I'm strongly considering going with 3.08's

[rumblebox]

I'm about to build a stump-puller big block, and I want to use 3.08 gears so I can just use granny low as first gear, and 4th gear will only turn about 2400 RPM at 70. I know the gap between 2nd and 3rd really sucks, but with the torque curve this engine will have, I think I should be ok. Have any of you tried this and regretted it?

Engine will make 600+ TQ and probably about 450 straight off of idle with a redline around 5500.

SM465, 14bolt FF, D44, 265 75 16

 

[MadOgre]

Ya you should be ok with that especially since your keeping the smaller tires. That's an enormous amount of power so my concern would be all about the clutch and structural integrity of the SM465 lol. More so the clutch!

 

[rumblebox]

Ya you should be ok with that especially since your keeping the smaller tires. That's an enormous amount of power so my concern would be all about the clutch and structural integrity of the SM465 lol. More so the clutch!

I've heard the SM465 is insanely strong. The front axle is what concerns me.

 

[MadOgre]

I've heard the SM465 is insanely strong. The front axle is what concerns me.

Ya well everything has a breaking point lol I would see how it goes with the front 10 bolt and be looking for a Dana 60 in the mean time

 

[firebane]

I've heard the SM465 is insanely strong. The front axle is what concerns me.

I've heard that the SM465 is good to about 450-500 before it will crack under pressure.

 

[rumblebox]

I've heard that the SM465 is good to about 450-500 before it will crack under pressure.

I guess i should forego the gear swap and just hold out for an Allison or NV4500 then.

 

[MadOgre]

What ever you put behind that much power will have issues! You will have to invest some $ into whatever you put back there.

 

[rumblebox]

What ever you put behind that much power will have issues! You will have to invest some $ into whatever you put back there.

The Duramax makes way more torque than I'm going to make, and in a way heavier truck. The Allison easily goes a hundred thousand miles without problems unless you abuse the **** out of them.

Another option would be to build a 4l80, because those can take pretty much anything I throw at them with even a minor build-up. People run 1000+ HP turbo LSX engines thru those things all day long

With this kind of power band, I won't need 6 gears anyway.

 

[MadOgre]

The Duramax makes way more torque than I'm going to make, and in a way heavier truck. The Allison easily goes a hundred thousand miles without problems unless you abuse the **** out of them.

Another option would be to build a 4l80, because those can take pretty much anything I throw at them with even a minor build-up. People run 1000+ HP turbo LSX engines thru those things all day long

With this kind of power band, I won't need 6 gears anyway.

Ya exactly.

 

[MadOgre]

If you put a 6spd Allison in there. You will be the first one on this site to do so that I am aware of. So if you do be sure and post lots of pics and info of your swap!

 

[rumblebox]

If you put a 6spd Allison in there. You will be the first one on this site to do so that I am aware of. So if you do be sure and post lots of pics and info of your swap!

Is it too large, or what?

 

[MadOgre]

Dunno. Never tried

 

[bucket]

It's hard to break an SM465. And if you do break something, you can more than likely blame it on 30-40 years of abuse and fatigue. Then toss in another cheap and common SM465.

 

[Irishman999]

First gear in a SM465 is not synchronized so you cant really drive it like a 4 speed. I rarely ever used low in my 85 but to get into low I would have to be stopped and hold the clutch long enough to let everything in the transmission slow down so it would go into gear. I dont recall ever trying to go from first gear to low while moving but im pretty sure it would just grind.

 

[rumblebox]

First gear in a SM465 is not synchronized so you cant really drive it like a 4 speed. I rarely ever used low in my 85 but to get into low I would have to be stopped and hold the clutch long enough to let everything in the transmission slow down so it would go into gear. I dont recall ever trying to go from first gear to low while moving but im pretty sure it would just grind.

It is pretty rough trying to go into L while moving, even if you revmatch. Even going into 1 from 2 without almost coming to a complete stop takes effort. I don't know if that's just a characteristic of this transmission or if the synchro is wearing out.

The more and more I think about this, the more I think it's a bad idea. My plan is to eventually have either an Allison, a 4L80, or in NV4500 in here. All of which would really suck with 3.08 gears, except the NV4500, and i really don't like manuals in trucks.