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Rebuilding a TH400

Discussion in 'The Garage' started by 6.2puller, Sep 2, 2006.

  1. 6.2puller

    6.2puller 1/2 ton status

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    SO I am rebuilding the TH400 in my 88 V3500. It sits behind a very mildly built 454 and used for towing 10K trailer loads frequently.
    I plan on a new larger tranny cooler, pressure guage to go with the temp gauge (pump failure killed this one) and the basic rebuild with new seals and friction plates.

    Would you run a synthetic fluid or what?

    Should I remove the "in radiator" part of the cooler routing or leave that for cold new england runs?

    So far I just have a basic rebuild kit. Anything else you would do while in this thing?

    My convertor was replaced with the motor work about 10K miles ago. Leave it alone, or replace with a higher than stock stall or.....?
     
  2. hack500

    hack500 1/2 ton status

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    from all I've read and understood you should keep the converter at the stock stall speed if you're going to be towing. I'd still use the radiator in the cooling loop especially since you say it'll be run in the winter.
     
  3. 76zimmer

    76zimmer Flyin Rat Premium Member GMOTM Winner

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    I would replace the convertor with a new one if you had a pump failure, it may have contaminated the convertor. There are also special convertors for towing available.
     
  4. 6.2puller

    6.2puller 1/2 ton status

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    The pump started whinning loud then the tranny started slipping. It still engaged but did not pull away firmly, it was slipping. Replace the converter? I was thinking that it was good since the tranny still engaged. Is their a way to test it out of the truck?
     
  5. diesel4me

    diesel4me 1 ton status Premium Member

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    crude tests..and flushing fun..

    A tranny guy can "test" the one way stator clutch in the converter,by the way it feels when spinning it with his fingers--it should only engauge in one direction..takes experience to tell if its not working correctly..

    I'd definately either flush the converter on a flushing machine,at the least!--or get a towing converter ,they are not too expensive..there is bound to be bits of metal and clutches floating in the converter that'll wipe a new tranny out in a few minutes!...the vanes in a converter are easily damaged--its best to replace it if your going this far..

    I've heard a clogged or restricted tranny cooler is responsible for many pump failures..also puts excessive force on the converter,causing it to "balloon",and push on the crank,leading to wiped out thrust surfaces on the crankshaft..remember to flush the cooler(s) too!..and the lines!..


    My friend had a 2001 Dodge Caravan towed to his shop recently--with a "blown" tranny--it was making a loud whining noise,and shifted sluggishly into gear,and slipping when attempting to drive or back up...he gets a "good used" low milage tranny,and installs it..

    After its all done,he starts it up,and adds fluid to top it off...it starts to whine ,just like the "blown" tranny was!--then when he takes it for a short test ride,its slipping worse that the "blown" tranny was!--and when he returned it was howling like a police siren!..

    He pulls it inside,puts it on the lift--pulls the pan off,to see if its filter might be clogged--to our suprise,no dirt,or other debris in the pan,and no filter blockage...we wonder whats up,it worked tits in the van we pulled it from,we drove it and it felt fine--had 58,000 miles on it!..

    I asked him if he flushed the tranny cooler,and his face kinda paled!--he said "no,I forgot all about that!":doah: :blush: ..we pull the hoses off it,and no fluid pours out...hmmmm!...even the AIR HOSE would not blow thru it!..:eek1:

    Next day,he gets a new cooler from the Dodge dealer..about 100 bucks--we put it in,and the tranny is quiet as a church mouse..shifts perfect--no slippage!...:rolleyes: --I'm still wondering if the "blown" tranny really was--or if the plugged cooler made it appear to be junk???....:crazy:


    :crazy:
     
  6. 85-m1028

    85-m1028 1/2 ton status

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    Get the master rebuild kit with the heavy duty tow option, comes with stronger front band and lower stall converter. Always a good idea to put a shift kit in "I like the Trans-go kits" and a stack plate cooler routed through the radiator cooler first.
     
  7. 6.2puller

    6.2puller 1/2 ton status

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    I thought the reason for the tank in the radiator was to warm the tranny fluid on cold days. Tranny fluid isn't that much warmer than coolant on a hot engine I doubt it does much for cooling. Based on this wouldn't it be better to run it through the cooler first than the coolant?
     
  8. 85-m1028

    85-m1028 1/2 ton status

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    the radiator cooler can lower the trans fluid temp usauly about 10-15 degrees once its hot. The radiator cooler will help to get trans fluid up to operating temp quicker. A stack plate cooler doesn't really start cooling until the fluid is really hot "cold fluid is bypassed through the lower plates". This is my theory on routing through the radiator first, I don't think it matters much "But it's debatable".
     
  9. alec78

    alec78 1/2 ton status

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    85-m1028 is right. Any tranny cooler you can add to the system is an auxiliary. It is extra. First off, as liquid being denser than air, removes heat better than air, so you keep the in radiator cooler. Second, the aux cooler provides additional cooling so it comes after the radiator cooler. That is how it was explained to me at GM's training center.
     
  10. Storm Trooper

    Storm Trooper 1/2 ton status GMOTM Winner

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    Put a shift kit in it. Tranny's last longer and work better with a tight shift.
     

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