Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

torque convertor, deezel vs gas

Discussion in '1982-Present GM Diesel' started by 55Willy, Sep 5, 2005.

  1. 55Willy

    55Willy 3/4 ton status

    Joined:
    Jun 2, 2001
    Posts:
    9,946
    Likes Received:
    0
    Location:
    Keizer, Or
    is the only thing different between a diesel th400 and a gas th400 is the torque convertor?
     
  2. AgDieseler

    AgDieseler Certified Scrap Producer Premium Member GMOTM Winner

    Joined:
    Jan 25, 2001
    Posts:
    1,038
    Likes Received:
    1,106
    Location:
    Dallas
  3. BowtieBlazer

    BowtieBlazer 1/2 ton status

    Joined:
    Jul 15, 2001
    Posts:
    2,462
    Likes Received:
    0
    Location:
    Baton Rouge, Louisiana
    does the same hold true for a th350 and 700r4???
     
  4. big_truxx

    big_truxx 1/2 ton status

    Joined:
    Oct 8, 2004
    Posts:
    2,272
    Likes Received:
    0
    Location:
    Canaan, Maine

    yup ;)
     
  5. camiswelding

    camiswelding 1/2 ton status

    Joined:
    May 25, 2003
    Posts:
    2,545
    Likes Received:
    0
    Location:
    Redding, CA
    What is the difference? stall speed?
     
  6. 6.2 man

    6.2 man 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    636
    Likes Received:
    1
    Location:
    Curtis , WA
    Diesel torque converters have a lower RPM range . If swapping transmissions you need to swap governers . The Diesel one has a lower RPM for shifts .
     
  7. 86dieselburb

    86dieselburb 1/2 ton status

    Joined:
    Oct 20, 2004
    Posts:
    219
    Likes Received:
    0
    Location:
    Crestline, CA
    I believe the shift modulator is different also. I have a built gas turbo 400 in my 6.2 burb. It works, just shifts at higher RPMs than the diesel 400 normally would. Mine seems to shift out of first at about 35mph and into 3rd at 55mph. I kinda like this for normal driving because you get up to speed faster, but it sucks if speed limits are 25-35, never gets a chance to get out of first.
     
  8. BowtieBlazer

    BowtieBlazer 1/2 ton status

    Joined:
    Jul 15, 2001
    Posts:
    2,462
    Likes Received:
    0
    Location:
    Baton Rouge, Louisiana
    just installed a 350 in place of a 6.2 and it looks like the TQ bolt holes dont line up to a 350 flywheel.

    This is on a 700r4
     
  9. diesel4me

    diesel4me 1 ton status Premium Member

    Joined:
    Jul 24, 2003
    Posts:
    17,566
    Likes Received:
    942
    Location:
    Massachussetts
    dual bolt pattern??

    Perhaps the flexplate has 2 sets of bolt holes?--most GM's have two,one set fits the TH350 and the other fits the TH400 and others..never looked at my 6.2 convertor,so you could be right!..

    86 DieselBurb--I think the modulators might be listed as "different" in the parts catologs,but are basically the same thing as a gas tranny uses--the spring inside MIGHT be a hair less or more tension..its likely the GOVENOR in your tranny being calibrated for a gas engine thats causing your "late" shifts..a modulator "'adjustment" screw only varies the speed of the shift about 5-10 mph and the "firmness" of the shift from one end of its adjusment range to the other...

    I ran the vacuum directly from the vacuum pump to the modulator on my TH400 in my 82 K20--the "VRV" valve (Vaccum regulator valve) was shot on my truck,it regulates the amount of vacuum sent to the modulator,so it mimics the vacuum a gas motor has(a diesel with a vacuum pump makes vacuum at ALL speeds,and INCREASES as the RPM goes up--just the opposite of a gas motor,and that valve bleeds off the vacuum to the modulator as rpm increases)...

