How do i find out what my gear ratio is?

[MarineGreen]

Wanting to know what the gear ratio of my differential is in my truck is and how i go about finding it out?

Its a 73 gmc k1500 and it has:
Chevy 350
3 speed Wt306 (SM330)
Np205 With dana 44 in the front and 12 bolt in the rear, And i am currently running 235/75/15 tires.

Help is appreciated!

 

[DanMcG]

try this;
https://www.youtube.com/watch?v=fB0jrucjlxg

 

[74 Shortbed]

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[Keith Seymore]

Wanting to know what the gear ratio of my differential is in my truck is and how i go about finding it out?

Its a 73 gmc k1500 and it has:
Chevy 350
3 speed Wt306 (SM330)
Np205 With dana 44 in the front and 12 bolt in the rear, And i am currently running 235/75/15 tires.

Help is appreciated!

In addition to the above you could also pull the cover and count the teeth on the ring gear and on the pinion (ie, 41 / 11 = 3.73; 41/ 12 = 3.42).

It's a good time to change the fluid in the diff while you are at it.

K

 

[bucket]

3 speed as in, is/was a 3 on the tree? If so, that's a very neat and unusual trans to have in a 4x4!!!

 

[MarineGreen]

3 speed as in, is/was a 3 on the tree? If so, that's a very neat and unusual trans to have in a 4x4!!!

Yeah, my dad had to replace the column a few years back since it was shot but other then that it shifts like butter. And apparently the transmission is a "rare" beefed up 5 bell housing bolt SM326, I do not know if this is true its only what people told me and what i have read, could anyone shed some light on this?

 

[MarineGreen]

In addition to the above you could also pull the cover and count the teeth on the ring gear and on the pinion (ie, 41 / 11 = 3.73; 41/ 12 = 3.42).

It's a good time to change the fluid in the diff while you are at it.

K

I tried the tape on the wheels and drive shaft and it turned out to be a 3.73, Seems fine but is does rev pretty high on the highway because of the transmission only being 3 speeds.

The fluid was actually replaced a little while back so i think i am good on that, But i get what you are saying.

 

[HotRodPC]

The 3 speed column shift 4x4's weren't all that common. With the NP205 that sounds like an extremely reliable combo. 3.73's IMO is about the perfect ratio for a half ton and no OD. It's still quite freeway driveable at 65-70mph especially if you had 33in tires. Even 31in isn't to bad.

 

[bucket]

The 3 speed column shift 4x4's weren't all that common. With the NP205 that sounds like an extremely reliable combo. 3.73's IMO is about the perfect ratio for a half ton and no OD. It's still quite freeway driveable at 65-70mph especially if you had 33in tires. Even 31in isn't to bad.

These are my thoughts exactly. Except I won't say a 3-speed 4x4 is uncommon, I think it's downright rare.