Ack's FAQ Fabbing a Fozzy Locker

Fabbing a Fozzy Locker

by Bob Smith with Jim Cambron

A Fozzy Locker is a form of welded differential where a bead of metal is laid down between the two opposite teeth of each spider gear in a differential.

In this field modification - which took place at the campground next to The Badlands during the 2006 ZookiMelt - only one tooth gap was filled instead of two to allow even more rotational play in the the front differential. This was done to see if it would steer easier. The differential used in this pictoral is actually a front gear carrier from a Tracker unit using the stronger sidegears. After a severe beating on the trail at the hands of Bob's nephew Adam, this Fozzy Locker held together really well!

Here is a pictorial of the process:

Remove the axles. In this case the hubs were removed from the backside as this saved us from having to monkey with the wheel bearings. This method is the option if you have Birfield cups or other strengthened front axles,

Once you have the axles out you can remove the third member.

The next step is to remove the cap bolts and carefully mark and keep track of the sidegear components as you remove them. You want to get them back together exactly as they came apart so your ring and pinion are lined up like they were when you started this project. Make sure that the parts for each side are kept separate.

Strap it in a vice (or whatever at hand that will substitute for a vice) and remove the ring gear bolts.

Here is what it looks like after the ring gear is removed.

In order to get to the spider gears (there are two on the front differential) you must knock out the pin that holds the shaft that the spider gear turns on as shown in the picture, above. The pin has been driven from the hole in the housing seen at the top edge of the center cavity of the assembly. With the shaft partially removed in the picture, you can see the hole where the retaining pin slides through.

Now we are ready to do some welding!

Place the spider gears on a surface that can absorb the heat of the welding. Weld full 1 gap between teeth each gear being careful not to overheat the gear. The metal surface will help prevent the steel from losing it's temper. No, we don't mean that it will get angry -- welding heat can cause the gear metal to turn brittle and shatter under heavy load. That is something that could cut short a day of wheeling... and make you lose your temper!

Before welding

After welding

Remove all weld spatter from the face and teeth of the spider gear.

Slide the spider gears onto the shaft to check for smooth rotation.

Here is the tricky part. In order to get the maximum amount of rotation on the Fozzy Locker, you must carefully install the welded spider gears so that you get the maximum available rotation between contact with the welded teeth.

Note the white mark on the face of the pinion gear in the picture above. The idea is to install the second gear in such a way that it allows maximum rotation of the white mark. You may need to assemble, test, disassemble, reassemble and test until the white mark and moves the farthest.

The animated picture above shows the position of the white mark on the pinion gear as it is rotated as far as it can go before the welds stop it.

Reinstall the sidegears using the original identical set for each side.

Adjust the Sidegear backlash to it's original position (you DID mark everything, didn't you?)

The finished Fozzy Locker ready to re-install!