ARB Locker Fine Spline vs Course

[Ironmanfj45]

Hi Guys,

I just traded some old parts I had laying around for a rear third member with an ARB air locker. The gearing is wrong so I was going to just remove the air locker and put it in my third member. I found that the ARB that I got is fine spline, late model, and I believe seeing that my FJ45 is a 1965 that I will find that my axles are course spline.

First question, is there a way to tell if my rear end is course or fine spline without removing the axels? Second question is can I find a set of fine spline axels that will just slide into my existing rear diff or are there other changes in the late model rear diff that will not allow this? Third question is, if all else fails, does anyone have a course spline ARB that they would like to trade for my fine spline?

Thanks in advance for your help.

Cheers,

Jim

 

[tornadoalleycruiser]

keep the fine spline.. Put it in the rear axle for now as it's simpler to do. for starters I think you can swap shafts to fine spline. TO put it in the front it'll take a whole axle and disk conversion.
One way to possibly id without pulling apart is the bolts holding the diff in are smaller. meaning the studs in the diff are smaller than the newer ones.
I can't remember exactly what size but it's like a 10mm wrench vs a 12mm on the bigger stuff. Im sure someone here knows exactly but since i'm at work and the early rear axle i own is at home i'm not much more help.

 

[Ironmanfj45]

keep the fine spline.. Put it in the rear axle for now as it's simpler to do. for starters I think you can swap shafts to fine spline. TO put it in the front it'll take a whole axle and disk conversion.
One way to possibly id without pulling apart is the bolts holding the diff in are smaller. meaning the studs in the diff are smaller than the newer ones.
I can't remember exactly what size but it's like a 10mm wrench vs a 12mm on the bigger stuff. Im sure someone here knows exactly but since i'm at work and the early rear axle i own is at home i'm not much more help.

Thanks Erik,

This is just what I was looking for. I will check the bolts in the rear end to see what size they are. This locker is for the rear and I have had one in the front for a few years but did not want to hook it up until I found the rear locker. Now she will be all locked up and with the Orion transfer case I should be all setup to go nice and slow over the obstacles. Do you know if they made a full floater in fine spline, I think that would be the ultimate setup and the one in my FJ45 was gone before I bought it. Thank you very much for your response.

Cheers,

Jim

 

[Living in the Past]

The coarse spline axles were gone by 69. The ARB air locker didn't come around for a long time after that. Don't believe ARB ever made them for the coarse spline axle. Not that it would have been a good idea. The only locker I knew that was made for a coarse spline was a Lock-Right. That was until a few years back and I picked up a FJ25 with Torsen diffs front and rear. The Torsen isn't a true locker but it is the only other diff that I have ever seen in the coarse spline axle besides the stock open diff.

 

[tornadoalleycruiser]

any FJ40 or 45 full floater will indeed go into your truck. Probably not cost effective but it can be done.
any rear axle 1970 and newer will be fine spline. don't ever recall seeing a full floater that was course spline so you'd probably be ok with any full floater rear axle for a 40/45.
Looks like Marv has some for bout $400+ that your diff will drop right into.

 

[Ironmanfj45]

One way to possibly id without pulling apart is the bolts holding the diff in are smaller. meaning the studs in the diff are smaller than the newer ones.
I can't remember exactly what size but it's like a 10mm wrench vs a 12mm on the bigger stuff.

The bolts on the rear of the pumpkin take a 12mm socket. Can anyone verify that this is the late model fine spline diff or not?

any FJ40 or 45 full floater will indeed go into your truck. Probably not cost effective but it can be done.
any rear axle 1970 and newer will be fine spline. don't ever recall seeing a full floater that was course spline so you'd probably be ok with any full floater rear axle for a 40/45.
Looks like Marv has some for bout $400+ that your diff will drop right into.

Thanks, I agree that is a little to much to spend due to the economy and my "economic" retirement.

The coarse spline axles were gone by 69. The ARB air locker didn't come around for a long time after that. Don't believe ARB ever made them for the coarse spline axle. Not that it would have been a good idea. The only locker I knew that was made for a coarse spline was a Lock-Right. That was until a few years back and I picked up a FJ25 with Torsen diffs front and rear. The Torsen isn't a true locker but it is the only other diff that I have ever seen in the coarse spline axle besides the stock open diff.

Good information, so the trade is out of the question. Looks like I will be looking for some fine spline axles unless I get lucky and I already have them. Thank you to everyone that responded!

Cheers,

Jim

 

[Living in the Past]

A FJ55 rear axle will have the tabs for your sway bar. Not that big of deal, but if one was available.

 

[Ironmanfj45]

A FJ55 rear axle will have the tabs for your sway bar. Not that big of deal, but if one was available.

Thanks for all the help with this. My FJ45 is set up with spring over suspension so I would prefer to keep the same rear diff housing and just change out the axles if possible. This would save me doing the relocation of the spring perch on a FJ55 rear axle housing.

Cheers,

Jim