86 C10 Trailing Arm Conversion

[SCOTI]

Pics . . ....

[bluex]

Thanks for the pics Scoti. I feel kinda dumb asking for them now. It was/is really obvious, but the only pics of them I had seen was installed on a truck.

[JW76]

I see that this has some new interest. I am home and started mocking things up. When I initially started researching this project I found the CPP kit and called on it and they said that it would work on long beds too.... It has been almost a year and I still have no part number for longs beds or further information. I started mocking up my truck with the 60s stock crossmember and the stock arms and I figured out that CPP informed me incorrectly. The kit will ONLY work on short beds. If you look at their install, the crossmember mounts under the cab where the frame starts to bend downward. You need a custom crossmember like the HRH truck to make anything work on a long bed. The crossmember cannot go between the frame rails because it puts way to much of an angle on the arms. It also cannot be mounted underneath because it is too low. Instead, you need to make a crossmember that mounts the arms so that the pivot point is even with the bottom flange of the frame. Also, I found that the frame widths are the same, so you can use the stock shock mount crossmember. In addition you could in theory use the stock style springs mounted to a bracket air ride part number A002E just mount them to the outside of the frame rails. It will give you the right width to use the coils since the coil frames flared out at that portion.

[joe231]

I would have to disagree
the difference in wheelbase between long and short beds is 14"
and that 14" difference is straight and horizontal frame, so it wouldn't change the relationship of the crossmember to the rear axle

[Super73]

Originally Posted by JW76

I've read many articles about how great the trailing arm suspension is in the 67-72s and how it has been used in Nascar, etc.

FYI, the only reason they are still used in Nascar is because it has been standardized to make things more even for all the teams/drivers. it's written in to the rules. There are better designs for turning corners. However, it can be made to work well..

Originally Posted by SCOTI

Try finding a rear housing that's ready for truck arms. While this can be done several different ways, 12-bolt 67-69 truck rears aren't commanding premium dollars in used,

Neither are the 63-66's. The nice thing about the earlier ones is the panhard bar is longer and located on the axle tube. A longer PH is going to have less side to side movement under a bump. Although, this could always be addressed with a custom fabed ph bar. You want it as long as possible.

Originally Posted by SCOTI

From what I remember, they should be 51" from C/L of the front bushing bolt to the C/L of the rear u-bolt/axle tube.

This sounds about right. FYI, for every 1" of movement up or down, there is aprox 1.1" of pinion angle change.

Originally Posted by JW76

HRH sets their vehicles up almost identical to NASCAR. They install the trailing arms almost level with only a slight maybe 6 inches of pitch to the crossmember. They use screw jacks and coils for easy adjustment. For the panhard, they attach to either the drivers side axle tube above where the trailing arm connects or they catch the trailing arm then they anchor it on the right side frame rail with an adjustable mount with maybe 4-5 inches of vertical adjustment. They then set the panhard bar so that it is level at ride height. The panhard seems to run horizontal right along the axle tubes. This setup seems to work perfect form them allowing them to adjust to run drag, drift, or road courses.

http://67-72chevytrucks.com/vboard/a...1&d=1254223571

Originally Posted by JW76

Reading some other articles I read that the panhard should run at an angle with the center of the panhard crossing the differential, or that the panhard can be over the axle running parallel to it.

PH bar should be level with the axle center, if not at he same height too. This will help your roll center in a corner. Making it adjustable is a good thing to accomadate ride height changes.

Originally Posted by JW76

Also, I've read that having the trailing arms flatter will increase traction without pulling the front end off the ground and that the more angle you get, the more it wants to squat the rear end and lift the front.

Angle of the control arm is not important, period.. What is important is where the front mounting hole is. The diagram above that you posted shows you the importance of the location that hole has. It will change your instant center of gravity. If your instant center is above your center of gravity ( >100% antisquat ) you will induce antisquat during acceleration. What this does under acceleration is seperate the rear and body, forcing the tires in to the ground hard (hitting the tires harder). If it passes exactly through the center of gravity (100% antisquat) the rear will be neutral under acceleration. If bellow CG( < 100% AS) you will squat the rear under acceleration hitting the tires less hard.

BTW, the more AS you have, the less front rise you will have.. IE the more squat, the more the front will come up.

Originally Posted by JW76

Also, when I mentioned putting the crossmember under the frame, it makes my geometry identical to that of the HRH truck. I intend to keep my 15 inch wheels and can only afford to drop the truck in the back about 3 inches or so so with that drop it gives me identical geometry to the HRH truck which the owner of HRH swears by.

Putting the X-member under the truck is going to force you to gussett it and reinforce it. Why not put it in the rails (which is stronger). Why not do this: http://67-72chevytrucks.com/vboard/s...d.php?t=278864



Might I suggest starting here: http://67-72chevytrucks.com/vboard/s...d.php?t=326863

Then if you can find it, purchase Herb Adams Chassis Engineering. There is a lot of really good info in that book.

[joe231]

Nice Post Super73!!

is this the book you referenced?


Amazon.com: Chassis Engineering HP1055...

[SCOTI]

Originally Posted by Super73

...Neither are the 63-66's. The nice thing about the earlier ones is the panhard bar is longer and located on the axle tube. A longer PH is going to have less side to side movement under a bump. Although, this could always be addressed with a custom fabed ph bar. You want it as long as possible.

I listed the 67-69's as they're typically the sure thing because you get 30-spline axles already. The earlier 63-64's (maybe some 65's) had the weaker 17-spline axles.

[JW76]

and you can't do a decent drop because the arms will hit the frame

[JW76]

i can post pictures of it mocked up with the crossmember between the rails and such if anybody is interested

[joe231]

what is your definition of a decent drop?
you can get low enough that the diff hits the bed floor, if you wanna go lower you will need to modify the frame and bed anyway, so just make a bigger notch to to clear the arms or Z the frame.....


pictures would be great

[tymbom]

Porterbuilt can make'em lay frame with trailing arms... That should be more than low enough for most people

[SCOTI]

Originally Posted by JW76

.....and you can't do a decent drop because the arms will hit the frame....

i can post pictures of it mocked up with the crossmember between the rails and such if anybody is interested

Can't do decent drop on a 73-87? You sure can on 60-72's......
Post those pics.

[Super73]

Yes, that is the book..

Scotti, good point on the spline count.. Interesting enough, mine had an aftermarket posi and axles in it when I bought it.. Didn't realize there was a difference.

The trailing arms are wider than the frame where they meet the Rear on my 63.. I'd assume it's that way on all the 60-72's.. Also, the spring in stock location sits in between the LCA and frame rail. If you were to bag it or use coil overs, you could notch the frame and have no issues with the rear suspension.