Something a lot of folks with street machines or drag race cars take for granted is rear end alignment. No, we’re not talking about camber and toe adjustments for an independent rear end. Instead, we’re talking about how square the rear end is in the car or truck.

Not a big deal?

It sure is. Plenty of us have followed a pickup truck or car going down the road that’s dog tracking. The big reason here (aside from the fact it could be seriously bent) is that the rear end isn’t aligned with the rest of the chassis. Imagine a drag car launching and going down track skewed. It costs precious ET and simultaneously, could be a handling bomb waiting to go off.

Race Car Chassis off-axis Centerline Illustration
(Image/Jerry Bickel Race Cars)

For cars with an adjustable four link (splayed OE four bar or ladder bar) rear suspension, it’s not that difficult to get the rear out of whack when performing the initial housing/suspension install or adjustment. But with quality rod ends on the links, you can adjust it back to square.

You may enjoy this article too: A Guide to Tuning Your Four-Link Suspension System

For cars with leaf springs on the back, adjustment isn’t so easy. With these applications, there is a tiny amount of front to back and side to side movement between the leaf spring pins, thanks to pin hole tolerances and shackle movement. It all adds up and it is still possible to have the housing skewed in the chassis. But with many leaf spring cars, getting the housing square side to side can be an issue, particularly if the tires are close to the edges of the wheel well.

(Image/Wayne Scraba)

So how do you check for it?

There are a number of ways to handle this. Some are complex. Some are pretty easy.

This is how my old, late friend, Jerry Bickel explained it, and it’s ideal for a car with a four link rear suspension arrangement. The same basic principles can be used in a car with OE-style splayed four link assemblies (GM A & G bodies; Fox Mustangs and so on). It can be adapted to work on a leaf spring setup:

Follow these steps for squaring the rear end in the chassis:

Remove all chassis pre-load by disconnecting one end of the upper rear four link bar. I prefer to remove the bar as it will be adjusted for preload later.

Disconnect one of the rear stabilizer bar end links if so equipped.

It is very important that the rear end is not hanging crooked for this measurement. Level the chassis at the rear crossmember first. Then level the rear end housing. Hang a plumb bob off the front edge of the axle flanges and measure the distance to the crossmember on both sides. Adjust the links until the measurements are exactly the same on both sides.

Align the rear end with the chassis centerline. You can place a straight edge against the rear brake rotor surfaces and measure to the chassis rails or four link brackets. The measurements on both sides of the car must be the same. Adjust your centering link to keep the rear end in this alignment. Recheck the plum bob to rear crossmember dimensions to be sure the rear end did not move out of square.

Jerry Bickel
According to JBRC: “Be sure the chassis rear crossmember and rear end are level. Square the rear end by adjusting the bars until this measurement is the same on both sides of the car.” (Image/Jerry Bickel Race Cars)
JBRC notes: “To center the rear end, this measurement must be the same on both sides of the car.” (Image/Jerry Bickel Race Cars)

What about a leaf spring car? In the photos that follow, we’ll also show you how we used some of Jerry’s knowledge to check the rear alignment in our leaf spring Nova. Take a look:

When it came to my own leaf spring car, the first step was to set the car up on axle stands. The stands were arranged to allow the rear end to droop completely. To get there, I slid the axle stands under the frame connectors. (Image/Wayne Scraba)
Next the car was leveled front to back. Here it has a bit of a forward rake, which is acceptable. Both sides of the car were checked using a common carpenter level. The idea here is to have both sides of the car close to the same. (Image/Wayne Scraba)
At this point, the chassis was checked for level, side to side. Once again, a common carpenter level works great. (Image/Wayne Scraba)
The rear end housing was checked for level, side to side. In this case, I switched to a small digital level with a magnetic base. It was close to level at 0.9 degree, which is fine. FYI, the small Digi-Pas level you see here came from my Quick Trick Alignment tool set. (Image/Wayne Scraba)
I measured and then calculated the centerline of the rear axle. (Image/Wayne Scraba)
Next, the centerline was marked on the brake drum. (Image/Wayne Scraba)
I clamped a straight edge to the brake drum (axle) surface. The idea here is to set up the straight edge so that it extends as far forward as possible. (Image/Wayne Scraba)
I Measured from the rear axle centerline forward. In this case, I went to front edge of the OEM wheel well lip. And then I measure from wheel well lip to centerline of the leaf spring eye. I repeated this on the other side of the car. This determined if the rear end was centered front to back in the car. In my case, it is—now. (Image/Wayne Scraba)
A plumb bob was hung from each inner wheel well lip. The idea here is to measure the distance from the straight edge to plumb. This was repeated on the other side of the car. This measurement determines the rear end side to side dimension. (Image/Wayne Scraba)
If the car is out of square, loosen or in some cases, remove all spring, traction bar (and if equipped sway bar mounting) fasteners. On the initial setup, my car wasn’t quite right. To fix it, I simply used a big ratchet tie down strap to pull it into square. It worked great! Retighten the fasteners and you’re done. (Image/Wayne Scraba)

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Author: Wayne Scraba

Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.