1970 Rear Spring

[Mark A.]

I'm looking for info on the black plastic liners that go between the leafs.

The car is suppose to have a nine leaf spring with plastic liners between the leafs except between #6 & 7 leafs.

Which direction do you start from when determining #6 & 7 leafs ??
Is the longest leaf considerd #1?

Is this really important to worry about when being judged? I'd rather have the liners on all the leafs.....

Any help would be appreciated..

Thanks,
Mark
East Otis Ma.

[Keith B.]

Re: 1970 Rear Spring

there is a reason why GM never put the liners on the two. they don't need them.

[Gary B.]

1970 Rear Spring; inter-leaf liners

Mark,

The longest leaf is #1 and putting a liner between 6&7 will result in a points deduct and that liner will tear apart if the car is driven if you're using the correct two-stage spring.

Gary

[Mark A.]

Re: 1970 Rear Spring

Thanks Gary.....
I assumed that the longest was #1.

When I got my car back from restoration I noticed it sitting too high in the rear so I started looking into things and my guy put a 7 leaf spring in (HD F-14) where everything I have read calls out a 9 leaf for the car as it did not have the F-14 option, I do have a big block but it should still have the 9 leaf spring and hopefully it will bring it down about an 1 1/2 or so ??

Thanks again for your help.

Mark

[Alan S.]

Re: 1970 Rear Spring

Hi Mark,
According to the trim heights chart in the 71 AIM the F-41 cars actually rode LOWER than a car with standard suspension.
For dimension 'R'... Ground to a point in rear body wheel arch at wheel center line. With oil, water, full tank of fuel and recommended tire pressure. (24 lbs.) These are described as an average for SB and BB cars.
STD 27.91"
F-41 27.58"
I read many discussions about cars with replaced rear springs riding 'high'. Is the car completely back together with a full tank? That weight hanging out back makes a difference. Has it been driven some to 'settle' the suspension?
Regards,
Alan

[Mark A.]

Re: 1970 Rear Spring

Alan,
Thanks for your reply.......I didn't really want to hear that the F-41 sat lower......
I just got the 9 leaf spring that my restorer guy got me before he left for vacation. The arch on this 9 leaf spring is almost twice the 7 leaf I took out.

I just got the new 9 leaf mounted up with the 4 bolts in the center but have no idea how I'm going to pull up the sides 6" to get the nuts started?? Somethings wrong and my guy won't be back for another week.

The ride height with the 7 leaf spring was 30.5 in the rear.

I'm kinda at a loss right now, any suggestions.

Thanks,
Mark

[Jack H.]

Re: 1970 Rear Spring

You'll note that the standard 9-leaf spring has a compound design. The lower six leaves do the lion's share of the work never touching the upper three UNTIL the suspension is under MAXIMUM compression. That's when the upper 'stage' of the compound spring 'kicks' in.

It was only in 1963, that the 9-leaf spring had all leaves equally arched. But, that was a complaint aspect from those who reviewed the new Corvette's handling characteristics...suspension was too stiff and 'unforgiving'. So, starting in '64, the base suspension changed featuring the 2-stage, compound design, you see.

That's why you don't need a liner between the leaf's at that point. They seldom touch/rub against each other.

The more aggressive high performance suspension spring with its 7-leaf design is a through-back to the early days. You get a stiffer overall ride and as such, you don't need as much ride height...

[Mark A.]

Re: 1970 Rear Spring

Jack Thanks,
So with the 7 leaf spring my ride height was 30.5 are you saying that the 9 leaf is going to raise me up more?

For judging purposes the car calls out a 9 leaf spring??

Any suggestions on what to do?

The pre load on this 9 leaf spring is unreal, I have no idea how I'm going to get it hooked up....

Thanks,
Mark

[Michael W.]

Re: 1970 Rear Spring

Mark,

It's possible that either/both of the springs you are attempting to use are simply poor quality repros that will not give the correct height no matter what you do. The various discussion boards are full of similar stories and attempted work around fixes.

I have heard that Eaton spring makes a 9 leaf spring that will give a satisfactory ride height.