    I had to screw the adjustment screw on the modulator IN all the way to compensate for the excessive vacuum,(at the advice of an experienced tranny rebuilder,this is what he does in cases like mine)--and it still shifts a bit too soon and soft for my liking--I'd replace the valve,but GM no longer sell it,and junkyards wont "break up" a running motor,or they are junk like mine already :doah: ..I'm hoping it wont shorten the life of my tranny--I plowed 25 bad storms last winter,and so far its holding up fine--hope it stays that way! :crazy:
     
  10. 6.2 man

    6.2 man 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    636
    Likes Received:
    1
    Location:
    Curtis , WA
    They should line up my tranny came out of a gas 350 and thats all I changed was the govenor
     
  11. BowtieBlazer

    BowtieBlazer 1/2 ton status

    Joined:
    Jul 15, 2001
    Posts:
    2,462
    Likes Received:
    0
    Location:
    Baton Rouge, Louisiana
    Alright maybe its a year to year difference thing. The tranny is in a 1984 model c-10 with a 6.2 it has 6 bolt holes in the TQ convertor(700r4)..... the block is a rebuilt 4 bolt main out of a 90 model 3/4 ton.....was in front of a th400....thinking about it now I bet thats where the difference is, if i remember right though that was a 6 bolt hole flywheel as well :thinking:
     
  12. diesel4me

    diesel4me 1 ton status Premium Member

    Joined:
    Jul 24, 2003
    Posts:
    17,566
    Likes Received:
    942
    Location:
    Massachussetts
    6 bolt converters?

    Only 6 bolt torque converter I ran into on a GM was in a chevy van that had a 292 straight six in it,I think it was a TH350,but I'm not sure(long time ago!)..We bolted it to a 3 bolt flexplate ,the three holes lined up..just left the other 3 empty!--not sure if you can do this in your case.. :crazy:
     
  13. rugger03

    rugger03 1/2 ton status

    Joined:
    May 14, 2000
    Posts:
    829
    Likes Received:
    0
    Location:
    around
    My th400 has 6 bolts as does my 4l80...both diesel units.
     
  14. 6.2 man

    6.2 man 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    636
    Likes Received:
    1
    Location:
    Curtis , WA
    All GM converters had 6 bolts remans have 3 go figure ????
     
  15. big83chevy4x4

    big83chevy4x4 3/4 ton status

    Joined:
    Mar 22, 2002
    Posts:
    6,587
    Likes Received:
    0
    Location:
    Sheridan, Michigan
    not true, you can get remans with 3 and 6. it depends on the application. almost every diesel has 6 bolts while almost every gas has 3. there are a few that crossover, but not many.
     
  16. 55Willy

    55Willy 3/4 ton status

    Joined:
    Jun 2, 2001
    Posts:
    9,946
    Likes Received:
    0
    Location:
    Keizer, Or
    so whats the lock up rpm for a diesel convertor? i may just run it if it will match my engine, probably not though.
     
  17. big83chevy4x4

    big83chevy4x4 3/4 ton status

    Joined:
    Mar 22, 2002
    Posts:
    6,587
    Likes Received:
    0
    Location:
    Sheridan, Michigan
    a diesel converter usually stalls around 1000-1200. the lowest gas converter stalls around 1400.
     
  18. imiceman44

    imiceman44 1 ton status

    Joined:
    Aug 5, 2002
    Posts:
    15,160
    Likes Received:
    1
    Location:
    Sacramento, CA
    There are some gas TC that lock up at 1250 and the diesels are 950 to 1100.
    All diesel TC have six bolts.
    You need to change the governor and the TC that is all.
    I ahve doen some of those swaps and I have talked to tranny builders, some claimed it was more and then I started asking them questions, specific questions about what and why and I explained what you would only need those 2 items and they eneded up saying oh well you could do it that way but we have different part numbers for GAS and DIESEL.
    :doah:
     
  19. aj johnson

    aj johnson 1/2 ton status

    Joined:
    Nov 2, 2004
    Posts:
    232
    Likes Received:
    0
    Location:
    Idaho Falls, Idaho
    question... I'm using a caddy 472 engine with it's early torque curve, and using a TH400 out of a M1008. which parts should I switch to get the best economy? I have both the caddy 400 and convertor, as well as the diesel one.
     

Share This Page