79 5sp 620 rear end gearing.

[620_Brian]

See attached pics.

Does that “383” represent the gearing in my pumpkin?

3rd member.

Whatever you want to call it. 

 

Is is there anyway that is what a 79 5sp KC came with? It’s ridiculously too low.

 

I know I can get a...pumpkin..from a 720 ooor anything else?

Not a hardbody correct?

And what casting stamp (gearing) should I look for? I’m doing that KA swap with the 240 trans. I want it to be 240ish obviously. 

 

[datzenmike]

No. that would be some kind of mold identification or revision number cast into the case. That H-190 differential can hold any of these gear sets in it..... 3.364, 3.545, 3.70. 3.889, 4.11, 4.375, 4.625 or 4.875 ratios. Depending on truck model and the year.

 

The '79 4 or 5 speed 620 is the only year to have 4.11 gears.  If you want lower you should look at the 720 which ranged from 3.354, 3.545, 3.70 to 3.889. On the 720 look below the passenger side hood hinge on the inner fender. There you will find an aluminum tag with information stamped on it. At the bottom find...

 

TRANS/AXLE........ FS5W71B.................HF38 The number is the differential ratio. HF35 would be 3.545, HF41 would be 4.11 and so on.

 

 

Why change the gearing anyway?

[620_Brian]

Well....with the current 5sp and rear end I have to shift so quickly just to get going. I’m in 5th gear constantly even on surface streets. On the interstate the RPM’s are just screaming in 5th (broken tach). 1st gear is basically useless. 

Its by no means quick. 

I’m assuming it’s because someone put some different gears in it at some point (hauling or towing use?)

 

Once I have that KA and a 240 trans won’t I want “longer legs”?

Or am I thinking about this wrong?

Should I just wait and see how the KA and the 240 trans behaves?

Edited January 2, 2019 by 620_Brian

[datzenmike]

I would wait and see.

 

The 620 usually has a 4.375 differential and the 4 and 5 speeds have a mid ratio 3.321 first gear. Everything works about right with this combo. The '79 uses a lower 4.11 so to compensate for the added effort to get a loaded truck moving perhaps on an up hill start, the transmission was also changed for a wide ratio 3.592 first gear. Both are now comparable in first but 4th or 5th will be lower revving on the highway, maybe saving a little fuel.

 

 

A/ 60 MPH on stock 4spd and 175/70R14 tires is 3,510 RPM for the '79 with 4.11s

B/ 60 MPH on stock 5spd and 175/70R14 tires is 3,296 RPM for the '79 with 4.11s about 200 RPMs lower than A/

C/ 60 MPH on stock 4spd and 175/70R14 tires is 3,735 RPM for the '79 with 4.375s about 200 RPMs higher than A/

 

I'm pretty sure you could easily maintain highway speeds with 3,000 RPM and likely less in the 620

 

D/ 60 MPH on stock 4spd and 175/70R14 tires is 3,331 RPM for the '79 with 3.90s

E/ 60 MPH on stock 4spd and 175/70R14 tires is 3,160 RPM for the '79 with 3.70s

F/ 60 MPH on stock 4spd and 175/70R14 tires is 3,510 RPM for the '79 with 3.545s*

 

* With an L20B it might cruise down the highway at 3K but hills, strong wind and passing will be a challenge. In town take offs at the lights will be sluggish and all gears a long pull and 4th never used. A much higher torque KA engine would handle this better but it doesn't sound like much fun.

 

 

 

[620_Brian]

Gotcha. I’ll wait and see. Great info.

Thank you. 

[G-Duax]

I run a 4.62 gear set in my 620, with a 280Z 5-speed, 225x60-15 tires, and it only turns 5300-ish rpm at a 100 mph. And when I have clear highway, I'll do that for 20-30 miles strait.

Just why do you think you are spinning your engine too fast ?

 

 

 

[datzenmike]

Seems like all L owners think their cars are over revving when obviously Nissan did it's homework and these things ran like this for a lifetime. The engine screaming is subjective. Get a tach and you'll see. The L20B red line is 7,000 RPMs, or 119.65 MPH.... you're no where near that.

 

There's no sound deadened in the engine compartment of the 620.  They're pretty primitive and not like today's cars.

[DanielC]

I do not normally disagree with Mike, but in this case, I am, just a little.

I have driven 521 trucks since the 1970's, and with a L-16, or a L-18, the 4.375 rear axle ratio in my opinion is ideal.  I put a L-20-B engine in one of my 521 trucks, and have been daily driving it, and I do this about three times a month, 20 bales at about 70 pounds each.

 

and about every other month in the winter, I do this.  50 forty pound sacks of wood pellets.

 

I would like to put a 4.11 rear axle in my truck.

 

One more thing,  The original poster lives in Florida.  I think there is more elevation change on my eight acre property in Oregon, than there is in the entire state of Florida.

 

Mike is right about the Datsun L-engine being happy with lots of RPM's.  5,000 RPM Is perfectly fine, and a L-engine can and will run there all day long. 

Edited January 2, 2019 by DanielC

[620_Brian]

I just can’t believe Nissan engineered and released the setup that is in my truck right now. Im pretty sure that rear end has been changed to something higher than stock (I do vaguely remember the PO saying something about it as well but he unfortunately died I think sooo...)

Earlier this week when I had a payload as pictured below, a loaded KA, an engine hoist, 2 jacks, 2 jack stands and an engine stand, 1st gear was still worthless.

I mean it did do fine in 5th at a constant interstate 70-80mph for a 4hr round trip to Orlando and back..but just wow. There was absolutely nothing left in that right pedal. Scream-ing. 

And I totally get it the that the L20B is designed as a high redline engine and that screaming is subjective to someone who normally drives modern cars.

I get it, I get it. 

 

Anyway, we’ll just wait and see what the KA swap does with whatever is in that ?. 

Maybe it’ll be just right (to me). 

 

[datzenmike]

 

If you're curious enough to lay this to rest.

 

All '79 models with 4 or 5 speed standard transmissions were 4.11 with the exception of the Camper and the Cab/Chassis option which came with the 4.375. (which I think only came with 4 speeds) All '79 automatics were 4.375.

 

My information says that the 4.375 was an optional choice  over the 4.11 but how many buyers actually knew of this, and how many actually ordered them? Most new cars are just bought off the lot. The 4.11 is predominant but anything is possible.

[Stoffregen Motorsports]

If the truck was purchased with the sole intention of being a work vehicle, the buyer would (should) have been aware of the powertrain options. My father in law worked in the Texas oil fields in the 60's and he remembers using Datsun 320s as go-fer trucks. They bought them for fleet service around the oil fields.

 

Not all of the vintage trucks we have today were brought home on day one by Mr and Mrs homeowner.

[og620]

I ordered/bought your same truck in 79 . It was 4.11 5 spd. great combo.after driving older 620,s with 4spd and lower gears it was a vast improvement.....enjoy.

[Cardinal Grammeter]

Just thought I'd ad more about the feeling that the rpm's are too high.

 

I had a new stock exhaust put on my 74 L18 and on the way home, I found myself driving 70 mph on the highway w/55 mph speed limit - I didn't realize I was going that fast.  

 

I drive this road all the time and usually go about 60.  But with the super quiet exhaust, I found myself driving 70. 

 

I also found driving on the interstate, after about an hour, my speed creeps up to 70-75 mph as I get "used to" the engine noise (but that was with a leaky noisy OE exhaust.)