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jagman

85-86 720 diff ratios for auto and manual trans

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Did Nissan use two different ratios?  One for the automatic trans and  another for the 5 speed manual?

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All automatics were 3.70 on the 2wd '85 720 truck. None of the other 4 had that ratio... although one of those 4 never came with an automatic, so really there were 3 other ratios.

 

 

Find the engine tag riveted to the passenger side inner fender just below the hood hinge.

 

this is for a 5 speed....

buF8TkE.jpg

 

Bottom line...

 

 

TRANS / AXLE............... FS5W71B................ HF38  or HF43 or HF 35

 

38 is 3.889 ratio

 

An automatic tag would say...

 

TRANS / AXLE...............3N71B.................... HF37

 

37 WOULD BE 3.70 RATIO

.

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Mike I ran across a 1980 720 king cab 2 wd L20B automatic that had a 4.11 gear ratio.  This is the wiring harness I started with on my 66 520.

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My info is for the '83 and up 720 which is what he wanted. I had an '82 long bed automatic and it was also 4.11. The '80 L20B long  wheelbase reg cab were 4.625!!!

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3 hours ago, datzenmike said:

All automatics were 3.70 on the 2wd '85 720 truck. None of the other 4 had that ratio... although one of those 4 never came with an automatic, so really there were 3 other ratios.

 

 

Find the engine tag riveted to the passenger side inner fender just below the hood hinge.

 

this is for a 5 speed....

buF8TkE.jpg

 

Bottom line...

 

 

TRANS / AXLE............... FS5W71B................ HF38  or HF43 or HF 35

 

38 is 3.889 ratio

 

An automatic tag would say...

 

TRANS / AXLE...............3N71B.................... HF37

 

37 WOULD BE 3.70 RATIO

.

Mines an 85 auto and I got the 3.889 gears

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The tag says 3N71B and HF38??? 

 

Well ultimately Nissan may have changed the published specs, ya never know. But 3.70 is what it's supposed to be. The other thing is that in 35 years maybe the differential was swapped.

 

Any chance the speedometer is reading 5% high? That's only 2.5 MPH @ 50 MPH and may not be noticeable. 

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19 hours ago, datzenmike said:

The tag says 3N71B and HF38??? 

 

Well ultimately Nissan may have changed the published specs, ya never know. But 3.70 is what it's supposed to be. The other thing is that in 35 years maybe the differential was swapped.

 

Any chance the speedometer is reading 5% high? That's only 2.5 MPH @ 50 MPH and may not be noticeable. 

Mines a L3N71B HF38. Nope stock  rearend. Grandpa brought  the truck from the dealership  with just 4 miles on it.

Edited by 85"720
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Well I'll try to keep track of that info.

 

L 3N71B? L may be for locking torque converter. There were also E3N71Bs in the 280zx but not the 720. The E was a heavier duty transmission.

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50 minutes ago, datzenmike said:

Well I'll try to keep track of that info.

 

L 3N71B? L may be for locking torque converter. There were also E3N71Bs in the 280zx but not the 720. The E was a heavier duty transmission.

Yea mine has a locking  torque converter. I can feel it lock up  at 40-45 mph.

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53 minutes ago, datzenmike said:

Well I'll try to keep track of that info.

 

L 3N71B? L may be for locking torque converter. There were also E3N71Bs in the 280zx but not the 720. The E was a heavier duty transmission.

I believe  the e stands for electronic if I'm not mistaking. Kinda like  GM's 4l60e. 4=the amount  of  gears. L= longitude. 60 =the strength of the trans. E = electronic. 

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Nissan uses the E on engine codes to signify multi port EFI. D for dual OHC, i for throttle body injection, R for supercharged and so on. The 3N71B has no electronics. Well reverse light switch and ignition interlock.

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Mike I also ran across an 85 720 regular cab short bed that had a HF 35, 5 speed & Z24.  I know the tag was correct as we pulled that set of gears for Shawn's 521 convertible.  He has a Z24 5 speed out of a 84 720.

 

Resized_20180519_134125.jpg

 

Needed a colorful picture in this thread!  LOL

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Well DatzenMike, I looked all over the firewall, inside the door panels, inside the dash, under and in the fenders and I can't find a plate like you show in the picture.  When I have a chance I will look at the long bed and see if it has the plate affixed.  Thanks for the info on what should be there and if the long bed has a lower ratio than 3.70 (like 4.11 can I swap rears?  Will I have to change the speedometer cable as well? 

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On 3/1/2019 at 3:44 PM, datzenmike said:

 

 

Find the engine tag riveted to the passenger side inner fender just below the hood hinge.

 

 

.

 

 

Charlie yes for the standard transmissions there was a 3.545 gear for the Z24 5 speed pick up. There was a 3.364 on the Mileage Option Z20S which only came with 5 speeds. There was a 4.375 on the 5 speed Cab/Chassis only with a 5 speed and 3.889 on the diesel trucks that were also 5 speeds.

 

The question was what was used on the '85-'86 Z24 automatics and I say 3.70. My info shows only the 3.70 was used. But as suggested maybe the 3.889 was also used.

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Well,  I have looked and it must have been forgotten during the build cause there aren't any holes there either.  Can you make a lightweight samurai sword from aluminium?

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What year is your 720.  I am not sure if the 1979 and 1980 720s had the little aluminum information plate

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Charlie, I think this truck is about the same age as my long bed which is 85-86.  I don't know what the run of years is for the 720 but based on the build number they have to be close.

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June of the previous year is the usual change over for model years. June '79 was the first '80 model year 720.

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I don't know how many 720's sell per year  but the build numbers are 372089 for the long bed and 308468 for the junker.  That's 63,621 units earlier than the long bed.  Would that make it an 81-82 assuming they sold ~ 20,000 per year?

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There were reg cab short wheelbase, reg cab long wheelbase and KC

 

For 1980 there were 168,999 reg cab short wheelbase trucks made and the same number of King Cabs... then there were the Long beds and the Cab Chassis models and to further confuse there were two plants operating with even more on top of these. That's a lot of trucks.

 

What truck do you have?

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I have an 86 std cab long bed with a 5 speed tranny.  The junker is a king cab short bed with an automatic tranny.

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I've found a 372,89 made sometime between April and May '85???. The driver's door jam tag should have the build date on it.

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