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Thread: HELP!! I need to find the right drive shaft??

  1. #1
    Senior Member Chevy_Finatic79's Avatar
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    Question HELP!! I need to find the right drive shaft??

    Hey fellow bowtie lovers. I have a 85 2wd long box that came with a 4.3L/TH375B ( thats a TH400 case and guts with a TH350 output shaft I believe) any way it had a "2 piece" driveshaft = short shaft in the front + carrier bearing + long shaft to the back (maybe it's a 3 piece) IDK.

    I switched from the TH375B to a rebuilt TH350, well the tranny mounts are in different loctions so I had to move the cross member toward the engine like 4 inches to mount the TH350 there were already factory holes drilled Which made this nice-N-easy.

    My current combo is 5.7L/TH350

    Here is my Problem: all that moving everything forward made my drive shaft come up a little short. The slip-yoke only goes up about an inch on the output-shaft not even reaching the rear tranny seal.

    I want to know if I can just get a one piece drive-shaft off of a junkyard long box truck with a smallblock/th350 combo or does that even exist?

    my carrier bearing is shot so if I go that route I would have to replace the carrier and get a longer short shaft. I have been looking on the net but cant find much on driveshafts.

    I also have no clue what points to measure from to find exactly how much longer it needs to be. and what considerations do I need to make about my rear end gear ratios?

    Do they make a longer slip yoke i could just change out?

    Please reply I dont know a whole lot about driveshafts and could use all the help I can get on this. I dont have alot of money to throw at this problem either maybe $200 tops.
    Any help is appreciated Thanks

  2. #2
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    Intresting,,,,, while I can appreciate you dilema, I question the use of a salvage yard component, especially a driveshaft.
    The two piesce shaft has certain advantages, and attemting to use a 1 piece unit might bring its own problems. If you go longer and one piece, the diameter has to be increased to compensate for the additional length, or vibrations will result.
    How large? Who knows.
    I would suggest calling a local driveshaft repair shop, and asking them what a two piece, VS one piece shaft would cost new. Most shafts start right around your budget price, and if they re-use most of your components, you might even save some bucks.
    They will tell you where to measure from, and you will probably save a bunch of time and potential problems associated with using a salvage yard component.
    A quality shop can take all of the guesswork out of this.



    Just for the sake of arguement, the THM375B was basically a 350, same case, and considered a "heavy duty 350", while the THM 375 was a 400 case with the smaller output shaft which shares nothing with the 375B and is a light version of the 400. The 375's use a 350 yoke, so this should be a very easy swap.
    Another piece of worthless trivia..............

  3. #3
    Senior Member Chevy_Finatic79's Avatar
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    Worthless to who? you seem like the all knowing transmission/driveshaft Guru glad I can get facts like that for free.
    Well that means I have the THM375 because when changed the filter and pan gasket I got THM400 parts. and I guess I woundn't have had to move the cross member either if it was a THM375B since it is the 350 case. and it has the electric detent line.

    Okay so lets say I keep the 2 piece set up I get a new carrier bearing for $20 @ O'reily's. that leaves me with getting new U-Joints and a longer shaft from the carrier to the transmission which brings me back to my question can i just get a longer "yoke" on the end of the exsiting drive shaft that is like 2-3 inches longer? do they make such a thing?

    My THM375 has the capitol letters "HD" rasied up around the peak of the bellhousing on the pass side does that mean Heavy Duty or is that just some kind of different ID marks?

    I plan on having the 375 rebulit any suggestions while I have it on the table under the knife? Besides new heavy duty spragues, clutches and a shift kit?

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    You won't get a longer yoke. Take your whole shaft to a driveshaft shop and ask about lengthening the front shaft. To get the length you need put the yoke all the way in the tranny then pull it out 1", measure from the back of the tailshaft to the center of the u joint, record this measurement. (example- 2.5") Now mount the shaft and measure the same way. (example- 7.5") In this example you subtract 2.5 from 7.5 and this is the amount to lengthen the shaft, = 5".

    I don't think you'll find a shop to make you a 1 piece shaft for that length, atleast inexpensively. Look on the bright side though, atleast your truck already had the 2 piece shaft. It's a big pain the other way around.

