351m 4x4 manual swap

[Dawson81]

So I'm planning on swapping my C6 out for a manual I want a four speed with Granny low it's my daily I do a lot of driving I know I'll need a bellhousing and a pedal assembly my truck is a 4x4 long bed 9 inch rear end with 3.22 gears I have an np205 tcase I've been told it'll bolt right up any advice would be appreciated

[Gary Lewis]

I'm going to paste the majority of my previous comments from your New Member thread here, and then add on to them:

Here are some things to consider. First, there are basically three 4-speed transmissions with a granny low. You can see their gear ratios on the page here, but all are 1:1 in 4th: Documentation/Driveline/Calculators.

But, why a 4-speed? Why not a 5-speed since that would have an overdrive. Perhaps that unusual 3.22 gearset is high enough?

• NP435: Lowest 1st

• T-18: These were typically used behind any of the engines except the 460 and the diesel. Good low gear.

• T-19: These are basically the same as the T-18 but were used behind the 460 and diesel and have a pretty "tall" first gear, although it is synchronized where the T-18's isn't.

Also, tell us about the engine. I think you said 351M, which is a good engine in my estimation. But unless you've performed some magic with it, like a new straight-up timing chain and a 4bbl, it is probably not all that strong. And that could play into your gear ratio choices as you may not want to go too high if you don't have a lot of power.

And the NP205 should bolt right up. That's a stout t-case, but heavy.

[Dawson81]

I'm going to paste the majority of my previous comments from your New Member thread here, and then add on to them:

Here are some things to consider. First, there are basically three 4-speed transmissions with a granny low. You can see their gear ratios on the page here, but all are 1:1 in 4th: Documentation/Driveline/Calculators.

But, why a 4-speed? Why not a 5-speed since that would have an overdrive. Perhaps that unusual 3.22 gearset is high enough?

• NP435: Lowest 1st

• T-18: These were typically used behind any of the engines except the 460 and the diesel. Good low gear.

• T-19: These are basically the same as the T-18 but were used behind the 460 and diesel and have a pretty "tall" first gear, although it is synchronized where the T-18's isn't.

Also, tell us about the engine. I think you said 351M, which is a good engine in my estimation. But unless you've performed some magic with it, like a new straight-up timing chain and a 4bbl, it is probably not all that strong. And that could play into your gear ratio choices as you may not want to go too high if you don't have a lot of power.

And the NP205 should bolt right up. That's a stout t-case, but heavy.

I've been rounding pieces up and I'm going to find another 351m block and put some 4 valve aluminum heads on it some crane beehive springs aluminum roller rockers a timing gear set and I'm going to stick a split lift split duration cam in it and bolt and an aluminum intake with a 780 carb

[Dawson81]

I'm going to paste the majority of my previous comments from your New Member thread here, and then add on to them:

Here are some things to consider. First, there are basically three 4-speed transmissions with a granny low. You can see their gear ratios on the page here, but all are 1:1 in 4th: Documentation/Driveline/Calculators.

But, why a 4-speed? Why not a 5-speed since that would have an overdrive. Perhaps that unusual 3.22 gearset is high enough?

• NP435: Lowest 1st

• T-18: These were typically used behind any of the engines except the 460 and the diesel. Good low gear.

• T-19: These are basically the same as the T-18 but were used behind the 460 and diesel and have a pretty "tall" first gear, although it is synchronized where the T-18's isn't.

Also, tell us about the engine. I think you said 351M, which is a good engine in my estimation. But unless you've performed some magic with it, like a new straight-up timing chain and a 4bbl, it is probably not all that strong. And that could play into your gear ratio choices as you may not want to go too high if you don't have a lot of power.

And the NP205 should bolt right up. That's a stout t-case, but heavy.

