Last month we covered building the frame of our rat rod in great detail, and if you have followed our technique, you should be ready to install a rearend. This is where you should be extremely knowledgeable about what is available, because you can spend a fortune on a rearend – but that would be silly on a budget build like this. To keep this rod at $1,500.00 as promised, we will pull a rearend out of an old van or truck (or old boat anchor car) of some kind. It won’t be a positrac or have 4.11 gears or whatever the latest gearhead talk is, but it will cost $50.00 to $75.00, and that’s what we’re aiming for.
These deals can provide you many parts for a little bit of nothing. Old cop car auctions are another option, and the older crown Vic rearends are killer. Some things to consider are the bracketry on the rearend you are planning to use. For instance, a Chevy rearend has fewere brackets, whereas the old Crown Vic rearends have brackets for shocks, coils, anti-sway bars, panhards on some, and on and on.
Another major consideration is that everything works freely and properly. You don’t want to start by having to free up a hub, deal with leaks, or have slop where your drive shaft hooks up. Width is another consideration. If your using a 1969 Dodge truck front axle, which measures 60 inches side-to-side, you won’t want to use a Chevy S10 rearend measuring 54 inches for obvious reasons. So be sure to measure backing plate to backing plate on both straight axles and rearends to keep everything in proportion.
That is enough housekeeping. Now we can get on to the build. Step one is to determine what ride height you want. If you want to ride at 5-inches off the ground for instance, you can cut a 2×8 piece of lumber in 12-inch blocks, and sit them under your frame in front and back. A 2×8 measures 7 1/4-inches, and once the rod is complete with drivetrain, the ride height will settle 2 inches. This puts us riding at 5 1/4-inches.
If you want to ride higher, simply use taller blocks during the setup. Once the frame is on the blocks, we will roll the rearend under the tail section of the frame. We have already chosen a location of 12 inches for the rearend to set behind the L kick-up. This placement puts the front side of the rear tire right at the cab corner of the truck.
Once the rearend has been situated in place, you will need to measure each side to ensure the rearend is centered. You will also need to measure from the front of frame on each side, to the rearend to make sure everything is setting square. At this point, you will need to block the rear tires so they can’t roll and change your dimensions. In the images, you will notice a block under the center section of the differential holding the input section of the rearend up. The driveshaft needs 6 degrees of pitch to prevent the U-joint from wearing out too quickly.
The drivetrain’s angle, where the driveshaft connects to the input pinion, is referred to as pinion angle. The angle can be determined by the height at the transmission, at the rearend, or most likely a combination of both. The important detail is that you end up with a 6-degree angle. Once that has been achieved, tack weld a 1/2-inch piece of rebar from the rearend to the frame to maintain the proper measurements. The rebar will be knocked off when the work is completed. (Note: I did say tack the rebar on each side – not weld).
Rear Suspension Components
The components we are adding will be an inexpensive way to go. Using the same material that we used to make the frame, you can build a cheap set of traction bars. The shock brackets on the rearend can serve as one mounting point while the top end will mount to the frame. Simply drill through the rectangular tubing and insert a round tube that is just large enough to allow a 1/2-inch bolt to go through. Weld the round tube in place for a strong joint. We opted to use a flat-stock tab welded on to the frame, and another one on the shock bracket. Builders that plan on driving a little more aggressively may want to use two tabs on each mount for a double-shear style mount.
Our next step is to acquire a set of rear springs from a small car. A quick trip to a wrecking yard will offer plenty of choices. We recommend small-car springs, because heavier springs will beat you to death with a rough ride. The coil buckets can be made on the cheap by going to a scrap yard and finding a round tube slightly larger in diameter than the small car rear coils you just procured. The tubing can also be a size smaller so that it fits inside the coils.
The tubing should be cut about two-inches in height, and welded to a piece of 3/8-inch flat plate that is slightly larger than the coil spring diameter. You will need two on each side, one for the top and one for the bottom. The bottom buckets will be welded directly to the rearend, and the top buckets will be welded to the frame.
The coils may be a little too long to fit between the two spring buckets, but can be cut off to fit properly. Do not cut more than a coil and a half off of the spring, or the ride will be fairly stiff and you won’t want to drive your rod. These coils can be compressed if you ever need to remove them later for maintenance.
One of the most under-rated components in the rear suspension is the panhard rod. The panhard bar’s job is to locate the rearend housing laterally in the frame, and are commonly used in vehicles that use coil spring suspensions. Our panhard bar will run from the left side of the frame to the back right side of the rearend.
The quickest and simplest way to make a panhard bar is to use a stick of 3/4-inch black iron gas pipe with heim joints on each end. A 1/2-inch heim joint will fit perfectly in the 3/4-inch pipe. Weld a nut to each end of the pipe and use a jam nut on each heim joint to prevent the pipe from turning. Using a threaded heim with jam nuts will also allow for some adjustment.
A little pitch on the bar is alright, but generally speaking, the straighter the bar is, the more stability the rearend will have. This bar keeps the rearend from shifting in corners, where stability is most important.
You can also mount the panhard bar by cutting 1/2-inch ears from flat stock to use as mounting brackets. These pieces can be 2 inches long by 2 inches wide with a 1/2-inch hole in the ear for mounting the bar.
Dispelling Old Myths
To dispel an old myth, you can weld on rearends, and front axles too for that matter. I hear the talk about changing the molecules and making them brittle. I would simply say a good welder can make it happen with no problems. Welders successfully weld on cast iron everyday with no cracks (just saying).
When it comes to shocks for the rod, it is pretty straight forward. The existing brackets on the rearend are probably not going to line up with your new frame, so you will need to add some homemade 1/2-inch mounting ears. For this build, it doesn’t matter if the shocks are set in the front of the rearend or behind it. Once the components are in, you will be able to see where the vacant areas are and where you can add your other components.
First, add the battery box because of the size and limitations of the location. Some 1 1/2-inch angle stock will work well. Just ensure to cut the frame to the size of the battery you will be using. We will be tackling the gas tank once the bed is on, and we know how much room is left.
Last month we covered the body, and it might seem to make sense to add the truck’s bed with the body. However, we were tight on space for the article, and leaving the bed off the frame until the rearend is in place makes the most sense construction-wise. So we opted to add it here. Making a good looking cheap truck bed is pretty simple.
For material, 18-gauge sheetmetal works great and is less than $100.00 for a 4-foot X 8-foot sheet. Our design calls for two sides that are 36-inches long and 22-inches tall. For a traditional look, you want to come up the side 16-inches and bend the last four-inches at a 45-degree angle.
The front and back of the bed are 43 inches wide and 16 inches tall. These can be tack-welded together to form the bed. Adding a 1/2-inch diameter gas pipe to the top of the 4-inch bend on the side panels will give the bed the appearance of an old 1940s truck bed. All totaled, this put you into a truck bed around the $100.00 range. Welding the bed to L-brackets on the inside of the frame, the bed becomes very rigid. If you wanted to get trick, you could hinge a piece of sheetmetal across the top to hide your rearend or make a bottom for the bed, but it will cost you a little more.
In our next issue, we will get into the straight axle and all of its pitches and parts. You can check out Tommy Ring’s other work and products at Ring Rods Hot Rod Shop.