Parts Interchangeability 72/78

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I've got a '72 FJ40 that has not been converted to disc brakes. I've also got a '78 that is basically for parts. I'm considering swapping out the entire front axle assembly on these 2 cruisers in order to economically get disc brakes on the '72. After a quick look, everything looks pretty much the same. I haven't checked the ratio, but I'm assuming they both have 4.10 gears. (I'm certain they are both original from factory) Is there anything I should be aware of that might not work out? Thanks, in advance, for the help.
 

pb4ugo

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You just need to confirm ratios. They're most likely 4.11. Disc and drum frt brake lines are run differently. I opted to run mine like stk disc. I think the drum master has a larger piston than the disc m/c, but should work.
 

pb4ugo

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You'll need to swap the pinion flange to accommodate the early drive shaft.
 
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You'll need to swap the pinion flange to accommodate the early drive shaft.

I haven't checked that, but I was wondering if they were the same size. That's a bummer. Those things can be a real pain to remove.
 
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You just need to confirm ratios. They're most likely 4.11. Disc and drum frt brake lines are run differently. I opted to run mine like stk disc. I think the drum master has a larger piston than the disc m/c, but should work.

I forgot to mention, but I DO plan to swap the master cylinder. I've heard of people having problems with that.
 

4Cruisers

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I haven't checked that, but I was wondering if they were the same size. That's a bummer. Those things can be a real pain to remove.
As an alternative, you can swap out the yoke on the front driveshaft.
 

pb4ugo

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Back in the 80's I had a 76 parts 40 and swapped the whole driveline into my 72.
 
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I thought the ratios changed to 3.78 in '78.
 

DickM

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so for the U.S. models, the ratio from ‘72-‘78 should be the same?

As far as the pinion splines go, that shouldn’t matter as long as the driveshaft flange matches.
 

pb4ugo

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so for the U.S. models, the ratio from ‘72-‘78 should be the same?

As far as the pinion splines go, that shouldn’t matter as long as the driveshaft flange matches.
To confirm ratios you can pull the rear covers or rotate each 3rd member and count revolutions. Your dealing with 40yr+ old parts, I would not assume ratios are stk. The 78 should have a fine spline pinion flange w/a different bolt pattern so it wont work on the 72 3rd member because its coarse spline. I think you can swap the female ends of the drive shaft slip joints to get the right bolt pattern for the 78. This will put the slip joint towards the diff. The long ends of the drive shafts are probably different lengths, if not you could swap them instead. They just need to be in phase. If your not a purist, you could swap the whole driveline and run the 78 4 speed/tcase, and diffs along with the stk driveshafts.
 
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I'm not really a purist. I just want to keep the outer parts of the vehicle looking mostly factory or at least period correct. However, it's looking like I might be better off just buying a conversion kit for the disc brake swap.
 

pb4ugo

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I'm not really a purist. I just want to keep the outer parts of the vehicle looking mostly factory or at least period correct. However, it's looking like I might be better off just buying a conversion kit for the disc brake swap.

The best frt disc brake conversion is using factory Toyota brakes like your asking about. Imo, It's a top 3 mod. Swapping the whole axle is the simplest way. A fine spline pinion is stronger than the early models. Cruiser outfitters sells a pinion flange that is drilled for late models and can be easily drilled for your driveshaft if necessary. Removing and installing your pinion flange is easy.
 
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To confirm ratios you can pull the rear covers or rotate each 3rd member and count revolutions. Your dealing with 40yr+ old parts, I would not assume ratios are stk. The 78 should have a fine spline pinion flange w/a different bolt pattern so it wont work on the 72 3rd member because its coarse spline. I think you can swap the female ends of the drive shaft slip joints to get the right bolt pattern for the 78. This will put the slip joint towards the diff. The long ends of the drive shafts are probably different lengths, if not you could swap them instead. They just need to be in phase. If your not a purist, you could swap the whole driveline and run the 78 4 speed/tcase, and diffs along with the stk driveshafts.

Bolt pattern difference isn't because of coarse spline versus fine spline. Difference was three speed versus four speed. 1/74-8/84 bolt pattern stayed the same. 1/78 the pinion switched from coarse to fine spline. To use the 78 axle will require getting a universal flange if you want keep you three speed driveshaft original. In other markets the H41/H42 started 9/73. I show a 9/73-1/74 had a third bolt pattern for that four speed (at least a different part number) but to my knowledge the four speed started 1/74 in the US.
 
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The fine spline is good with me. (especially since they are stronger) I would prefer to keep the driveshafts all the same, if I can make it happen. I will eventually be using at H55f transmission, so it may not matter anyway.
 

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