Rear suspension upgrade\spring rates

[G72Zed]

@Bruce1968, I would pay close attention to what Schubitzky says, he is bang on the money with is post(s), can't argue with results, regardless if Gen I or Gen II. Lots of info missing with just 245 F , 275 R tires.

When picking suspension options and spring rates one has to factor in the tires design and their profile to a point. I have witnessed cars with great suspension parts with the wrong tire/rim combo and they handled well below expectations, I have also witnessed very basic "stock" type OEM based setups with a well thought out tire/rim combo absolutely kick a$$ on the Autocross/road course.

 

[Bruce1968]

a smaller front tire will induce push. what kind of tire is it?

I'd invest in a good square tire setup and competition leafs before spending a ton of money on a 4 link or torque arm. That will get you out there and having fun instead of fighting the car. I'm fairly competitive on leafs and single adjustables.

Nitto NT555G2. I will add that since I was mostly goofing off at the AutoX I didn't give any thought to tire pressure either.

Given the fact the rear leafs are worn out, I need to address that before I start looking at other stuff. I think I'll go with Hotchkis for now, just need to decide on 1.5" or 3.0" drop. If it still pushes, I'll add a sway bar to the rear.

 

[Lowend]

Go with the 1.5" drop, if it's not enough you can add a 1" lowering block.
To be clear, there are different kinds of understeer (push), there are only a couple a rear swaybar will help with.
Most streetcars have "corner-entry understeer". meaning you turn the wheel and the car starts sliding straight, or at least not turning-in as much as you would like. This is solved with suspension geometry, tire size, tire inflation, or wheel alignment. A rear swaybar will affect this for sure, but not as much as you'd think. You'd be shocked how much 1/4 degree of wheel alignment or 2PSI of tire pressure can change the world.

The rear swaybar is more for "mid-corner or corner-exit" understeer there is where the car has adopted a vector gets into the turn before it starts to push.

My point is, get the springs and shocks, you need those. Hold off on the rear swaybar for now. They are a PITA to install on 1st gens, and there are lots of over levers you can pull first.

 

[Bruce1968]

Go with the 1.5" drop, if it's not enough you can add a 1" lowering block.
To be clear, there are different kinds of understeer (push), there are only a couple a rear swaybar will help with.
Most streetcars have "corner-entry understeer". meaning you turn the wheel and the car starts sliding straight, or at least not turning-in as much as you would like. This is solved with suspension geometry, tire size, tire inflation, or wheel alignment. A rear swaybar will affect this for sure, but not as much as you'd think. You'd be shocked how much 1/4 degree of wheel alignment or 2PSI of tire pressure can change the world.

The rear swaybar is more for "mid-corner or corner-exit" understeer there is where the car has adopted a vector gets into the turn before it starts to push.

My point is, get the springs and shocks, you need those. Hold off on the rear swaybar for now. They are a PITA to install on 1st gens, and there are lots of over levers you can pull first.

Thanks, that’s very helpful. I was thinking of doing just as you suggest. It was definitely a corner entry push.

 

[Bruce1968]

I see suspension geek has the Hotchkis and DSE leafs. Hotichkis is are 150-180 lbs and DSE are 175 lb. I assume the Hotchkis are progressive. The DSE say they have anti friction pads between the leafs to improve ride quality. Any one have thoughts on the two?

 

[biker]

I see suspension geek has the Hotchkis and DSE leafs. Hotichkis is are 150-180 lbs and DSE are 175 lb. I assume the Hotchkis are progressive. The DSE say they have anti friction pads between the leafs to improve ride quality. Any one have thoughts on the two?

I think I mentioned that I just installed the Hotchkis ones. Very happy with them, they got rid of the bad wheel hop I had with the stock springs. Stance is bang on what I wanted, and they ride nice. Firm, but not harsh. They have plastic shoes between the leafs. Hardware is very nice too, but takes some work to drill things out for the larger u bolts.
I know DSE makes great stuff, but i would think a 3" drop would require some definitely driveline/pinion angle work to keep u joints happy.

 

[Bruce1968]

I think I mentioned that I just installed the Hotchkis ones. Very happy with them, they got rid of the bad wheel hop I had with the stock springs. Stance is bang on what I wanted, and they ride nice. Firm, but not harsh. They have plastic shoes between the leafs. Hardware is very nice too, but takes some work to drill things out for the larger u bolts.
I know DSE makes great stuff, but i would think a 3" drop would require some definitely driveline/pinion angle work to keep u joints happy.

Thanks. The DSE springs on Suspension Geek are a 2" drop so I think that would be manageable.

 

[biker]

Thanks. The DSE springs on Suspension Geek are a 2" drop so I think that would be manageable.

Agreed.

 

[tomsti]

Interesting discussion, lots of options.

Couple of questions, from a leaf spring guy:

How do you know your leaf springs are warn out in the first place? I'd assume mine are only because they are original but dont have a great way to tell. I guess the way I was thinking was to measure sag from garage floor to lip of the wheel well. +/- some amount = they are warn. How do people assess if their leaf springs are needing to be replaced?

 

[G72Zed]

With the car on level floor, I measure from the floor to quarter lip (masking tape helps) and/or from wheel center, jot down the measurements on said Masking tape, both sides.

Next toss in 125lbs of weight in the middle of the trunk, note the measurement on the tape, calculate how much this has dropped, average left and right. (I have used water softener salt as they are 25-50 lbs bags and are fairly accurate)

Let's say the factory springs came with 125# rate, this would drop the rear by .500 (1/2 inch) if it's more, your rate is less, and as the rate drops, the springs can not control axle tramp (when the rear get's sucked into the body) and a host of other ailments.

Most performance springs have higher rates to control these issues, staggered setup, teflon pads, and better bushing, the better tires of today that are light years ahead of the bias ply of yesteryear, and the average SBC making 400+ hp with ease has made the rear leaf spring upgrade in design and rate almost a no brainer and a requirement.

This also is a good method to confirm the new springs actual rate as installed should you buy a new set. If it's to "high" of a rate based on the weight added in the trunk based on the manufacturers specs, you can bet there's binding going on, EX: over tightening of the Poly bushings while the car is on jack stands.

Hope this helps.