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Heres yet another 620 4 to 5 speed trans question..


Perez620

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Ah, that's much different. The title says 4 into 5 speed. The '74 L18 with automatic had a 4.625 differential. You would definitely want something closer to 4 with the higher torque L20B. .

 

'73-'78 manuals......... 4.375

'79 manuals............... 4.11

'73-'74 automatics..... 4.625

'75-'79 automatics..... 4.375

I installed a L20B automatic in my 66 520 with a 1980 720 3.89 ratio rear end.  If i do not like the 3.89 I will go to a 3.70.  I drive fast.

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:thumbup:

 

Just so you know an LSD would require both wheels off the ground.

Question Mike,

 

If I happen to get a 5 speed or of a ‘80 720, which would be wide gears, do you think I’d have to change my 4.625 rear gears or would they work well together? I’m just unsure of how to actually calculate if they’d work

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Question Mike,

 

If I happen to get a 5 speed or of a ‘80 720, which would be wide gears, do you think I’d have to change my 4.625 rear gears or would they work well together? I’m just unsure of how to actually calculate if they’d work

 

Out on the highway it will run like a 4.265 differential but first is insanely low with a wide ratio transmission. You'll barely get into the intersection and the engine will be screaming for a gear change. Mileage won't be that good either.

 

Look at it this way. Assuming 175/70R14 tires, 4.625 differential and wide ratio transmission on your truck, at....

 

3,000 RPMs in first you will be going only 12 MPH.

 

Above but with 3.889 diff... 15 MPH that's 25% faster!!!

 

60 MPH in 4th with 4.625.... 3,950 RPMs.... 5th.... 3,484 RPMs. A little high for cruise rpms on the highway

60 MPH in 4th with 3.889.... 3,322 RPMs.... 5th.... 2,930 RPMs. Around 3K is pretty good for L20B truck.

 

If getting the wide ratio transmission I think I would get a lower differential than the 4.625.

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The 1980 standard cab 720 had 3.89 gear ratio. My rule of thumb is I get a trans I also try to get rear end punkin from same truck. This usually will keep speedometer read correct.

If I were to find a 720 donor, does the third member direct swap or would I have to physically swap gears? I’d love to find a truck to pull everything from. Easier said than done though!

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Out on the highway it will run like a 4.265 differential but first is insanely low with a wide ratio transmission. You'll barely get into the intersection and the engine will be screaming for a gear change. Mileage won't be that good either.

 

Look at it this way. Assuming 175/70R14 tires, 4.625 differential and wide ratio transmission on your truck, at....

 

3,000 RPMs in first you will be going only 12 MPH.

 

Above but with 3.889 diff... 15 MPH that's 25% faster!!!

 

60 MPH in 4th with 4.625.... 3,950 RPMs.... 5th.... 3,484 RPMs. A little high for cruise rpms on the highway

60 MPH in 4th with 3.889.... 3,322 RPMs.... 5th.... 2,930 RPMs. Around 3K is pretty good for L20B truck.

 

If getting the wide ratio transmission I think I would get a lower differential than the 4.625.

I understand what you mean. The truck is definitely going to be more of a cruiser than a highway driver

 

I may just have to find my 5 speed and at a later date swap the diff because this is becoming harder than I thought it’d be to find one!

 

I definitely wouldn’t want to be screaming in first gear at only 3k rpms either :(

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You may find that you can just skip first and start in second. I have 4.11s and as long as the car is rolling I use 2nd rather than 1st. It goes around corners in town in 3rd easily and can be driven in 5th at in-town speeds (30MPH)

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Diff should be easy to find. Damn near every truck from 70 to 80 had a 4.375.

Every truck as in Nissans? Also I’m assuming it’s not just a direct swap if it’s not from an actual 620

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The 520/521/620/720 and some D21 Hardbodys, Xterras had the H-190.

 

4.875

4.625

4.375

4.11

3.889

3.70

3.545

3.364

This is if I want to just swap out the actual gears though correct? Which is fine just trying to see what the easiest option is

 

Also I must ask Mike, you must have a few years under your belt with Datsun/Nissans. You know your stuff dude!

