my 100/100 once you took the motion ratio into account).

Interesting, I'm curious as to how it's going to work out for you.

[John Coffey]

The Bilstien Motorsports 36mm shocks will come with 5 different tarmac valvings and 2 different gravel valvings. That will cover most of what people will run on a S30. Revalving is $60 per unit (estimated) with a two week turn around.

[LeonV]

The Bilstien Motorsports 36mm shocks will come with 5 different tarmac valvings and 2 different gravel valvings. That will cover most of what people will run on a S30. Revalving is $60 per unit (estimated) with a two week turn around.

Excellent, thanks!

[Carl Beck]

I have the Bilstien shocks for the 240Z, that they sold in the 70's - on my Blue 72. As I recall I put them on in 74.. they are STILL the best shock I've ever had on a 240Z. Wish Bilstien would offer them again..

FWIW,

Carl B.

[Hardway]

So I finally got around to messing with the Chevette springs this evening and apologize for the delay in getting back on this topic. I have had my rear suspension apart for a rebuild and figured this was the time to look closer in to them. Below is a picture of the Chevette spring on the left with the King lowering spring on the right. As you can see there is a big difference between the two. The coil diameter on the Chevette spring is 12.56mm and on the King spring it is 11.90mm. The height of of the Chevette spring is 14 2/8 inches and the King is 12 1/4 inches. I installed them as-is, got the lower control arm connected and the half shaft, all temorarily so I could do a mock up with the wheel on. Once it was on I jacked up the hub assembly to see how far it would compress before it lifted the car off the jack stand. As soon as the jack started pushing up it lifted the car off the stand, the spring just barely compressed if any at all. Granted, the gas tank is almost empty and there is no one sitting in the car but I was hoping it would compress a little. Based on the other info I could find I need to cut atleast one coil. Do any guys that remember using the springs cut off more? If so how many and what was the result? I want to regain a factory ride height or just slightly lower.

[240260280z]

Search John Coffey and Chevette spring on Google. I recall him writing about them in a positive way.

[John Coffey]

The math is in here.

Installing Tokico 280Z HP Springs in a 240Z - Brakes, Wheels, Suspension, and Chassis - HybridZ

[Hardway]

Thank you John. From the looks of it I need to cut off 1 coil and possibly 1.5. I will start with 1 and go from there.

[Hardway]

I thought I would post an update on this topic. I cut 1.5 coils off of all 4 springs and installed them thus resulting in the picture below.

I like where the rear is at but as you can see it is sitting nose high. So earlier this week I took the front driver side spring off and cut off another coil giving the spring an uninstalled height of 10.25" I was hoping to see a .5 - .75 inch drop once it was installed but only saw about .25 inch drop. It still looks a little nose high so I am going to do the other side this evening or tomorrow and see if that helps. If not I may pull them off again and cut off half a coil and see where that gets me.

[John Coffey]

You can't just cut one corner and expect a major change on an end of a car. What's happening is the right rear is helping to hold the right front up (sounds crazy but its true - diagonal corner weights and all that).