driveshaft max length?

Discussion in 'The "Juice Box"' started by WQ59B, Jan 6, 2020.

  1. WQ59B

    WQ59B Well-Known Member

    GM used 3 different tailshaft lengths on the TH400 to --I believe-- mitigate the length of the driveshaft in different wheelbase cars. Yet some 'non-huge' wheelbase cars still got 2-piece DS (like the 119" WB Rivieras, I believe).

    I have a 123" wheelbase Buick and am set on using a long-tail TH400, since I already cut the bellhousing off for an UltraBell. Don't have any driveshaft yet- would be built for the car.

    A short tail TH400 is 9" shorter overall than a long tail. Is there any known caution/concern RE driveshaft length if I switched over to a short tail TH400? Is there a recommended max length?

    Just curious; short tails seem to be a lot more common.
  2. WQ59B

    WQ59B Well-Known Member

    Poking around online... I think the reason the Riv had a 2-piece DS was because it was an X-frame thru ('70?).

    Also seeing Inland Empire state a good limit to 1-piece DS length is 60". The rear & motor/trans is mocked up in my car, will check what neck of the woods I'm at currently.
  3. Mark Demko

    Mark Demko Well-Known Member

    Im my meanderings some 30 plus years ago, the short tail 400 was more scarce.
    The long tail being used in full size whether it was a T-350 or T-400 was more common.
    The short tail T-350 was around quite a bit due to most midsize 350/350 combos.
    The 400 short tail was kinda scarce due to fewer midsize big block/400 combos.
  4. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    Denny's driveshaft has some good recommendations on their site regarding length.
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    The only problem with a long tail trans might be pinion angle, a pair of adjustable upper control arms will fix that. I have a GV Overdrive that necessitates a 14” shorter drive shaft.
  6. WQ59B

    WQ59B Well-Known Member

    ^ still possibly a problem on a 123” WB, you think? My car has adjustable ladder bar set-up, so that should help.
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Not sure, but maybe a shorter drive shaft is stronger, so the long tail may be the better transmission for you anyway.
    WQ59B likes this.

    BRUCE ROE Well-Known Member

    A longer tail will require the trans mount to be farther back. Also consider
    if your output shaft will have the O ring, for the yoke with the overlapping sleeve.
    Bruce Roe
  9. Matt69olds

    Matt69olds Well-Known Member

    One problem using a short shaft 400 with a long wheelbase car is “driveshaft critical speed”. Basically what happens is the driveshaft wants to wobble or “whip” in the center at high speeds. At the minimum, it wears extension housing bushings and causes vibrations. In extreme cases, the driveshaft wads up under the car.

    The short shaft 400 are much harder to find, I seem to find 3 or 4 long shafts for every short shaft cores.

    If the car had a long shaft from the factory, it would be much better to use one than try to make a short one work. I’m not familiar with Riviera, but transmission mounts are in much different positions between long and short shaft units. That means the crossmember needs to be moved to match.
    Last edited: Jan 11, 2020
    Mark Demko likes this.
  10. WQ59B

    WQ59B Well-Known Member

    My car had a DynaFlow originally :eek: - everything's different now (except the wheelbase).

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