C3 Rear Spring, Bolt, Ride Height and Dimension D

[Jack O.]

Ok, so I have my trailing arms back in and had previously completely rebuilt the rear suspension. I restored my original leaf spring which appeared to be fine. Per the assembly manual, I'm trying to make sure that the ride height is correct, it specifically has you check dimension D, before torqueing the front trailing arm bolts. Dimension D is the difference between the centerline of the two ends of the control arm. I've also pulled the car in and out of the garage and up and down the driveway to get the suspension back in shape after having the car on jack stands. I'm not so concerned about dimension D being per spec since the car is old and not outfitted per original specs.

My concern is that the left and right measurements differ. Dimension D on the left is 2 3/8 and right is 2 5/8. Also, when I measure from the top of the tire to the opening of the wheel well at about the tire centerline right side is about 5/8" higher on the right. I know the leaf spring bolt can make a difference in ride height and have the correct length ones and simply tightened the bolt until it lined up with the cotter pin hole. The two bolts appear to have their nuts tightened equally and also measured to ensure the bolt is equally tightened.

Finally my questions. Should I be concerned with the difference from left to right or simply attribute it to the car being old and probably having someone in the driver seat much more than the passenger seat or some such thing? Or perhaps the front suspension is causing the difference since I haven't done anything to the front suspension yet and I'm sure the bushings and perhaps springs are wore out. Or should I attempt to get the two sides equal by making adjustments to the leaf spring bolt? I'm not even sure this is possible since it can't be adjusted too much and still line up for the cotter pin. Anyone know about how much difference in ride height turning the bolt can make - is it even significant?

Goal is to get the trailing arms torqued and then have the rear aligned.

Thanks in advance,

Jack

[Gene M.]

Re: C3 Rear Spring, Bolt, Ride Height and Dimension D

Jack,
You stated " I restored my original leaf spring which appeared to be fine". What does that mean? Did you re-arch the leaf components? Did you balance the spring loading as an assembly end for end? Was the car sitting level before you started tear down? Original spring? If camber is not set the level can be who knows where.

[Joe L.]

Re: C3 Rear Spring, Bolt, Ride Height and Dimension D

Ok, so I have my trailing arms back in and had previously completely rebuilt the rear suspension. I restored my original leaf spring which appeared to be fine. Per the assembly manual, I'm trying to make sure that the ride height is correct, it specifically has you check dimension D, before torqueing the front trailing arm bolts. Dimension D is the difference between the centerline of the two ends of the control arm. I've also pulled the car in and out of the garage and up and down the driveway to get the suspension back in shape after having the car on jack stands. I'm not so concerned about dimension D being per spec since the car is old and not outfitted per original specs.

My concern is that the left and right measurements differ. Dimension D on the left is 2 3/8 and right is 2 5/8. Also, when I measure from the top of the tire to the opening of the wheel well at about the tire centerline right side is about 5/8" higher on the right. I know the leaf spring bolt can make a difference in ride height and have the correct length ones and simply tightened the bolt until it lined up with the cotter pin hole. The two bolts appear to have their nuts tightened equally and also measured to ensure the bolt is equally tightened.

Finally my questions. Should I be concerned with the difference from left to right or simply attribute it to the car being old and probably having someone in the driver seat much more than the passenger seat or some such thing? Or perhaps the front suspension is causing the difference since I haven't done anything to the front suspension yet and I'm sure the bushings and perhaps springs are wore out. Or should I attempt to get the two sides equal by making adjustments to the leaf spring bolt? I'm not even sure this is possible since it can't be adjusted too much and still line up for the cotter pin. Anyone know about how much difference in ride height turning the bolt can make - is it even significant?

Goal is to get the trailing arms torqued and then have the rear aligned.

Thanks in advance,

Jack

Jack-------


My 1969 had a slight lean (about 3/4") to the driver side FROM THE DAY IT WAS DELIVERED TO ME NEW. The GM reps told me that it was within specification.

[Jack O.]

Re: C3 Rear Spring, Bolt, Ride Height and Dimension D

Gene,
I'm pretty sure the spring was the original but can't be 100% sure. I simply disassembled the spring, stripped and repainted it and put it back together with new liners. Now that you asked, I'm pretty sure the car sat a bot higher on the passenger side and you make a good point about the camber.
Jack

[Jack O.]

Re: C3 Rear Spring, Bolt, Ride Height and Dimension D

Interesting, I guess I'm not going to worry about it and press on with the alignment.

[Alan S.]

Re: C3 Rear Spring, Bolt, Ride Height and Dimension D

Hi Jack,
In my 71's restoration I've used the original spring, bushings, shock absorbers, and bolts. (46K miles). The only things that I replaced were 2 spring liners.
The left side 'R' dimension is about 1/4"-1/3" less than the right side dimension after driving the car about 50 miles.
You're right, with the configuration of the original spring to trailing arm bolts there's really VERY little adjustment to be done.
Regards,
Alan

[Duke W.]

Re: C3 Rear Spring, Bolt, Ride Height and Dimension D

"Dimension D on the left is 2 3/8 and right is 2 5/8."

Sounds like it's okay per GM tolerance, however, the shorter the bolt the higher the ride height. You can effectively shorten the bolt by placing a quarter-inch worth of washers above the castle nut on the side that is low. Of course, this will be visible, but you can make them less obvious by removing the link bolt and placing the washers under the bolt head where they will not be as obviously visible.

Another persective that is used on serious competition cars is "corner balancing", the purpose of which is to get equal right/left weight distribution on both ends with the driver inside and about half a tank of fuel. This makes right/left dynamic response more consistent even if ride height is slightly unequal.

It's easy to do on some production cars like early Porsches that have adjustable torsion bars. The reason why purpose built race cars have coilover type spring/shock units is that they offer quick adjustment of both shock valving and ride height/corner balancing. It's fairly easy to do on C2/C3s at the rear using different length bolts or shims (washers) as I described above. It's a lot tougher on the front as the only way I know is to use spacers on the either end of the coil springs.

It's a tricky procedure because as you adjust one end the other will change. It's usually worth the effort on serious competition cars, but not such a big deal on a road car as long as right /left dynamic response is resonably the same.

Duke

[Erich M.]

Re: C3 Rear Spring, Bolt, Ride Height and Dimension D

Jack,

I am the original owner of my 72 coupe. The "R" dimension from the floor to the top of the rear wheel well is 28" on the passenger side and 27 1/4" on the driver's side. The car has 59,500 miles on it and the rear end was never restored. It has the original unrestored rear spring, shocks, and bushings. The rear suspension was disassembled to the extent necessary to replace the rear wheel bearings and differential seals.

Erich Meyer
"72 LT1 Bowtie & Top Flight