I am in the process of trying to get the rear spring mounted to the differential in my 74. This forum has been a wealth of information as I have progressed through my complete front and rear suspension rebuild, but I can't find an answer to this. I am trying to mount the leaf spring to the differential. It is a new stock style replacement. I can get the bolts to start into the differential. The curve of the spring is too great to allow the bolts to start. I thought maybe the new bolts were too short, so I compared them to the originals. They are actually longer!! I have read that bolts that are too long can be bad so I want to reuse the originals. This will only make it more difficult to get them started. So, how do I flatten the spring enough to start the correct length bolts?

 

Hi G,
Welcome!
First Post!!

Is the new spring the same number of leafs as your original spring?
Have you used the center bolt to pull the leafs together so it can be mounted?

Regards,
Alan

Without center bolt in place.


With center bolt tightened.



Bolt length of 9 leaf spring.


Dimension for 9 leaf spring.

 

Thanks for answering Alan,

Spring is as it came to me from vendor. Its a 9 leaf. I didnt tighten the bolt. The bolt to the right is the new one, original to the left.

 

Might the shoulder on the new center bolt be taller than the old one.
Maybe run the bolts in and measure what’s left hanging out.
Be careful of the 2blind holes. And don’t torque them down
Until the car is back down on the ground. Good luck.

 

VERY important to note: if the total thickness of your replacement spring is less than the total thickness of the original spring, you'll need to either buy shorter bolts for the center dog bone plate or you'll need to shorten (grind) them by the difference in total spring thickness. If you don't do this, you'll risk breaking through the blind holes in the diff case, causing you much trouble with a ruptured diff case and leaking gear oil. If replacing bolts, make sure you match the grade steel in the bolts.

You also will want to cut the excess length off the small socket head bolt that runs through all the replacement spring's leafs. Make it look like the original.

Hope this helps.

 

I read here recently that the replacement springs are made of thicker material. Even though it has the same number of leaves, they are each thicker and therefore the whole stack is thicker. Yours appears to be about 1/2" thicker than the picture of Alan's spring. I would be tempted to remove 1 or 2 of the shortest leaves as they mostly act as spacers anyhow. Or if your new spring is 1/2" thicker than the old, you could get 1/2" longer bolts.

 

Thanks for responding Redrdstr72,
my replacement spring is 1/2 inch thicker than the spring Alan posted a picture of. It looks like the liners are thicker. Also mine is the 6/3 style where the top three leafs are flat.

Also I have not removed the bands from the spring that were put on to keep the spring from moving around during shipping. Would removing them make any difference in the installation?

 

I have yet to ever have a rear spring bolt be able to go into the differential cover and at least hold the spring so I can get them all started. So this seems odd.

AS previously mentioned..and THIS IS NO JOKE!!! You must measure your OLD spring and compare it to your new spring and see how thick the over all thickness is and then do the math. Incorrect bolt length can either poke a hole into your cover like previously mentioned if it is to long OR not have enough threads going into the cover.

Once you do get the four bolts to hold the spring. SNUG them up but do not tighten them too much. Just get them good and snug. Then that is when I clamp a fixture I made onto the spring close to the end of it so I can slowly lower the car down onto it and it will not allow my jack stand to slide up the rear leaf spring due to its arc. I compress the spring so I can get the outer long bolt in place. I do one side at a time.

Then like it was previously mentioned...you need to get the car on the ground. By doing this...it will flatten the spring out and you will see that it is flat against the machined surface of the rear end cover...and then that will be when you go in and hand torque those four bolts.

I believe it is GRADE 8 bolts and split lock washers are required. And I have to cut these four bolts just about every time due to the aftermarket rear leaf springs are thicker than stock by about 1/4" to 1/2" or so. And for me...that is enough for me to have to get new bolts and get them to the right length.

DUB

 

Thanks for responding DUB,
I unfortunately have already disposed of my original spring so I can't compare the two. As I mentioned before my (assumed) original bolts are about 1/4 inch shorter than the new replacement ones I purchased. Can I run a bolt up into the differential and tell when it bottoms out? Then measure how much is exposed and determine how many leafs to remove and what bolt to use accounting for the thickness of the dog bone?

 

Hi G,
What was the source for the spring?
Can you post a photo that shows the entire spring so we can get an idea of what you're working with?
What's the WIDTH of the spring?
Is the head of the bolt running through the spring fitting into the guide hole in the differential case properly? (JB's question.)
Is the spring mounting against the notched surface of the differential cases's spring pad properly?
Regards,
Alan

 

Hello Alan,
Spring came from Corvette Central.
Width is 2 1/4 inches.
Bolt lines up into guide hole fine.
Spring seems to butts up to notched edge, but not sure if the liner is hitting it and moving it to the rear of the car a tiny bit.

 

Hi G,
At first glance this spring seems to still be 'spread'.... has the bolt at the center been tightened enough to pull the leafs tight against each other?
Mine is back on the car so I can't make a corresponding measurement.
Regards,
Alan

The shipping bands should come off but I don't think they're part of your situation.

 

Alan,
i just went out and put a wrench on it. It turned a bit, it's very tight now, measurement didn't change but about a 1/16 of an inch.

 

Dub explained.
one side then the other.

 

Alan,
looking at your spring it jumps out to me how much thinner the liners are compared to mine.the liners on mine are about the same thickness as the leafs. Could that cumulative difference be the problem?

 

Calwldlife thanks for responding,
my issue is not attaching the spring to the trailing arms, it's mounting it to the differential.

 

no.
the bow of the spring at attach is the issue as i see it.
yes, the spring interleaves are thicker so overall the spring is thicker.
put in the bolts at diffy without anything.
feel the bolt and watch for bottoming.
measure exposed length.
take spring, bolt up one side of diffy
measure to see how much squeeze the spring takes.
decide one bolt length.
loosen the attached bolts to allow the other side of diffy attach to be done.
use jack to push up spring on unattached side to better
flatten spring on diffy and allow the correct length bolts to be started.
careful on jack placement and watch for lifting car off the jackSTANDS.
snug bolts of correct length, attach to trailing arms, lower car
tighten bolts.
make sense?

 

Can't start bolts I to the diff with spring in place.

 

i understand.
you can use long bolts to attach ONE side.
then use jack at end of spring, where trailarms attach to
push the spring against the diffy to allow use of correct bolts.
c-clamp on spring to keep jack safe.
after putting in bolts on one side, do the jack on the other side
to put in correct length.
2 issues
1, correct length bolt that won't crack diffy when tightened
2, getting spring flat against diffy to allow starting bolts.

you just have to "walk" it in.
one side, then the other then maybe back to the other.
pain in the butt,

 

I get what your saying. When my assistant can help Saturday we will give it a try.
thanks a lot.