Fj80 9.5 vs fj40 9.5 diff questions

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I'm building some custom 9.5 axles and I bought some arbs already in fj40 diffs. I have 2 fj80 master gear installs and 2 fj80 9.5 diffs. The fj40 diffs with the arbs need rebuilds which leads to my dilemma. Should I build the fj80 diffs or build the fj40 diffs? Front is a 9.5/fj80 hybrid and the rear is a centered FF with fj80 parts. My question is, are the fj80 diffs stronger than the fj40s? Is there an advantage to one over the other?? Any help is appreciated.
 
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It depends on the year. If memory serves, the 40 rear ends got 3.78 gears in 1979; from 1974 to 1978, they had 4.10s (or 4.11s someone who has torn apart a 40 more recently than me could verify which one). I was told many years ago, that Toyota changed the gear ratio due to customers complaining about road noise.

I've never seen (or heard of) an analysis on the housings, but I'd suspect that Toyota made the 80 axle casting walls heavier, to handle the increased weight and torque.
 
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Gears don't matter as I'm going to 4.88s. I was looking more for 3rd member case strength, and bearing size. The little Differences like that.

One of the fj40 3rds has a Jantz load bolt setup installed, if that helps with deciding.

Thanks Landtank. I knew one of them had bigger bearings, but could remember which one.
 
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I have similarly built axles under my FJ 40 project and Land tank is right, only real difference is the carrier bearings. The ones on the 40/60 series third are the same as the V6 minitruck stuff IIRC and the 80 series third is a bigger inner race with the same outer IIRC. I ended up using a fj40 locker in a fj80 housing with the right bearing and it works just fine.

I doubt you will really ever break a 9.5" case or carrier bearing before the pinion shaft. you want to go really tough you can retrofit some 98+ 100 series thirds to get the nitro 32 spline pinion and 32 spline axle shaft count and then get some custom axle shafts made.

there was a guy that used 9.5" fj80 thirds with load bolts survive KOH with a v8 and 37's on pirate. I think Marlin sponsors a rock buggy with a similar setup as well.
 
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I'm new to these LC9.5 diffs, I come from mini truck stuff and a short stent with dana 60. I don't think I'll break a case or anything either, but I was just wondering if there was any structural differences. I would feel like a dip s*** if I built the weaker diffs and sold the others off.

One of my main goals for these axles was off the shelf parts. I don't want to do anything custom, besides the diamond housing that I stole. Mostly because I find the challenge fun.

If I need to go stronger the arbs actually have 35 spline setup in them. I would just put those back in and go that route.
 
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Does anyone know the size of the bearings? I remember seeing 50mm and 45mm, but I can't seem to find the info anymore.
 
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I'm new to these LC9.5 diffs, I come from mini truck stuff and a short stent with dana 60. I don't think I'll break a case or anything either, but I was just wondering if there was any structural differences. I would feel like a dip s*** if I built the weaker diffs and sold the others off.

One of my main goals for these axles was off the shelf parts. I don't want to do anything custom, besides the diamond housing that I stole. Mostly because I find the challenge fun.

If I need to go stronger the arbs actually have 35 spline setup in them. I would just put those back in and go that route.
i wouldnt advertise stealing on the internet....JK

the 35 spline ARB is a great option as well. I am with you though, 30 spline and 9.5" ring gear is pretty tough. i plan on sunning a v8 through a nv4500/atlas through a 9.5 with chromo 30 spline axles.
 
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i wouldnt advertise stealing on the internet....JK

the 35 spline ARB is a great option as well. I am with you though, 30 spline and 9.5" ring gear is pretty tough. i plan on sunning a v8 through a nv4500/atlas through a 9.5 with chromo 30 spline axles.
Haha I just meant I got it cheap. I almost felt bad only paying $300 for it lol.

I've got an LS 6.0L/T56/Ecobox/Dana 300.

The guy I am getting the diffs from broached the 30 splines in the arbs out to 35 spline. It's already setup. I just don't have any 35 stuff right now.
 

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