Correct Driveshaft Length for 700-R4/NP208/14bolt FF

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,122
Reaction score
6,038
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
I agree, but you've referred to it as being installed or possibly being upside down multiple times...
My point is, it's not nor could it be.
I dont know, Ive seen aftermarket, albeit that is not stock, have the same design which were mounted in rails used the center for the very ass end of a 2wd trans then the output shaft while what is left is exhaust clearance that doesnt reduce ground clearance. I dont know what all the late 80s had and they seemingly were plenty and thats both an auto and a 2wd, i have 4wd, manual so whos to say what variations may have been. or, with the similar wavey, that one could look normal upside down and i saw someone who modified to make it work that way, but that is different. did look interesting.

point is, i know its not the right direction and often the crossmmebrrs were slotted side to side but either were offset if you cut them in half, one way biasing prob to keep them from being backwards for skidplates or carrier brackets to fit right or keep the offset holes the right way because maybe something about certain year frames had multiple holes and the wrong way could fit somehow or tilted. prob an ease of assembly thing. IDK. BUt then I do know for a fact the mounts are generally reversible despite being offset, so you could put it on backwards and the t case adapter wouldnt know anything different other than its a tight fit(ha)
Because my grandfather was spiteful and very much kept ramming the square peg into the round hole until he made it fit i dont make any assumptions of normalcy or logic in trying to understand how he did things


The 6+ pieces of rebar in random spots, hard to access spots, and the other devious ways he installed the wood chute on the house is a great example. He either was thinking about how to make it hard for the next ****** or he knew it wouldnt be coming out in his lifetime and just went and overbuilt it without a concern or care lol. He had frequent displays of both those in most things he did.
Like screwing my rooms window shut by doing the siding over the edges of the window but he had to make at least 15 custom pieces of siding(wood siding inpanels with trim over where they butt, panels are a few feet wide, stained , and some interesting heading stuff.) because of where the window sits, he had to and I mean had to have made the panels on the ground, get up on the roof of the garage, and install from end to end of the wall following the gable v of the garage on the bottom, the gable v to the top of the roof over the house, so pieces that would be angle cut on both ends, and 8 ish feet tall, a little more or less, roof slops are also different. and when he got to the window, he either had it all measured proper to overhang all 4 edges or he setup some temporary benches of some kind on the roof of garage and was cutting them all out test fitting, which is just as possible but knowing how much he loved to sit down and figure dimensions for things he built and also how much he likes to stew on paper, I feel he may have done the first thing. because then under the window the piece is smaller by a lot based on where it sits(chest high while in front of it, makes sense.) it wasnt as hard to mock up for sure. But if that all seems like a lot of ******* energy to make a window not open, you are right. context story to the reasons for blocking window:

he did it because my cousin and I were like 10-13 and played ps2 on the TV in the bedroom and it gets about 110 degrees in the summer with the window shut and the door to hallway even opening. its facing the so much sun where we live and he kept the house at abotu 90 because he where he sat in his chair, in the basement, it would get chilly.. under the vent... if the upstairs was kept at a modest 70-80 :|
and one day he came in, threw the tv off the stand, closed the window, and wouldnt talk or look at us for like a month because he was outside and saw the window was open and we were wasting all the AC that he worked a lifetime to pay for and in 1946 in his parents ****** house with 9 siblings they didnt have AC and you couldnt play video games because your hands were calloused and they didnt exist.


So please, can your enthusiasm for your disproval of me, not all of us have driving gloves, which also differ from the golfing gloves. and make emphatic gestures getting out of chairs or expressing shock/uneasyness instead of grunting (age universal) and using words or not being so fragile that the behavior of emphatic gestures is a noticeable trait when faced with... adversity... thats not a word I use for the stuff IM refering to but it would be for the golf gloves getting mixed up with the driving gloves.


that was an insult. it was wordy but if you understood it then good. if you didnt..refer questions to someone else

GPA was sadistic in is games and lifes's issues looked like nails, he was a hammer, and the issues were very much lag screws. It doesnt fit 100% but lag screws are strong, put in with a lot of force, over a screw, and may take some work to put in like drilling etc. But he used a hammer. And if it didnt fit/work he just kept hammering until it did. so imagine a threaded lag screw with the labor invovled having been installed with nothing but a hammer. Doesnt make sense like i hoped it to.

He put square pegs into the round holes with a hammer. He also put round pegs in with a hammer. He put torx in with a square, phillips in with what i can only assume was a ill fitting standard and square heads in with what i assume was pozidrive. maybe he just sunk a lot of screws with drill bits and made sure to leave no useable remains. except the porch, he used the right bits just alternated between all of them.

