Peterson Fabrication shows us what’s involved in building a variety of components for all types of vehicles, from street to strip! This month, it’s a diff built to handle 1500hp
Words and Photography: Taylor Peterson
There are a few things that are important when building a nine-inch, especially behind a high-power engine. Firstly, the housing needs to be strong; for that reason this build uses Strange Engineering housings. With internal gussets and thick, quarter-inch wall axle tubes, they are far superior to factory Ford housings and, nowadays, much more readily available.
Secondly, the pinion angle needs to be correct. The number of cars we see arrive at the workshop with incorrect pinion angle never fails to amaze me. This can cause vibrations, premature universal joint wear, and inefficient power delivery. The pinion angle is always measured relevant to the crankshaft/transmission centreline. For leaf-sprung cars, I aim for four degrees pinion down; on a stock style four-link with rubber or urethane bushes, I aim for two to three degrees down; on a proper four-link car with rod ends, I aim for around 0.5 degrees down. There are always exceptions to the rule but those are a good starting point. The idea is that, under full power, the pinion should lift up to exactly the same plane as the crankshaft centreline.
Third, and very importantly, the housing needs to be straight. Any brackets you weld on have the chance of pulling the housing with the weld. Therefore, I always fit all the bracketry and weld it up before the final step of welding the bearing ends on with the line-up bar in place.Here are the steps we took to build a nine-inch that is destined for a 1500-ish horsepower ’57 Chev on leaf springs. Time taken to date: approximately 8 hours.
This is a bare Strange Engineering housing. I’ve used a DA sander with 80-grit sandpaper to clean it back to shiny bare steel — an important step when it is getting TIG welded
This is part of my Mittler Bros narrowing jig; it bolts to the face and gives me an accurate pinion centreline to work off to ensure everything is square
I figure out the housing width — wheel face width less rotor thickness and 2.5-inch axle offset per side — then subtract the width of the bearing ends and mark the housing. I use a pipe wrap to mark an accurate line around the tube, then use a 1mm disc on the 5-inch angle grinder to cut the tube to length Pro Tip: Leave a couple of millimetres, then use an engineers square and flap disc to get the ends square
Vernier calipers are used to measure the pin size on the leaf spring; in this case it was larger than the spring pads I’m welding on, so I used the drill press to open them up to size — you want a nice tight fit. Once drilled, I recommend cleaning them up by deburring the hole with a countersink
I clean the mill scale off the spring pads using a strip disc on the grinder — these work well for this; must-have in the workshop
Set the pinion angle using an angle finder and a level, then tack the pads in place, after marking the spring centres off the pinion centreline to get the width correct
I fit up the back brace; the better the fit-up on this, the less it will distort while welding
Next I fit up the adjustable shock mounts, which are Mood Motorsports items that stock. I used some thick card and a bolt in the shock mounts when setting the width to allow for paint/powder coat then TIG weld the brackets together
Next, the anti-roll bar mounts are welded to the shock plates
Everything is tacked together — note the cut-out in the back brace to get the U-bolts through
Back brace and all bracketry TIG welded on. I move from side to side while welding to minimise distortion; I also run the TIG on pulse setting to lessen the heat input
I bevel the end of the tubes for penetration, and do a root run around the ends before doing the cover pass
The line-up bar is fitted to the housing with a dummy diff head and bearing ends tacked in place. While welding the ends on, I spin the bar constantly to make sure they don’t pull out of line — this is important for bearing life!
Before fitting the Mood Motorsports anti-roll bar kit, I use a dual-action sander with 80-grit paper to clean the scale off the chromoly tubing
Here is the completed housing / anti-roll bar ready to go in the car. There are still brake lines to make up and paint to be applied, but we’ll bring you those steps in the next issue
This article originally appeared in NZV8 issue No. 210
