Granny Low - other options

[wayno]

I have what I believe to be the SM465 in my 64 stepside - living in south jersey this granny low makes me want to cry - looking for options that will bolt in without a whole lot of grief and want to stick with a standard tranny. My eyes are burning from browsing through search results and I figure as a newbie the lashings can't be that bad. Thanks in advance.

[markeb01]

The easiest and cheapest solution would probably be any of a variety of 3 speed (truck or car) or 4 speed (passenger car) transmissions. The newer 5 speed overdrive transmissions can also be fitted, but the cost and effort goes up. As purchased my truck (1960 GMC) originally had an SM420 and now carries a Richmond Super T10 4 speed. It’s certainly a lot more fun than the granny box was.

You might want to take a look at the details in this link, particularly regarding the diameter of the bearing retainer. If you have an SM420 instead of an SM465, I don’t think this is an issue.

http://www.novak-adapt.com/knowledge/sm465.htm

And welcome to the forum!

[Captainfab]

You're not starting out in 1st gear all the time are you? For 90% of your driving you should be starting out in 2nd gear.

Originally Posted by wayno

I have what I believe to be the SM465 in my 64 stepside - living in south jersey this granny low makes me want to cry - looking for options that will bolt in without a whole lot of grief and want to stick with a standard tranny. My eyes are burning from browsing through search results and I figure as a newbie the lashings can't be that bad. Thanks in advance.

[ChrisDollins]

Originally Posted by Captainfab

For 90% of your driving you should be starting out in 2nd gear.

That's what I was thinking. I had a granny low 4 speed in a '79 4x4 and just used low when it was needed in the field.

Chris
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[**grumpy**]

My solution was to swap a 72 C10 3.08 rearend in my old 64 which had a granny 4spd.

The difference it made was so dramatic.

I could treat the granny 4spd as a normal 4spd. And it would run 75 down highway all day and not scream.

I actually have 2 more 72 rearends with 3.08s, one is a posi.
just to have for future projects.
I buy every one I run across.

[LostMy65]

Originally Posted by **grumpy**

My solution was to swap a 72 C10 3.08 rearend in my old 64 which had a granny 4spd.

The difference it made was so dramatic.

I could treat the granny 4spd as a normal 4spd. And it would run 75 down highway all day and not scream.

I actually have 2 more 72 rearends with 3.08s, one is a posi.
just to have for future projects.
I buy every one I run across.

I picked up a 12-bolt out of a 69 blazer earlier this year.
3.07 gears.
I've done lots of research on this, and so many posts say that 3.42 is the best ratio.
Although those saying 3.42 are perfect are up in the 30" tire height.
My tires are only 26" tall.
So I took the gear ratio spreadsheet and did a side by side.
Based on the side by side comparison, I won't be any 'doggie'r' than 3.42 & 30" tires.

[63burban4x4]

My son just shipped me a manual overdrive 3 speed he had. Nice thing about this is no changes needed to the crossmember. (replacing my SM420 4 speed) I'll use an aftermarket floor shifter, for now, and someday probably install a standard shift column.
I switched out my 3:93 gears for 3:73's. Havent got it together yet, but with the approx .70 to 1 top gear, I'm hopeful it will work out well for cruising, and should still not be a slug in low gear. I have a stock 350 truck engine with a 4 barrel carb.

[shawno72]

I would like to see how my 29" tires measure up to that with a 3.08 rear end.

[wayno]

Thanks guys... the forum has been great so far - I guess the first thing I should do is to figure out for certainty whether it's a SM420 or SM465 - but grumpy's 3.08 rearend is a definite possibility.

[**grumpy**]

Im not a print-out type of guy. I go by seat of the pants...

My truck wouldnt do 60 without screaming for mercy.

Simple rearend swap and it would run 75 without breathing hard.

Ran 180 miles to GGs in columbus doing 75, and occasionally 80ish
And got 17mpg
that was with a tired 70s era 350 and quadrijunk 4bbl.
and I had 255-70-15s on rear. So I dont remember how tall they were but they were huge. Likely 29-30"

[wayno]

I grew up in Maine and the granny low would be perfect up there... down here 70MPH is a sunday drive and you had better be in the slow lane. With a 327 out of a vette in this thing it sounds like your setup might work well for me. Thanks for the insight... and I can't believe you got 17MPH that's crazy

[**grumpy**]

If I remember correctly, gear ratios are based off a 27" tall tire, so at 27" a 3.08 is a 3.08
at 29-30" tall tire, the gear equates to a 290-ish
Just as with a 25" tall tire, the gear jumps to a 320-ish gear.

My tires were 255-70s or 265-70s, cant remember, but big.

[LostMy65]

Originally Posted by **grumpy**

Im not a print-out type of guy. I go by seat of the pants...

My truck wouldnt do 60 without screaming for mercy.

Simple rearend swap and it would run 75 without breathing hard.

Ran 180 miles to GGs in columbus doing 75, and occasionally 80ish
And got 17mpg
that was with a tired 70s era 350 and quadrijunk 4bbl.
and I had 255-70-15s on rear. So I dont remember how tall they were but they were huge. Likely 29-30"

Yeah, I was just being told by some that it would be doggie. I used the spreadsheet to check the numbers against what others are running, and saw it should be fine.
You actually having that combo and liking it, makes me want to get that 3.07 under my 65 this winter.
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[wayno]

Wondering what year C-series 3.08 rears would fit in my 64 C10 - 72 to 88? Thanks in advance.

[Doug19]

Is there a way to change the gear ratio in a SM-420 to something more highway freindly?
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[Captainfab]

A '63-'72 12 bolt will be a nearly direct bolt in. A couple differences will be 1) the '65-'72 panhard bar is shorter and mounts differently. 2) the '71-'72 12 bolt has the 5x5 wheel stud pattern, plus they are 1.5" wider. A '73-'87 12 or 10 bolt can be used, but cutting, wleding anf fabrication is required. These are also the 5x5 wheel stud pattern and 1.5" wider.

Originally Posted by wayno

Wondering what year C-series 3.08 rears would fit in my 64 C10 - 72 to 88? Thanks in advance.

Not that I know of. The only way that I know of to get an OD and keep your SM420 is to add a Ranger OD unit in front of it.

http://www.advanceadapters.com/categ...lete-units/91/

Personally I would look for a NV4500.

Originally Posted by Doug19

Is there a way to change the gear ratio in a SM-420 to something more highway freindly?
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[wayno]

So I'm heading out to some pick and pulls tomorrow to look for a rear fender for my stepside 64 - while out I wanted to see if I could scratch up a 3.08 rear end - I have read dozens of post telling me how to take the cover off and divide to determine the ratio but clearly that isn't going to happen at a pick and pull - so what are other people doing to identify them?

[Fastest32]

I put 2:73s in mine that I bought on craigslist. It runs great on the highway now. Straight six motor.
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