Register now to get rid of these ads!

TH350 to TH400

Discussion in 'The Hokey Ass Message Board' started by FireBurb, Dec 4, 2018.

  1. FireBurb
    Joined: Dec 4, 2018
    Posts: 8

    FireBurb

    Alright so my 350 went bad so i thought instead of fixing the 350 i’d just get a th400. when i got it i didn’t notice that it has a tail housing for the trans brake thing. so now i am completely confused as to what yoke to get or if it’ll even work. if you need pics just lmk. the th350 has the short tail shaft. i think i’m good as to figuring out the how much driveshaft to cut.


    Sent from my iPhone using The H.A.M.B. mobile app
     
  2. Mr48chev
    Joined: Dec 28, 2007
    Posts: 25,624

    Mr48chev
    ALLIANCE MEMBER

    That's a trans out of motorhome or something like a 1-1/2 or 2 ton truck.
    I'm not sure that you can remove them without changing the tail shaft housing and tail shaft.
     
    Hnstray likes this.
  3. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,246

    gimpyshotrods
    Member

    That is not a TH400. It is a TH475.

    You need a 2wd TH400 tail housing, and yoke that goes with it. It is a bolt-on, fixed yoke.

    You will need a slip-spline drive shaft. Your existing shaft will not work.

    Also, unlike the helical gears in a TH400, a TH475 has straight cut gears. Strong, but noisy.

    What might be the deal killer: a TH475 does not have a parking pawl. You park it in neutral, and use the ring and pinion multiplied parking brake, on the tail housing.
     
    Last edited: Dec 5, 2018
    Jalopy Joker, XXL__, Hnstray and 2 others like this.
  4. 1934coupe
    Joined: Feb 22, 2007
    Posts: 3,422

    1934coupe
    Member

    I didn't know that Gimpy, good info there. Thanks.

    Pat
     
    Register now to get rid of these ads!

  5. Hnstray
    Joined: Aug 23, 2009
    Posts: 10,740

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

    You didn’t mention the vehicle type or hp you are dealing with. One thing to consider is that a TH350 uses less hp to operate than does a TH400.....I have seen the number 16% more required for a TH400. That is not a criticism of the 400, only pointing out that in lighter to medium duty applications, a 350 may be a wiser choice for that alone plus it weighs less.

    On the other hand, if your application is high hp and/or a heavy weight vehicle, or often used for towing, etc., the 400 is great.
     
  6. FireBurb
    Joined: Dec 4, 2018
    Posts: 8

    FireBurb

    [​IMG] would i be able to use a normal short tail housing and then this yoke? i found it in another thread and they said that should solve the problem


    Sent from my iPhone using The H.A.M.B. mobile app
     
  7. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 856

    Jmountainjr
    ALLIANCE MEMBER

    Solves the driveshaft issue. You still won't have a park feature in the transmission.
     
    gimpyshotrods likes this.
  8. Hnstray
    Joined: Aug 23, 2009
    Posts: 10,740

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

    The bolt on output yoke is common on GM lighter duty trucks that do not have the external parking brake assembly you have. I suspect that is far more common than the RV/medium duty truck TH400 etc. that you have. That alone would justify the modified yoke design Neapco offers.

    “Park” position aside for the moment, I suggest you research this further to find out if the output shaft of the transmission you have, with the output mounted parking brake, is the same as the standard TH400 truck shaft that uses a bolt on yoke, but without the external brake.

    It may be as simple as changing the tail housing...or it may not. The time to determine all that is before you buy any parts.
     
    Last edited: Dec 5, 2018
    FireBurb likes this.
  9. Last one I had, ( 1988 P-30 , 454) had a park in it. The P-30 was the "bread truck " chassis used for Class A RV 's.
    ( discs all around, 19.5 rubber)
     
  10. FireBurb
    Joined: Dec 4, 2018
    Posts: 8

    FireBurb

    okay thanks. so i just need to find out if the output shafts are the same and if so that would mean i can use that yoke and then what’s the issue with just swapping the tail housing? what are some things i would have to look out for regarding the tail housing?


    Sent from my iPhone using The H.A.M.B. mobile app
     
  11. oldsman41
    Joined: Jun 25, 2010
    Posts: 1,134

    oldsman41
    Member

    Rebuild the 350 you will come out ahead.
     
  12. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 5,779

    56sedandelivery
    ALLIANCE MEMBER

    I "think" you'll be alright using a "regular" short extension housing, and the counter-bored slip yoke. I have never heard of this transmission not having a "Park"; in fact, this is the first time I've heard this, but I don't know everything. I did have an old Dual Range, cast iron, 4 speed Hydramatic once, that had an extension housing mounted, drum style, parking brake. It had a "Park", and used a bolt on "trunnion"; came out of a dump truck. You will have to shorten your drive shaft, unless your TH350 had the 9 inch long extension housing. When I got tired of the TH350's my DD truck had going out, I swapped in a TH400 from a passenger car, used a longer slip yoke, and kept the stock 2 piece drive shaft. You might call up a transmission shop or two, and ask them what you'll need to do in order to use your TH400/475 transmission. What's the trans going into? If needed, do you have the available resources to have a drive shaft made up with the "slip" made into the shaft, if an extension housing/special slip yoke won't work? I am Butch/56sedandelivery.
    I just did some checking on a few other sites, and there was only one mention that "SOME" TH475's did not have a "Park" position, and some did, so you'll just have to run it through it's detents, and see if yours has a "park" or does't. Learned something new today! There's another thread here, TH400 to TH475, that's been resurected, that may answer some of your questions also.
     
