Another Spring Question

[Ed D.]

I am going to refresh the rear spring on my 72 while I have the rear out. My question is, when reassemblying how much pressure is used to clamp the spring leafs before bolting together? The last time I did this I held the spring in a vise with little pressure. I have been told that if you do not use a large amount of pressure to clamp the leafs you will get spring walk.
Ed

[John H.]

Re: Another Spring Question

I am going to refresh the rear spring on my 72 while I have the rear out. My question is, when reassemblying how much pressure is used to clamp the spring leafs before bolting together? The last time I did this I held the spring in a vise with little pressure. I have been told that if you do not use a large amount of pressure to clamp the leafs you will get spring walk.
Ed

Ed -

The vise method will work fine; when installed, the four spring plate bolts capture the spring and won't allow the leaves to become misaligned. That's why when the spring got wider in '78, the four bolts changed from 9/16" to 7/16" in diameter.

[Steve L.]

Re: Another Spring Question

I just used a C-clamp. It didn't take a lot of force.

[Ed D.]

Re: Another Spring Question

I just removed the spring and the leafs are not aligned with each other (out of alignment by about 1/4"). They are twisted counter clockwise (looking at them for the rear of the car). This spring is the original spring, which was refurbished about 15 years ago. The 4 support bolts where torqued to spec with the wheels on the ground. The car has been driven about 8000 miles since the refurbishment. I was told by a spring manufacturer that a typical leaf spring is pressed to 80 tons when being assembled. That sound like a lot of pressure to me. I would like to know if anyone knows what pressure the original manufacter of the spring used to assemble the spring?

[Gary B.]

Another Spring Question; 80 tons? No way

Ed,

That spec of 80 tons makes no sense whatsoever to me. That amount of force would destroy the poly liners between the leaves.

Gary

[Tracy C.]

Re: Another Spring Question

80 tons..?? Ridiculous!! Like Steve said, a C-clamp is all you need. Sound to me like you are talking to someone who wants to sell you a new repop spring.

tc

[Joe C.]

Re: Another Spring Question

Ed,

The clamping force on the leaves exerted by the center fastener is a strict function of the bolt used, and how it is lubricated.....or not.

This should be your guide:

http://www.raskcycle.com/techtip/webdoc14.html

Be sure to cut and deform the bolt after you torque it, which will retain the nut.

In the final analysis, the four bolts to the diff rear cover exert a FAR greater clamping force than that center bolt. If the leaves continue to walk around as you have experienced, I would suspect a wheel alignment/chassis problem. Is your car dog-tracking? I would also look into the possibility that the diff cover is being strained and is in danger of cracking from this condition.

As John said, there should be no clearance between the four bolts and the leaves. If the leaves are sliding over each other like a deck of cards, then the four bolts will take a portion of the strain and deform. After a small amount of deformation of those bolts, then the cast cover will crack.

[John H.]

Re: Another Spring Question

I was told by a spring manufacturer that a typical leaf spring is pressed to 80 tons when being assembled. That sound like a lot of pressure to me.

Ed -

Here's the fixture Eaton Detroit Spring uses to assemble all of their leaf springs; I've been there several times and watched them use it, and I doubt if it applies more than a 100# load while they tighten the center bolt.

[Gary B.]

A question for John Hinckley

John,

By any chance have you had a chance to closely inspect the repro 7-leaf spring sold by America's Finest Corvettes? I recently saw a close-up image of their spring and the 45 degree cuts at the ends of the main leaf don't seem to be as close to 45 degrees I would expect, although the angle of the photo may not have been dead-on perpendicular.

Gary

[John H.]

Re: A question for John Hinckley

John,

By any chance have you had a chance to closely inspect the repro 7-leaf spring sold by America's Finest Corvettes? I recently saw a close-up image of their spring and the 45 degree cuts at the ends of the main leaf don't seem to be as close to 45 degrees I would expect, although the angle of the photo may not have been dead-on perpendicular.

Gary

Gary -

No, I haven't had a chance to see one yet; don't know if they do those cuts separately (which is cheaper) or with a double 45* die.

Eaton has many sets of dies for the end trim, and the one for the Corvette spring is a single die that does both 45* trims simultaneously. Don't have a photo of that one, but the photo below shows the die set for a curved end trim; the spring is red 'cuz it's HOT!

[Ed D.]

Re: Another Spring Question

Joe, Thanks for your information. This is a no hit car that has spent most of its life in a garage. So I am sure the frame is straight and the alignment is correct as the car tracks straight as an arrow, as you witnessed from traveling behind me on the road tour to the 2010 National. The tires also show not uneven wear.

John, I am always amazed at your research and terriffic knowledge on so many subjects. Thanks for your valuable information.

I forgot that when I replaced the spring 15 years ago, 1 of the spring bolts stripped the treads in the carrier. It was repaired in the car with a heil coil. I will check tommorrow if the hole was dilled straight. I there was any angle to the repair, this would allow room for the leafs to shift. I will report back after checking.
Ed

[Ed D.]

Re: Another Spring Question

I got under the 72 this morning and put the 4 bolts in the carrier and measured the distance front to back on each side. There is a 1/8'' diffierence form side to side. By the way there were 2 heil coils both on the divers side of the carrier. So much for my ability to drill straight and for my aging memory. Thanks for everyones help.

While we are on springs, I have another spring topic. The Spring of 2011 is the CNJ Wildwood NJ Regional (May 19-21 2011). Hope to see everyone there.

Ed