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3485.jpg

 

The H-190 differential is a contained unit within the axle housing. By pulling the axles out to the side, unbolting the drive shaft and the 10? mounting bolts it can be just pulled out and replaced.

 

Trucks have 29 spline axles so you need truck differentials with 29 spline side gears for an easy swap. Cars are 23 spline but with careful work the side gears can be swapped for use in a truck. Some of the very early trucks (320s?) had 13 splines.

 

Early differentials were made of aluminum the rest were steel with the later ones probably the strongest.

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If I were to find a 720 donor, does the third member direct swap or would I have to physically swap gears? I’d love to find a truck to pull everything from. Easier said than done though!

Simply yes.  Truck to truck H190 reaends swap.  Drain rearend grease, remove rear wheels,  remove drums, remove 4 nuts on the back side of the the brake backing plates pull axles out as far as you can, sometimes you have to slacken the packing brake cable to get the axles out of the sides gears and carrier bearings.  remove the nuts holding the carrier after removing the rear univesal bolts and straps.  I usely will put a little pressure on the pinion bearing area of the third member with a floor jack an tap the third member with a big hammer on a 2x4. you have to pull both axles.

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My 71 521 and my 620 both have the 4.375.

 

 

If you weren't so far away I have one to get rid of.

Where are you located? Would probably be pricey to ship I suppose. I just need to dig deep and find one

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3485.jpg

 

The H-190 differential is a contained unit within the axle housing. By pulling the axles out to the side, unbolting the drive shaft and the 10? mounting bolts it can be just pulled out and replaced.

 

Trucks have 29 spline axles so you need truck differentials with 29 spline side gears for an easy swap. Cars are 23 spline but with careful work the side gears can be swapped for use in a truck. Some of the very early trucks (320s?) had 13 splines.

 

Early differentials were made of aluminum the rest were steel with the later ones probably the strongest.

Thanks for the info Mike. I’ll see what I can find for a swap

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Simply yes. Truck to truck H190 reaends swap. Drain rearend grease, remove rear wheels, remove drums, remove 4 nuts on the back side of the the brake backing plates pull axles out as far as you can, sometimes you have to slacken the packing brake cable to get the axles out of the sides gears and carrier bearings. remove the nuts holding the carrier after removing the rear univesal bolts and straps. I usely will put a little pressure on the pinion bearing area of the third member with a floor jack an tap the third member with a big hammer on a 2x4. you have to pull both axles.

Sounds easy enough but doesn’t most stuff then it’s a headache! I’m definitely on the lookout for a rear. If you come across one I’m in the Kansas City area

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I know where there is a 370 but the yard it is in here is expensive and I only buy from them if I have to have it.

 

On the inner fender well on the 720 is a 3" x 2" plate that gives the engine transmissin and rear end ratio.  This gives you a good rule of thumb before pulling the third member.  But always do the math off the stampings on the ring gear after pulling the rear end to be sure it is the ratio you want.

 

Ring_Gear_Stamping.jpg

 

45/11=4.09 Known as a 410 ratio

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Where are you located? Would probably be pricey to ship I suppose. I just need to dig deep and find one

Eastern Washington.

 

You move West and you'll have all the Datsun parts you need.

 

 

Do you already have the pedals for a manual? Cuz I have those too.

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I know where there is a 370 but the yard it is in here is expensive and I only buy from them if I have to have it.

 

On the inner fender well on the 720 is a 3" x 2" plate that gives the engine transmissin and rear end ratio. This gives you a good rule of thumb before pulling the third member. But always do the math off the stampings on the ring gear after pulling the rear end to be sure it is the ratio you want.

 

Ring_Gear_Stamping.jpg

 

45/11=4.09 Known as a 410 ratio

Thanks for the advice! Hope to come across one soon. If you come across one im in Kansas City

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Eastern Washington.

 

You move West and you'll have all the Datsun parts you need.

 

 

Do you already have the pedals for a manual? Cuz I have those too.

Thats what it seems like that majority of Datsun parts are all west of here. I do have the clutch pedal but just have to order/find the reat of the bits to go from Auto to Manual

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