Suspension Swap (leaf to trailing arm)

[ARG0220]

Hello everyone,

I'm building a 65 SWB GMC truck with my Son. It's his first vehicle and we are making solid progress. Here is a link to the build:

http://67-72chevytrucks.com/vboard/s...d.php?t=697657

We located a donor chassis/drivetrain from a 69 long bed truck. The donor chassis has a trailing arm suspension with 12 bolt 6 lug rear axle. We are using the 350 small block with AC and power steering from the donor as well. The 65 GMC has a leaf spring suspension and a Dana 44 rear axle.

My question is related to measurements. My understanding is that the trailing arm lengths are the same for long and short bed trucks but the trailing arm cross member mounting location is different. I was hoping someone could verify that for me. Also, regarding the other components what should I be aware of before I pull the components on each truck for the swap? Lastly, I know that I will need a new trans cross member but not sure how to tackle the E-brake?

Thanks in advance for any help.

[ARG0220]

Here is a pic of the two side-by-side.

[bs46488]

Argo,

I have a 1972 that started life as a long bed. I cut the frame and truck bed down to short bed measurements.

When cutting the frame, the extra length comes out in front of the trailing arm cross member. So I would interpret that as the trailing arm cross member is located in the same position on both trucks, relative to the rear axle center line

[69gmcc10]

I did the trailing arm swap a few years ago, but I didnt shorten the frame. Here is an image that helps put into context the 2 frame lengths side by side with dimensions to help with shortening the frame and the correlation of the crossmember the trailing arm mount to. As bs46488 stated the shortening occurs before the crossmember and a short length is taken off the rear of the frame.

I hope this helps.

[ARG0220]

Bs46488 and 69GMCcc10 thanks for the reply. I wasn't clear enough in my original post but my intent is to swap the suspension components from the long bed and transfer them to the short wheel base frame. The donor is a 69 lwb the project is a 65 swb. I was hoping I could use the trailing arms and mounting brackets from the donor on the 65? 69GMCcc10'that diagram is super useful thanks. I know the mounting locations are different but was hoping it would work?

[69gmcc10]

Oh! if you inspect the 2 diagrams closely you will see that the rear suspension dimensions are the same from short to long wheelbases. The arms are the same on both wheelbases, the crossmember on the leaf spring system is the same crossmember with the same hoes for trailing arm mounts as the coil spring system. The only thing you will not be able to just bolt up form the trailing arm system to the leaf truck is the upper shock crossmember and the panhard bar frame mount. You will need to locate, drill and bolt those things in. The diagram I posted will show you exactly where to install them.

good luck

p.s. There is a crossmember on the leaf truck you can remove if you would like, but it wont hurt you to leave it. Leaving it will probably makes the chassis a little more rigid, that is all.

[69gmcc10]

I looked over the diagrams just now and the panhard mounts on the bottom of the existing crossmember, so you dont even need to locate that, just drill out some rivets and bolt it in.

[ARG0220]

69GMCcc10, Thanks! very helpful since I'm a visual learner. So from my understanding of your reply and diagrams I should be good to go with swapping the components. Any advice on the ebrake? not sure how to tackle that one?

[69gmcc10]

The ebrake is routed the same way on bot systems, through the crossmember. After the cable goes through the crossmember on the leaf system it mounts to a tab on the frame. you must cut that tab off and run the cable down to the mount on the trailing arm instead. the brake cable from drum to the mount on the arm is longer on the trailing arm system (not by much, but longer) than the leaf system so you must use the parking cable from the trailing arm system.

This should be a real strait forward job since you have both systems in front of you. Disconnect the shocks, brakes, the upper spring mount, pan hard bar and the trailing arms from the mounts and roll the suspension out of the way. Remove the panhard frame mount, the trailing arm frame Mounts, the shock mount crossmember (you will need to locate and drill holes for mounting on this one), and bolt all those parts onto the other chassis. cut off the frame mounted parking brake mount and then bolt up the trailing arms, upper spring mounts, panhard bar, shocks and brakes. If you are cleaning bushings (advised, rubber on the trailing arms and polly on the panhard) and/or painting the parts it is a little more involved, but the same process.

[ARG0220]

69gmcc10 thanks for the help. I'll post up some pics when we make some progress.

[69gmcc10]

Good luck! Cant wait to see!