5500 NAPCO front ???

[3QTRTONS]

1969 USAF GMC5500 with NAPCO front axle (7.20 ratio) believe it's an Eaton. What numerically smaller gearset could I use to make this beast more highway-able? It can't be that easy as installing a ring gear/pinion from a rear axle of similar weight rating, can it?
Any input appreciated!

[1976gmc20]

Crazy idea: is the wheelbase long enough to install an auxilary OD transmission in the rear drive line ???

When you're using 4wd you probably don't need to go that fast

[3QTRTONS]

Originally Posted by 1976gmc20

Crazy idea: is the wheelbase long enough to install an auxilary OD transmission in the rear drive line ???

When you're using 4wd you probably don't need to go that fast

The wheelbase is plenty long enough. Aux o/ds wicked pricey though, aren’t they?
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[1976gmc20]

Originally Posted by 3QTRTONS

The wheelbase is plenty long enough. Aux o/ds wicked pricey though, aren’t they?
Posted via Mobile Device

Sorry, no clue about that. I was just thinking one change instead of changing gears in both (or three?) axles.

I wonder if you could still find an old under/direct/over three speed from the 1950s?

I drove an old GMC with one of those (5x3). You would just have to make sure to be only in direct when engaging 4wd.

[sweetk30]

if you have wheel base length put the browny box after trans but before divorced rockwell t-case .

but the bigger problem is these old trucks were NOT made to do long distance speed or todays highway speeds . the brakes are not as good as todays and other problems can show up .

i did a 4x4 napco swap for my old boss and it tops out 45-50 mph safe and decent rpm range . i dont think i would want to go much faster on them old driveline parts .

[3QTRTONS]

REALLY appreciate the replies! All good info, for sure. There isn't a whole lot left around these parts; this truck was definitely a strange bird right from the start. I have a set of one ton (4.10) axles from an '89 V3500 SRW that I could use - would 'bob' the frame by several feet and dump bed or flat bed it. That would make it more of a pickup than a Heavy Hauler, but would be more usable on the highway. I've seen on here that the 1 ton idea has been done. More research I guess!

[1976gmc20]

What size tires do you have now?

If say 8.25-20 maybe go to 900-20 or 1000-20 for a little less highway rpms ???

(I hate seeing these big trucks cut down )

[MJN]

I don't have any documentation for Napco stuff newer than 1960 but in my Napco parts book it shows a 6.17 ratio available for '56-57 1.5 and 2-ton trucks, no idea if they continued to offer this later on. For pickups Napco only offered one ratio; 3.90 for 1/2tons, 4.57 for 3/4tons and 5.14 for 1 tons.

[3QTRTONS]

Originally Posted by 1976gmc20

What size tires do you have now?

If say 8.25-20 maybe go to 900-20 or 1000-20 for a little less highway rpms ???

(I hate seeing these big trucks cut down )

Presently 9.00x20 - Originally equipped with a 292 I6. Even with 12.00x20, the rpm would be 'howling' at highway speed (3,574 @ 65 mph).
The heaviest Hauling planned is a car trailer with a Military Ambulance for Shows and Parades.

[1976gmc20]

I never drove my C/50 much over 50 mph. Was up in the mountains and back then the max limit was 55. I was warned about over speeding the big V-6 but hardly ever had a place to go that fast anyway. I bought another engine with a big hole in the side of the block just for the extra parts: heads, manifolds, carb, power steering, etc.

You might get a laugh out of our old 6x6 army water tenders going down the highway at 45 mph with the emergency lights flashing and all the rest of the traffic passing instead of pulling over

[Dannny B]

I've got a 4 speed Browny that I will let go of.