AT 400- Has anyone out there split the case on your Trans?

Discussion in 'General Tech' started by Cadillac Kid 1, Dec 1, 2017.

  1. Cadillac Kid 1

    Cadillac Kid 1 Active Member

    Joined:
    Jun 18, 2008
    Messages:
    824
    Likes Received:
    34
    Location:
    San Antonio Texas
    Got all the gremlins sorted out and was taking a final run to be sure. Just ran up to 500 in first, shifted to second and pulled about 5K and then went onto third. Drove about two moles when a severe vibration started followed by smoke due to trans fluid leaking. Flat bedded to transmission shop that did the mods. They found the case split.
    Anyone else had a case split on them?
    Greg Surfas
     

    Attached Files:

  2. PJ McCoy

    PJ McCoy Active Member

    Joined:
    Jul 11, 2015
    Messages:
    681
    Likes Received:
    95
    Location:
    Camden NC
    Man thats not good. Ive never seen anything like that Greg. Sorry to for you bro.
    Whats the tranny shop saying about that?
    Have they ever seen anything like that
    ?
     
  3. Cadillac Kid 1

    Cadillac Kid 1 Active Member

    Joined:
    Jun 18, 2008
    Messages:
    824
    Likes Received:
    34
    Location:
    San Antonio Texas
    They are pulling the trans apart art to check for a possible cause. Their prelim theory has to do with the long tails haft. I was just wondering if anyone else out there has spli a case like this . Absolutely zero full bore launches with slicks and less than 100 miles on trans.
    Greg Surfas
     
    Last edited: Dec 1, 2017
  4. 8ad-f85

    8ad-f85 Well-Known Member

    Joined:
    Jul 25, 2014
    Messages:
    1,560
    Likes Received:
    107
    What a great idea, I should have people ship me blown up engines to analyze failures! :D :D

    Just messing around, curious about the verdict
     
  5. Darius

    Darius Well-Known Member

    Joined:
    Oct 15, 2004
    Messages:
    3,442
    Likes Received:
    156
    Dang Bro! What kind of power are you laying down?? (Twin turbos, feeding a Roots blower, topped off with a 350 shot of N2O)

    bro. d
     
  6. Cadillac Kid 1

    Cadillac Kid 1 Active Member

    Joined:
    Jun 18, 2008
    Messages:
    824
    Likes Received:
    34
    Location:
    San Antonio Texas
    Nope
    Just a 10:1 NA roller cam turning 3.7 rear gears
     
  7. 8ad-f85

    8ad-f85 Well-Known Member

    Joined:
    Jul 25, 2014
    Messages:
    1,560
    Likes Received:
    107
    I can picture a few reasons for failure, so now I'm curious if the shop is looking for a cause and a solution or if this is going to be one of those blameless situations.
    Is it bad that I jump right to that?
    I'd definitely be checking the driveshaft over closely for it's potential contribution.
     
  8. Cadillac Kid 1

    Cadillac Kid 1 Active Member

    Joined:
    Jun 18, 2008
    Messages:
    824
    Likes Received:
    34
    Location:
    San Antonio Texas
    Drive shaft? How so?
     
    Last edited: Dec 1, 2017
  9. 8ad-f85

    8ad-f85 Well-Known Member

    Joined:
    Jul 25, 2014
    Messages:
    1,560
    Likes Received:
    107
    Shaft, yoke, or anything that has leverage against the rear of the trans or could bottom out taking up all the clearance inside.
    Do I think that's likely the cause?
    Probably not.
    I have a tendency to check anything out remotely related or affected.
    It seems like the cause is inside the case and after it's solved, I'd still look everything over.
     
  10. PJ McCoy

    PJ McCoy Active Member

    Joined:
    Jul 11, 2015
    Messages:
    681
    Likes Received:
    95
    Location:
    Camden NC
    trans5.jpg Here some pics from my trans. Back in april this year. Im trying to think about what failure could cause this? The large C ring lands fail? Maybe. It could allow the directional force of the cluthes to push on the rear support. That might be the possible. Perhaps with the drive shaft pushing forward if the rear suspension is old and fatigued. Just brain storming.
    Is tour rear suspension in good shape. Ill tell you mine is not. Hmmmm.
    Hope the pics help.
     
