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Spring offensive

antijam

CCCUK Member
To correct a list to port in my '71 I recently replaced the rear spring bolts and rubbers. The bolts were longer than original and not split pinned so allowed differential adjustment side to side. However this adjustment made me realise the core problem was really a tired spring.

So time for a replacement. Hindsight suggests a rear spring swap is easier tackled with the assistance of a helper, the car on a full lift and with the rear exhaust removed but Covid barred any assistance, I don't have a lift and I didn't fancy removing the recently fitted exhaust, so with the car raised sufficiently on my QuickJack to allow me to crawl underneath, I tackled it on my back.

My recently fitted new spring bolts and rubbers were easily removed so time to tackle the four bolts securing the spring to the diff housing. These are beefy 1/2" NC and have been exposed to the elements for 50 years, so I don't expect them to yield easily. My initial efforts with a long ring spanner producing no result, I deem it sensible to attack them with an impact wrench. This seems particularly prudent with the rear two as these are threaded into extended lugs on the rear diff cover and these could well crack under heavy loads applied from a breaker bar and/or hammer. The pure torque from the impact wrench is safer. Even so, it takes several repeated applications of Plus Gas and the wrench to break these free.

To prevent the (heavy) spring landing with a resounding crash onto my exhaust I strap the spring to the diff mount crossmember with a couple of lengths of rope while I remove the bolts and anchor plate.....

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.....then support the tailpipes with a jack under a timber bridge and lower the spring gently to rest on them....

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......when I can then winkle it out sideways.

I want to clean up the threads in the diff cover but don't have the right tap so I grind a groove in one of the old bolts and use it to chase them out.....

1-P1370007.JPG

The spring supplied by CK as a replacement for the original has the same nine leaves but these are now interleaved with rubber rather than plastic, which makes the stack thicker so longer bolts are needed. The originals are 3¼" long and the replacements 4"....

1-P1370002.JPG

New above, old below.

The extra thickness makes it difficult to manoeuvre the new spring past the exhaust and into position but I finally get it resting on the still supported exhaust ready to bolt up. The long new bolts are fine in the two rears as the holes are tapped through the cover bosses but the front two are blind tapped and to ensure the bolts don't bottom before torqueing up I shorten them to 3 11/16". This gives plenty of engagement but ensures they won't bottom, so after hauling the spring into position with my two ropes I insert the bolts through a new anchor plate and tighten them up.

Now just need to refit the spring bolts and rubbers, so clamp a vice-grip to the spring (to prevent a jack slipping ) and jack it up enough....

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.....to fit the lower rubber, washer and nut.....

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With everything back in place I lower the car to the ground before torqueing the four spring clamp bolts to 60 lbf. ft. After a few miles driving I'll re-torque these as the spring will probably settle a bit.

So now, what's next on my list.......?
 

antijam

CCCUK Member
Nice work, what's it done to your ride height and have you lost your list?
Thanks. With the longer spring bolts I originally fitted I could adjust the ride height and get rid of the list but that required different bolt adjustment side to side, which indicated to me that the old spring rate had degraded - at least on one side.

I've adjusted the bolts with the new spring to give standard ride height (which for a '71 convertible is 7.95" at the rear) and the car now sits level with equal adjustment both sides.
 

kentvette

CCCUK Member
Nice work! I swapped out the rear spring on our '78 back in about 1999, in a "lock-up" but had the assistance of wife June. We did remove the exhausts, but only had a trolley jack and axle stands. The old spring bolts and spring all came away easily (thankfully) and my replacement was a composite unit, which transformed the car! It's one of the many jobs we did back then that I wish I had had the Quick Jack for!:rolleyes:

I suspect that editor Mark Eaton would like your story in "magazine format", especially given his remark about C3 articles, or lack of. :)
 

antijam

CCCUK Member
Nice write-up.
Does the ride feel any different with the new spring?
Thanks. Having done the work it's easy to convince yourself that it's made a difference but being realistic I'm not sure it has. The ride is perhaps just a tad more fluid, which ought to result from the rubber interleaves in the new spring. The original spring was supposed to have plastic interleaves but looking at mine I couldn't detect any interleaves at all - perhaps it was already a replacement?

