Rear Suspension Travel

[Bob Winn]

Hi all, anyone know what the "stock" rear suspension travel is? On my car, when I received it, the swaged tubes were making contact at full droop when the car was jacked up, with the QA1 shocks on it, and was getting maybe 2" of travel on the rear wheels. I do not know if they were ever set up correctly, as the car us just a roller. If I take the shocks out and adjust my rod ends way out, I can get a whole lot more travel, 3.44" without any contact of the pushrod with the upper arm, BTW 3.44" is also about what I can get with the push rod disconnected. However, the rod ends are way out to get this travel. My push rod is a 12" long, 5/8 ID, looks like .81" OD (which is odd, as everything I see online is 7/8") LH/RH swaged tube. In the setup where I get the most travel, I would like to have a 14" rod on there. Seems a little strange.

What is normal out there? I have read rear travel is limited on most cars, but just looking for hard numbers. My setup I am assembling does not have the shock at the stock position, so I am not limited by over extension/compression of the dampener.

 

[Terry Oxandale]

Not an SLC owner, but, I did sleep at a Holiday Inn while looking at web photos of this suspension. Being no one has jumped in, I'll be the catalyst.

From what I can tell, extending the rod ends to their max (effectively lengthening the pushrod) indicates to me some poor geometry of the bellcrank (for an OEM positioned shock maybe). Plus, "...does not have the shock at the stock position..." is very telling to me that you may need to investigate that more, or perhaps go with a shorter shock to return the bellcrank geometry to a satisfactory position (only guessing at this point). Regardless, some photos for this question would be extremely helpful. Without any photos (multiple angles), I'm not sure anyone is going to be able to provide a solution or suggestions other than normal travel, which seems to be perhaps an insignificant part the issue here.

 

[Mark B.]

I have about 3" wheel travel on the rear and 3.5" on front of my SLC. I haven't measured it with the springs off to check the full travel though. The rods definitely shouldn't be making contact with the frame at all. If I recall correctly I have about 1/16" - 1/8" clearance, not much.

 

[Bob Winn]

My push rod was defiantly making contact with the top A arm in the rear. I am going to be running torsion bars for my springs, so I am not using a dampener at the stock location. I should be able to get the full ~3.5 inches of travel, even with the lift kit on there. My feeling is that the car was set up as a roller, with no motor or trans in it, I bet they just push the springs perches up as far as they would go to make pushing it around easy.

Thanks for the input.

 

[Mark B.]

My push rod was defiantly making contact with the top A arm in the rear. I am going to be running torsion bars for my springs, so I am not using a dampener at the stock location. I should be able to get the full ~3.5 inches of travel, even with the lift kit on there. My feeling is that the car was set up as a roller, with no motor or trans in it, I bet they just push the springs perches up as far as they would go to make pushing it around easy.

Thanks for the input.

Sorry, yes I meant A-arm, not frame clearance. Yea I'm sure you're right -- they don't do any setup for rollers, just get it bolted together so it rolls

 

[Howard Jones]

The suspension setup on an SLC is more complicated than one simple measurement. The entire process needs to address two things.

1. Clearance of body panels to tires throughout wheel travel: You can help yourself quite a bit by cutting the wheel arch returns down to about 1/4 inch through the top of the arch down to about 90 degrees to horizontal and then less than 3/4 inch tapered from 1/2 down to the bottom at both the front and back. This should be done right at the start because you will do it anyway so don't fight it.

Then centering the front and rear clips on the tires to best fit in conjunction with the center section. all for this must be done with the car at ride height and the suspension set to zero camber and no toe in or out. At these settings, you can see that once it all fits well you can add toe in and negative camber and you will only add clearance.

The car must have the correct tires and wheels as well as at or very near the finished total weight otherwise you will have the car sitting in a droop condition. This will effect pushrod clearance to the a-arm.

2. At both the front and rear my car worked best with the rod ends turned almost all the way in on the chassis side leaving 3 or 4 threads exposed. Then I set the top rod end that attaches to the upright to achieve zero camber. I have been able to add as much as 2 degrees neg camber from there. Here you can use the inboard rodends and the single upright one to improve clearance to the pushrod but don't do this first. Set the car up as I describe and then make those final adjustments based on what you need for camber. On a street car I would set the rear at 1/2 neg and leave it there. More will just eat tires. This will give you a bit more room between the push rod and the a arm as well.

