Granny Gear

[K5Fan]

Good Morning All...

I know I've asked or seen a post on this before, but I have a a 70 K5 with a 350CID engine and a manual four speed with the "Granny Gear", but 1st gear is useless to me. I can put it in 1st (Granny) and walk faster that the truck will go. I'm happy with the manual gear box, but it's a waste to have an extra gear and not to be able to use it.

I'm going to check the ratio, but is changing the differentials to a higher gear the the only way to make 1st Gear usable?

It runs very well from 2nd to 4th as is, but being able to turn the RPMs down for highway use, as I'm sure you know, would make less RPMs on the highway, and not only save on gas, but engine wear.

This is an awesome site and forum, and I'm glad to be a part of it! If I could only figure out how to make my profile picture look better! Thank Youuuu!

[K5Fan]

So... I saw some of my earlier posts about the same questions and I will do some more research. Thank Youuuuuuu!!

[hemi43]

Most likely you already have 3.08:1 gears, so no, you can't change gears. Even if you could, it may make 1st gear a bit better but the rest of the gears will suffer.
Your only option is to scrap the existing transmission, or live with it. No magic pill here.

[Getter-Done]

It will not hurt to check your axle ratio.
The fluid in most can always stand to be changed
The Transmission is Most likely a SM465.
Unless it has been swapped over the years.
Link Below for SM465
The gear ratios for that transmission
are as listed below (According to Wikipe.)
1st is 6.56
2nd is 3.58
3rd is 1.70
4th is 1:1

1st gear is great for rock crawling or pulling down a house

There is so much difference between the Ratio of 1st and second gear and axle swap will not make much noticeable change.

Even if (BIG IF) you had a 4:11 rear axle and swapped to a 3:08
Here would be the results per on-line Ratio calculator.

With 4:11 @ 2000 rpm with 31" tires
1st gear= 6.84 mph
2nd gear= 12.54 mph
3rd gear= 26.41 mph
4th gear= 40.81

With 3:08 @ 2000 rpm with 31" tires
1st gear= 9.13
2nd gear= 16.73
3rd gear= 35.24
4th gear= 54.46

With 4:11 @ 2000 rpm with 33" tires
1st gear= 7.29 mph
2nd gear= 13.35 mph
3rd gear= 28.11 mph
4th gear= 43.45 mph

With 3:08 @ 2000 rpm with 33" tires
1st gear= 9.72 mph
2nd gear= 17.81 mph
3rd gear= 37.52 mph
4th gear= 57.98 mph


Link to info on SM465: https://www.novak-adapt.com/knowledg.../manual/sm465/

[truckster]

I agree with Getter-Done. I think a rear gear swap is going to leave you disappointed. That first gear is just too low to be useful for anything other than pulling a heavy load. Think of it as a three speed with an auxiliary low gear.