I did toy with the idea of a composite replacement but these are much stiffer than the originals and also really need the shocks to be changed to counteract the increased 'bounciness'. Also the composites are more susceptible to impact damage and in my case at least, would have mounted very close to the exhaust - and composites don't like high temperatures.
 

Forrest Gump

CCCUK regional rep
I did toy with the idea of a composite replacement but these are much stiffer than the originals and also really need the shocks to be changed to counteract the increased 'bounciness'. Also the composites are more susceptible to impact damage and in my case at least, would have mounted very close to the exhaust - and composites don't like high temperatures.
I need to replace my rear spring. It’s far too soft (maybe gone soft with age) and the car has excessive squat under hard acceleration.
I‘ve heard the same concerns about composite springs but I‘ll probably still go the composite route and fit a 360lb. That will in turn mean uprated front springs to keep a balance.
 

TimP

CCCUK Member
Interesting post! I had to replace the interleaves on my car as they were completely perished. As I was doing a complete rebuild the exhaust and spare tyre container had already been removed and that gave me a fair bit of space to put in a jack to lower the spring, reasonably gracefully, as they are heavy.

I used a similar arrangement - a 'c' clamp and a piece of wood to stop the jack slipping - to raise the spring but it was quite straightforward to get the spring disconnected from the trailing arm as the bushes on the spring bolt had perished and collapsed effectively lengthening the bolts so the spring tension was relatively relaxed.

All was well until it came to installing the spring bolts and threading them through the spring - at first glance when the spring is relaxed it looks like the bolts will never go through the spring as they are so far misaligned but if the trailing arm is raised until it is roughly parallel with the ground it all starts to make more sense. There is a good You Tube video by CorvetteBen on this. However, in my case to get the bolts and cotter pin on required the spring to be compressed quite a long way and raising the jack just lifted the car off the stands rather than compressing the spring. A few 25kg sand bags placed in the passenger compartment weren't enough and eventually my (petite) wife sat on the sill which allowed the spring to compress just enough to get the nut on.

One cautionary tale: I had put my car (with engine still installed) on 4 stands to provide some element of safety whilst rebuilding the rear suspension. My rebuild required the rear wheels, dampers, brake rotors, trailing arms, struts and spring to be removed, but this was done over a period of a few months. As I was removing each part I had not considered the effect on the centre of gravity of the car, which was slowly moving forwards with the weight being removed at the rear. The last straw was removing the spring and this made the car a little floaty on the stands - which was unnerving to say the least. Another set of stands under the front cross member corrected this but it goes to show how careful you need to be ....
 

kentvette

CCCUK Member
I need to replace my rear spring. It’s far too soft (maybe gone soft with age) and the car has excessive squat under hard acceleration.
I‘ve heard the same concerns about composite springs but I‘ll probably still go the composite route and fit a 360lb. That will in turn mean uprated front springs to keep a balance.
Before I bought the composite spring I'd heard a number of negative comments for various reasons. ride and the tendency to break being paramount and the aversion to heat. It's been on the car for 20 years now and done a LOT of miles. I put Knoi adjustable shocks all round when the spring went on - yes you do need better, double acting shocks. Mine is a 315lbs unit, and given the amount of miles, and the type of driving we do in this car, I was interested in the increased comfort the composite spring gave, and we were not disappointed. The huge weight saving perhaps also helps the ride a bit and it gives a bit of piece of mind when we are fully "luggage loaded"! If I'm honest, now the shocks could do with being a tad stiffer - age is catching up on them I suspect. And, our exhaust does run fairly close to the spring, something I was concerned about. An extra heat shield came with the spring a TRW unit) which I fitted, and so far, so good!

