What does it take to do? I've heard that all you need are the 31 spline spider gears. Is there more to it? I've got the axles and stuff, but my center is junk(carrier bearing exploded) and 28 splined seem to be way more common. Thanks. -Bugman Jeff
actually what you need are 31 spline side gears. It is just about that easy. You also need to have a working knowledge as to how to setup the ring and pinion in a ford carrier. To replace the side gears you are going to have to split the ring gear carrier open. After you have done this you would need to reset the backlash on the ring and pinion or you will chew up the gearset fast.
Just make sure it's a big bearing carrier, or the axles won't fit into the pig because the holes are too small. Even some of the big bearing carriers will have to be bored out for axle clearance. You can bore out a small bearing carrier, but it gets too thin and loses too much strength. Just about all truck rears have big bearing carriers.
Check out www.superioraxle.com They put together my 9" with 31 spline axles. They have everything you need and they also offer custom lengths. They have been manufacturing their own stuff for more than 65 years - in the USA and it's top quality. He is a long-time friend and racing buddy of mine since high school.
I think it also has a little to do with the weight of the vehicle and the HP ratio. I have a model A coupe (fairly light) with around 365 HP (not too bad)with a 4 pinion 9" posi, 28 spline, not one problem since the rebuild 4-5 years ago. I mention this cause the 28 spline stuff is usually cheaper. But like I said, probly depends a little on power to weight ratio. Sounds like you have a hevier car with more HP. Good Luck....
Here ya go...right off a hamber's website. Conversion from 28 Spline to 31 Spline | Back to top -------------------------------------------------------------------------------- To change the third member to 31 spline, the only parts needed are the differential side gears, they are available from Ford, about $20 apiece. The other part of the conversion is the carrier bearing size. There are two carrier bearing inside bore sizes, and two carrier bearing outside bore sizes. There are three possible combinations, small ID-small OD , large ID-small OD , and large ID-large OD. Factory 31 spline axles came with the last two bearing configurations, but not with the first. On 28 spline carriers, the axle bore on some of them are not large enough to allow the 31 spline axles to pass through. The carriers with the large ID bearings can be bored out to use the 31 spline axles. Not a precision job, just big enough for the axle to pass through, I use a cut off end from a 31 spline axle to check when it's large enough. I takes less than an hour to do both sides, and could be done at a vocational school by a novice. The small ID bearings won't have enough material left for reliability if bored out for 31 spline axles. Also if your housing has the small axle bearings, you will have to have axles custom made, as there are no factory axles with 31 splines, and small axle bearings. Both the large axle bearing, and the extra large axle bearing (some F150 trucks) had 31 spline factory applications. From about 1970 on, the big Fords, Mercury's, and Lincoln's has axles big enough to respline with 31 splines if they are shortened about 4" per side. Both 4 1/2" and 5" bolt patterns are available. If you want to redrill to a 4 3/4" Chevy bolt pattern, use truck axles, as there is more room for the new pattern without hitting the other holes. The drum pilot may have to be turned down, depending on the drum used. The Chevy drums of corresponding size to the ford brakes will fit if the pilot is turned down.
Why convert? Extra strength? Are your 28-splines failing? Not much point converting to 31-splines if that's not where the problem is.....a better bet would be to buy some aftermarket 28-spline axles that will have the extra strength you need. Was only talking about this thing with some drag racers Sunday night.
I want to convert because I already have the complete axle setup, just a busted carier that I didn't know about till I took it apart. So, I have the 31 spline axles and big bearing housing already, an early 80's truck I think. Just needs to be narrowed a bit. Why 31 splines you ask? 700 blown Hemi horsepower in a 4500 lb '55 Plymouth. I need about the strongest stuff I can get, and I'll still probably break it alot. Anybody have any idea what the actual measurments for the ID/OD on the carrier bearings is? Thanks -Bugman Jeff
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