SM465 to auto conversion or something else?

[gtojohnny]

Hi all, I'm new to the site and was looking for some advice. Currently driving a 1976 C20 with 454 and SM465. As you can imagine, it is geared with 4.10's and will hit 3000 rpm's pretty quickly in top gear. It was originally equipped with a rare Hone overdrive that was working and did help drop abou 4-500 rpm's at the top. However, it has stopped engaging and I can't find any literature on it and I doubt I will find parts or anyone who can fix it. I don't even know what fluid is in it. It has leaked most of it out and that may be why it wont change gear. It is not hydraulic, the fluid is for lubrication only and the gear change is lever operated. Anyway, I was considering removing the unit and putting in an original 2-piece driveshaft with carrier bearing etc. If I do that, I will need to drive at 55 on the highway. Not acceptable. So, I am already running the largest tire I can 265/70/16 unless I stagger the tires. I don't really want to do that.

1) I could change the rear gear. If I did, what gear should I go with and how much difference will it make? Will it kill my low end? The 454 has gobs of power.
2) I could switch to an auto with overdrive (700r4?). How hard is that and is it worth it?
3) I could find some sort of other overdrive unit. Is there one out there and is it too costly?

I welcome suggestions from those who have experience or knowledge in this area. Thanks in advance for your time.

 

[pduffyd]

Welcome gtojohnny.

I have settled on the same setup you have.
454 with an sm465.
I looked into a 4l80e swap but at around 6k to do the changes I just rebuilt my 465, for a few hundred bucks, which included new anti hop out 3rd (2nd) gear, syncros bearings and gaskets.
A 700r4 wont last behind a 454, the torque monster will rip it to shreads. lol
It would have to be built, thats expensive. Not to mention, changing crossmembers changing driveshaft lengths etc etc.

Anyway, to your real question.

I have a GT5 rear end (4.10) same ratio as you. Yukon, and various other brands make 3.73, 3.42 and 3.21 ratios for our 14 bolt ff axles.
I am looking at either the 3.42 or 3.21

Looking at rpm of your 454 verses speed.

For a given speed, 3.42 ratio compared with your 4.10. The engine will rev at about 83% of your original with these gears, or with 3.21, it will be about 78%.

So 3000rpm, could be 2490rpm, with 3.42, or 2340rpm with 3.21.

Given the low, 1 2 3 sm465, you wont have a problem pulling away, you may even use low !

In the end its your choice.

 

[PrairieDrifter]

I would prefer the 465 as well..

 

[Shorty81]

I would prefer the 465 as well..

X2

 

[SirRobyn0]

I've got the 700R4 and I'm relatively happy with it. I commute in the truck and for that it is nice, but I also haul with it and there are plenty of times that I would like to have the SM465.

With that said there are heavy duty 700R4 rebuilds that are suppose to be able to live behind a BB, though you'll get varying opinions on the legitimacy of that.

Even though you have a BB it can be run at 3K on the freeway with no harmful effects provided that your cooling system is up to ***** and can cool properly. Your set up right now is perfect for a truck that either tow or hauls, so if you do that you might consider leaving it as is.

From the early 80's though the end of the 90's my Dad had a 78 K20 with 4.10's and he regularly took it on the freeway and would drive out to the coast which is about 4 hours of driving. Yes he could have got better mileage with higher gears, but when he went to tow his trailer or hauled a load of gravel the 4,10's were there to make the possible and easier on the truck. So just consider those things before making any drastic changes.

Well I was going to suggest the ranger gear splitter / over drive, but while I was living in my cave it looks like it was discontinued by advanced adaptors. If you could find a used unit they still support those with parts.

 

[Catbox]

I have a '79 with the 454 and SM465.
It is simply a sloooooow shifting transmission and has become kind of a drag to drive around.
We may end up installing a simple Turbo 400 we have in the truck to make it more pleasurable to drive.

If I were to put any other auto into the truck it would be a 4L80 due to the fact it is still a big block powered 3/4 ton truck. It will see more heavy foot action than actual hauling work, but we still need it to be beefy no matter what or how it is hauling...

 

[AuroraGirl]

Welcome gtojohnny.

I have settled on the same setup you have.
454 with an sm465.
I looked into a 4l80e swap but at around 6k to do the changes I just rebuilt my 465, for a few hundred bucks, which included new anti hop out 3rd (2nd) gear, syncros bearings and gaskets.
A 700r4 wont last behind a 454, the torque monster will rip it to shreads. lol
It would have to be built, thats expensive. Not to mention, changing crossmembers changing driveshaft lengths etc etc.

Anyway, to your real question.

I have a GT5 rear end (4.10) same ratio as you. Yukon, and various other brands make 3.73, 3.42 and 3.21 ratios for our 14 bolt ff axles.
I am looking at either the 3.42 or 3.21

Looking at rpm of your 454 verses speed.

For a given speed, 3.42 ratio compared with your 4.10. The engine will rev at about 83% of your original with these gears, or with 3.21, it will be about 78%.

So 3000rpm, could be 2490rpm, with 3.42, or 2340rpm with 3.21.

Given the low, 1 2 3 sm465, you wont have a problem pulling away, you may even use low !

In the end its your choice.

i wouldnt use Low pulling away when first gear is good unless youre trying to move something heavy AF or pull stumps since its not mesnt to be the regular shift pattern at all. normal driving wise

You must be registered for see images attach

 

[bucket]

Hi all, I'm new to the site and was looking for some advice. Currently driving a 1976 C20 with 454 and SM465. As you can imagine, it is geared with 4.10's and will hit 3000 rpm's pretty quickly in top gear. It was originally equipped with a rare Hone overdrive that was working and did help drop abou 4-500 rpm's at the top. However, it has stopped engaging and I can't find any literature on it and I doubt I will find parts or anyone who can fix it. I don't even know what fluid is in it. It has leaked most of it out and that may be why it wont change gear. It is not hydraulic, the fluid is for lubrication only and the gear change is lever operated. Anyway, I was considering removing the unit and putting in an original 2-piece driveshaft with carrier bearing etc. If I do that, I will need to drive at 55 on the highway. Not acceptable. So, I am already running the largest tire I can 265/70/16 unless I stagger the tires. I don't really want to do that.

1) I could change the rear gear. If I did, what gear should I go with and how much difference will it make? Will it kill my low end? The 454 has gobs of power.
2) I could switch to an auto with overdrive (700r4?). How hard is that and is it worth it?
3) I could find some sort of other overdrive unit. Is there one out there and is it too costly?

I welcome suggestions from those who have experience or knowledge in this area. Thanks in advance for your time.

On a stock width wheel and stock backspacing, you can run a 285/75/16 at all four corners. It is what I run on my daily driven C20 Suburban with 454. Mine has 3.73 gearing, but figuring in the convertor slip of my th400, road speed RPM is going to be about the same as your direct drive. I blast down the interstate in the left lane, keeping pace with the rest of the traffic and it does just fine. MPG is not far off from keeping at slower speeds either.

Another option is a Ranger splitter from Advance Adapters. It mounts to the input side of the 465 and gives you an overdrive that can be used in any gear. I've got one in another truck and it's a neat little unit, imho.

 

[pduffyd]

i wouldnt use Low pulling away when first gear is good unless youre trying to move something heavy AF or pull stumps since its not mesnt to be the regular shift pattern at all. normal driving wise

You must be registered for see images attach

@AuroraGirl.
What I meant was, you may even use Low, if you got 3.21 rear gears.
Mind you heavy as, also works! Lol