-___-

The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.
 

scrap--metal

Full Access Member
Joined
Sep 15, 2021
Posts
678
Reaction score
1,266
Location
MN
First Name
Calvin
Truck Year
'85, '81
Truck Model
K10, K20
Engine Size
305, 350
Like screwing my rooms window shut by doing the siding over the edges of the window but he had to make at least 15 custom pieces of siding(wood siding inpanels with trim over where they butt, panels are a few feet wide, stained , and some interesting heading stuff.)

He sounds like a very willful man, and just maybe a little protective of his granddaughters.
 

scrap--metal

Full Access Member
Joined
Sep 15, 2021
Posts
678
Reaction score
1,266
Location
MN
First Name
Calvin
Truck Year
'85, '81
Truck Model
K10, K20
Engine Size
305, 350
FWIW, I'm still looking for a driveshaft measurement from anyone running a 700-R4/NP208/14bFF in a K20 with an 8' bed.

I have two more potential leads as of this week, one in New York and one in southern MN. If those fall through, I'll likely be having a new driveshaft made.
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,122
Reaction score
6,038
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
would the 700r4 shaft match any other combo, if so, just let me know I may have somethingI have 2 np208 sm465 8 foot bed 14 bolt ff shafts

one is a 8600gvw and one is under
also, what is your trucks gvw? From what i read from keith, a higher numbered rear end, so 4.10, combined with how much weight it needs to be good for, that decided often if it was a solid or slip
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,966
Reaction score
23,484
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
FWIW, I'm still looking for a driveshaft measurement from anyone running a 700-R4/NP208/14bFF in a K20 with an 8' bed.

I have two more potential leads as of this week, one in New York and one in southern MN. If those fall through, I'll likely be having a new driveshaft made.
Just need to find anyone with a 208 in a truck with a 14ff, which as far as I know, was never a factory combo. K20's in the 80's had the 14sf originally. All of the factory trans/208 combos are the same overall length.

I have a K Burb with a 208 and a 14ff (I had the shaft made longer after replacing the original 10bolt), with about 5 inches of lift in the rear. The wheelbase is 2 inches shorter than a longbed truck. I can measure it if you would like.
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,122
Reaction score
6,038
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
OP, i should ask I think, do you know your springs are good and your dif is nice and where it should be including the up down for pinion angle. did the truck it come out of by chance have smaller springs?
 

scrap--metal

Full Access Member
Joined
Sep 15, 2021
Posts
678
Reaction score
1,266
Location
MN
First Name
Calvin
Truck Year
'85, '81
Truck Model
K10, K20
Engine Size
305, 350
would the 700r4 shaft match any other combo, if so, just let me know I may have somethingI have 2 np208 sm465 8 foot bed 14 bolt ff shafts

one is a 8600gvw and one is under
also, what is your trucks gvw? From what i read from keith, a higher numbered rear end, so 4.10, combined with how much weight it needs to be good for, that decided often if it was a solid or slip

AuroraGirl, please do measure your driveshaft for me. U joint to U joint if possible.

I don't think the sm465 is the same length as the the 700-R4, but bucket claims all factory trans and 208 combos are the same length. If that's the case, your driveshaft should be the length I need.

I have no idea on the GVW. The truck has a 2wd cab, and 4.10 gears in the 14bFF. A real Frankenstein's monster.
 

scrap--metal

Full Access Member
Joined
Sep 15, 2021
Posts
678
Reaction score
1,266
Location
MN
First Name
Calvin
Truck Year
'85, '81
Truck Model
K10, K20
Engine Size
305, 350
Just need to find anyone with a 208 in a truck with a 14ff, which as far as I know, was never a factory combo. K20's in the 80's had the 14sf originally. All of the factory trans/208 combos are the same overall length.

I have a K Burb with a 208 and a 14ff (I had the shaft made longer after replacing the original 10bolt), with about 5 inches of lift in the rear. The wheelbase is 2 inches shorter than a longbed truck. I can measure it if you would like.

Thanks for offering, bucket, but the 5" of lift and 'burbon wheelbase is enough to complicate the comparison beyond my expertise.

If the 208 was never paired with a 14bFF from the factory, which I have no knowledge of, that may explain my inability to find a proper length driveshaft.
 

scrap--metal

Full Access Member
Joined
Sep 15, 2021
Posts
678
Reaction score
1,266
Location
MN
First Name
Calvin
Truck Year
'85, '81
Truck Model
K10, K20
Engine Size
305, 350
OP, i should ask I think, do you know your springs are good and your dif is nice and where it should be including the up down for pinion angle. did the truck it come out of by chance have smaller springs?
I do believe the rear springs to be good. I know there are no broken leafs (or leaves, lol), and the truck sits level from side to side. The leaf springs have a similar amount of rust as the frame rails, so I would assume that they've never been off the truck but that could be incorrect.

