521 diff ID

[domn8tr]

I'm changing the chunked up diff on the 521 so I can finally be back on the road we were crusing the yards and I picked up one but It appears different. It was supposed to be from a 720 . The castings are different on the pumkin with my 521 having parallel fins and the new one having radiating pattern. Problem is it appears to be longer by almost an inch. Is there any way to swap the internals on these or do i have to shorten my driveshaft??

 

 

 

 

 

 

[domn8tr]

sorry about the small pics

 

[flatcat19]

Was there a question here?

:blink:

 

 

 

 

 

 

 

 

 

Count the bolt holes holding the pumpkin on.

 

Will your axles fit into this new-ish diff?

[ggzilla]

Didn't the later 720s use the C200 diff instead of the H190 that the 320/520/620 used?

[jesusno2]

that c 200 isnt a dropout

[domn8tr]

I havent tried to fit it in yet but i guess my question would be do all H190 have the parallel casting fins as opposed to the other design? there were several other 4cyl hardbodies that appeared to have the same diff. Both diffs have 10 bolt holes around the casing.

[datzenmike]

Didn't the later 720s use the C200 diff instead of the H190 that the 320/520/620 used?

 

Only the 720 4X4s made after November '83 had the C-200... and it only came with 4.11 ratio. All other years and 2wd had the H-190.

 

 

 

The 521 has an H-190-AL which is an aluminum case and the webbing doesn't mean much. The 620 started using the steel case.

 

Did you try swapping the yoke onto the 720 diff? To see if that will 'shorten it?

 

The 521 has a slip joint on the rear drive shaft so will it not collapse slightly and still bolt up?

[domn8tr]

The dust cover and seal underneath are different sizes, no can swap! i spent a few hours back at the yard looking for the right diff but the later flange was larger still . i ended up getting another diff from a 76 620 right flange but I'm still at 437 i threw it in for now but I'll proabably go to 390 later if i can find one cheap.what year would be my best bet ? 88-89 D21 2.4?

[Laecaon]

When at the junkyard, lock one side of the axle and spin the other side 2 revolutions. Count the times the driveshaft spins.

 

 

If it spins slightly more than 4 turns, it is 4.11

 

If it spins slightly less than 4 turn, it is 3.889

[wayno]

You can use any 720 with a front drop out type gearset, pre 84 has the driveline flange you can use even though it is round and it looks bigger, it has the same pattern for your driveline connection, some of the 4WD flanges are obviously bigger, but most of them are years 85-86.

All that matters is getting the right gearset ratio that you want. Some of the early datsun(pre 84) 4WD flanges on the transfer cases will work on your diff. also. Here is a photo of an early 521 driveline connected to a 720 round pinion flange.

 

 

[domn8tr]

Thanks Guys! good info. Will the 720s be 437? I'd like to ask the guys at the yard for a specific year that would most likely be 388 or 411.

[datsunaholic]

3.89 was used in Z22 and Z24 MANUAL 2WD 720s, so that'd be '81-86. 4.11 was used in 2WD MANUAL in '80 only, and ALL 2WD Automatics. 4.38s were only used in 4WD.

[wayno]

In my searches of the wrecking yards, I have found the most plentyful diff. is the 389 or 370 gearsets, 411s are out there, but harder to find. There is a tag/plate in the 81-86 720 engine compartment on the pass. side just in front of where the wiper motor is that has the gear ratio on the bottom right, if it says 38, then it is the 389 gearset, 41 is the 411s, 37 is the 370s, ect. This doesn't mean that is what is in it, as they get changed for various reasons, so everytime you see a tag/plate with the ratio that you want, you pin one of the wheels so it will not turn, put the tranny in neutral, e-brake off, then make a mark on the other tire/drum, make another mark on the pinion flange, then turn the tire/drum two complete revolutions counting how many times the driveline/pinion flange turns, just over 4 turns is a 411 gearset, 3 and 3/4 turns is a 370 gearset, almost 4 turns is a 389 gearset, ect, ect. Another thing that you should check is how much play is in the pinion gear, I don't wast my time with anything that has more than an 1/8 inch, and I prefer less than that. Also, don't buy any gearset without the pinion flange.

[domn8tr]

Once again excellent info guys, thank you very much . Now I know exactly what to look for, and I'll make sure it has the right flange this time !