Spring bolt torque

[Chas Henderson #28127]

I am cleaning up my rear spring and I am ready to put it back together. I checked to rear of my chasie manual for the center spring bolt and they have everything but that bolt torque number. It's a 71 nine leaf rear spring.
Also, I read on the forum something about being careful when you reattach the spring to the differencial. My manual stated to reattach the spring with the car in the air, tighten to specifications, lower to the ground then tighten to the proper specifications. By lowering it to the ground, putting weight on the spring, why would what one has already done suddenly change and it not be as tight?

Chasman

[Kent K.]

Re: Spring bolt torque

Chas --- First, do not tighten to specifications with you car in the air!!!
Snug the bolts up, lower the car putting full weight on the rear tires and then tighten to specifed torques. If you tighten the bolts first without weight on the rear tires, you'll break the differential cover ... then you'll BE UP THE CREEK.
Best regards, Kent #6201

[Chas Henderson #28127]

Re: Spring bolt torque

Kent, Thats what I thought. But why does that damage the cover? The differencial is attached to the crossmenber and is attached at the front as well. It would seem that as you lower it, all the weight is transfered up to the housing -cover- but that should be rather solid.

Chasman

[Kent K.]

Help explain this

Chas --- Don't ask me how I know. I've never broken one but, there are people on this board who give good advice not to be tinkered with. Hopefully someone else will explain.
Kent #6201

[Dick W.]

Re: Spring bolt torque

By torquing the bolts in the air you are putting extra stress on the ears of the cover which are somewhat marginal in strength. By putting weight on the spring, it is compressed and you will not have to overcome the extra tension placed on the bolts and cover by trying to compress the spring.

[Joe L.]

Re: Spring bolt torque

Chasman-----

The spring center bolt torque is not critical. Use a torque of 20 lb/ft.

[Chas Henderson #28127]

Re: Spring bolt torque

O.K. That makes sense. The springs would compress if all the weight is on them.

Joe, thaks for the info on the center bolt.

Thanks,
Chasman

[John H.]

Re: Spring bolt torque

Chas -

The rear spring isn't attached to the differential housing, nor is the differential housing attached to the rear suspension crossmember; the spring is attached to the rear cover, and the rear cover is attached to the rear suspension crossmember.

If the four spring retaining plate bolts are torqued without the car's weight on the wheels (which flattens the spring), odds are excellent that you'll break an ear off the rear cover before the bolts reach torque. Unfortunately, Chevy didn't add this tidbit to the Service Manual until about 1971 (they probably wondered why they were selling so many rear covers).

[mike cobine]

It takes more force to compress the spring

than to hold it once compressed.

Unfortunately, the strength of the rear cover can sometimes fall between those two.