I have a 2 piece drive-shaft in my 73 f100.

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I put a New process 4spd in after taking the auto out. I moved the transmission cross-member to the forward mounting hole and got a longer front driveshaft section for the manual. I assembled the drive-shaft and it is fully stuffed when I have the pickup jacked up like the picture above. Obviously this is a problem.

Is it a bad idea to cut 3/4" off the back of the front shaft? There is about and extra 1" of splines on it when the front and back shafts are fully stuffed.

Rear connection:
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Transmission cross member location:
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Transmission connection:
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Center bearing:
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The idea would be to cut the tip of the shaft off.

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If the NP 435 was an option for your truck and it is 133" wheel base then there are lots of junk yard shafts available for you .. No cutting required .. Cutting bad idea, if shortened should be done at the tube and rebalanced $$$

 

How many drive shaft lengths options are there? I have a regular cab long box. I had the one for the auto that was about 16 inches from the u-joint to the hanger bearing. This one is longer. Is there another that was only 1" or so shorter than the longer one I have now?

 

Look at the motor perches and holes on the frame rails can you get your 1" there .. There would have possibly been only 2 options I can think of auto or manual .. Numberdummy can verify that .. It may have all been done at the motor perches .. what motor is in the truck ?

 

it's a 300. I moved the transmission cross member to the forward position already though. I don't think I can move anything forward farther.

 

Looking closer at your pics .. The trans cross member shows no hole in the frame to move the motor and trans forward so I am leaning towards different size drive shafts available .. The rear shaft is probably the same in both options it would be the forward shaft that would have been 1" shorter .. either way cutting the shaft should not be necessary ..

 

The only other thing it could be is the tail shaft on the NP 435 may not be correct for 2wd application ..

 

the transmission came out of a mid 70's reg cab long wheelbase pickup truck. It was 2wd. It looked like maybe an f350 and it might have had a dump box or something on it because the tranny has a pto. I have a picture of it at home somewhere. I don't remember if it had a 2 piece shaft or not, or any left at all.

Thanks for helping by the way.

 

Re-tube and balance, $200 or so. You can spend a lot of time looking for a shaft that will fit. If you find one, it may or may not be straight and balanced.

Do it right and your conversion will last.

 

$200.00 is way high. Yes, it was a couple of years ago but I had a driveshaft re-tubed and balanced for $90.00.

 

shoot where I live I can get one cut and balanced for 60!

 

I just got one done today for 50. There's no reason to retube it when shortening it unless it's damaged.
You need to have it balanced anyway since you replaced one section. The whole thing needs to be balanced as a unit.

 

I am in a similar situation with doing a transmission/engine swap now. I peeked in the parts manual for these trucks and learned a couple of things that you guys might already know. First, the front section of the driveshaft is called the coupling shaft and it is the one that comes in different lengths depending on the engine & transmission that is used. Second, there are a lot of different coupling shafts for these trucks--way more than I ever thought. There are more than just a coupling shaft for automatic or manual transmissions. The length and diameter of the coupling shaft depend on engine size as well (Each V8 can use a different one as well. It gets mind boggling when you start to think of all of the different transmission combinations that came in these trucks. The parts manual at least gives the dimensions for each shaft if one needed to be made (or shortened).

You might find something at a junkyard that works, but I wouldn't bet on it--especially if it is a more unusual engine/transmission combination. I would just get a shop to shorten the one you have. It will cost a few $$$, but then you don't have to go with one that "almost fits properly".

 

The 133" wheel base is the most common and easiest to find and is what he has .. The price of cutting and rebalance keeps going down with each post in this thread so if he waits a few days it stands to reason it might be free