4-leaf springs - 250lb rate?

[cudak888]

I know Q will probably beat me over the head for this, but before I go ahead and frame table my '71 Mach to verify whether I've got a tweaked framerail or not (long story - check the build thread for details), I figured I might as well swap the rear leafs - just to make sure the slight squatting I have on one side isn't by chance a sagging spring.

At any rate, I've found a rather good deal on a pair of what are claimed to be new, 4-leaf, factory-ride height springs, which is what I want - except that the seller also claims they have a 250lb spring rate. 

That sounds a bit exaggerated for 4 leafs. I could see that with 5 leafs though. But maybe I'm completely mistaken.

Anyway, the only real data I've found is the Eaton chart on NPD - and the toughest spring listed is an 152lb rate application for the Boss 351. Unfortunately, it also doesn't list the number of leafs.

And so that's my question to those in the know here - given your experiences, is it a good chance that the seller is just a wee bit on the hyperbole juice, and that there's no real chance that these 4-leaf springs are that aggressive? Sure hope that's the case.

Thanks!

-Kurt

 

[midlife]

Maybe that's the weight of the two springs for shipping rates...

 

[cudak888]

Maybe that's the weight of the two springs for shipping rates...

Doubt it.

"They are the 4 leaf stock height 250lb more weight capacity helps with squating under hard accel."

He knows what it means. Still, sounds like a hell of an upsell.

-Kurt

 

[HighOctane]

I have the same issue on my 73. The rear driver side sags and it has gotten worse in the last 3 or 4 years as I measure both sides periodically. The suspension is all original..

I plan on putting 5 leafs on Veterans weekend if all goes as planned. I have had everything for awhile but the wife's car came first.

The rating on the new springs is 195lbs.

 

[Stanglover]

As a suggestion, go to Eaton Springs website directly or call them. You should be able to get a better listing for rear springs rather than NPD's list.

In my case, I wanted 4.5 leaf standard eye springs as my old girl is an open dif and wheel hop is an issue. TCP has only mid and reverse eye, so I had to go to Scott Drake Grab-A-Trak 4.5 standard eye that are rated at 175lbs. The only issue was the ride height was 1.5" higher than the old worn out originals. To overcome this. I made a set of 1" lowering blocks as a temporary fix until they settle. They are down over a 1/2" already!

The ride on my Mach 1 is great. No more bumpty-bump!! Just a smooth ride and the handling is way better. If you go much more than 175 lbs, I think you're in for a harsh ride and back problems, but that's your choice.

As for the 250lbs rated springs you're looking at, I don't see it unless they're drag springs or something out of the ordinary.

Just my thoughts on the subject,

Geoff.

 

[Don C]

The AMA specs for competition rear suspension for 1971 351C-4V and 429-4V cars is a 135 lbs/in rate.

 

[Stanglover]

The AMA specs for competition rear suspension for 1971 351C-4V and 429-4V cars is a 135 lbs/in rate.

 True, that's what Eaton show if I remember and that's why I thought the Grab-A-Trak would be too stiff, but as they are 4.5 leaf, they are good, but I wouldn't want to go any higher than 175 lbs/in rate. If I recall, the TCP 4.5 leaf are 195 lbs, but I could be off a bit there without checking.

 

[Hemikiller]

All 71-73 springs were four leaf. I run the 429 spring and wouldn't want anything stiffer. 250lb/in would beat the bejuzus out of you and your car.

 

[Jeff73Mach1]

I have 200# rate 5 leafs-if those are 250-run as far away as you can as fast as you can cause the suspension will not travel

 

[cudak888]

Pretty much adds up then.

Decided to pass on those springs, even though I think "250lb" was more of a convenient number that the seller pulled out of his butt than anything else...

-Kurt