  5. #5
    Senior Member Chevy_Finatic79's Avatar
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    I still have a hard time accepting that i cant buy a longer replacement Carrier to tranny shaft that i can just swap out. I know damnn well that from '73-87' they made countless trucks with my frame and body style that came with a smallblockV8/THM350 and the driveshaft I'm looking for. there has got to be a better way to find this shaft with no guesswork.
    my truck is not lifted or lowered and I dont have extreme tires or low-pro
    this should be a lot easier

  6. #6
    Senior Member
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    Quote Originally Posted by Chevy_Finatic79 View Post
    I still have a hard time accepting that i cant buy a longer replacement Carrier to tranny shaft that i can just swap out. I know damnn well that from '73-87' they made countless trucks with my frame and body style that came with a smallblockV8/THM350 and the driveshaft I'm looking for. there has got to be a better way to find this shaft with no guesswork.
    my truck is not lifted or lowered and I dont have extreme tires or low-pro
    this should be a lot easier


    There is no reason why you cant.
    I had suggested above that you migh consider just taking the shaft to a driveline repair facility to have a new one made, but there is no reason why the shop can't modify your existing unit.
    You can try to find a "junkyard jewel" that might be laying around in a salvage yard, but you are not sure of the condition, (could be dented, or out missing weights).
    You could find one that is absolutely perfect, but you will know that shafts are balanced as a complete assembly, and by mixing components will compromise this.
    The potential for vibration increases greatly, which means that you will have to remove the entire shaft (again) and take it to the driveline shop anyway. They will charge you probably as much to balance a shaft, as they would to have modified the thing, and balanced it in the first place.
    Once you look at the time, gas, and labor involved with searching for a half of a shaft that will work, and you might end up at the driveline shop anyway, it only makes sense to me, to just go straight to the shop, and get it out of the way in one trip. I do not believe that this modification will be that expensive. I have complete double cardan shafts made for less than 300 bucks. All new components. Since you are bringing in a functional shaft, you are only looking at replacing one tube. This cant be expensive at all.
    Just trying to suggest an alternative to running around, laying on the ground at a salvage yard, and taking the time to find the correct part.
    This correct part could have problems that need to be corrected, and you will only know this after you install it.
    You might get lucky, but I seldom do.
    Savng time, and eliminating a little frustration is always a good idea.

  7. #7
    Senior Member Chevy_Finatic79's Avatar
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    since you put it that way I guess I'll take my stubburn *** to the driveshaft shop and be done with it

  8. #8
    Senior Member
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    Not trying to tell you what to do, simply trying to share some of my previous experiences with you, and help prevent some potential problems.
    Sometimes it an cost more in time and money by using a slavage yard part.
    Maybe call the driveline shop, and ask what the cost would be to lengthen a shaft by the amount that you need. Would bet that the distance between mounting holes for the x-member is the difference in length you will need.
    Now while a shop cant stretch the shaft, the entire tube can be replaced easily, and I would imagine that it would be a very cost effective solution, and then you could have some certainty that it would be right the first time, eliminating you from performing redundant work.

  9. #9
    Senior Member Chevy_Finatic79's Avatar
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    well today I finally decided it was time to start looking for a longer drive shaft so even after getting advised against it I went to the junk yard to see if they had a longer what I'm calling short shaft=(from tranny to carrier bearing) well I went thru the pile and couldn't find one.

    So I decide to take a look around the yard and I came across a Chevy truck with a short shaft 350thm so I thought I was in business but that setup was way too long like 5 inches. so I kept looking then I found a Chevy 80' long bed 2WD diesel with a long shaft 350thm so I measured from the tranny seal to the rear-end and got the same measurement that my truck needed. needless to say I took the drive shaft off and paid $25 dollars for it now I just need to spend another $30 and get two new U-Joints. it's crazy I'll spend more on U-Joints then whole Drive shaft

    Oh I almost forgot to mention that I was able to get rid of my tiny little 2-peice steup and got a real truck's 1-peice driveshaft=(Man Stuff) here's a comparison pic


    "She's gonna Freak when she see's my wheels"

    85' Chevy C-10 Longbox (Rat)
    TBI 327 Cu.In./THM350

    90' Chevy Suburban 4x4
    TBI 350 Cu.In./700R4

    http://www.truckforum.org/forums/truck-pictures-176.htm

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