Rear spring installation question
Thread Starter
Team Owner
Joined: Mar 2002
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Rear spring installation question
I bought the 7 leaf F41 rear spring from Duntov.
I got the 3.25" grade 8 bolts from Zip which is what they list for the 7 leaf.
Now measuring the thickness of the spring at the middle, I get 2.5". The bolt holes are around 0.75" deep. So for full thread engagement, that puts me right at 3.25". But once you add in the thickness of the mounting plate & lock washers, and the fact that the spring is slightly arched at the middle because it's fully relaxed, I can't even get these bolts to start threading in.
Am I missing something here? Should I have used the 3.5" bolts for the 7 leaf? Are there significant variations on the thickness of the spring depending on manufacturer?
At the rear holes, I guess it doesn't matter because they're open at the top so I can use as long as bolt as I want. The front holes however, I run the risk of punching through the cover if I use the wrong bolts. And in fact that's why I have a new cover now because the last owner torqued right through the old one.
I got the 3.25" grade 8 bolts from Zip which is what they list for the 7 leaf.
Now measuring the thickness of the spring at the middle, I get 2.5". The bolt holes are around 0.75" deep. So for full thread engagement, that puts me right at 3.25". But once you add in the thickness of the mounting plate & lock washers, and the fact that the spring is slightly arched at the middle because it's fully relaxed, I can't even get these bolts to start threading in.
Am I missing something here? Should I have used the 3.5" bolts for the 7 leaf? Are there significant variations on the thickness of the spring depending on manufacturer?
At the rear holes, I guess it doesn't matter because they're open at the top so I can use as long as bolt as I want. The front holes however, I run the risk of punching through the cover if I use the wrong bolts. And in fact that's why I have a new cover now because the last owner torqued right through the old one.
Last edited by wcsinx; Nov 7, 2009 at 08:07 PM.
Pro
Joined: Oct 2007
Posts: 549
Likes: 5
From: punta gorda florida
spring
i used a small floor jack with a 2by4 on its side to put some tension on the spring about 15 in. long this helped to flaten it out somw to help gget things started
I bought the 7 leaf F41 rear spring from Duntov.
I got the 3.25" grade 8 bolts from Zip which is what they list for the 7 leaf.
Now measuring the thickness of the spring at the middle, I get 2.5". The bolt holes are around 0.75" deep. So for full thread engagement, that puts me right at 3.25". But once you add in the thickness of the mounting plate & lock washers, and the fact that the spring is slightly arched at the middle because it's fully relaxed, I can't even get these bolts to start threading in.
Am I missing something here? Should I have used the 3.5" bolts for the 7 leaf? Are there significant variations on the thickness of the spring depending on manufacturer?
At the rear holes, I guess it doesn't matter because they're open at the top so I can use as long as bolt as I want. The front holes however, I run the risk of punching through the cover if I use the wrong bolts. And in fact that's why I have a new cover now because the last owner torqued right through the cover.
I got the 3.25" grade 8 bolts from Zip which is what they list for the 7 leaf.
Now measuring the thickness of the spring at the middle, I get 2.5". The bolt holes are around 0.75" deep. So for full thread engagement, that puts me right at 3.25". But once you add in the thickness of the mounting plate & lock washers, and the fact that the spring is slightly arched at the middle because it's fully relaxed, I can't even get these bolts to start threading in.
Am I missing something here? Should I have used the 3.5" bolts for the 7 leaf? Are there significant variations on the thickness of the spring depending on manufacturer?
At the rear holes, I guess it doesn't matter because they're open at the top so I can use as long as bolt as I want. The front holes however, I run the risk of punching through the cover if I use the wrong bolts. And in fact that's why I have a new cover now because the last owner torqued right through the cover.
Thread Starter
Team Owner
Joined: Mar 2002
Posts: 24,160
Likes: 78
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
I usually put the 2 rears in snug, so the spring won't go anywhere, and then let the car down to flatten it as much as possible. Then I use a set of V calipers in the hole to measure.
Sorry, didn't record the lengths.