    Last edited: Dec 2, 2017
  11. El Diablo

    El Diablo Active Member

    Joined:
    Apr 25, 2013
    Messages:
    277
    Likes Received:
    28
    Location:
    Yuma, AZ
    What vehicle(s) do you drive?:
    1959 Cadillac Sedan deVille
    Back in the early 90s when I was taking auto shop in high school (Yuma High Criminals), I saw a th-400 case have a similar problem when the override clutch locked up at about 65 mph in a Chevy Suburban. At least thats what the student admitted to. Lol

    Another time was on a dirt track stock car after a hard hit with the wall bent the drive shaft.

    Thats not counting the dozens of broken bell housings I've welded up for various reasons.
     
  12. MIHELA

    MIHELA Member

    Joined:
    Apr 29, 2016
    Messages:
    84
    Likes Received:
    23
    Location:
    Sioux Falls, SD
    I am thinking driveshaft or mounting related failure causing stress to the case. The vibration you experienced is consistent with a driveshaft problem like throwing a balance weight, bent, bottoming, or bad u-joints.
     
  13. 8ad-f85

    8ad-f85 Well-Known Member

    Joined:
    Jul 25, 2014
    Messages:
    1,560
    Likes Received:
    107
    One of my customer's destroyed his thm400 in a similar way.
    I didn't get to see anything but was informed that his driveshaft was too long.
    Also a c-10 truck.
    I have subsequently found a couple other custom shafts made by the same reputable place with runout issues.
    They admitted to me that they didn't ever indicate the machine's chucks after any type of crash or for periodic set up reasons.
    "As long as it balanced...it was good" !!
     
  14. Cadillac Kid 1

    Cadillac Kid 1 Active Member

    Joined:
    Jun 18, 2008
    Messages:
    824
    Likes Received:
    34
    Location:
    San Antonio Texas
    Shop is tearing the trans down. We'll see what they say. Noticed that some of the racing trans (400) "specialists" have a "supercase" option. I will talk to them on Monday and see what they say.
    Greg Surfas
     
    8ad-f85 likes this.
  15. mario

    mario Well-Known Member

    Joined:
    Oct 14, 2004
    Messages:
    2,817
    Likes Received:
    56
    Location:
    san francisco bay area
    Hi greg:
    I talked to my brother albert. He said that he had broke a few t400s in the late 70s. His Chevy truck, 76 or 77, had a 550 hp 454 with 3.70 gears. If the tires, 5 inch wide, hooked up without slip, he could break a case. That truck was a monster. Is it possible that those "fingers" were starting to fracture?
    Good luck.
    ciao,
    mario
     
  16. superbinder

    superbinder Member

    Joined:
    Feb 20, 2012
    Messages:
    63
    Likes Received:
    2
    Location:
    topeka,ks
    Make sure the trans mount is not solid, something has to give with motor torque, especially with soft or bad motor mounts.
     
    PJ McCoy and 8ad-f85 like this.
  17. Cadillac Kid 1

    Cadillac Kid 1 Active Member

    Joined:
    Jun 18, 2008
    Messages:
    824
    Likes Received:
    34
    Location:
    San Antonio Texas
    Trans shop found everything inside "pristine". got another case and will put it back together. Going to check drive shaft balance and alignment.
    Greg Surfas
     
  18. Darius

    Darius Well-Known Member

    Joined:
    Oct 15, 2004
    Messages:
    3,442
    Likes Received:
    156
    Here I am passing along something "I heard" years ago and have no idea whether or not the counsel is right. It was said that both the engine and the transmission ought to have the same rigidity in their respective mounts. In other words, don't have a solidly mounted engine with a rubber mounted transmission - or vice versa. Anyone else have pearls of wisdom to share??

    Reflecting d
     
    El Diablo likes this.
  19. Cadillac Kid 1

    Cadillac Kid 1 Active Member

    Joined:
    Jun 18, 2008
    Messages:
    824
    Likes Received:
    34
    Location:
    San Antonio Texas
    Using stock mounts, motor and trans. Left side of motor is chained down to prevent it rolling ober the right fender, but all riubber mounts are in and good.
    Thanks
    Greg Surfas
     
    8ad-f85 likes this.
  20. DaveM

    DaveM Member

    Joined:
    Oct 20, 2004
    Messages:
    930
    Likes Received:
    0
    Location:
    Springfield MA
    I was just thinking , what year was that case? The earlier cases were the heaviest and by the time they got to 77-79 they lost a lot of weight, then in the 80's they were real weak.
     

Share This Page