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One geared TH350 (No upshift) [Update]

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blazer_Boy, Sep 18, 2001.

  1. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    1981 K5 w/350/th350/np208/2.76s

    I'll try to make a long story short. I was comming a while back and the Blazer lost all upshift. It does have reverse, and is full of fluid. I just started drving the truck for about a month when this happened. Before that my mom was using it. She put on a set of 32"s without checking the gears. Well after the transmission puked I found it has 2.76s and she always ran the thing low on fluid. My guess is that a clutch assembly crapped out in it. Anybody have a clue that a rebuild would get it shifting again. I'm also putting on 235s so it wont be so bogged down. I figured I might as well drive this around in the winter instead of its current lawn ornament status.

    Thanks :)

    <a target="_blank" href=http://www.geocities.com/bigkern76>http://www.geocities.com/bigkern76</a>
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Re: One geared TH350 (No upshift)

    Stupid question maybe but is the vacuum modulator hooked up and functional? I've had more than one vehicle that would not upshift and every one was a modulator problem.

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
     
  3. 77GMC15

    77GMC15 1/2 ton status

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    Re: One geared TH350 (No upshift)

    Did you put too much fluid in maybe?

    The road is calling you.......ignore it!
     
  4. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Re: One geared TH350 (No upshift)

    Well long time no see there buddy. I had the modulator off and mananged to break the bolt. All of that "looked" alright but Im not sure though (vac lines looked good). I bought the transtar service manual (which is the GM service manual exactly with there name on the cover). It has a chart with things to check and its all either a fluid flow problem (tons of them), governor or the clutch assemblies.

    <a target="_blank" href=http://www.geocities.com/bigkern76>http://www.geocities.com/bigkern76</a>
     
  5. hammer

    hammer 1/2 ton status

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    Re: One geared TH350 (No upshift)

    check the vacume hose to the modulator. Also where it connects to the engine does it T off to something else that has a broken vacume line. Had that problem before. the tranny couldn't get enough vacume
     
  6. SWAMPRNR

    SWAMPRNR 1/2 ton status

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    Re: One geared TH350 (No upshift)

    When i was still running a 350 auto it got stuck in first gear due to a very small piece of cork off the pan gasket getting stuck in the valve body and not letting it shift.

    A BIG HAMMER CAN FIX ANYTHING.. [​IMG]
     
  7. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Re: One geared TH350 (No upshift)

    Well if you just had the modulator off and now you have an upshift problem I'd be back checking the modulator.
    Most trouble shooting charts don't take into account recent rebuilds, or other wierd mistakes. They base their diagnosis on an unmolested vehicle that begins to have the described problem.
    If you have another vehicle with a TH350 unhook the vacuum line to the modulator and go for a short drive...see whether or not its similar to the problem you're having now.

    BTW...welcome back!

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
     
  8. TorkDSR

    TorkDSR 1/2 ton status

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    Re: One geared TH350 (No upshift)

    put an air gun on the breather tube on the drivers side of the trans. unleash some air untill fluid comes shooting out the dipstick tube onto your buddy who you told to "see if this does anything" it may not work for you, but it did for me, and it was funny as hell.

    Tork DSR
    I just got a winch, it takes the fun out of things.
     
  9. BurbinOR

    BurbinOR 3/4 ton status

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    Re: One geared TH350 (No upshift)

    I would bet its a vacuum line off the modulator under the truck...........try that first. Happened to me a few months ago after my motor rebuild............very simple fix!

    <font color=blue>'79 ONE TON TPI K5 - See it at---&gt;<a target="_blank" href=http://www.blazzinor.rockcrawler.com>www.blazzinor.rockcrawler.com</a>
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: One geared TH350 (No upshift)

    Do you mean that there is NO forward gear, or just 1st and reverse? if you've got a forward gear, try driving it while shifting through all other forward gears, repeatedly, and quickly. A "sticky" governor will make the tranny stick in one gear (like 2nd) and shifting like that attempts to free it. My TH400 did this, and after shifting it like that a few times, it freed itself up, and never did it again. That would be the easy fix. But low on fluid, thats gonna hurt everything internally..if you get no forward gears, time for a rebuild.


    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</a>
    No anti-theft measures on your truck? No pity when its stolen
     
  11. Zepplin

    Zepplin 1/2 ton status

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    Re: One geared TH350 (No upshift)

    My TH350 did the same thing. I checked everything out underneath and all the vacuum hose were in place. Unfortunately, it was burnt out clutches because I only had low gear. Time to find a TH400!

    74 Blazer
    Zepplin
    Check out my Blazer<a target="_blank" href=http://community.webshots.com/user/zepplin1976>http://community.webshots.com/user/zepplin1976</a>
     
  12. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Re: One geared TH350 (No upshift)

    Well I was bored this weekend so I decided I tear something apart. I took out the transmission because it looked like my vacuum line was alright. I yanked it out and when the fluid started to spill out it could be described as more of BBQ sauce then Dexron. Really brown and stinky. Sooooo, looks like its cooked inside. I took in to be rebuilt and should have it back next weekend. Getting a new lock up convertor just for the hell of it too.

    <a target="_blank" href=http://www.geocities.com/bigkern76>http://www.geocities.com/bigkern76</a>
     
  13. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Re: One geared TH350 (No upshift)

    I take it it's a TH 350C?

    Tim
    '84 Chevy K10, lifted, loud, fast, and 3/4 ton axles
     
  14. Mudzer

    Mudzer 1/2 ton status Author

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    Re: One geared TH350 (No upshift)

    Sounds like your vaccum line popped off the modulator or off where it connects to the intake.

    Mudzer 1978/91 K5
    <font color=blue><a target="_blank" href=http://www.mudzer.rockcrawler.com>www.mudzer.rockcrawler.com</a></font color=blue>
     
  15. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Re: One geared TH350 (No upshift)

    Yup it's got lock up. I have no idea if thats a detrament or not but without overdrive its nice to have it on the highway. Never really had a problem with, its worked up until the upshift troubles. I've been over that modulator and vacuum since last july and there's no leak. I'm pretty sure with the fluid that bad looking when I dropped it that the clutches are burned out in it. 2.73 and 32"s in hindsight were not a good combition. Oh well, back to fun little 235 doughnuts till I get some 3.73s in the truck. Hmm, 2.5 shackle flip sounds good too.

    <a target="_blank" href=http://www.geocities.com/bigkern76>http://www.geocities.com/bigkern76</a>
     
  16. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    I got it back from the transmission man and found out all the dirt. The one thing I wrote off because I was to lazy to check it was the problem, the governor. The whole thing just flew apart, kinda funny lookin' cause he kept the old one to show me. The tip of the input shaft was worn down and the o-ring didn't seal well so I got a new shaft. The clutches were also burnt and starting to look bad.

    So, I got an overhaul and new convertor for $315, not to shabby if I say. It took me all weekend to put it back in but I had absolutely no help. I also found out I can bench press an NP208 transfer case into poisition and not have it fall on top of me. I threw in some stop leak to fix a very mild head gasket problem for now (temporary). I got to try some GM top end cleaner on my motor too. I got about 1/2 through the can when it was like someone turned a switch and the motor was as smooth as could be. I put on some new brakes and checked some other knick nacks that need attention after 15 months stationary.

    I pulled it on the highway and it has all three gears and the motor didn't miss a beat. I'm kinda proud of myself because the poor truck sat there for over a year and its future looked to be the scrap heap, not now thank God.

    <a target="_blank" href=http://www.geocities.com/bigkern76>http://www.geocities.com/bigkern76</a>
     

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