Rear Diff gearing ?'s

[irish.spy]

So my truck was a Automatic and now is a 5 speed I cant drive it yet do to my clutch slave cylinder not arriving yet, but will the truck be peppy or sluggish off the line with the rear end that came in the truck when it was a auto. Some one told me with it being a auto it will have taller gears compared to a truck that came with a manual. Any feedback on this?

[kelowg]

I say try it and see. All depends on variables,tire size,5th gear ratio,ect. Taller gear (like 3.88 from a 4.33)means increased mpg and comfortable cruizin speed. So its a matter of type of driving u will b doin.

[datzenmike]

The '77 used the same ratio rear end for 4 or 5 speeds and automatics.

[sprocket_jim]

Similar question....doing an auto to manual swap in a 77 KC. Were there any differences in rear ratios between a '77 and a '78 KC? I have a '78 KC that can be a donor but may not need to be. I have a few options. I have the original 5speed that came with the "extra" parts when I bought the '78 truck. When I bought the '78, it was set up with a 280zx 5speed. Very happy with the setup and the short shift is nice. I understand the truck 5 speed to be the same as the zx 5 speed. Is this true? Rather than cannibalizing the '78, I may be able to round up the parts for my '77 conversion.

[ggzilla]

It doesn't matter which ratio it has, it will be more peppy after you take out the automatic and put in the 5-speed

[datsunaholic]

ZX 5-speeds are bolt-compatible, but had different ratios than the truck 5-speeds (taller overdrive, closer ratio 1-3 gears). Now, the 280Z 5-speed had the same gears as the 77-78 truck.

 

Rear ratios on 620s are the same on ALL 75-78 trucks. 4.375:1. Doesn't matter if it's Automatic, manual, 4-speed, 5-speed, Shortbed, longbed, king cab. All the same. Can't say what the "Cab & Chassis" version had, but how many of those are out there? A few Motorhome conversions, that's about it.

[datzenmike]

The '79 cab/chassis had only 4 speeds and 4.375s. Only the automatics had the same gearing that year. Four and five speeds were all 4.11.

[sprocket_jim]

ZX 5-speeds are bolt-compatible, but had different ratios than the truck 5-speeds (taller overdrive, closer ratio 1-3 gears). Now, the 280Z 5-speed had the same gears as the 77-78 truck.

 

Rear ratios on 620s are the same on ALL 75-78 trucks. 4.375:1. Doesn't matter if it's Automatic, manual, 4-speed, 5-speed, Shortbed, longbed, king cab. All the same. Can't say what the "Cab & Chassis" version had, but how many of those are out there? A few Motorhome conversions, that's about it.

 

Thanks. Very helpful. Explains why the truck is very "snappy" and loves to haul down the highway at 85mph!!