Newbie gear set question - are FJ40 and FJ60 ring & pinions different? (1 Viewer)

[tdskip]

One more question in my crash course on FJ40s, nothing like a project to snap things into focus.

My '68 has a FJ60 front axle and it's OEM FJ40 rear axle. Both are running some crawl gear set, I want to go back to 4.11.

My question is this - do the 4.11 ring and pinons interchange between the FJ60 and FJ40s? How about front to back?

Thanks in advance for the help!

 

[pjohnson]

What do you mean by 'crawl gear set'? What is the gear ratio?

4.11 is pretty standard. And, yes they are interchangeable between models but not front to back.

Edit: They are interchangeable front to back as corrected below.

 

[tdskip]

Good morning @pjohnson - I was told the current ring/pinon is 4.56 or 4.88.

I suppose I could check by rotating the input shaft and counting the turns?

 

[Living in the Past]

What do you mean by 'crawl gear set'? What is the gear ratio?

4.11 is pretty standard. And, yes they are interchangeable between models but not front to back.

Yes there the same front to back. Need to C clips and block spacer on the rear. Different years had different flange patterns. Earlier years had coarse inner axles, 68 some time. Very early years had different gear set options here in the US. For the most part of to 1/79 had 4.11:1 and after had 3.70:1.

 

[Cruiserdrew]

If they are 4.56 or 4.88 they have already been swapped and likely to fine spline pinions (desirable).

I would just run it as is. Even if 4.88, it won't make that much difference to swap back to 4.11. Just upsize your tires a bit.

It's a fair amount of work to swap gearing, and so I would leave it alone unless there is a really good reason to change it. You might be able to find someone will to swap complete third members, which is easier but still a whole lot of work.

 

[AZMoonshadow]

What size tire combo are you running? I have a 1970 FJ-40 (production date 7/69) and I run 35" tires. The 4:88's I installed have really brought me back to "near-stock" drive-ability.

 

[tdskip]

Thanks for all the input/info guys, trying to sort all this out.

@AZMoonshadow - she has a SBC 350 with a TH350 auto, NP203 crawl box and stock transfer case. I have 285/70/17s on her, whicj works out to about 33s.

 

[tdskip]

OK - So I had a chance to run over to the rig and for every two revolutions of the axle I get approximately 8.25+/- revolutions of the input shaft to the differential. That looks like I have 4.11s in rear then?

 

[AZMoonshadow]

tdskip,
You have two transfer cases? A NP 203 (New Process 203) is a transfer case. Hmmm...

 

[reddingcruiser]

I'm a fan of fine spline pinions and I agree with @Cruiserdrew, pinion splines (and axle) for a 60 would fine spline, coarse on the 40 (except LATE model). If you already have fine spline axles and pinions keep them. Changing thirds is the easiest way to get 'er done, but there is still no getting around almost completely dismantling the front axle to change the front diff, whichever way you go.

 

[Living in the Past]

Did you ever confirm if your rear is coarse or fine spline inner axle? I know the 68 model did start the model year with coarse spline.

 

[tdskip]

@reddingcruiser and @Living in the Past - since I apparently have 4.11 in the rear, and presumably matching 4.11 in the front, I think I can leave the front alone. 4.11 gears with 33rd should be OK, or so I have been coached. I did a quick calculation and I believe this will give me about 2800 RPM at 65 MPH which seems livable.

I didn't have time to check the spines yet.

@AZMoonshadow - I have a doubler.

 

[reddingcruiser]

33's are fine, though it that is the minimum recommended size for most serious off road trails. "Back in the day", that's what everyone had.
As mentioned, all you need to do to drop the RPM is up the tire size a little. With a doubler tire size shouldn't be a issue.

 

[tdskip]

@reddingcruiser - thanks, have sourced a replacement rear differential and full speed ahead!

 

[Marn0]

When I found out that the rear diff in my 64 model was rooted i ordered up a new pinion and ring gear. When it arrived it was different, so from this i do believe they are different between the coarse and fine spline. They were the same ratio, but different physical sizes.

 

[tdskip]

Good morning @Marn0 , thanks for the post.

 

[tdskip]

OK gentlemen, just to close this part of the build out I was able to connect with a semi-local forum member here. I picked up a complete new matching 4.11 differential set up so I should be good on this part of the puzzle.

Thank you all for the help and information, it is very much appreciated.