Rear Axle Modifications - Axle-Chop How-To

'We're all slaves to traction. After all, what good is a 600hp thumper gonna do underhood if it just turns into tire smoke when you mash the honker pedal? Though suspension tuning can take you part of the way, real traction gains always come from increasing the contact patch via bigger meats. To fit the big rubber, you may need to narrow your rear axle.

To get the scoop on how it's done, we visited with Ed and Mando Sutton of Sutton Engineering. All they do is rear axle work of all kinds, and they have a special place in their hearts for guys working on a low budget. Big proponents of cutting and resplining stock axleshafts for use in narrowed axlehousings, they say they've seen hundreds of customer cars crank off 11-flats (automatic transmission) and 12-flats (stick cars) on reworked stock axleshafts. At about $140 a pair (plus shipping), it makes pretty good economic sense too.

Of course, the guys are quick to point out that the added cost of aftermarket axles is a small price to pay versus the potential consequences of breaking a stock axle and smacking the wall. So be smart and realistic when you choose your specific axle strategy. As for narrowing the axlehousing, the Suttons charge between $100 and $150 for the labor. Let's have a look at what it takes to get more rubber under any car.

The most critical step is fitting the fully inflated tires to the wheels you'll be using and taking careful measurements. If the car is under construction and has no rear axle, support the body and place the wheels and tires under it for your measurements. If the rear axle is still in the car, support the car on the axle so the ride height is accurate, then make note of where the sidewalls contact the body. On this '63 Dart, the Radir 10.00-15 piecrust slicks (12.5-inch bulge width) and Cragar 15x7 wheels (3 1/4-inch backspacing) just barely fit. We need to gain 1 inch of fender clearance for safe street and strip action. In case you were wondering, no, the slicks won't clear the Dart's stock leaf springs. We had to install an inboard spring relocation kit to get inboard clearance. That's another story for another time.

The Dart's stock 7 1/4 rear axle measures 57.5 inches from drum to drum. We know that we need to reduce this total width to 55.5 inches for sidewall clearance. Also, because there will soon be an infusion of 440 big-block power, this weakling axle goes into the scrap bin.
The Dart's stock 7 1/4 rear axle measures 57.5 inches from drum to drum. We know that we n
To cope with the 440, we scored an 8 1/4 rear from a '68 Dodge A100 van in the junkyard. The bare housing measures a whopping 56.5 inches-not including brakes and axles. We need to narrow it 6 inches to arrive at a 50.5-inch width. Once the axleshafts and drum brakes are installed, the drum-to-drum dimension will be 55.5 inches, just what we want. The fingers point out the two close-spaced differential studs that indicate the top of the Mopar 831/44 housing. By contrast, Ed and Mando Sutton point out that the Ford 8-inch housing has no up or down thanks to its symmetrical differential bolt pattern.
To cope with the 440, we scored an 8 1/4 rear from a '68 Dodge A100 van in the junkyard. T
Mando Sutton used a plasma cutter to remove all traces of the A100's useless shock-absorber mounting brackets and spring perches. They get in the way of the cutting and welding operations and aren't compatible with passenger-car mounting strategies.
Mando Sutton used a plasma cutter to remove all traces of the A100's useless shock-absorbe

Lots of guys screw up right here. Remember, our goal is to reduce the total housing width from 56.5 inches to 50.5 inches. But because the welded-on outer axle-bearing carriers will be reused, we must remember not to simply measure 3 inches from the outmost ends and chop. Instead, the correct way is to measure in 3 inches from where the axle-bearing carriers meet the axlehousing tubes and make the cuts there. Be sure the axlehousing is resting perfectly flat on the chop saw table for straight cuts. Also, be sure to compensate for the 11/48-inch thickness of the chop saw blade.
Lots of guys screw up right here. Remember, our goal is to reduce the total housing width
After cutting, the bare housing measures 45.5 inches wide, but we still need to reinstall the outer axle-bearing carriers. To guarantee perfect alignment, the Suttons use a bare differential fitted with precision hubs in place of the carrier bearings. The steel alignment bar floats in the hubs and will ensure accurate installation.
After cutting, the bare housing measures 45.5 inches wide, but we still need to reinstall
The ends are aligned and MIG-welded to the axletubes. After surgery, the total width of the bare housing came out at exactly 50.5 inches.
The ends are aligned and MIG-welded to the axletubes. After surgery, the total width of th