    Last edited: Dec 5, 2018
    Elcohaulic and Truckdoctor Andy like this.
  13. I've never heard of one not having park either, I was surprised to read that and thought I read something new. I have a trans out of a cube van that has the bolt on yoke, no parking brake garbage and I also have one of those slip yoke conversion yokes.
     
  14. 4tford
    Joined: Aug 27, 2005
    Posts: 1,596

    4tford
    Member

    I have the turbo 400 with the bolt on yoke and you need the slip yoke machined to allow the slip yoke to slide in all the way. I had Denny's driveshafts do my driveshaft it fit good they knew the slip yoke I needed.. A portion of the spline must be removed to allow it to engage properly on the yoke style tailshaft that's what is shown above in " neapco" yoke in post #6
     
  15. Jalopy Joker
    Joined: Sep 3, 2006
    Posts: 23,407

    Jalopy Joker
    Member

    - or find a replacement or get a upgraded 200R4
     
    gimpyshotrods and Hnstray like this.
  16. oldsman41
    Joined: Jun 25, 2010
    Posts: 1,134

    oldsman41
    Member

    Jalopy yeah but he has to watch his ratio in the rear end. That od tranny wont like a 3;08 or higher. It could live with a 3:54 or 3:70
     
    Atwater Mike likes this.
  17. saltflats
    Joined: Aug 14, 2007
    Posts: 9,556

    saltflats
    Member
    from Missouri

    There are two short tail housings, the difference is in the yoke bore hole, some use the 350th size.
     
    Hnstray likes this.
  18. Hnstray
    Joined: Aug 23, 2009
    Posts: 10,740

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

    ^^^^^^^yep, stumbled into that issue a couple years ago. Easy to fix once you know....and find the correct tailhousing...;)
     
    saltflats likes this.
  19. Crosley
    Joined: Mar 3, 2001
    Posts: 1,029

    Crosley
    Member
    from Aridzona

    Easy enough to check for the function of parking pawl parts with a pair of slip jaw pliers. Place unit in park.. check for rotation of the output shaft.. Some added info; Military equipment with a 4L80E in them like a HumVee do not have parking parts in them either. With the age of the T-400 , it may have been swapped out decades ago for a unit with parking bits & pieces inside
     
  20. ClOckwOrk444
    Joined: Jun 15, 2017
    Posts: 43

    ClOckwOrk444
    Member

    We used a TH400 from a 2wd fullsize van and it had normal park, short tailshaft, and slip yoke. Broke the bellhousing off with transbrake, Upgraded to reid case now. Good luck
     
  21. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 5,779

    56sedandelivery
    ALLIANCE MEMBER

    That's the "TH375"; a TH400 with a TH350 output. There's one of those currently for sale in the Seattle area Craig's List. Why GM did that, who knows? There is also a "regular" TH400 that does take a different bushing, and therefore a different slip yoke; thankfully, they're not real common. But, if you do get one, and don't know about that oddity, it will drive you nuts trying to figure it out. I am Butch/56sedandelivery.
     
    saltflats likes this.
  22. Probably an o/t car. That's okay ..A quick learner ;-)
    I'd say fix the T350 unless we hear more detail.
     
  23. elba
    Joined: Feb 9, 2013
    Posts: 606

    elba
    Member

    The 350 is a great street rod tranny . I would keep it .
     
  24. FireBurb
    Joined: Dec 4, 2018
    Posts: 8

    FireBurb

    was gonna drop all of this in my 71 monte carlo now im not sure if i wanna go through the hassle of getting the yoke and tail housing and driveshaft cut for a “maybe it’ll fit”. i found another 400 hopefully this one has the short tail i need and slip yoke that would be perfect. if not then guess i’m stuck with this thing. welp thanks everyone for the help. learned a lot lol idk just got overwhelmed i rather just sell this and get something a little more compatible


    Sent from my iPhone using The H.A.M.B. mobile app
     
    Elcohaulic likes this.
  25. Good luck, and read the rules for this site , before you post again;)
     
  26. Atwater Mike
    Joined: May 31, 2002
    Posts: 9,795

    Atwater Mike
    ALLIANCE MEMBER

    TH 350 is a repairable automatic transmission. A strange 400 is a crap shoot.
     
    gimpyshotrods likes this.
  27. FireBurb
    Joined: Dec 4, 2018
    Posts: 8

    FireBurb

    where can i find them?


    Sent from my iPhone using The H.A.M.B. mobile app
     
  28. I don't know . I know I've read them. I can see how you might have missed them.
     
  29. FireBurb
    Joined: Dec 4, 2018
    Posts: 8

    FireBurb

    oh the cutoff year thing?? sorry i had no idea. they should make a rules section or something i just kept seeing people asking things for newer stuff and people telling them the cutoff year is 60 something and i figured that’s what the problem was. sorry bout that


    Sent from my iPhone using The H.A.M.B. mobile app
     
  30. I'm with jalopy Joker on this thing. I've had pretty much every GM tranny that they make. If you going through all that work to swap out a different transmission, why not bump it up a notch? Go with a 200 or 700. You'll be worlds ahead at the end of the day
     
    gimpyshotrods likes this.

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.