Now before you go to my build thread and ask why I made my own upper rear arms let me splane myself. I intend to make adjustable sleeved rod end bushings and install them into the upper a arms on both the front and back so that the camber can be set without removing the rod end from the through bolt. I haven't got to that yet but in the end, I am going to make both tubular front and rears anyway. This was a dry run really as I had material and a welder so I just went and made them as a first run-through. I also thought I had a clearance problem like you have eluded to above but in the end, it would have all fit anyway.

Back to 2. The process of setting the body position and the suspension setup is very much one process. Include trial fitting the windshield in this and to a lesser degree the doors. DO NOT leave the windshield to after the whole body is set in final placement and then check to see if the windshield fits.

Once you have the body clearance and a baseline suspension setup as I describe I think you will find that the suspension travel clearance will take care of itself. These cars don't really use a lot of travel when they are sprung correctly anyway. Mine uses about 1-inch droop and maybe 1 1/2 inches compression on track. It is very stiff but that's needed due to downforce compression at high speed.

AND.............don't take it off road!!

I hope this helps.

 

[Jeff W]

Howard, were the wheel well lip mods to both front and rear?

 

[Howard Jones]

Yes, I ended up with very little return (lip) on front and back. Start with 1/4 to 3/8 inch and see how it all fits. Then you can remove a bit more if you have to. I think you will but this depends on wheels and tire choice somewhat. I have 18 and 19 inch C6 corvette wheels with 285/30/18 and 345/30/19

 

[Bob Winn]

Thanks guys, big help on this.

 

[Aaron H.]

The suspension setup on an SLC is more complicated than one simple measurement. The entire process needs to address two things.

1. Clearance of body panels to tires throughout wheel travel: You can help yourself quite a bit by cutting the wheel arch returns down to about 1/4 inch through the top of the arch down to about 90 degrees to horizontal and then less than 3/4 inch tapered from 1/2 down to the bottom at both the front and back. This should be done right at the start because you will do it anyway so don't fight it.

Then centering the front and rear clips on the tires to best fit in conjunction with the center section. all for this must be done with the car at ride height and the suspension set to zero camber and no toe in or out. At these settings, you can see that once it all fits well you can add toe in and negative camber and you will only add clearance.

The car must have the correct tires and wheels as well as at or very near the finished total weight otherwise you will have the car sitting in a droop condition. This will effect pushrod clearance to the a-arm.

2. At both the front and rear my car worked best with the rod ends turned almost all the way in on the chassis side leaving 3 or 4 threads exposed. Then I set the top rod end that attaches to the upright to achieve zero camber. I have been able to add as much as 2 degrees neg camber from there. Here you can use the inboard rodends and the single upright one to improve clearance to the pushrod but don't do this first. Set the car up as I describe and then make those final adjustments based on what you need for camber. On a street car I would set the rear at 1/2 neg and leave it there. More will just eat tires. This will give you a bit more room between the push rod and the a arm as well.

Now before you go to my build thread and ask why I made my own upper rear arms let me splane myself. I intend to make adjustable sleeved rod end bushings and install them into the upper a arms on both the front and back so that the camber can be set without removing the rod end from the through bolt. I haven't got to that yet but in the end, I am going to make both tubular front and rears anyway. This was a dry run really as I had material and a welder so I just went and made them as a first run-through. I also thought I had a clearance problem like you have eluded to above but in the end, it would have all fit anyway.

Back to 2. The process of setting the body position and the suspension setup is very much one process. Include trial fitting the windshield in this and to a lesser degree the doors. DO NOT leave the windshield to after the whole body is set in final placement and then check to see if the windshield fits.

Once you have the body clearance and a baseline suspension setup as I describe I think you will find that the suspension travel clearance will take care of itself. These cars don't really use a lot of travel when they are sprung correctly anyway. Mine uses about 1-inch droop and maybe 1 1/2 inches compression on track. It is very stiff but that's needed due to downforce compression at high speed.

AND.............don't take it off road!!

I hope this helps.

And no snow driving in it either.. LOL