[Timothy B.]

Re: 1970 Rear Spring

Mark,

First of all you don't tighten (torque) the four center bolts until the weight of the car is on the spring and it's been bounced around some. Just snug to keep the spring in place for now.

I have been successful using a floor jack with a piece of thick rubber to lift the leaves one side at a time to bolt them. Works good for me and the rubber will keep the jack from sliping. Make sure the jack is positioned to roll a little when you lift the spring so it does not roll over. Don't get near the spring when doing this, just stay behind the jack.

Double check the bolt lengths as this has a affect on ride height. The correct length is in the archives from previous discussion.

I agree with the post above in that the car will settle after it's been driven and some gasoline added.

[Jack H.]

Re: 1970 Rear Spring

I'm just an electrical engineer, so I'm not accustomed to the term 'pre-load' being used with spring/suspension systems. I do recognize that term in conjunction with bearing surfaces and gear lash setup. Maybe you can elaborate?

If you suspect the 9-leaf spring lacks correct geometry, then just measure and compare to factory original spec. The term is 'free arch'.

Lay the spring on a flat surface on its side. Draw a chord between the centers of the end mounting holes. Measure from the center of this chord up to the bottom of the spring. That's the parts' free arch. It ought to come in at 10".

The 7-leaf version of the spring had MUCH less free arch... I'm going from memory, but I believe the factory speck was in the 6.5-7" range.

The spring's free arch spec, plus its deflection rate and your car's specific weight is what (among other things) determines final ride heigth. There's no magic here, it's science...

[Mark A.]

Re: 1970 Rear Spring

Thanks for the input Mike......My restorer will be back in town next week, we'll have to do some research....

Mark

[Jeffrey S.]

Re: 1970 Rear Spring

Mark:
Most reproduction springs leave the car very high. You can do several things. You can have the spring re-arched. You can return these springs and buy from Eaton who says they have the original drawings and tooling for correct ride height. You can use the spring you have but use a longer end bolt. The longer the bolt, the lower the car will get. This will lose judging points for the length of the bolts.
Jeff

[Mark A.]

Re: 1970 Rear Spring

Jack,
Pre load is probably not the right term, by reading yours and others responses I think my biggest mistake was to do this on my lift.

It's a drive on lift so the tires are on the rails and I supported the car under the frame and was able to remove the 7 leaf spring with just a small amount of tension on the end bolts.

Now when I go and put the 9 leaf in the spring end is about 6" away from the end bolts because of the huge arch in it. It just seems to me that this is going to take an unbelievable amount of load to bring that spring up to be able to get those nuts engaged.

I obviously need to use the weight of the car to do this but I would hate to go through all of this and then have the car sitting higher then when I started....

I need to check your "free arch" dimension to see where i'm at. Where did you come up with the 10" ? Is this documented somewhere?

Thanks for your time and help.

Mark

I'm just an electrical engineer, so I'm not accustomed to the term 'pre-load' being used with spring/suspension systems. I do recognize that term in conjunction with bearing surfaces and gear lash setup. Maybe you can elaborate?

If you suspect the 9-leaf spring lacks correct geometry, then just measure and compare to factory original spec. The term is 'free arch'.

Lay the spring on a flat surface on its side. Draw a chord between the centers of the end mounting holes. Measure from the center of this chord up to the bottom of the spring. That's the parts' free arch. It ought to come in at 10".

The 7-leaf version of the spring had MUCH less free arch... I'm going from memory, but I believe the factory speck was in the 6.5-7" range.

The spring's free arch spec, plus its deflection rate and your car's specific weight is what (among other things) determines final ride heigth. There's no magic here, it's science...

[Terry M.]

Re: 1970 Rear Spring

Not to steal Jack's thunder, but I can think of two sources:

There was a story on the standard rear springs in The Restorer back when I was Editor (I think the first article was in 1999 or 2000) by Gary Beaupre. If my memory is right the free arch dimension is there.

I believe that number has been quoted on this tech board in the past, but you would need to use "search" to find it.

Of course Jack may know of other sources if those are not adequate for you.