'80 720 Axle ID

[Stinky]

I am trying to change axle ratios on my 720. I have the 3.73? ratio. I am in touch w/a guy 5 states away. He has a '80 720. The plate inside the passenger fender. It is dif style and it doesn't have the axle code on it.

 

Any other easy way to find it out.

What should it be?

Is there another plate?

I have gone to 15" tires and my truck is sorta boggy...it needs some rpm.

I already have rolled D21 and it should have a 4.11 in it. But, it is a bit wider, and the E-brake hook up is dif. I'd have to adapt that and also change the perches. I'd rather drive out to Riverside, CA and snag it and come back.

[datzenmike]

The '80 2wd 720 had an H-190 with 3.889 differential. He has an '80 so will be the same if 2wd. You don't need to change the entire axle assembly just the third member...

 

 

15" tires do not mean the gearing might have changed. You can buy 14" and 15" tires that are the same diameter. What tire size do you have? How much too fast is your speedometer at 50??? This will tell you how much gear to add to slow it down and restore the speedometer and acceleration.

[Stinky]

15" tires because bigger is better...off-road.  I am prone to getting around in the back country.  I have 215/75-15 ATs

 

My speedo reads 5 mph to fast.  IOW, I need to drive 60 mph to actually drive 55mph.  I know that that is backwards, but the thing is 34 years old.  I have verified this by GPS and every flashing construction and curve sign, that shows your speed that I have ever seen. 

 

 

[datzenmike]

I was saying that the rim size is meaningless. The tire diameter is what changes your effective gear ratio the engine 'sees'. You can have a 14" tire that is taller than a 15". The tire itself is what determines the diameter.

 

Speedometer error is not constant. It won't be 5 mph out at all speeds, instead, if out 5 at 50 it will be 10 out at 100 and 2.5 at 25. 

 

If your tires now are 215/75-15 then the diameter is 27.7". A stock 720 2wd is probably 195/75/14 which are 25.52" can you confirm this is what you had?? If yes then your truck will be going faster than what the speedometer reads... or you could say the speedometer is slow.

 

Going to this taller tire.... at 60 you should be reading exactly 55.28MPH so that checks out almost exactly. This is also almost exactly 9% difference so IF you have a 3.889 differential changing to a 4.24 would cancel this out by slowing you down and making the speedometer accurate. Unfortunately Nissan does not have a 4.24 differential but there is a 4.375 which is a 12.5% increase. This would mean your speedometer would read 3.5% high or 1.75 MPH high at 50. Or reads 51.75 MPH while dong an actual 50MPH. That's pretty damn close I say. And this gives you slightly more torque than the original tire and differential. Cake... and eat it too.

 

The 4.375 was used extensively in the 620 truck. You said '80 but what year truck are you referring to??? What's this going into???

 

 

[Charlie69]

On 1980 2wd trucks I have had a 3.889 and a 4.11 ratios with the 3.889 most common.  The 4.11 was on a L20B automatic King Cab truck.  I have only had one of these.

 

Mike the trucks that came stock with the ST aluminum wheels came stock with 205/75R15s.

Edited April 10, 2020 by Charlie69

[datzenmike]

Looks like it. I only have the '84 FSM. The 4x4 had 215/75R15. I always liked the 720 alloy rims. The Z car had the same design in 4 lug.

[Stinky]

Well, I bought a 4.11 drop-out this weekend, and 2 switches (only one for this vehicle).

 

The yard was quite interesting and was the most organized one that I've ever been in.  Blake's in Erie, CO and he does not ship.

 

[datzenmike]

I did say a 4.375. A 4.11 is only 5.6% and you need 9% so you are 3.4% on the low side. A 4.375 would have given you less 'bog' n 4.11

[Stinky]

I started w.the 3.7? ratio.

 

The change was in the 10% range.

 

I based this all on my rpm at cruising speed.  2,200-2,500, depending on the speed (45-60mph).  A 20% change woulda gave me, roughly, 2,650-3,000 and that was more than I wanted to do.

 

He had a 4.37 and it was on the same shelf that I got my 4.11 from.  I wavered there for a bit, but in the end, I went w.what I originally wanted.  One of the reasons was that my gearing will now matche 4x4 PUs of that timeframe...w.my 215/75s.

[yenpit]

On 4/12/2020 at 9:33 PM, Stinky said:

Well, I bought a 4.11 drop-out this weekend, and 2 switches (only one for this vehicle).

 

The yard was quite interesting and was the most organized one that I've ever been in.  Blake's in Erie, CO and he does not ship.

 

 

How did you get in Blake's??  I thought they shut down 3-4 years ago??  They had a 510 in there 8 years ago, let me strip it completely down right there in the yard, even let me cut the front rad core support & tail lamp panel off, they scrapped the rest of the shell.

 

I'm in Arvada, have a 1980 720 2WD parts truck & a 620 parts truck, if you need anything!

 

TJ

[Stinky]

He advertises on carpart.com.

 

You're right, he is closed and shutting down.  There is a sub.division 100 yards away.  Once they get closer, and they really want to buy, things will be scrapped.

 

I called him up...youll get a machine, say I am looking for a part that carpart says that you have.  He calls back in a day or so.  He then verifies that he has it, calls you back, and Then you make an appointment.

 

There was 2 of us in there at the time.  The other guy got a toyota bed.

 

He has a 720 camper.shell....it needed something w.the rear glass.  50 bucks.

 

He has 2 720s....pretty well picked over.  One had a backglass...this, about 2 weeks after i looked all over for one and barely found one.

 

The buses, around the property are full of crap...sorted, shelved, and in bins, switches (steering wheel, turn, cruise, E.window), levers, gizmos, etc.  In my case, a 720 dif.  He had carbs, heads, manifolds in that bus.  They are all numbered and cataloged.