The wheels look like they sit where they should in the wheel wells, but could it be possible that the springs or axle are put together wrong? That's something I have not spent as much time investigating.

Pinion angle can definitely affect driveline vibrations, 2nd gen Camaros are notorious for that issue, but the slop where my slip yoke enters the NP208 is more than an improper pinion angle could cause. I have no idea on what kind of Chevy truck each component was sourced from.
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,122
Reaction score
6,038
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
@AuroraGirl your driveshaft is also a bit on the short side isn't it? I thought we discussed that in the past?
Yes we have lol I am saying he should check the things that are definitely affecting mine. Because my truck sits on pretty tall springs with one being broken(that’s nice, right???) but if he has less leaves than an HD rear suspension and his driveline is sitting on 2wd mounts(lower?), would that soak up any of the distance?

I hurt my ankle but I’ll try and commando(ha, not that one)my way out there at some point. “I ain’t got time to bleed” lol.
I’ll also measure the diameter.
Based on my np208 saying 84 date, I’ll assume it was 85 which bucket has also been the one to learn me the crossmember is for 85-86. If it doesn’t match we will know something for someone. I do have a drive shaft that’s rather large, like, I am guessing it’s a slip shaft for a 1 ton because the 77 k25 has a slip shaft 2 piece which is smaller diameter.

I also have my original driveshaft for the old sm465 and np205


I also did some reading the other day ajd it appears the early 80s used some tall np208 adapters?i wonder where that put driveline compared to the late 80s
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,122
Reaction score
6,038
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
I do believe the rear springs to be good. I know there are no broken leafs (or leaves, lol), and the truck sits level from side to side. The leaf springs have a similar amount of rust as the frame rails, so I would assume that they've never been off the truck but that could be incorrect.

The wheels look like they sit where they should in the wheel wells, but could it be possible that the springs or axle are put together wrong? That's something I have not spent as much time investigating.

Pinion angle can definitely affect driveline vibrations, 2nd gen Camaros are notorious for that issue, but the slop where my slip yoke enters the NP208 is more than an improper pinion angle could cause. I have no idea on what kind of Chevy truck each component was sourced from.
I didn’t mean necessarily for the whole overall angle, more or less the amount up or down the input for the 14 is. If it’s pointed upward like a little over level i would think the distance is ever so slightly shorter than if it’s pointed down. My spring is broken on one side and the loaded with 2000 pounds the truck works rather normal but unloaded it kinda stilted on one side, which has its affects lol. The truck also isn’t using the right spring pack size for the rpo which would have an overload I think and I know my gpa probably broke at least the originals so prob threw on whatever which means I might have it worse lol if I had the full pack. If you knew your SPID options it would give an idea but that’s ok. I was just trying to see if any variances account for your slip yoke sticking out as far as it does

@bucket do the np208 rear slips share anything or how different are lengths? I know at one point my gpa owned a GMC jimmy but I had a confusion with how long they would have had it because they referred to the gmc k25 as jimmy too…so I’ve heard what some things are or may be from possibly from the Incorrect source here or there abs I was like oh nice
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,966
Reaction score
23,484
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
@scrap--metal I found your post over on NastyZ28 and responded there too. I forgot all about the M1008, a shaft from one of them should work for you.
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,122
Reaction score
6,038
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
@scrap--metal I found your post over on NastyZ28 and responded there too. I forgot all about the M1008, a shaft from one of them should work for you.
Find snd donate for meeeee
I’m actually kidding I figure I’d rather aspire for the 205 back into it and the original trans

One day

With how hard and rugged I would continue to use it gear drive is prob better than chain
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,966
Reaction score
23,484
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
@AuroraGirl it seems like all the slip yoke style T-cases used a yoke roughly the same length. They are longer than your average car type TH400 yoke, but some newer 2wd trucks and vans use the same long style slip yoke.

My '88 Burb was originally a 700/208/10bolt rig. When I lifted it and put the 14ff under it, the shaft was a bit short and I just ran a conversion u-joint at the rear and kept all the yokes as the 1330 or 3R or whatever they were (1350 on the differential, obviously). I ended up gathering a long slip yoke from a '00 4L80e van (1350), a section of C30 shaft with two yokes and same tube diameter as my original shaft, then took it all to my local driveline shop. Using a new tube, they built a "new" shaft using all the parts I brought them. The same shaft is in use now with the 400/208 combo in there now.

Another interesting bit of swap info. That original 1/2 ton np208 slip yoke came in real handy when I swapped the long tail th350 for a short tail th400 in my C10. It killed two birds with one stone- lengthened the shaft and converted it to 32 spline.
 

Forum statistics

Threads
41,858
Posts
903,634
Members
33,371
Latest member
Linemanjl
Top