Chevy Nova Forum banner

1 - 20 of 48 Posts

·
Registered
1970 2-Door Barn Find
Joined
·
58 Posts
Discussion Starter #1
I recently purchased a '70 plain-jane, 307 Nova and I am doing a restomod to get it in shape. It came with REALLY tired mono-leaf springs so a conversion to multi-leaf was in order. I picked up a Detroit Speed conversion kit (p/n 041101) and a set of Summit Racing multi-leaf springs (p/n7081GM, 4 leaf, 110 lbs/in spring rate). There were some issues during installation but I got them in. Then the trouble started.

Ride height is great and its fine around town but, when I get on the freeway, it starts wandering around. The entire front suspension is new and have been professionally aligned. However, it feels like the backend is moving around. VERY unnerving at highway speeds.

During the installation, I didn't notice the Detroit Speed note that said their conversion kit was made for THEIR drop leaf springs which have a 1 11/16" thickness at the spring perch. It turned out that the Summit springs were only 1 3/16". My solution was to leave out the aluminum spacers and tighten the U-bolts until the bottom plate started bending. This might be the source of my instability.

I am open to suggestions on how to get out of this dilemma. I'd like to keep the springs (good height) but everything else in on the table.

411277
Leaf spring 1.jpg


411278
 

·
Premium Member
72, 2 Dr, 383, 700r4
Joined
·
1,336 Posts
The problem is the clamp on the spring, it's bowed. With a mono perch you will need the proper spacers that will give equal clamping force across the spring.
 

·
Registered
1970 2-Door Barn Find
Joined
·
58 Posts
Discussion Starter #3
What if I just replace the lower plate with an aftermarket multi-leaf plate and 1/2" u-bolts? Would the mono-leaf spring saddle handle that?
 

·
Premium Member
72, 2 Dr, 383, 700r4
Joined
·
1,336 Posts
I'm not sure, my monos were shot but I did find a 3 leaf that would mount and clamp correctly with the original mono perch on the rear. You do have to get rid of the original rubber pads. I'm not on the road yet so I cant speak to how it came out. It looks like it has equal clamp without the bowing as they advertised I just don't know how to measure the force.
 

·
Registered
Mike - 74 Nova Baltimore, MD
Joined
·
1,534 Posts
When you are driving your car on the highway, does the vehicle begin to rock from side to side while you are driving at a consistent/steady speed?... and especially if you slightly turn your steering wheel back and forth (like a lane change)?
I had this happen to me (but in another type of vehicle)... so I know exactly what you mean by "VERY unnerving ".

If so, this rocking could be caused by "rear steer".... the rear differential could be shimmying back and forth at higher speeds. I would recheck all front and rear leaf spring mounting locations. Raise the rear of the vehicle and support the weight of the car by placing jack stands under the rear frame (not the rear axle). Try to pry on both sides of the differential/rear wheels and check for any movement/play in the front spring eye sections and rear shackles. Confirm all of the nuts/bolts are properly torqued and tight.
 

·
Registered
1970 2-Door Barn Find
Joined
·
58 Posts
Discussion Starter #7 (Edited)
When you are driving your car on the highway, does the vehicle begin to rock from side to side while you are driving at a consistent/steady speed?... and especially if you slightly turn your steering wheel back and forth (like a lane change)?
I had this happen to me (but in another type of vehicle)... so I know exactly what you mean by "VERY unnerving ".

If so, this rocking could be caused by "rear steer".... the rear differential could be shimmying back and forth at higher speeds. I would recheck all front and rear leaf spring mounting locations. Raise the rear of the vehicle and support the weight of the car by placing jack stands under the rear frame (not the rear axle). Try to pry on both sides of the differential/rear wheels and check for any movement/play in the front spring eye sections and rear shackles. Confirm all of the nuts/bolts are properly torqued and tight.
"Rear Steer" sounds right. I have the car up on a lift now to replace the spring plates with stronger ones... ones made for multi-leaf springs. I may also replace the (new) 7/16" u-bolts with 1/2" ones. The original mono-leaf spring "saddle" welded to the axle tube doesn't look particularly strong. May reinforce those as well....

Mike
 

·
Registered
1970 2-Door Barn Find
Joined
·
58 Posts
Discussion Starter #8
Do I barely see an aftermarket rear sway bar ?.

I wonder is this is affecting anything ?.

Jim
I don't think so. The ends of the bar attach to the body using links so they should "swing". I will look at them, though.

