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TH400 rebuild suggestions/prices/etc

Discussion in 'The Garage' started by k20, Apr 12, 2004.

  1. k20

    k20 3/4 ton status

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    Ok, lotta questions gonna be in this. Anyway, my tranny is leakin like a sieve, and its starting to be a pain to get into reverse. Also likes to slip alot in Reverse, like if i got my back tires in the gutter forget backin out of it. Just for reference I have a 496MPFI, call it 450hp, and 640tq, peaking tq at 2000-2500rpm and hp at 4k-4500. Least according to Desktop Dyno. This is the HD case th400 I have. I have a 36 case th400, but I have heard the HD case is thicker. (the HD or the 36 is stamped into the bellhousing area).
    1. What internal parts should I swap
    2. What stall converter should I go to (stock seems to be good, but I dont know what I would gain, its a DD, mud/trails, hauling truck)
    3. Im going to have a stage 2 shift kit, unless that will put unnecesary wear, then I will go stage 1.
    4. Any brand of parts better than others, B&M, TCI, etc.
    5. Wont be doing this myself, will pull and install myself, what would be approx cost with all the goodies mentioned above, shop labor, parts, seals, etc..
    6. Should I pull it with the t-case attached or take t-case off first.
    7. Should I run synthetic tranny fluid after I rebuild it? 8. Is there a break-in period on a tranny like on an engine w/ no synthetic?
    9. Which type of tranny cooler is better, a stacked plate, or a tube and fin. I already have a tube & fin for my oil cooler, a 6 pass permacool, should I get same type for tranny or is one of the B&M stacked plate style better.
    Thanks guys, I know this is long, but answers are much appreciated. Chris.
     
  2. daleearnhardt01

    daleearnhardt01 1/2 ton status

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    Thats sucks to hear Chris....

    Chris
     
  3. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Lots of questions, I'll tackle a couple. I would talk with a reputable local shop, and have them rebuild it with an eye on strength. A pretty big cooler that still fits in front of radiator is the best idea , most parts stores stock them. As for the shift kit, it wouldn't make it wear out faster. Soft cushy shifts generate more heat, when shift kitted vehicles snap into gear faster , it produces less heat due to less slippage, so shift kit is great idea. Thats what I know /forums/images/graemlins/k5.gif
     
  4. dhdescender

    dhdescender 1/2 ton status

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    Give the Tranny to the shop w/o the T case, they Don't need it.

    if you don't have one already, get a pan with a fitting for a temp gauge.
    You'll want to upgrade the sprag to a 32element sprag, and possibly upgrade your clutch packs.

    A shift kit is a good idea, although they do wear driveshafts and driveline components from the jolt the tranny will give.

    If your after a reverse manual valve body, now's the time to do it.

    I went to a Allison 540-3 Severe duty convter, it has a welded steel stator, billet splines, and brazed fins. It was $360CDN.

    You'll want a stacked fin style tranny cooler, and the higher the GVW rating the better. The B&M's are good, and they're a good price.
     
  5. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    Turbo 400 in Reverse only uses the direct clutch and the Low/Reverse Band. So one of those things is worn...
    The only other time the direct clutch is on is 3rd gear, and the only other time the low reverse band is on is when you drop it down in Manual Low..
    If you think you've gotten any slipping in 3rd gear i'll bet its the direct clutches...
    If you drop it in Manual 1st... Get going up to 25mph or so, let off.. and if you have little or no engine braking.. i'll bet its the low/reverse band.

    Behind that kind of power I'll bet its the direct clutches getting burned in 3rd gear. I've toasted those clutches in my camaro behind 550HP 550FT/LBS. With a 3000 stall converter, a stage 2 shift kit and a modulator that barely works off of no vaccum, it was always searching for a gear when i'd leave it in 3rd or D. I decided to put in a TCI manual valve body so both the transmission and myself would always know what gear it was in. No more slipping and hunting for a gear.

    1. One thing you can look into, B&M # 130-20279 $60 TH-400 intermediate sprag. This basically replaces 16 one way rollers with 34 of them so it increases torque capacity by 110% they claim. However you must use a '65- '69 th400 intermediate sprag drum.
    ...Another cool thing to do is put in the lower planetary gearsets. TCI # 890-227500 $365... Gives you a 2.75 first, 1.57 second.
    ...Another thing you can do is have them add a clutch/steel to each clutchpack- measure clutchpack clearance, then write down and measure each clutch and steel... THEN you can do some math and order two thin undersized clutches/steels to replace 1 thick one and still be within spec... That way you can maintain clutchpack clearance add an additional clutch and steel for more torque handling. /forums/images/graemlins/thumb.gif
    2.RockCrawling=stock conveter. DragRacing= 2000-2500 to match your peak torque. To compromise, a 1800-2000 converter might be nice.
    3.B&M stage 2 shifts nice and hard, chirps 2nd a lot. The problem is it still depends on the vaccum modulator for the load signal. If you have a big cam and no vaccuum the tranny will always shift very hard and late.
    In my case, the Manual valve body shifts not quite as hard, but feels even more solid through the upshifts, since it eliminates the vaccum modulator signal. Just what i was after. Only downside is full manual in gear will always run almost max line pressure, great for holding those clutches up to serious power, but not as fuel economic for a daily driver.
    4.I've been happy with both B&M and TCI parts. The B&M rebuild kits are supposed to be their high performance racing clutches but they have "Raybestos" printed right on the clutches. /forums/images/graemlins/rotfl.gif
    5.Clutches, Bands, Seals, Bushings, ~$150, Conveter ~$150 Shift kit~ $50. More for any other worn parts... Another few hundred for labor... probably $700+.
    6.If you have a good tranny jack that you trust, pull em together. If your using a floorjack and a block of wood like me, i'd pull the t-case, then the tranny.
    7.I just run ATF fluid and not worry about it.
    8.Stacked plate, as big as you can get. And a tranny temp gauge.
    /forums/images/graemlins/thumb.gif
     
  6. Nonesuch

    Nonesuch 1/2 ton status

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    [ QUOTE ]

    You'll want to upgrade the sprag to a 34 element intermediate sprag

    [/ QUOTE ]

    I fixed it for ya /forums/images/graemlins/thumb.gif

    Get yourself a book on auto tranny rebuilds and give it a read. Shouldn't cost you more than $15 bux or so. Then decide if you want to try and rebuild it yourself. I would if I were you. /forums/images/graemlins/grin.gif
     
  7. k20

    k20 3/4 ton status

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    [ QUOTE ]
    However you must use a '65- '69 th400 intermediate sprag drum

    [/ QUOTE ] Where would I get this part at?
     

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