rear suspension design help needed

[wedged]

Now we are getting somewhere ! Thanks everyone.

just to clarify a few things:

I will end up with at least 1" clearance from the tire to any body sheet metal, probably closer to 1.5". In the pictures it's at about 1". I'll build the rear axle to be about 1" total narrower than I want and then I can use thin spacers to dial in the final width.

For the mounting the upper links, I had already thought of the off road diff or making a tube bridge over the diff to weld mounts to. There may even be diff covers with mounts already on them, but I have not searched enough yet.

I will probably start with coil overs, but may eventually end up with bags all around. I'm just not sure if I want to add the tank, compressor, etc.

Am I correct thinking the uppers are 60 degrees compared to each other and not an upper compared to a lower ?


I just test drove a pro street '68 barracuda that I put a new set of gears and one new axle into. It's a ladder bar car with heim ends. I'm not putting up with the constant clunking and clanking and that's why I want to use urethane in the truck.

I also have a '68 satellite in the shop that has an Air Ride 4 bar in the rear. I had thought of taking measurements off of it, but I feel that set up is compromised from being ideal in order to be a bolt on kit. So why bother copying it ?

[exwestracer]

You probably won't find a diff cover with exactly the mounts you are looking for, but there are some out there that would be a good start. I wouldn't bother with the bridge on that Dana 60...a 10 bolt is a different story.

You are correct about the 60deg referring to the angle between the 2 upper links.

[wedged]

I made a quick 2d overhead view cad drawing. O-O of the rails at 30.0", upper links mounted 6" apart on rear. I came up with 58 degrees included angle with an effective length of 18" for the uppers. Using the 70%-100% idea, the lower links would be 26" or less. I forgot to dimension the actual length of the uppers.

If i kept the frame rails wider in front of the tires, or had a crossmember in directly in front of the tires, I could make the upper links longer.

I'm going to fiddle around with the drawing and see what i can come up with.

[exwestracer]

Originally Posted by wedged

I made a quick 2d overhead view cad drawing. O-O of the rails at 30.0", upper links mounted 6" apart on rear. I came up with 58 degrees included angle with an effective length of 18" for the uppers. Using the 70%-100% idea, the lower links would be 26" or less. I forgot to dimension the actual length of the uppers.

If i kept the frame rails wider in front of the tires, or had a crossmember in directly in front of the tires, I could make the upper links longer.

I'm going to fiddle around with the drawing and see what i can come up with.

I usually try to get the uppers really close together on the axle, to help with angle/bar length and keep the roll center close the axle centerline. I've found we can get johnny joints down to 4" apart on center, and 3/4" heims down to 2" on center. If clearance above the housing is an issue, you'll obviously have to move them further apart to get them lower.

[wedged]

I think I can probably get the mounts closer together on the housing, but i figured 6" was a decent starting point. I don't have any clearance issues above the housing as I'm not too concearned about bed space.

Does it matter where the forward mount points of the upper links land in relation to the lowers in an overhead view ? I know they are typically inboard of the lowers, but could they be outboard ? The front frame from the dakota donor is about 38" to the outside. I could extend those rails back as far as I can in front of the rear tires, before squeezing it down to fit between them.

[wedged]

I found some joints and brackets and bushings that will probably work well to build the links. They also have very heavy duty Dana 60 covers.

[exwestracer]

Originally Posted by wedged

I found some joints and brackets and bushings that will probably work well to build the links. They also have very heavy duty Dana 60 covers.

Wow, the skull is sooo COOL!
The location in top view isn't really as important as the included angle. I'd keep the mounts as close to the frame rail as possible for strength, as long as you can get the right down angle for the Instant Center.

[wedged]

I played around with the crude CAD drawing, keeping the rails between the tires at 30" O-O and the rails in front of the tires at 38" O-O. I was able to make the upper bars have a 23" effective length with a 70 degree included angle. The actual length was 28". Would 28.75" be a good length for the lowers- that makes the upper effective length 80% of lowers ?

In the drawing, the frame starts to widen from 30" to 38" at a point 18" in front of the axle centerline for clearing the 29" diameter tires.

This may sound weird, but I'm getting excited about the possibility that this is going to work out well.

[exwestracer]

Originally Posted by wedged

I played around with the crude CAD drawing, keeping the rails between the tires at 30" O-O and the rails in front of the tires at 38" O-O. I was able to make the upper bars have a 23" effective length with a 70 degree included angle. The actual length was 28". Would 28.75" be a good length for the lowers- that makes the upper effective length 80% of lowers ?

In the drawing, the frame starts to widen from 30" to 38" at a point 18" in front of the axle centerline for clearing the 29" diameter tires.

This may sound weird, but I'm getting excited about the possibility that this is going to work out well.

Nothing sounds out of whack... Just curious, if the frame starts getting wider 10" back from your lower bar mounts, how do plan to attach them to the rails?

Hey, being excited is always better than worried....

[wedged]

I'm planning on making a crossmember that will be a driveshaft loop and front lower bar mount. I stilll need to make a front loop and trans crossmember but I'm going to build the rear suspension first.