Mike
 

·
Registered
Joined
·
2,918 Posts
I don’t feel like we have enough information and pictures to diagnose the problem with the car.

I don’t think that the problem is where the springs mount to the axle as it is clearly clamped tight enough to bend the lower plate. I’m not saying it’s correct just that I don’t believe it could cause the conditions you are describing.

You stated that you had some issues with the installation..
What were the problems..?
Why do you think it is “rear steering”..?
How do your forward spring pockets look..? I know some have had trouble with the mounting hardware with the pockets..
What did you do the the front suspension..?
What condition are the front subframe to body mounts in..?
Does your car have any rust issues in structurally critical areas..?
What kind of shape are your tires in..?
Was the road your were experiencing the unusual handling characteristics heavily grooved either rain grooves or ruts from heavy use..?
 

·
Registered
Joined
·
538 Posts
How is the spring located in the mono perch??

A stock mono perch has no hole in the top center of the perch for the spring center pin in the multi leaf stack.....the stock mono spring just had a formed lump in the BOTTOM of the leaf that located in the hole in the lower spring plate.
That hole in the lower spring plate is way too big to accurately locate the small nut on the end of the multi leaf pin...the stock multi leaf welded perch has a pocket for the head of the pin.

If the head of the center pin isn't solidly located in a guide hole at the top of the perch the entire axle will slide for and aft on the spring set no matter how tight you clamp it.

What is that thick pad on top of the sprinf stack, between the stack and the perch?? A rubber isolator/spacer?
 

·
Registered
1970 2-Door Barn Find
Joined
·
58 Posts
Discussion Starter #11 (Edited)
What were the problems..?
The Detroit Speed kit came with aluminum spacers that were suppose to between the plate and the saddle. However, when in place, the plate would not clamp onto the spring leaving almost a 1/2" of space. I left out the spacers so I could clamp the springs.
Why do you think it is “rear steering”..?
Example: When changing lanes on the freeway, the car feels loose as if the rearend wants to come around when I straighten out in the next lane.
How do your forward spring pockets look..? I know some have had trouble with the mounting hardware with the pockets..
I did not experience any problems when I installed them but I am going to remove the and inspect them more closely.
What did you do the the front suspension..?
The front suspension is completely new, including CPP tubular a-arms, stock-height coil springs, 2" dropped spindle and Series 500 Steering Box. It has be professionally aligned twice.
What condition are the front subframe to body mounts in..?
The subframe was removed, cleaned, inspected (no defects), painted and reinstalled with new body mounts and hardware.
Does your car have any rust issues in structurally critical areas..?
The body is rust-free.
What kind of shape are your tires in..?
The tires and wheels are new and balanced.
Was the road your were experiencing the unusual handling characteristics heavily grooved either rain grooves or ruts from heavy use..?
The problem is experienced on both smooth and rough roads (at freeway speeds). Rain grooves
and "wear ruts" do make the problem worse.

Mike
 

·
Registered
1970 2-Door Barn Find
Joined
·
58 Posts
Discussion Starter #12
How is the spring located in the mono perch??

A stock mono perch has no hole in the top center of the perch for the spring center pin in the multi leaf stack.....the stock mono spring just had a formed lump in the BOTTOM of the leaf that located in the hole in the lower spring plate.
That hole in the lower spring plate is way too big to accurately locate the small nut on the end of the multi leaf pin...the stock multi leaf welded perch has a pocket for the head of the pin.

If the head of the center pin isn't solidly located in a guide hole at the top of the perch the entire axle will slide for and aft on the spring set no matter how tight you clamp it.
I believe you are correct. I had to install a steel spacer with a hole in the middle (came in the kit) on top of the spring stack so the guide pin did not impact the axle tube. I thought the pressure from the u-bolts would hold it in place.

Mike
 

·
Registered
1970 2-Door Barn Find
Joined
·
58 Posts
Discussion Starter #13
How is the spring located in the mono perch??

A stock mono perch has no hole in the top center of the perch for the spring center pin in the multi leaf stack.....the stock mono spring just had a formed lump in the BOTTOM of the leaf that located in the hole in the lower spring plate.
That hole in the lower spring plate is way too big to accurately locate the small nut on the end of the multi leaf pin...the stock multi leaf welded perch has a pocket for the head of the pin.

If the head of the center pin isn't solidly located in a guide hole at the top of the perch the entire axle will slide for and aft on the spring set no matter how tight you clamp it.
Here is a picture of the bottom of the mono-leaf spring plate. The nut is the guide pin bolt. It looks like a tight fit but I will see more when I take it off.

