1968 HD 31 spline diff
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1968 HD 31 spline diff
I have a 1968 O axle HD 31 spline posi diff and I'm trying to replace the 3.90 ring and pinion with a higher gear ratio but can't seem to find anyone who makes a ring and pinion for that rear. I would be happy finding a good used set if I can't purchase new. Anyone have suggestions? Thanks, Jay
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Joined: Jul 2008
Posts: 5,506
From: Seneca Falls, NY
I have a 1968 O axle HD 31 spline posi diff and I'm trying to replace the 3.90 ring and pinion with a higher gear ratio but can't seem to find anyone who makes a ring and pinion for that rear. I would be happy finding a good used set if I can't purchase new. Anyone have suggestions? Thanks, Jay
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Joined: May 2011
Posts: 3,688
From: Delta BC Canada
Fyi
I have a 1968 O axle HD 31 spline posi diff and I'm trying to replace the 3.90 ring and pinion with a higher gear ratio but can't seem to find anyone who makes a ring and pinion for that rear. I would be happy finding a good used set if I can't purchase new. Anyone have suggestions? Thanks, Jay
Your factory gear is a 3.91 not a 3.90. That OEM posi carrier can be used with OEM 3.42, 3.91, 4.33, 4.66 & 5.00 gear sets. There are no aftermarket gear sets for your carrier. If you want to go to 3.08 or 3.23 gears you will also need to change your carrier. The aftermarket 3.42 gears are made for the 3.08 / 3.23 carrier but wont work on your OEM carrier.
Best bet is a wanted ad for used gears of your choice & a carrier if mandated by the gear choice.
Old(s) Fart
Joined: Mar 2007
Posts: 50,768
From: Northern VA
You can't physically put a lower (numerical) ratio than 3.42 in that carrier because the smaller the number, the larger the pinion gear, which requires the ring gear to move further away. This is why there are different carriers. Also, since most people want to go the other way, you can buy thick aftermarket gears for higher (numerical) ratios, but not gears for the lower ratios. And of course, this is a Type O axle, so new gearsets are almost nonexistent.
More importantly, a Type O with 3.91 gears is worth more intact. You'd be better off both selection-wise and financially to swap the complete axle for a Corporate ten bolt. Don't be fooled by the 12 bolts on the cover of your Type O, it only has an 8.5", ten bolt ring gear.
More importantly, a Type O with 3.91 gears is worth more intact. You'd be better off both selection-wise and financially to swap the complete axle for a Corporate ten bolt. Don't be fooled by the 12 bolts on the cover of your Type O, it only has an 8.5", ten bolt ring gear.
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Posts: 7,286
"You can't physically put a lower (numerical) ratio than 3.42 in that carrier because the smaller the number, the larger the , which requires the ring gear....."
=================
The other day I noticed that CO.com would NOT let me enter a certain phrase. I appeared when I typed it, but when submitted it was absent. Nothing naughty either. like above. Correcting it had no effect.
more site issues.
=================
The other day I noticed that CO.com would NOT let me enter a certain phrase. I appeared when I typed it, but when submitted it was absent. Nothing naughty either. like above. Correcting it had no effect.
more site issues.
Old(s) Fart
Joined: Mar 2007
Posts: 50,768
From: Northern VA
"You can't physically put a lower (numerical) ratio than 3.42 in that carrier because the smaller the number, the larger the , which requires the ring gear....."
=================
The other day I noticed that CO.com would NOT let me enter a certain phrase. I appeared when I typed it, but when submitted it was absent. Nothing naughty either. like above. Correcting it had no effect.
more site issues.
=================
The other day I noticed that CO.com would NOT let me enter a certain phrase. I appeared when I typed it, but when submitted it was absent. Nothing naughty either. like above. Correcting it had no effect.
more site issues.
Apparently the problem is you, Chris...
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Joined: Mar 2008
Posts: 4,024
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