th350 to th400 swap ?'s

[88bigburb]

ok guys, i know i dont contribute a whole lot here, but i definitely appreciate the info i can find. and now i have a couple more questions. I'm basically looking for any pointers on things i missed as far as this swap goes, and a couple other questions. i'll try to lay out as much info as i have and hopefully not miss anything.

Vehicle: 1975 Blazer, 350/th350/np203, D44 front, 12 bolt rear.

the 400 i have to install is from a 79 burb, it is coupled to a 203 as well.

1. Unbolt and remove th350/203, either as one or in 2 pieces,
2. mount up th400/203, and relocate crossmember.
3. Reattach shift linkage-the one i have should work right?
4. Reattach cooler lines-can i reuse the stock ones?
5. speedo cable-should be the same attachment right?
6. Measure new rear driveshaft length.
7. After getting driveshaft shortened re-install.

I have a "new" front driveshaft, that came from a 1-ton with a th400/203
will that work to attach to the 44 front, or will it be too short? and will i need a conversion u-joint? if so part numbers would be great.

I have the stock rear driveshaft from the 75 on it still, should i get that cut down, pretty sure its aluminum, and i have driveshafts from a 70 f-250 that i believe to be steel i'll take a magnet to it on my lunch to check, should i have that cut down instead... assuming the yokes are the same.

do i need to get the new driveshaft balanced? or should it be alright without.

alrighty, i think that just about covers it, thanks in advance,

Ps. i'll repost on the material of the driveshafts later

 

[88bigburb]

I forgot to mention I got the throttle kick down switch, 1 wire goes to power the other goes to the transmission, correct? does it matter which wire is which?

 

[76zimmer]

ok guys, i know i dont contribute a whole lot here, but i definitely appreciate the info i can find. And now i have a couple more questions. I'm basically looking for any pointers on things i missed as far as this swap goes, and a couple other questions. I'll try to lay out as much info as i have and hopefully not miss anything.

Vehicle: 1975 blazer, 350/th350/np203, d44 front, 12 bolt rear.

The 400 i have to install is from a 79 burb, it is coupled to a 203 as well.

1. Unbolt and remove th350/203, either as one or in 2 pieces,
2. Mount up th400/203, and relocate crossmember.
3. Reattach shift linkage-the one i have should work right? i believe so.
4. Reattach cooler lines-can i reuse the stock ones? yes
5. Speedo cable-should be the same attachment right? yes
6. Measure new rear driveshaft length.
7. After getting driveshaft shortened re-install.

I have a "new" front driveshaft, that came from a 1-ton with a th400/203
will that work to attach to the 44 front, or will it be too short? And will i need a conversion u-joint? If so part numbers would be great.

I have the stock rear driveshaft from the 75 on it still, should i get that cut down, pretty sure its aluminum, and i have driveshafts from a 70 f-250 that i believe to be steel i'll take a magnet to it on my lunch to check, should i have that cut down instead... Assuming the yokes are the same.
stock should be steel

do i need to get the new driveshaft balanced? Or should it be alright without. a driveshaft shop should balance it before it goes out the door, ask them to be sure.

alrighty, i think that just about covers it, thanks in advance,

ps. I'll repost on the material of the driveshafts later

that 400/203 is the start of a doubler...hang on to it!

Good luck

 

[sweetk30]

ok guys, i know i dont contribute a whole lot here, but i definitely appreciate the info i can find. and now i have a couple more questions. I'm basically looking for any pointers on things i missed as far as this swap goes, and a couple other questions. i'll try to lay out as much info as i have and hopefully not miss anything.

Vehicle: 1975 Blazer, 350/th350/np203, D44 front, 12 bolt rear.

the 400 i have to install is from a 79 burb, it is coupled to a 203 as well.

1. Unbolt and remove th350/203, either as one or in 2 pieces, yes if big tranny jack and friend help 1 unit.
2. mount up th400/203, and relocate crossmember. holes in frame redrill and mabye only 2 required as it might be back to line of 2 holes.
3. Reattach shift linkage-the one i have should work right? yes will fit
4. Reattach cooler lines-can i reuse the stock ones? yep will fit
5. speedo cable-should be the same attachment right? yep should fit just check length .
6. Measure new rear driveshaft length. yep should be able to shorten if its all same size tube dia and not a baloon shaft style thats toss away. save money also.
7. After getting driveshaft shortened re-install. same as above

I have a "new" front driveshaft, that came from a 1-ton with a th400/203
will that work to attach to the 44 front, or will it be too short? and will i need a conversion u-joint? if so part numbers would be great. will be direct fit other than possible to short by as dana 60 front is longer pinion stick out over dana 44 / corp 10 bolt. check length.

I have the stock rear driveshaft from the 75 on it still, should i get that cut down, pretty sure its aluminum, and i have driveshafts from a 70 f-250 that i believe to be steel i'll take a magnet to it on my lunch to check, should i have that cut down instead... assuming the yokes are the same. 75 would not be aluminum and ford be diffrent joint sizes.

do i need to get the new driveshaft balanced? or should it be alright without. balence yes or vibes possible.

alrighty, i think that just about covers it, thanks in advance,

Ps. i'll repost on the material of the driveshafts later

and wire from switch fits in fuse panel and then threw hole in firewall and down to 1 wire tab on tranny.

and i am just up the road in horseheads , ny from your location.

 

[88bigburb]

76Zimmer
You called it, steel it is. and the price at the shop was effectively doubled if i wanted it balanced as well. was trying to do this as uber cheap as possible. make the vehicle reliable while not droppin too much money around christmas, and for a doubler is the reason i originally bought the tranny, but i think my plans have changed, my budget is next to non existent, so my mind has ages to change plans before i'll ever actually get around to putting them into play.

Sweetk30
thats what i was assuming on the front driveshaft. and from the measurements i took, either the dude i bought the driveshafts from was a liar, or was mis-informed what they came from, or my favorite option, i'm a moron, dont know how to measure and the front driveshaft will fit.
and do they make conversion u-joints from any given size to another? cuz its looking like i will need to get 2 cut down. and if i can use the ones i've got laying around thats a plus.

heres the measurements i came up with today.
correct any known mistakes.
1.from what i'm reading, the 400 is approximately 3.5 inches longer, then the 350, pushing my transfer case back approximately 3.5 inches, making my rear driveshaft approximately 3.5 inches shorter, and front 3.5 longer.
2. current front driveshaft is about 25.5 inches at rest.
3. 1-ton donor front driveshaft is about 27 with same extension of slip as current.
4. 1-ton donor front driveshaft about 28.5 fully extended
5. dana 44 center of u-joint to "centerline" of axle is 12"
6. dana 60 center of u-joint to centerline of axle is 12.5"
7. current rear driveshaft is 36"
8. Projected new front shaft length =29"
9. Projected new rear shaft length = 32.5"


if 5 and 6 are wrong, then i may be way off on the 1-ton shaft being from something different. I'm trying to get everything all planned out before i actually attack this project, thanks again

 

[88bigburb]

Oh, and I forgot to mention, no suspension lift, appear to be factory original negative arch front springs, lol