I'm strongly considering going with 3.08's

[Irishman999]

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.

Its been a few years since I watched mine get rebuilt but if I remember right low gear had no syncro ring at all. The other 3 forward gears had them, just not low.

If you want to keep it simple get on craigslist and find a TH400 and run that. I rebuilt the one in my 454SS for cheap. They will handle big block power no problem.

 

[rumblebox]

Its been a few years since I watched mine get rebuilt but if I remember right low gear had no syncro ring at all. The other 3 forward gears had them, just not low.

If you want to keep it simple get on craigslist and find a TH400 and run that. I rebuilt the one in my 454SS for cheap. They will handle big block power no problem.

L is definitely not synchro'd

If i put any effort or money at all toward a different trans, it'll have OD. Preferably a 4L80 with a stand-alone or manual body and manual TCC.

 

[rumblebox]

Actually.... after doing some math, an NV4500 with 3.08s would be totally killer. Shift out of 1st at 30mph and do 1800RPM at 80.

 

[DoubleDingo]

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.

Going into first from second is doable but you have to be going very slow, almost to a crawl. Even first to second can be done but you have to start the truck in first gear. Had to do that once when my clutch decided not to work while driving to my brother's place in Canyon Country. On a major road and I couldn't use the clutch, so I had to roll to a stop, turn off the truck and wait for the green. Start it in first until it popped out on its own, and then got the rpm's to match for second, and then it was easy power shifting. I don't recommend doing that with the 2 bolt starter, but the 3 bolt starter used on the SM420 handles it just fine. I never had an e-brake on my old '65 so I always left first gear fully engaged and I had to make sure my keys were not in the ignition when my daughter wanted to play in the cab of the truck. One turn of the key and she would have been idling down the road.

 

[DoubleDingo]

Actually.... after doing some math, an NV4500 with 3.08s would be totally killer. Shift out of 1st at 30mph and do 1800RPM at 80.

That would be fun,

 

[rumblebox]

Do 3.08's and 4.10's use the same carriers?

 

[rumblebox]

So after 30 seconds of googling, i found out that 3.21/3.23 are the highest i can go. Still not bad.

 

[HotRodPC]

JMO, I see what you're trying to accomplish here. In short, you want to run a tall gear since you have the horsepower and granny gear to compensate. I still don't like it. I'd be going for the NV4500 swap to gain the OD before I'd go with gear swaps on 2 axles and have the better of all worlds. Also keep in mind, If you go to taller gears, you're still putting that strain on all of powertrain past the flywheel even if the engine does have the torque. The clutch, trans, U joint's and all are going to feel that strain.

 

[rumblebox]

JMO, I see what you're trying to accomplish here. In short, you want to run a tall gear since you have the horsepower and granny gear to compensate. I still don't like it. I'd be going for the NV4500 swap to gain the OD before I'd go with gear swaps on 2 axles and have the better of all worlds. Also keep in mind, If you go to taller gears, you're still putting that strain on all of powertrain past the flywheel even if the engine does have the torque. The clutch, trans, U joint's and all are going to feel that strain.

Im doing 3.21's AND an NV4500 swap. Both are required to do what i need.

 

[HotRodPC]

Im doing 3.21's AND an NV4500 swap. Both are required to do what i need.

I would first do the NV4500 Swap. Then see what you got and how it fits your needs. A good chance you won't need the 3.21 swap after adding the OD I would not think. Also, what gear ratio are gearing for your front axle to, cuz there is no 3.21 ratio available. Possibly a 3.23 which is close enough, but I'm not sure that's even available to a 10 bolt front.

Just so you know, my dad has a 94 1 Ton Chassis Cab truck with a flatbed on it. Came OEM with NV4500 and 4.10's. After about 8,000 miles on the truck that he bought brand new in Jan 94, he swapped to 3.21's to increase mpg. He didn't gain a damn thing. In fact, it struggles since with the TBI 350 engine. I also had 3.21's in my 84 C20 with a 454/Th400. It also struggled towing an 18 foot utility trailer with an 88 Burb on it without any engine or trans in it. That tall ratio is really going to hurt any kind of towing capacity.

 

[MadOgre]

Apparently 3:73 gears are supposed to be the sweet spot where maximum fuel economy and maximum towing meet. Just like 90 KM/H or 55 MPH is the best speed for fuel economy.

In the big truck world of heavy hauling the 4:10s are the ticket, for best fuel economy. Unless you just want to do 80 MPH all day long.

 

[rumblebox]

Almost every highway around here is 75mph. So yes. I frequently go 79mph. With 3.23/3.21 and a 5 speed, i will do exactly 2k@80. With 4.10's, It's 2600, which is unacceptable. 3.73's put me at 2300, which isn't bad, but not optimal.

I don't plan on pulling anything heavy enough to need low gears. My 2014 DI 5.3L doesn't have any problems pulling a compactor or 8,000lbs of concrete scraps on a dump trailer with 3.08 gears and 380 lt lbs of torque. So i highly doubt a 480ft/lbs big block would have trouble even if i did use it for that. I'm using it for mild off-roading, beach cruising, and light pulling/recovery on job sites when the weather is too bad for a 2wd.