C2 Rear Leaf Spring

[John L.]

This post has to do with my '66 Big Block car. Just recently I heard like a clunkering noise coming from the rear of the car when I was driving around town. So I jacked up the back to take a look and found that two of the four bolts that hold the center metal plate over the spring in place are missing and that the seven leafs of the spring are no longer aligned as the bottom two have started to drift to the side. This is a spring that I purchased from Eaton Spring a few years ago and had a local mechanic install for me.

I would like to see if I can fix this situation by myself and plan to order the missing bolts for installation. My question, can the spring be properly aligned without removing it from the car? Also, what is the torque specification for the metal plate bolts and what keeps the leafs of the spring in alignment, is it the center bolt that runs through the middle of the spring? Thanks for the info!

[Stephen L.]

Re: C2 Rear Leaf Spring

1.The bolt in the spring center is to keep all the leaves together in a stack. It is not meant to keep leaves in rotational alignment.

2. You may be able to realign the leaves in the car unless there are spring spacers between the leaves. These typically have a edge on them that would not allow realignment.

3. The missing bolts may be a big problem. The differential housing may be damaged where these bolts screw into or even worse the ears are broken. You'll need to inspect the housing. Also, carefully inspect the screw holes for damaged threads on the 2 remaining bolts.
I can venture to say what happened to cause this problem having replaced the spring. The 4 bolts in the center must NOT be tightened until the full weight of the car is on the wheels. Doing this with the weight off the suspension causes severe stresses to the differential housing by the spring and will break off the mounting points.

4. The torque spec for these bolts is in the service manual as are the instructions for proper installation of the spring.

I would remove the spring from the car, inspect the differential etc, disassemble the spring, install new spring liners if damaged, rassemble the spring and reinstall in the car. Again; DO NOT tighten the 4 bolts until you have the full weight of the car on the wheels.

Good luck.

[Larry M.]

Re: C2 Rear Leaf Spring

In addition to what Steve says, two of the four attaching holes in the differential are "blind holes". For these two, bolt length is critical to avoid bottoming out the bolts and not having sufficient clamping force on the rear spring. The replacement spring and/or liners thickness may have affected this dimension, and you may need to shorten these bolts.

I have just went through this, and am speaking from experience. I had to shorten these bolts on my car by 1/8 inch each due to the replacement liners being thinner than original.

Larry

[Terry M.]

Re: C2 Rear Leaf Spring

In addition to what Steve says, two of the four attaching holes in the differential are "blind holes". For these two, bolt length is critical to avoid bottoming out the bolts and not having sufficient clamping force on the rear spring. The replacement spring and/or liners thickness may have affected this dimension, and you may need to shorten these bolts.

I have just went through this, and am speaking from experience. I had to shorten these bolts on my car by 1/8 inch each due to the replacement liners being thinner than original.

Larry

Listen to Larry. Danger Will Robinson:
Not only will you have insufficient clamping force, but you run the risk of poking a hole into the interior of the differential -- then the grease will work its way past the bolt threads and you are in a pile of do-do. To make matters worse some replacement bolts are too long and will poke through as well. Joe Lucia has posted about this issue in the past and he has been kind enough to include the proper length for the bolts. Be sure you have the right parts before you begin assembly.

[John L.]

Re: C2 Rear Leaf Spring

Thanks for the reply. I checked the service manual last night and it makes no mention of tightening the leaf spring plate bolts with the weight of the car on the suspension, however, I understand your point. It justtalks about installing the leaf spring with the rear of the car on jack stands and then lowering the vehicle.

How do you go about installing the spring with the weight of the car on the suspension system? Are you driving the car onto a ramp and then doing the work?

[Larry M.]

Re: C2 Rear Leaf Spring

Thanks for the reply. I checked the service manual last night and it makes no mention of tightening the leaf spring plate bolts with the weight of the car on the suspension, however, I understand your point. It justtalks about installing the leaf spring with the rear of the car on jack stands and then lowering the vehicle.

How do you go about installing the spring with the weight of the car on the suspension system? Are you driving the car onto a ramp and then doing the work?

I think the instructions Terry stated are in the AIM.

You jack the car and support the rear FRAME on jackstands. Let the rear wheels hang free. Then you remove the spring end connections using a jack. Special precautions required at this point to avoid jack slipping or moving and suddenly releasing the spring. Service manual and archives has proper method.

After any repairs, you install spring to differential case and just hand-tighten (very lightly snug) the four mounting bolts, being certain they are of the proper length. Then reconnect the spring ends. Then let the car down on its wheels. In this way the spring mount has enough free play to allow it to equalize between both sides and fit-up correctly to the rear carrier. Then you bounce the rear around a few times to settle things and then you go back under the car and tighten/torque the four mounting bolts.

If you can't fit under the car, jack it back up and then set the rear wheels back down on ramps or solid support.....so that the car rear weight is on the rear wheels when you tighten the four mounting bolts to spec.

Larry

[Terry M.]

Re: C2 Rear Leaf Spring

Larry's got it. Works easily on a lift, but so long as the weight of the car is on the suspension (wheels) before you torque down the four rear spring bolts you are golden.

[Joe L.]

Re: C2 Rear Leaf Spring

Listen to Larry. Danger Will Robinson:
Not only will you have insufficient clamping force, but you run the risk of poking a hole into the interior of the differential -- then the grease will work its way past the bolt threads and you are in a pile of do-do. To make matters worse some replacement bolts are too long and will poke through as well. Joe Lucia has posted about this issue in the past and he has been kind enough to include the proper length for the bolts. Be sure you have the right parts before you begin assembly.

Terry------


Yes, the bolt length I posted will work just fine providing that the car has an original spring or a replacement that's the same overall height as the original spring. If the spring being used has a different spring height, then the bolts have to be adjusted or replaced by whatever difference there is compared to the original spring.

[Terry M.]

Re: C2 Rear Leaf Spring

Ah, yes. So many ways to do it wrong -- and only one way to get it right (well almost).

[John H.]

Re: C2 Rear Leaf Spring

Thanks for the reply. I checked the service manual last night and it makes no mention of tightening the leaf spring plate bolts with the weight of the car on the suspension

John -

The failure to include that note is what gave rise to the aftermarket "heavy-duty" rear cover, as owners (and dealer mechanics) broke the bolt anchor brackets off the rear cover casting by torquing those bolts with the rear suspension hanging in rebound.

No doubt driven by warranty costs, the note was finally included in the Chassis Service Manual in 1971; of course, few folks read the CSM, and people still break the rear covers every day.

[Tim G.]

Re: C2 Rear Leaf Spring


I still had the original spring that was re-arched and I finally put this back on the car. The problem is gone now.