can I install 3.70 diffs in my 64 fj40? (1 Viewer)

[thecrazygreek]

Thinking about it.
may not do it. it's running a 76 front axle with disc brakes, and the 64 stock rear axle. Can I stuff 3.70 diffs from an fj60 in there?

I know I can on the 76 axle but how about the rear?

never done it before. how hard is it? doesn't seem too difficult...

 

[Cruiserdrew]

Should be no problem. The only issue is driveshaft bolt spacing. You'll need a new flange or a new driveshaft.

 

[RustyNailJustin]

Easy
Let me know if you need 3rds.

 

[Living in the Past]

Need to be sure you 64 has the larger studs for the diff, earlier used smaller ones. The axle will also be coarse spline. Would need to address that. Research to me sure the coarse side gears will switch into the 3.70:1 diffs.

 

[N919HJ]

I don’t know anything about putting 60 thirds in a old 40 axles but knowing your skill set, wouldn’t it be easier to buy 3.70 ring gears and install them on the thirds you already have?

 

[Living in the Past]

I don’t know anything about putting 60 thirds in a old 40 axles but knowing your skill set, wouldn’t it be easier to buy 3.70 ring gears and install them on the thirds you already have?

Those were different too. Look at SOR's site shows different diffs depending on the year. Believe the early carrier were threaded for the ring gear. Later used a nut instead. The shape of the head may have changed also. SOR shows an3.70:1 ring and pinion for the early FJ40 but for the cost probably cheaper to find a newer axle to throw the diff in. Unless you know how to set up a ring and pinion your going to be paying someone to do that. Trying to mix and match the early 40s with later 40 and 60 series opens up a whole can of worms. Another one is the early diff will have a different flange pattern for the driveline and will be coarse spline. 3.70:1 we're all fine spline. Anything can be done just a lot more than pulling out the old diff and throwing in a 3.70:1 diff.

 

[Cruiserdrew]

The multi drill flanges will cover a lot of issues. @cruiseroutfit has almost every variation. Very helpful. You will need to match up fine spline vs coarse spline axles. It is likely easier to just get complete new axles from a later FJ40. '79 up would give you everything-fine spline, disc brakes, large bolt pattern, 3.70 gears.

But I do think you could work around all that with the later diff, later axle shafts and change the rear wheel bearing.

I had forgotten the early axles/diff carrier had the threaded holes instead of bolts/nuts. Good call on that.

 

[bikersmurf]

Bolting 60 series axles into a '74 40 axle or '77 45 axle is simple and straightforward. The 60 3rds I bolted into 40 housings no problem.

As Living in the Past posted, '64 axles complicate things a bit.

The 60 flanges i used were round so I turned the driveshafts 45 degrees and re-drilled the flanges to match the older driveshafts.

I agree with others that a newer axle in the front would make it easier. I'd convert the front to discs at the same time.

 

[thecrazygreek]

thanks forthe replies.

the front is already a 76 disc brake axle, so that will be easy. the 64 not so much.

I think I'll try to source a 79 + rear axle...

 

[Living in the Past]

If your using a 60 series diff on the rear 79+ is not the different when the bearing spline change. 8/80 was the change to a single brake cylinder and hand brake. Would have to do a search when all the flange pattern changes to match those but seems I remember in 84 the 60 series. Changing the flange is probably one of the easiest part of converting to later diffs.

 

[65swb45]

Just get a ‘65 and newer rear housing, install early axle bearings and seals, put early spiders in the third and reuse the 64 axleshafts. Done.

Although it’s probably useless to point this out, I have these parts available for sale. So far Angelo has a perfect track record for avoiding Marks Off Road.

 

[SuperDuperCruizer]

@65swb45 I've had a few differentials sitting on my bench; but never had the different ones side by side at the same time. Is the ring gear/differential case swappable between early/later differential carrier housings? I understand the spider gears will need to be swapped to match the inner axle splines. I'm just trying to sort out whether swapping the ring gear is necessary.

 

[archie73]

****Reviving an old thread to keep this information consolidated ***

I’m thinking of building up some FJ80 width axles for my next project. (Still in the dreaming stage-sorta). I currently have a set of ‘67 axles, that are likely ball and claw. Assuming that’s true and I’m desiring something wider that uses the Toyota 9.5 front and rear. So the housings are out for what I’m looking for this time.

That leaves me with a set of 67 differentials to start a build around. I’ll be regearing, so that and a new flange should solve the coarse pinion. From my reading, it sounds like I’ll need to replace the spider gears as well, but that’ll be included with the locker. Then there is the matter of the hole size for the studs. Can I simply enlarge the holes or are they a different pattern as well?

Am I chasing a rabbit down a hole by trying to utilize this differential for something that will be on 37’s? Basically I’ll just be using the shell.

 

[65swb45]

****Reviving an old thread to keep this information consolidated ***

I’m thinking of building up some FJ80 width axles for my next project. (Still in the dreaming stage-sorta). I currently have a set of ‘67 axles, that are likely ball and claw. Assuming that’s true and I’m desiring something wider that uses the Toyota 9.5 front and rear. So the housings are out for what I’m looking for this time.

That leaves me with a set of 67 differentials to start a build around. I’ll be regearing, so that and a new flange should solve the coarse pinion. From my reading, it sounds like I’ll need to replace the spider gears as well, but that’ll be included with the locker. Then there is the matter of the hole size for the studs. Can I simply enlarge the holes or are they a different pattern as well?

Am I chasing a rabbit down a hole by trying to utilize this differential for something that will be on 37’s? Basically I’ll just be using the shell.

Early’65 ended the 8mm carrier studs, so your’67 cases should be fine.

 

[archie73]

Early’65 ended the 8mm carrier studs, so your’67 cases should be fine.

So the 67 birds are the same as my 73 thirds? Good to know thank you.