Here’s the stock rear suspension...
Here’s the stock rear suspension that will be getting replaced.
It doesn’t make any sense to slam the front of your classic truck if the back end is gonna stay sky-high. So it only follows that we continue on where we ended back in July on our buddy Josh’s ’75 C10. The original intent was to slam the truck as much as possible without using air-ride while still retaining proper suspension travel. While this wasn’t so hard to achieve up front, out back it’s a different story.
The stock C10 chassis has only a minor kickup over the rear axle, which makes lowering the trucks more than a few inches out of the question without installing at the bare minimum a C-notch. Since we wanted a nice healthy dump (enter pun here) out back, we decided to go with KP Components’ eight-piece step notch kit which allows for as much as nine inches of axle travel depth. We don’t need quite that much, but it will be a good start.
To locate the rearend, we kept in line with the front suspension and hit up our friends at Fatman Fabrications. They recommended their quasi-universal four-bar kit, which fits all kinds of applications. Their kit is designed to be used with the four-bars mounted either inboard or outboard of the framerails, providing a variety of options for various make/models. We opted to mount the four-bars outboard of the framerails as it allows for more travel with less impedance from the exhaust system, etc.
While the kit is pretty straight forward to install, there are a couple of things that come into play that should be mentioned, most notably the necessary removal of the stock spring’s hangers and the second-most rear crossmember. It’s also necessary to box the frame on both sides of the new crossmember, but anyone who can handle installing a step notch kit can handle this as well.
One of the neat things about the Fatman kit is not only its universality, but the fact that it’s designed with a number of possible mounting positions for both the four-bars as well as the shocks, making ride height changes or adjustments down the road possible. This enables one to set their truck up with an initial baseline ride height setting and have the ability to change it later if they want to go to a different size wheel/tire combo for instance. The versatility of the Fatman four-bar kit is truly unique and is what lends it to such a wide variety of applications, be them early Ford or late Chevy. CCT
Before we get started, it’s...
Before we get started, it’s necessary to mark the axle centerline on each framerail.
The rear leaf spring hangers...
The rear leaf spring hangers bolt to the chassis, making for easy removal.
The front hangers, however,...
The front hangers, however, are riveted to the framerail. An air chisel and a plasma cutter work great together to remove the rivets.
With the hangers removed,...
With the hangers removed, we’re ready to get rolling.
We were unsure whether the...
We were unsure whether the stock crossmember needed to be removed or not so we mocked up the suspension components to see how we looked. Fatman calls for 25 3/4 inches from the rear axle centerline to the back of the new crossmember. It also became apparent at this time that it will be necessary to install the crossmember up into the framerails to get the truck as low as we’d like to go with it. That means that the stock crossmember will need to be removed and replaced with the new one.
It will also be necessary...
It will also be necessary to install a pretty serious C-notch kit so that the rearend can travel unimpeded. We opted to go with KP Components’ eight-piece step notch kit to get the job done. Here, we used a 3-inch steel spacer to hold the side plates up and level while they’re clamped against the framerail.
They’re then tacked in place...
They’re then tacked in place for the meantime. We’re using a Lincoln Power MIG 216 for all the welding on this project.
Next, the top plate of the...
Next, the top plate of the step notch is marked even with the top of the framerail…
…before it’s trimmed nice...
…before it’s trimmed nice and straight using a plasma cutter.
The top plate is then tacked...
The top plate is then tacked to the side plates and the top of the framerail.
This shot gives you a good...
This shot gives you a good idea what the step notch looks like at this point.
The bottom of the side plates...
The bottom of the side plates are cut flush with the bottom of the framerail before the bottom plates are welded in, completing the step notch.
With the step notch installed,...
With the step notch installed, we’ve gained nearly 8 inches of travel; more than enough to lay the truck out flat in the weeds and still have plenty of clearance for the rearend. Also note that the stock crossmember has been removed.
The rear suspension components...
The rear suspension components are back in place and now it’s time to setup the ride height. We’re going to setup the rearend at 15 inches from the ground to the center of the axle to simulate a 30-inch-tall tire.
With the side and top plates...
With the side and top plates of both step notches welded up, the stock framerail can be cut out, thereby creating the step notch. Welding up the step notch first and then cutting out the center section as opposed to cutting the frame first eliminates the possibility of tweaking the frame.
We adjusted the height of...
We adjusted the height of the chassis on the lift to get our proper ride height. Fatman calls for the crossmember to be even with the axle centerline so it will be necessary to move it up into the frame about three inches.
A Sawzall makes quick work...
A Sawzall makes quick work of removing the offending area.
The crossmember is now tacked...
The crossmember is now tacked up into the framerail and the four-bar brackets can now be tacked in place. They’re set in place 2 inches from the center of the bracket to the framerail.
The rear axle brackets can...
The rear axle brackets can now be tacked to the rearend. We had Currie slide them onto the axle housings before they welded up the axle flanges so we didn’t have to split them. The rearend was setup with 6-degrees pinion up with each four-bar measuring 23 inches, center to center.
We’re using Ride Tech coilover...
We’re using Ride Tech coilover shocks on all four corners on the ’75 and the Fatman kit requires the upper mounts be welded to the outside of the framerails. The shock does a pretty good job of holding the tabs in place, but Fatman says to locate them 5 1/2 inches behind axle centerline, roughly 12 to 12 1/2 inches above the mounting hole on the axle bracket. Here’s a hint: splitting the difference between the four possible mounting locations will give you a bit of ride height adjustment.
The Z-bar bracket mounts off...
The Z-bar bracket mounts off the passenger-side, rear lower four-bar bolt and connects to the driver-side front lower four-bar bolt. Both brackets and rod-ends are attached…
…before the bar is marked...
…before the bar is marked and cut to length.
The threaded bungs provided...
The threaded bungs provided in the kit are then welded to each end, completing the Z-bar assembly.
To stiffen up the chassis,...
To stiffen up the chassis, we decided to box the framerail from the step notch forward to the next crossmember.
It’s also possible now to...
It’s also possible now to finish off the ends of the crossmember by cutting off the unnecessary bit and capping the open end off.
A crossmember added between...
A crossmember added between the rear kickup of the step notch helps stiffen up the area where the shocks mount.
The disc brakes we’re using...
The disc brakes we’re using out back are Wilwood 13-inch drilled and slotted discs with four piston calipers. First, the caliper bracket is bolted to the axle flange using the provided spacer and hardware…
…followed by the rotor and...
…followed by the rotor and caliper.
Wilwood’s method of installing...
Wilwood’s method of installing brake pads is ingenious and makes swapping out pads a snap. Simply remove the center fastener and spacer above the brake pads and slide ’em out.
It should be pointed out that...
It should be pointed out that the Wilwood hat and rotor need to be assembled prior to installation; this means properly securing the fasteners via safety wire.
And there you have it! A four-link...
And there you have it! A four-link setup that will handle as good as it looks and get the C10 way down deep in the weeds.