The severed housing ends are then taken to the lathe, where the welds that bond the outer axle-bearing carriers to the housing bits are removed.
The severed housing ends are then taken to the lathe, where the welds that bond the outer
Here's a shot of the cleaned and chamfered outer axle-bearing carrier about to be reunited with the narrowed axlehousing. The chamfered end yields excellent weld penetration. Note how the alignment bar fits through the steel cap bolted to the carrier studs.
Here's a shot of the cleaned and chamfered outer axle-bearing carrier about to be reunited
Always remember to install new axle seals after surgery like this. The originals are always cooked during the welding process. If you don't have a proper seal-driving tool, a steel tube or socket wrench with 1.700-inch-od will do the trick.
Always remember to install new axle seals after surgery like this. The originals are alway

The stock 8 1/4 axlehousing is fabricated from several sections of welded-together steel stampings, but the axletubes are actually pretty beefy at nearly 1/4 inch thick. Though they are swedged into thinner sections where the differential bolts up, Mando says the stock housing is good to 10.99 e.t.'s before it starts to bend, and a welded back brace is highly recommended.
The stock 8 1/4 axlehousing is fabricated from several sections of welded-together steel s
Here's the alignment fixture all set up and ready for action. Before welding, a protractor is used to set the pinion-snubber support at 0 degrees horizontal to the floor. Then each outer axle-bearing carrier end is also zeroed with the protractor before welding as shown. This move ensures that the brake backing plates and shoe assemblies will be level after reassembly. The Suttons can narrow any type of axlehousing. The empty cases in the foreground are used for aligning the tube ends of (left to right) Hotchkis-type Olds/Pontiac, '55-'64 Chevy, 9-inch Ford, and 8-inch Ford axlehousings.
Here's the alignment fixture all set up and ready for action. Before welding, a protractor
Now what about those axleshafts? Unlike the Ford 8- and 9-inch, Mopar axles are always the same length. The axles that came with the Dodge A100 van measure 30.0 inches overall. As with the axlehousing, we need to remove 3 inches from each shaft, then cut in new splines.
Now what about those axleshafts? Unlike the Ford 8- and 9-inch, Mopar axles are always the

One word of caution is that a small percentage of Mopar 8 1/4 axleshafts (as well as some Fords) feature extralong 4-inch undercuts (pen points). Unless you are building a supernarrow Pro Street- or dragster-style axle, there isn't enough material diameter at the ends to allow resplining. Our A100 axles (top) have 3-inch undercuts; no problem with our 3-inch chop job.
One word of caution is that a small percentage of Mopar 8 1/4 axleshafts (as well as some
Next, the axles are chucked up in Sutton's Goodway lathe. In three steps, Ed removes 0.038 inch to achieve a constant diameter for successful resplining.
Next, the axles are chucked up in Sutton's Goodway lathe. In three steps, Ed removes 0.038
The pen points out the 0.187-inch-deep factory surface hardening that is only mildly affected by the 0.040-inch-deep spline cuts (right). There is still plenty of strength left for all but the most serious horsepower levels. Again, the Suttons say this operation is safe for 3,400-pound cars running 11.0 seconds with an automatic or 12.0 seconds with more brutal stickshifts.
The pen points out the 0.187-inch-deep factory surface hardening that is only mildly affe

As for you GM guys, the constant-taper shaft design of virtually every passenger-car axle type from the '55 Chevy to the classic 12-bolt cannot be resplined. Fingers point to where diameter reduces from 1.400 to 1.270 inches. Your only choice is custom-length aftermarket replacement axles to suit your narrowed housing.
As for you GM guys, the constant-taper shaft design of virtually every passenger-car axle
The pen points to the gradual radius Ed puts into the transition from the freshly machined and nonmachined axle surfaces. This eliminates the stress riser and potential failure point a sheer 90-degree merge would create.
The pen points to the gradual radius Ed puts into the transition from the freshly machined
Do the Suttons know axles? Here's a small selection of the over 30,000 ring-and-pinion installations they've performed since opening their shop in 1980. They sell the used-up stuff shown here to the local scrap man, who loves the high-grade metal.
Do the Suttons know axles? Here's a small selection of the over 30,000 ring-and-pinion ins

After careful measurement, the chop saw removes 3 inches from the end of each axle. Make sure they're resting flat on the saw table before cutting to get straight cuts.
After careful measurement, the chop saw removes 3 inches from the end of each axle. Make s
The vertical mill cuts one 0.040-inch-deep spline at a time using a specially designed cutting tool that spins at high rpm. A dividing head on the mill precisely controls the length and depth of each cut and in this case delivers the stock Chrysler 30-spline axle end specification.
The vertical mill cuts one 0.040-inch-deep spline at a time using a specially designed cut