Question: 79 Vette shocks/rear-end sag.

[Elliott]

I know; who has more questions on this site than me?

My car doesn't present level when comparing the front vs rear wheel openings; a slight sag in the rear. I've seen where many people mention replacing the leaf springs; is this the reason why? I plan to have the shocks checked because with only 58,000 original miles I suspect they are original. Yet I wouldn't think they would cause a sag. Also, I've read where some like the ride better with the original style oil shocks than the new gas ones. Others rave about the higher end replacement shocks. I'm just looking to level the car and improve the ride.

So I guess I have two questions. What's the solution for a rear end sag, estimated cost and is it worth it? I'm not really interested in an air shock solution. Also, what do you recommend for replacement shocks and why? TX Dave

 

[sstearns2]

You're right about the sag being due to the spring. Steel 'creeps', fiberglass doesn't. I replaced the rear spring on my old 77 with a fiberglass one. The fiberglass spring is only 8 pounds! The steel one is something like 40 lbs.

Changing the spring is pretty easy as I remember. If your shocks are original then I'd replace them for sure.

Scott

 

[ducvw2004]

I second that.

The rear spring replacement is a breeze and really not much cost.

 

[Bolisk]

I agree.

Just did my rear spring last night. Took maybe 2 hours. Here is the procedure I used.

1) Put the car up on jack stands (all four corners)

2) Removed the rear wheels

3) Removed the cotter pins that were retaining the castle nuts on the bottom of the spring link bolts.

4) Placed a pneumatic jack about 3 inches from the end of the leaf spring (basically left enough room to use a ratchet on the spring link bolt).

5) Jacked the spring up off the rubber bushing.

6) Placed a C clamp (with a v foot) about 4 inches inboard of the jack on the leaf spring, wedging the v foot up against one of the shorter leafs.

I used this C clamp to act as a stop to keep the jack from sliding along the lenght of the spring when the spring is lowered.

7) I loosed and removed the leaf link bolt

8) Then using a long 2x4, I had a friend position the 2x4 between the c clamp and the jack. . .this acts as a soft bumber so the jack doesn't mar the c clamp threads if it does move. Pluss the stress is more event distributed if the jack does move.

9) I VERY SLOWLY lowered the spring.

10) Repeat 1-9 on the other side of the car.

11) I disconnected the muffler mounting bolts and let the exhaust hang a little lower to gain better access to the 4 spring mounting bolts at the differential.

12) I loosed 1 bolt all the way, then threaded it back on several turns to act as a reference for the other bolts. On my car the spring was compressed to the diff. . .and was under pressure. . .so I wanted to loosed all four bolts (without removeing them) to equally release the pressure. Once they were all loose I removed the two diagional bolts, then I had a firend hold the spring up when I removed the other two bolts.

13) Installation of the new spring was the reverse of the above steps. . .however, my shop manual said to NOT torq the connecting bolts (mounting or links) untill the car was sitting on the ground.

This worked for me.

 

[Vettehead Mikey]

Shocks have no effect on ride height, one way or the other. Your problem is either a sagging spring or compressed rubber bushings at the spring ends. Easy fix.

 

[Elliott]

I agree.

Just did my rear spring last night. Took maybe 2 hours. Here is the procedure I used.

1) Put the car up on jack stands (all four corners)

2) Removed the rear wheels

3) Removed the cotter pins that were retaining the castle nuts on the bottom of the spring link bolts.

4) Placed a pneumatic jack about 3 inches from the end of the leaf spring (basically left enough room to use a ratchet on the spring link bolt).

5) Jacked the spring up off the rubber bushing.

6) Placed a C clamp (with a v foot) about 4 inches inboard of the jack on the leaf spring, wedging the v foot up against one of the shorter leafs.

I used this C clamp to act as a stop to keep the jack from sliding along the lenght of the spring when the spring is lowered.

7) I loosed and removed the leaf link bolt

8) Then using a long 2x4, I had a friend position the 2x4 between the c clamp and the jack. . .this acts as a soft bumber so the jack doesn't mar the c clamp threads if it does move. Pluss the stress is more event distributed if the jack does move.

9) I VERY SLOWLY lowered the spring.

10) Repeat 1-9 on the other side of the car.

11) I disconnected the muffler mounting bolts and let the exhaust hang a little lower to gain better access to the 4 spring mounting bolts at the differential.

12) I loosed 1 bolt all the way, then threaded it back on several turns to act as a reference for the other bolts. On my car the spring was compressed to the diff. . .and was under pressure. . .so I wanted to loosed all four bolts (without removeing them) to equally release the pressure. Once they were all loose I removed the two diagional bolts, then I had a firend hold the spring up when I removed the other two bolts.

13) Installation of the new spring was the reverse of the above steps. . .however, my shop manual said to NOT torq the connecting bolts (mounting or links) untill the car was sitting on the ground.

This worked for me.

Thanks for all the information. What size did you put in? It apears there are 300 - 360# options. It sounds like I should get a composite spring and I'm not into high performance options; all I want is a level car and an improved ride. I should also change the rear shocks because I bet they are still original, but I'm looking for input from everyone on this site as to which product people recommend. I've been told new gas shocks will be stiffer and yet others rave about the high-end, expensive shocks. Replacement oil shocks would be less expensive. Any suggestions in this area? TX Dave

 

[ducvw2004]

I went with a 330lb composite spring. Reasonably stiff but a very good ride.

 

[GTR1999]

The OEM steel springs are actually pretty good. Yes they do wear out. There have been plenty of documented issues over the years on all these vette forums so you may want to go to several an do some homework.

Some things I found over the years to consider.
GM springs are long gone, you probably have a better chance to hit the lottery then find a NOS steel spring.
I have used 7 & 9 steel springs, they all rode too high with the stock 6.25" bolts, I had to use 8" bolts on all. I used candian,mexican,and Eaton Springs all were way off. Once the body was back to normal they were/are fine.
Glass springs. past issues with separation/breakage. Require new shocks valved for them, weight 32 lbs less cost double or more of the steel. some have blown out the rear covers using the wrong length bolts, others broke the cover ears not correctly installing and loading them. Read the above post on torquing with the car on the ground. Also his 2x4 approach is similar to what I use and will never use a c clamp and jack again. Too dangerous and I've done these before.
The NCRs guys have pieced together old spring leafs with new liners and paint and they function fine and fit. Just another thought.
Good luck, you're going to get to know your car now.

 

[Elliott]

First I am going to check the factory specs on height, although I'm sure it is more of the rear being too low than the front too high. If you look at my photo above you can see the sag. If it is all in the rear, then I'm really tempted to just buy a new OEM steel spring and replace with standard shocks. The car rides fine down the road; just pretty bumpy in town on the side streets. I presume that is the case with all vettes, though. Again, my main concern is that the car doesn't sit level. Someone please let me know if this approach doesn't make sense. TX Dave