........One cautionary tale: I had put my car (with engine still installed) on 4 stands to provide some element of safety whilst rebuilding the rear suspension. My rebuild required the rear wheels, dampers, brake rotors, trailing arms, struts and spring to be removed, but this was done over a period of a few months. As I was removing each part I had not considered the effect on the centre of gravity of the car, which was slowly moving forwards with the weight being removed at the rear. The last straw was removing the spring and this made the car a little floaty on the stands - which was unnerving to say the least. Another set of stands under the front cross member corrected this but it goes to show how careful you need to be ....
I noticed in the spring fitting instructions that it specifically says to only lift the rear of the car and put it on axle stands. When we dropped the differential our of the car I had intended to put it 4 stands, but looking at how it sat on them I decided that there was too much weight at the front to risk it! When (and if!) I do the trailing arms over the winter I'm planning on using the Quick Jack, but I suspect i'll have an axle stand or two up front, just in case!
 

antijam

CCCUK Member
Just as an aside I would never work under a car supported on 4 jack stands. Most stands won't have a problem supporting the weight but unless they are of the very wide base professional type, the stability is marginal. It's far safer to have two wheels on the ground or the car on a dedicated lift. If the car needs to be raised on its wheels, cribbing blocks provide excellent support.
 
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Daytona Vette

CCCUK regional rep
I need to replace my rear spring. It’s far too soft (maybe gone soft with age) and the car has excessive squat under hard acceleration.
I‘ve heard the same concerns about composite springs but I‘ll probably still go the composite route and fit a 360lb. That will in turn mean uprated front springs to keep a balance.
I had an issue with rear squat when traversing a particular dip on the way home at speed, I had a new rear steel spring (heaviest duty) and new shocks, the car was solid at the back, you could not depress it, I changed the shocks for single adjust ones from VBP (may be QA11s - I can look it up if you wish) the Shocks sorted it, I thought it was the spring but was advised differently by a handling guru - I already had the same shocks at the front in coil overs.

If you go for a composite rear and adjustable Shocks, you will need double adjust Shocks. I had a composite many years ago for one afternoon.
 

kentvette

CCCUK Member
Just as an aside I would never work under a car supported on 4 jack stands. Most stands won't have a problem supporting the weight but unless they are of the very wide base professional type, the stability is marginal. It's far safer to have two wheels on the ground or the car on a dedicated lift. If the car needs to be raised on its wheels, cribbing blocks provide excellent support.
I noticed you had axle stands under the Quick Jack too....
 

antijam

CCCUK Member
I noticed you had axle stands under the Quick Jack too....
I certainly did! I was trained in the aircraft industry where redundancy is the key element of safety....
"Redundancy is the duplication of vital systems for use in the event of failure. Redundancy is one of the most useful tools for reducing the probability of a major fault affecting the safety of the aircraft and any passengers."
Old habits die hard.......
 

Forrest Gump

CCCUK regional rep
I had an issue with rear squat when traversing a particular dip on the way home at speed, I had a new rear steel spring (heaviest duty) and new shocks, the car was solid at the back, you could not depress it, I changed the shocks for single adjust ones from VBP (may be QA11s - I can look it up if you wish) the Shocks sorted it, I thought it was the spring but was advised differently by a handling guru - I already had the same shocks at the front in coil overs.

If you go for a composite rear and adjustable Shocks, you will need double adjust Shocks. I had a composite many years ago for one afternoon.
I did a freshen-up on my suspension some years ago fitting poly bushes throughout and KYB gas-adjust shocks. I didn’t change the Stock steel spring. The KYB shocks certainly stiffened up the ride, and despite the soft rear spring, the ride is quite harsh. If you push down on the car it won’t move. The shocks just lock it up. I hear what you’re saying but I think in my car the stock spring (rated at 196lbs) is never going to be man enough to prevent squat with my horsepower now. The car doesn’t bottom out on a dip though, unless I have a passenger.
Although KYBs are a “performance” shock, I don’t think they will be much good with a composite spring. I reckon I’ll go for the highly regarded Bilstein sport shocks.
 
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