for all you differential experts

From a discussion on another message board, a guy is trying to convert a 9" 28 spline trac-lok to 31 spline, don't knwo if its a 2 pin or 4 pin (if it even matters). I suggested he just swap in a set of 31 spline spider gears, because to my knowledge they will directly interchange. Is there any difference between trac-lok spiders and open spiders? What about converting from a 2 pin 28 spline trac-lok to a 4 pin 31 spline trac-lok? Can you just swap the pins, block, and the 4 spiders--or is the carrier different? As a side note, I've always read that 8" and 9" rears use the same spiders. If thats the case, would you not also be able to convert an 8" rear to 31 spline?
[addsig]

The 31 Spline axles have a larger diameter and dont fit into the hole on either side of the carrier.

that sounds right. What about on the 9", can the spiders just be swapped?

Gork1rogues is right. The holes on both sides of the differential that the axle shaft goes through is smaller on the 28 spline differential, so even though you could put the 31 spline side gears and spiders into the 28 spline diff, you'd have to machine/drill the hole larger to get the axle shaft to slide into the side of the diff.
[addsig]

It is an easy mod to bore out ring gear carrier to accept the 31 spline axle.
[addsig]

I have done the boring operation several times and it works out well. Least you get to use the existing parts you have. Tim.
[addsig]

Yeah I remember doing the 'bore' mod as well... in my dad's basement with a drill press and a holesaw. The case held up fine, but the spider gears held up about as well as the first set did (lasted about a year before a first attempt at power braking killed them).
[addsig]

It is fairly easy to find 31 spline 9 inch trac-loks, as they were used in trucks and vans up into the 80's but it seems as though the 28 spline ones are more rare.He might consider just pawning the 28 spline one off on ebay and picking up a 31 spline one as I have noticed the 28 spline ones seem to command a good price.

<font size=-1>[ This Message was edited by: ifergusson on 2/19/06 7:35am ]</font>