Need Help On 720 Rear Axle! Parts, Prices and ID-ing Diffs

[Wrench21]

  Hey everyone, I really need some help here, I just tore apart my entire rear axle becuase the pinion wouldn't grab anything, and i found it was totally stripped with a broken tooth/spline. I believe my diff is a H190, but i am not sure.

 

 My truck is a 1981.5 4x4 KC. The Diff has a welded back housing plate, the only ID i could find on it was this "1TSE" with a "A" below it inbetween the '1' and the 'T' above (on the back housing). The ringear is 190mm/7.5" Outside diameter and it has 35 teeth/splines. The Pinion gear 'had' 8 teeth/splines which are all but gone now and is 8.125" long with a diameter at the spline valleys of 1.375". The spyder gears are fine amazingly, but i don't know what ratio the diff is and i can't find the Ring and Pinion gears anywhere! I need to know if there is a place/person to buy a good set from that will work in my diff or if there is another diff/axle assembly from another 720 truck, be it RWD or 4x4 of the same/another year that will work.  I could really use this information and any other help! Thanks in advance!

[datsunaholic]

Ratio is easy.  Divide ring gear by pinion 35/8 = 4.375, the most common H190 rear axle ratio around.  And it's an H190... that's the only rear diff the 720 came with.  But the 190mm ring gear is the main clue there anyway, that's where the name comes from.

 

Almost every 620 will have that ratio, they're exactly the same differenttial.   Only 620s that don't are '79 Manuals and '73-74 Automatics.  Because it's a 4X4, you WANT to keep the ratio the same, unless you also change the front diff to match.

 

Other early 720 4X4s will have the same ratio (2WD 720s will NOT have that ratio for the most part), but it will be easier to find one from a 620.

[thisismatt]

35/8 = 4.375, which is unique to the early (80-81) 720's, 4.11 after that, and it should be the H190.

[datzenmike]

35 divide by 8 is 4.375.... no surprise there as this was the usual ratio for the early 4x4s. Yes it's an H-190. If you look on the passenger side inner fender back by the hood hinge you'll see a credit card size aluminum tag with the axle info on it.

 

Here is me '82 engine tag. Bottom line is TRANS/AXLE (faded away) FS5W71B..... HF43

The 43 is for 4.374.... a 3.90 would be 39 and so on. All 720 have this tag so if searching for a new diff just look here.

 

 

 

Later ones are clearer. HF38.... is 3.889 ratio

 

Have a care when getting a replacement. The early 720 2wd used to swap onto the 4x4 no problem but around '81-'82 the driveshaft yoke changed... and of course your 4x4 yoke wont fit the pinion spline on the 2wd. Just be sure your driveshaft will bolt up to any you find and you're good.

 

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[datsunaholic]

I didn't know the pinion yokes were different, or is that just a 4X4 thing?

[Wrench21]

Allright. I am really grateful. Looks like i won't have to spend $400-$600 online afterall... Looks like i am going to pull&save! Once i get this thing finished i promise i will post pics and the full story. Thanks a ton everyone.

[datzenmike]

I didn't know the pinion yokes were different, or is that just a 4X4 thing?

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The early 4x4s had the same drive shaft diameter and U joint but they changer to a larger diameter tube and U joint to match. The differential yoke is splined to the end of the pinion so I tried to swap them and the spline is different too. I was pissed off at that. So you can't use an easily found 2wd diff and you can' swap a 4x4 youke onto it.

 

 

Hard to make out but I cut and trimmed the 4x4 yoke and welded it to the 2wd yoke.

[Wrench21]

One Last Question for this thread. The 2WD and the 4x4 drivelines, One type is solid, i see this on most 2WD trucks. I assume the 4x4 drivelines have the slider joint in them, is this correct? My truck came with a solid driveline, unattached and without the yokes, so this is why i am confused. Thanks again!

[datzenmike]

Yup the 2wd are longer because the 4x4 has a transfer case between tranny and diff. The 4x4 does have a spline in the middle of the driveshaft.

[Wrench21]

Alright i lied, not the last question. Went to puul-n-save and took apart a mid-60's 620 rear axle and the gear ratio was 4.11 and it said "N2" on the top of the housing, mine says "N1". So it won't  work for mine. Also, there was no tag on the passenger fender in the engine bay, so i couldn't figure what gear ratio it was before tearing into it. Are there any other ways to identify the ratio? Or... could i swap out the entire rear axle and the front diff off from another later truck to fix my problem and upgrade to better (and more LSD options) gear boxes?

[datzenmike]

Mid '60s would be a 520 truck, there wee no 620s until '72....  and it should still fit as they were H-190s too. It would also have has an aluminum case.

 

Only the 720 had the ID tag on the inner fender.

 

The 520/521 with J13 motor had 4.88 gears.

L16 521s were 4.375

L16/18 620 automatics were 4.625

All L16/18/L20B 620s 4 or 5 speeds and automatics were 4.375 with the exception of the '79 standards which were 4.11.

 

If you found a 4.11 it was either swapped in, was really a '79 620 or it was an early 720 automatic.

 

 

Your truck runs 4.375 gears. Later Z24 720 went down to 4.11s and if swapping them you would also have to swap the front as well. Twice or more work and bother. '72-'78 620 standards will have that ratio (4.375)

[Wrench21]

 I'm sorry, i meant to say "mid-70's" 620. I was looking into entire axle swaps and i found that later v-6 hardbodies and the pathfinders had the H233B axle with mostly 4.375 gear ratios in them... What i need to know is the dimensions of that axle and spring mounts, and e-brake cable types to match everything up to my truck. I figured i would have to get a driveline cut and welded with matching ends on it. Does the H233B have the larger 4-bolt drivline or is it something totally different? Plan on going to the junk yard again this week to poke around and find possible matches and to take pics.