Question re: mid/later front drive shafts

[diesellibrarian]

Hi all -

I've done the requisite searching and FAQ-ing, and I can't find a clear answer to this question, so I'm looking for some advice.

I have an 11/71 FJ40 with three-speed and stock transfer case. The truck came without a front driveshaft, so I sourced a used one which I believe is from a '74 or later FJ40. I've just discovered that the flange nut spacing changes sometime in '73 to 60mm from 56mm, so the replacement shaft won't fit the T-case.

The plot twist is that I'll likely be swapping in a third member from a '74 and later FJ40 into my front axle housing, I'm likely to have 56mm spacing at the t-case, and 60mm at the axle. So, these are my questions:

• will the '74 later driveshaft be the right length? Like, will it fit at all? Or will I need to source a 69-73 shaft?
• if I keep the stock t-case but run the later diff, I will need two different flange spacings (56mm on the case end and 60mm on the axle end), correct?
• are the male and female ends of the shafts interchangeable between the 69-73 and 74-79 shafts? ie same length/spline count etc? And if so, can I assemble a "frankenstein" drive shaft using parts of the earlier and later shafts?
• OR should I swap an earlier pinion flange onto the later third? Are earlier and later pinion flanges interchangeable?

Thanks all for any advice you may have.

 

[pb4ugo]

Here you go. I found this in another thread by searching. The chart is from cruiser outfitters. I think the female portion is interchangeable and the same length, so you can have two different bolt patterns on the d/s. Idk, about the tube length differences. I think it would be trial and error. I think the 3 speed trans is shorter than the 4 speed, which would effect d/s lengths. The chart also references the different bolt diameters too.

 

[diesellibrarian]

Here you go. I found this in another thread by searching. The chart is from cruiser outfitters. I think the female portion is interchangeable and the same length, so you can have two different bolt patterns on the d/s. Idk, about the tube length differences. I think it would be trial and error. I think the 3 speed trans is shorter than the 4 speed, which would effect d/s lengths. The chart also references the different bolt diameters too.

View attachment 3766854

Thanks! Yes, I did find that image, which answered some of my questions, but not all. Appreciate the reply.

 

[pb4ugo]

Im pretty sure the coarse spline pinion flanges are interchageable too.

 

[cruiseroutfit]

IMO, flanges the easiest to swap

 

[peesalot]

You could just get the bottom half of a dline with the newer pattern and use a slip end from older pattern to go to tcase, the slip splines are the same.

 

[franklin40]

i just did this myself but the opposite way because i swapped a 4 speed into a 72 fj40. the drive shaft lengths are different so you’ll likely need to have that adjusted. if you’re having it retubed you could just have them put the later unjoint on. the two u joints are different so you can’t just swap the ends through the u joint. the whole end needs to be replaced.

otherwise you could just get it retubed and swap the pinion flange like kurt said. if you have to have it lengthened anyway i’d just get them to make the drive shaft with two different ends. the slip yoke is interchangeable but it won’t help with length.

 

[diesellibrarian]

You could just get the bottom half of a dline with the newer pattern and use a slip end from older pattern to go to tcase, the slip splines are the same.

This is the way I'm leaning right now, though if the 3-speed transmission is shorter, I may need to shorten the tube, which I assume will be no big deal. If I can't source an older prop shaft to steal the t-case side from then I'll swap out the t-case flange per @cruiseroutfit's suggestion.

Thanks everyone for your help! As a 40-series newb I really appreciate everyone's generosity with their hard-won knowledge.

 

[peesalot]

I will say that swaping flanges has a few benefits, you get a good check on the pinion bearing & seal, you know it's tight & staked when done, same goes at tcase, good time to swap the double seal tail housing & you get the larger dline bolts. The round flanges tend to roll off stuff while the square ones tend to grab, not that you should feel around with your dline anyway.

 

[diesellibrarian]

I have a new development on this issue, and of course another question.

I have a line on a disc brake axle from a later FJ40 that I was going to buy. Even though the carrier on this unit is marked "4.10" with paint marker, the seller tells me he's 90% sure it's a 3.73 diff, which I think means it's from a '78 or later FJ40. I want this axle for the knuckles and brakes, but I also need the differential since one of the 4.11s in my '72 is toast.

My question is: assuming the ring and pinion from my ruined 4.11 are not damaged (they look okay from what I can see - most of the damage was to the spider gears and center shaft), can they be swapped into the 3.73 differential? In this scenario I would re-use every part of the new axle except the ring gear, pinion, and pinion flange.

I'm sure folks will tell me to just buy a used 4.11 diff, but where I'm at, used parts are hard to come by. This axle's already going to cost me $1000 (CDN, but still) and since in theory I have all the parts to turn that 3.73 into a 4.11, I don't mind doing the work, IF it can be done!

Thanks in advance!

 

[cruiseroutfit]

Yes, the only appreciable variance between a 4.111:1 and a 3.70:1 is the ring and pinion proper.

 

[diesellibrarian]

Yes, the only appreciable variance between a 4.111:1 and a 3.70:1 is the ring and pinion proper.

Thank you! That's what I was hoping to hear.

 

[Living in the Past]

Here you go. I found this in another thread by searching. The chart is from cruiser outfitters. I think the female portion is interchangeable and the same length, so you can have two different bolt patterns on the d/s. Idk, about the tube length differences. I think it would be trial and error. I think the 3 speed trans is shorter than the 4 speed, which would effect d/s lengths. The chart also references the different bolt diameters too.

View attachment 3766854

I show 8/84 as a change for the bolt pattern. This is on the 40 series as well as the 60 series. Found it interesting they changed the pattern on the 40 so close to the 70 series which replaced the 40 series for general production. The PTO stayed the same when the 60 series and new 70 were single direction 10/84+.

 

[cruiseroutfit]

I show 8/84 as a change for the bolt pattern. This is on the 40 series as well as the 60 series. Found it interesting they changed the pattern on the 40 so close to the 70 series which replaced the 40 series for general production. The PTO stayed the same when the 60 series and new 70 were single direction 10/84+.

Agreed, I need to update the dates on our old website and redo the TT diagram.

Here’s and odd one: On the 6x t-case, the rear changed between 7/1984 & 8/1984, but the front changed from 10/1984 & 11/1984. So there were a few months of a mixed on short H42 models with the double cardan front shaft.