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Diesel Tranny behind a 350 TBI

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BadDog, Dec 28, 2001.

  1. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Ok auto gurus, I've got this TH400 that was behind the 6.2 and now lives behind a 350 TBI. I have a few questions.

    I still have the diesel torque converter in there. I'm thinking it might be good with the low stall unless it drags on the engine too much at low rpm. Kinda waiting to see. Any thoughts?

    I know that for street driving people recommend changing out the governor but I don't know about off road. Again, just waiting to see. Any thoughts? If I should change it, anything I should look for?

    I'm also thinking a manual valve body may be in my future.

    I have not had it out on the road but the previous owner said that he worked at a GM dealership and had their tranny expert (his friend) "build it up" and put in a "shift kit" along with complete rebuild "with heavy duty components". Now, the reality of that and what it really means is anyone's guess. He couldn't give specifics and had no paperwork on it so I basically discounted it from my consideration. However, the tranny shows all new seals, gaskets, recent thorough cleaning, etc. indicating it has been opened up and probably rebuilt. All I can say is that it works great in my back yard.

    So, any thoughts or recommendations on this? Converter suggestions, governor options, manual valve body, whatever? I know my way around autos fairly well, I've run them in many trucks and I'm not afraid to go into them (I even rebuilt one with the help of a manual, no big deal). Basically, I just want to know what the change from 6.2 to TBI 350 means for this tranny (since I know nothing about the diesel tranny changes).

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  2. 4x4_76

    4x4_76 1/2 ton status

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    I would change the torque converter.Other than that,I don't think that there's not much difference between diesel and gasser trannys.

    I'm too lazy to stick shift,that's why I prefer autotranny.
     
  3. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Yeah, I debated that and went back and forth on it for the 2 weeks or so it took me to find an engine. At the point where I bought the engine I was leaning toward, "I got it, I might as well try it" and then the engine was in making it a non-trivial issue. The only reason I considered running it is that with my old '75 Blazer (454/built TH350/205) I had some mild troubles when in big rocks, shelves, etc. where the engine would run up to about 1000-1500 while sort of surging and then all of a sudden "WHOOM" here we go. I didn't build that tranny but it was supposed to have a basically standard converter for 4x4 (it wasn't stock but not high stall either. It worked pretty good, I just hated that "I wanna go but can't" feeling followed by "hold onto your ass cause were goin' somewhere!" I blamed the converter for that feeling because the tranny was solid as a rock, shifted hard, never slipped, never burned fluid, and ran like a screaming banshee on the street with no weird behavior. Just easing up to obstacle. I read somewhere that a low stall converter would correct that behavior and, so, here I am. Smart thing to do would have been to ask before I put the engine in. But, I've never been accused of being particularly smart...

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  4. HarryH3

    HarryH3 1 ton status Author

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    You'll want to change the weights and springs in the governor. Diesels typically upshift at WOT around 3,000 rpm. While that drops a diesel right back into its torque curve in the next gear, it'll drop a gas engine back below the torque curve, and you'll never reach the HP peak of the gas engine. You'll want it to upshift more in the 4,500-5,000 rpm range at WOT.

    <font color=black>HarryH3 - '75 K5</font color=black>
    <a target="_blank" href=http://www.angelfire.com/super/ThunderTruck>www.angelfire.com/super/ThunderTruck</a>
    It's a great day to be alive...
     
  5. 4x4_76

    4x4_76 1/2 ton status

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    Oh yeah,I remember reading it too,might been a 4WOR,that using a low stall converter works good on rocks.If you use your truck mainly off-road,then diesel converter could stay there.I guess.
    To be honest,I read way too much,so when I need some info,I get confused all the stuff I've read,and I have to find some specific article and read it again.

    I'm too lazy to stick shift,that's why I prefer autotranny.
     
  6. pcorssmit

    pcorssmit 1/2 ton status

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    My experience is with 700s, but, I still run the diesel converter in mine. The accumulators springs are different in the diesel trannys, I think I changed mine out, not sure though. The converter works great for rockcrawling, its certainly tolerable on the street but I've always thought I would be better on the street with a gas converter. One thing I really do like about the trans, as far as off-road, is that when you put it in gear, it doesn't pull hard at idle, on a slight uphill it won't move w/out throttle. Part of this is probably also the low idle of the TBI motor. When you put it in gear, it doesn't jerk the whole vehicle like a lot of trannys do.

    I also changed out the govenor in mine, made a big difference on the street, I guess off-road too but not as much. I used a govenor out of a police package caprice, slightly higher shift points than a truck one but not as high as a Z28/Vette one (I was told and agree that my motor may have trouble with WOT shifts that high, ie it would have delayed shifts since there isn't much power at that RPM). It won't hit OD till about 55 mph or so. However, the tranny is pretty well smoked now and I need a new one. Really wishing I could start over on the drivetrain with a 454 TBI, 4L80E, 205, and top loaders (don't think I'd need the doubler with 6.72 gears). It always sounds good, then I look at the oil pan clearance. Darn.

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    I'd say run it and see how YOU like the way it shifts. Governor would be the only thing I might consider modifying, but since the tranny doesn't have to come apart (or likely removed from the truck, check that first though) it's something that can be messed with later on, with little hassle. You can always use the shift handle on the street, thats what its there for.

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>www.dorianyeager.com/index2.html</a>
    Why insist on counting when the ring gear has the tooth counts stamped in?
     
  8. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Thanks Pete, great info as always. I'll look for that Police Caprice governor if I notice any problems. Other than that, I'll just run it I guess.

    Hehe, we seem to think alike. I was checking into a pair of steerable top-load 2.5s recently (you may have seen my post on pirate). I really wanted the 2.5s for the gears and the ability to easily run 48s (gear, strength, and cheap/common wheel wise). Sanity finally won out though. I've got so much left to do to this truck (heck, I just got it running finally) and the 2.5s would just have delayed me using it even more as I dealt with all the fab/modification issues to mount them. That or they would be sitting around in my back yard for a year or so (given my pace on this thing). The final straw was the pinion clearance issue, especially with pinion brakes. I really want to avoid excessive lift. The most I'll even consider is 6", and I plan on using no more than 4" (maybe with a 1" zero rate for 5" total). From what I could figure out, looks like the Rockwell pinion/gear reduction will require a minimum of 8" lift to clear the oil pan (in stock location) if you expect to have any significant up travel. Otherwise you wind up with the springs about 2" from the bumpstops. So, for a change, sanity won out and I passed on the axles.

    I still second guess myself sometimes, especially since I have not yet found any tires. I would go with the 48s anyway but I'm afraid that will be like running 40s on a C10 and my gears are not deep enough. At a minimum I would need to go D70 rear and somewhere around 5.8:1. At that point, the 2.5s (price wise) start looking much better. But then there is the clearance thing. And so, round and round I go...

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  9. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Yeah, that's pretty much what I had decided on already. I just wanted to get an idea what others had encountered or thought about it. I'm not about to make any changes till I get a chance to try it out. Thanks for the input.

    Anyone have any experience with manual valve bodies in a TH400? I haven't priced them yet but I hear they are pretty expensive.

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     

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