Oh and as far as a rear end I'm going to shoot for 4.11 gears and posi

[Gary Lewis]

Oh and as far as a rear end I'm going to shoot for 4.11 gears and posi

Well, let me suggest a minor change or three in your plans. First, I wouldn't build a 351M. Instead, find a 400 crank and drop it in. The extra 1/2" stroke will do wonders for torque. But maybe more importantly you can find pistons for a 400 with any compression ratio you want, but not so for a 351M. Those will be limited to 8:1 rebuilder pistons. Tim Myer @ Tmeyer has the 400 pistons, and Scotty @ Parkland Performance says he does as well. And other than the crank and pistons, which you were going to replace anyway, there's nothing else to change to make a 351M a 400.

Tim did my 400 and it put out ~400 HP and 500 ft-lbs on his dyno. I wanted low RPM torque or he could have gotten bigger numbers, but I was happy with those.

And on the tranny, if you are going 4.11 gears and are going to drive it daily I'd recommend the ZF5. Unless you are running really big tires you are going to be turning 2900 RPM at 65 MPH with a 4-speed. (Use our calculator at Documentation/Driveline/Calculators.) But with the ZF5 you'll be turning 2200 RPM - assuming 31" tires.

But, while a ZF5 will bolt to an M-block nicely you'll have problems very early on. See the ZF5 Behind An M-Block tab on the page at Documentation/Driveline/Transmissions/Manual Transmissions/ZF5 for an explanation of why. But, as it says, Tim also has an adapter that will fix that problem.

But, a ZF5 was designed for a hydraulic clutch linkage, so you will either need to convert to that or modify the clutch release lever. And whatever transmission you chose, if you do a hydraulic linkage you should consider the firewall brace.

[Dawson81]

Well, let me suggest a minor change or three in your plans. First, I wouldn't build a 351M. Instead, find a 400 crank and drop it in. The extra 1/2" stroke will do wonders for torque. But maybe more importantly you can find pistons for a 400 with any compression ratio you want, but not so for a 351M. Those will be limited to 8:1 rebuilder pistons. Tim Myer @ Tmeyer has the 400 pistons, and Scotty @ Parkland Performance says he does as well. And other than the crank and pistons, which you were going to replace anyway, there's nothing else to change to make a 351M a 400.

Tim did my 400 and it put out ~400 HP and 500 ft-lbs on his dyno. I wanted low RPM torque or he could have gotten bigger numbers, but I was happy with those.

And on the tranny, if you are going 4.11 gears and are going to drive it daily I'd recommend the ZF5. Unless you are running really big tires you are going to be turning 2900 RPM at 65 MPH with a 4-speed. (Use our calculator at Documentation/Driveline/Calculators.) But with the ZF5 you'll be turning 2200 RPM - assuming 31" tires.

But, while a ZF5 will bolt to an M-block nicely you'll have problems very early on. See the ZF5 Behind An M-Block tab on the page at Documentation/Driveline/Transmissions/Manual Transmissions/ZF5 for an explanation of why. But, as it says, Tim also has an adapter that will fix that problem.

But, a ZF5 was designed for a hydraulic clutch linkage, so you will either need to convert to that or modify the clutch release lever. And whatever transmission you chose, if you do a hydraulic linkage you should consider the firewall brace.

I appreciate the advice I screenshotted what you suggested and when I find a good solid block I'll know what to look for and I'm definitely going to check into those pistons

[Gary Lewis]

I appreciate the advice I screenshotted what you suggested and when I find a good solid block I'll know what to look for and I'm definitely going to check into those pistons

Welcome. I went through a lot of this a few years ago when rebuilding the engine for Dad's truck. At the time only Tim had the pistons, but Scott said he now does. Both are members on here and are very reputable.

[Ford F834]

Th NP205 will indeed bolt up to the transmission, but be aware that the yoke position is different than what you find in the 80’s trucks and I believe you will need to have custom driveshafts made (or source them from an older truck). The NP205 also needs its own cross member because of the weight, so you will need to fabricate one or modify one from an earlier truck to fit your frame. They are very strong transfer cases but the low range ratio isn’t very low and they take more work and or parts to make them fit our trucks.