Sorry, didn't record the lengths.
Pro
Joined: Feb 2002
Posts: 709
Likes: 10
From: Carlsbad CA
Also, do NOT tighten the bolts until you have the car on the ground and the spring under full load. If you tighten the bolts fully without the spring under load, the differential housing can crack when you set the car down.
Pete
www.c3vettes.net
Pete
www.c3vettes.net
Thread Starter
Team Owner
Joined: Mar 2002
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I'm just going to type this up for my own sanity. I grabbed my calipers and crawled under there again tonight.
spring thickness at the center as 2.50"
Mounting plate is 0.25"
Lock washer is 0.15"
So that added up is right at 2.90"
The 7 leaf bolts I have are 3.25"
So that leaves you with 0.35" worth of thread engagement, which ain't much but I guess it's good enough.
I measured the forward bolt hole at 0.77" deep bottoming out the bolt by hand which means a 3.25" bolt leaves 0.42" of unused thread. So me being that **** rententive engineer I am, I grabbed some 3.50" bolts to use up another 0.25" of thread leaving just 0.17" of unused thread in the hole.
I'm not sure it matters, but I'll sure feel better knowing that spring is held on by more than ~1/3" of thread!
So FYI if you get a 7 leaf spring, theoretically the 9 leaf bolts won't damage your cover.
spring thickness at the center as 2.50"
Mounting plate is 0.25"
Lock washer is 0.15"
So that added up is right at 2.90"
The 7 leaf bolts I have are 3.25"
So that leaves you with 0.35" worth of thread engagement, which ain't much but I guess it's good enough.
I measured the forward bolt hole at 0.77" deep bottoming out the bolt by hand which means a 3.25" bolt leaves 0.42" of unused thread. So me being that **** rententive engineer I am, I grabbed some 3.50" bolts to use up another 0.25" of thread leaving just 0.17" of unused thread in the hole.
I'm not sure it matters, but I'll sure feel better knowing that spring is held on by more than ~1/3" of thread!
So FYI if you get a 7 leaf spring, theoretically the 9 leaf bolts won't damage your cover.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
3/8" certainly isn't much.
I ended up assemblying my own spring using a Guldstrand shortened lower leaf (twice as thick) and using the original bolts. I needed extra thickness, so I made a 1/4" plate the same dimensions as the oem clamping plate. Seem to remeber I had close to 1" threaded. Worked out well since the original ears were bending when tightened anyway, now they don't.
I ended up assemblying my own spring using a Guldstrand shortened lower leaf (twice as thick) and using the original bolts. I needed extra thickness, so I made a 1/4" plate the same dimensions as the oem clamping plate. Seem to remeber I had close to 1" threaded. Worked out well since the original ears were bending when tightened anyway, now they don't.
Thread Starter
Team Owner
Joined: Mar 2002
Posts: 24,160
Likes: 78
3/8" certainly isn't much.
I ended up assemblying my own spring using a Guldstrand shortened lower leaf (twice as thick) and using the original bolts. I needed extra thickness, so I made a 1/4" plate the same dimensions as the oem clamping plate. Seem to remeber I had close to 1" threaded. Worked out well since the original ears were bending when tightened anyway, now they don't.
I ended up assemblying my own spring using a Guldstrand shortened lower leaf (twice as thick) and using the original bolts. I needed extra thickness, so I made a 1/4" plate the same dimensions as the oem clamping plate. Seem to remeber I had close to 1" threaded. Worked out well since the original ears were bending when tightened anyway, now they don't.
But I sure hope you didn't thread 1" in on the forward holes because you poked through the cover if so!
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Thread Starter
Team Owner
Joined: Mar 2002
Posts: 24,160
Likes: 78
Yeah, that's what the guys at Duntov suggested as well. While I'm sure I can get the 3.25" bolts threaded like that, I'm going to go with the 3.5" bolts. I figure I might as well use all the thread I can!
Race Director
Joined: Mar 2006
Posts: 14,112
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From: Florida
Probably good idea to record all the measurements for future reference.
