1954 C-Notch Modification

[Houston54]

One of the many differences the 1954 truck has from the earlier models is the rear portion of the frame was redesigned for the new box style. This required the Kick-up over the rear axle to be reduced significantly. This is not a big deal unless you are running leaf springs and lower the truck beyond 6 inches which I have done.

My set up included the stock rear leafs swapped end to end with two leaves removed, 2.5" lowering blocks, axle flip, and the front spring hanger swapped out for the shorter one from the front suspension. All told this gave me about 7 inches off the stock height and left me with an axle to frame interference on larger bumps/dips and a rather bucky ride. Not something I wanted to live with.

The typical solution is to install a C-notch in the frame and install a 4-link/parallel bars/triangulated link/etc suspension set up with coilovers or air ride.

Not what I wanted to do this truck.

I wanted to retain the leaf springs but upgrade them and increase the suspension travel at the back. This would require a C-notch but the 54 frame is only 3.5" tall and 2.25 wide in the area over the axle. Not a whole lot of meat to work with.

To resolve this I designed a notch that would give me an additional 2 inches of travel and would retain the frame strength so using leaf springs would not be a problem.

The notch uses 3/16 and 1/4 material and relies on the use of doubler plates on the top and sides to provide additional strength.

The rear springs will be replaced with new units from Posies. They have stock replacement units that are rated for 400 HP and are designed to move the rear axle 3 inches rearward to center the wheel in the fender. I had previously accomplished this by flipping the axle end to end and having a 1.5 inch offset on the lowering blocks. The new springs will enable me to get rid of that and use the driveshaft I now have.

Here are some pics of the modification. There is a more complete write up on my picturetrail album:

http://www.picturetrail.com/sfx/album/view/21770193

[IvelDesigns]

nice work there. Looks like a pretty sturdy notch to me.

[bluemoontruck]

Howdy. This is weird one. I have a 1954 GMC long box 1/2 ton. I ordered new rear springs. I went to place the rear axle housing into the alignment pin in the spring - no go! It was off two - three inches.

[Houston54]

Nothing strange about it. That is how they were designed. The torque tube drivetrain originally in the truck moved in an arc.

If you can I would return those springs and get a set of 440A springs from Posies. They are designed to move the axle centerline aft 3 inches.

If you cannot return them you will either need to move the mounting points from and rear towards the back three inches - real pain, or you can swap the leafs end to end and install them. This will move the axle back 1.5 inches. You can get the additional 1.5 inches by using the front mounting hole on the spring perches you added to your axle. If there is only one hole then mark one and drill it.

This is a bit of kluge solution and I was running this for the first 9K miles. The ride though is not the best.

If you do not want to go through the hassle of a leaf spring kit then the Posies 440A springs are the way to go in my opinion.