Mike
411299
 

·
Premium Member
72, 2 Dr, 383, 700r4
Joined
·
1,336 Posts
The thing with the spacers is it is a fine line between bending the lower plate and getting proper clamp. I recall a thread on this site a few years ago addressing that. It became a custom fit issue that required shaving the blocks to get proper clamp. The problem I have is how do you measure that clamp. The torque of the U-bolt nuts can be deceiving. But like Thug said, there are many factors to consider.
 

·
Registered
1970 2-Door Barn Find
Joined
·
58 Posts
Discussion Starter #15
The thing with the spacers is it is a fine line between bending the lower plate and getting proper clamp.
I agree. And I don't like it. I think I am going to convert it to a standard multi-leaf spring approach. Not quite sure how (with that funky mono-leaf saddle) but I'm pretty sure I can get there.

Mike
 

·
Registered
Joined
·
458 Posts
It does sound like the rear axle may be moving. No detectable slop in the springs, bushings or shackles? The leaf springs are the only thing that locates the rear on that car right? With the car on the ground, can you make it move by pushing on the side of the car?


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
458 Posts
There is a couple of comments in the reviews section of those springs on the Summit site describing having to make a 1-7/16” plate to make them work?




Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
2,918 Posts
A lane change at 50-70mph is not a dramatic event that should upset the stability of forward motion in my book. A lane change is still basically a slight deviation from moving straight ahead. How does the car behave when transitioning from right to left/left to right like in a slalom or going around a corner..? An evasive maneuver like swerving to avoid something on the road is an aggressive move and even that shouldn’t result in the type of experience you are indicating..

In your OP you stated that it feels fine running around town but when you get on the freeway it starts wandering..

Ride height is great and its fine around town but, when I get on the freeway, it starts wandering around. The entire front suspension is new and have been professionally aligned. However, it feels like the backend is moving around. VERY unnerving at highway speeds.
The front suspension is completely new, including CPP tubular a-arms, stock-height coil springs, 2" dropped spindle and Series 500 Steering Box. It has be professionally aligned twice.
Is the 500 steering box a “quick ratio” box..?
What are your caster and “toe” specs..?
 

·
Registered
Joined
·
538 Posts
I agree. And I don't like it. I think I am going to convert it to a standard multi-leaf spring approach. Not quite sure how (with that funky mono-leaf saddle) but I'm pretty sure I can get there.

Mike
You can get replacement multi-leaf spring perches...but that requires cutting the old off and carefully welding the new on the axle tubes.

What I can suggest with the mono perch is a flat 3/8 to 1/2" thick plate with a hole for the spring center pin drilled through it, then weld that into the mono perch to be a locator to mimic what a multi perch has. Might only need to be a 1/4" plate depending on thickness of bolt head and if you can also drill some of a locator hole in the top of the mono perch.

Looks like the current shim in there now could do it, if it is steel and thus weldable, weld it to the mono perch after verifying axle is located correctly, then correct the spacer length as needed for around the U-bolts and and the correct lower spring plate.
 

·
Registered
Joined
·
611 Posts
You can get replacement multi-leaf spring perches...but that requires cutting the old off and carefully welding the new on the axle tubes.

What I can suggest with the mono perch is a flat 3/8 to 1/2" thick plate with a hole for the spring center pin drilled through it, then weld that into the mono perch to be a locator to mimic what a multi perch has. Might only need to be a 1/4" plate depending on thickness of bolt head and if you can also drill some of a locator hole in the top of the mono perch.

Looks like the current shim in there now could do it, if it is steel and thus weldable, weld it to the mono perch after verifying axle is located correctly, then correct the spacer length as needed for around the U-bolts and and the correct lower spring plate.
To the OP:
I think I'd start by swapping wheels/tires and playing with tire pressures first to eliminate that variable. Swap shocks next.

As far as adding a flat plate, take a look at DIY4x and offroaddesign.com. They have a steel block that installs in the spring pack similar to the Summit comments refer to as a 5th spring.
Replacing spring perches on the tube isn't particularly difficult. You can buy the Mopar ones from summit for $15 a pair and unbolt one side at a time, cut off old, weld in new maintaining alignment and angles. You can even temporarily tack weld a bar on the other side of tube so you can measure before and after then cut and remove when done.
 
1 - 20 of 48 Posts
Top