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What Part of my Tranny is Messed Up?

Discussion in 'GM Powertrain' started by Crawdaddy, Mar 30, 2008.

  1. Crawdaddy

    Crawdaddy Epic Member Staff Member 5+ Years 1000 Posts Platinum Contributor

    Hrm, where to start... Well, as I'm sure ya'll know, I replaced my transmission because my previous one burned up (see http://www.gmtruckclub.com/forum/showthread.php?t=9192 for more information on that). So, my uncle and I put the new rebuilt transmission in my truck and things started looking up. Before we put the rebuilt tranny into the truck, we filled the torque converter as best we could. I followed the procedure in the haynes manual to readjust the TV cable, in fact, I started from scratch and readjusted the cable 3 times to make sure it's right. From mile 1 with the new transmission it seemed like it shifted a little bit late from 1st to 2nd gear. Well, Friday night I went and picked up a very light 5x8 box trailer. I then loaded it with a fridge and dryer, nothing heavy and towed it around 50 mins away. About halfway through, the transmission seemed like it was shifting later and later for 1-2 and 2-3. It got to the point where it would shift from 1-2 at around 25mph and 2-3 at around 50mph. It barely ever got into 4th gear at all. At that time, I pulled into a gas station and checked the tranny fluid. Well, it was a TINY bit low, so I bought a quart of tranny fluid and filled it up. That didn't help anything. I got the truck home through lots of taking it easy. I did get it into 4th gear on the interstate through lots of coaxing. My buddy who went to school for trannies, but hasn't worked on one in a while, thought it could possibly be either a bad torque converter or a check ball, spring or servo that is dislodged or broken in the valve body. Any ideas as to what's screwed up in the tranny? I'm clueless, but something's messed up.
  2. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    That sucks.
    I think your buddies got the best diagnosis on this problem.
    Did you replace the torque converter with the tranny? Not required but you did have a high mileage drivetrain so it would be recommended.
  3. Crawdaddy

    Crawdaddy Epic Member Staff Member 5+ Years 1000 Posts Platinum Contributor

    The torque converter was replaced at the same time as the tranny with a rebuilt torque converter from the same company. Any ideas as to where to start looking? Should I got for the torque converter or valve body first?
  4. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Check the valve body first. It can be accessed by dropping the pan and filter. The Torque convertor requires the trans to be removed.
    Also check the vacuum module, I dont think its the problem but it wont hurt to check.
    Spray carb/injector cleaner around the vacuum hoses while the engine's running to see if they developed a leak.
  5. Davandy

    Davandy Moderator 5+ Years ROTM Winner 1000 Posts

    It sounds like a vacuum leak :neutral:
  6. Crawdaddy

    Crawdaddy Epic Member Staff Member 5+ Years 1000 Posts Platinum Contributor

    the TH700R4 for my year/truck does not have a vacuum modulator, or any modulator for that matter. The only connection that is present from the motor to the tranny is the torque converter and the TV cable.
  7. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Forgot youve got the electronically controlled trans.
    Then it's down to the Valve body and the Torque Converter.
  8. ChevyFan

    ChevyFan Administrator Staff Member 5+ Years 5000 Posts

    Sorry to hear you got troubles, that stinks becuase I know you worked hard on this and were looking forward to it. Let us know what you find out.
  9. Crawdaddy

    Crawdaddy Epic Member Staff Member 5+ Years 1000 Posts Platinum Contributor

    Tim, I don't know how the hell my tranny knows what to do, it's not computer controlled and it's not vacuum controlled. All the connections that were made to the tranny was the gear selector lever, speed sensor output, reverse gear sensor, tranny cooler lines, dipstick tube, TV cable, torque converter, bolting it to the motor, and that's it. At my first bit of spare time, I'm going to drain the pan and pull the valve body. I need to find a good supplier of all the hard parts in the valve body for a reasonable price. And, I guess while I'm at it, I'm going to get the shift kit I've been wanting to get and add that in. I wonder how much a brand new valve body would be....
  10. Crawdaddy

    Crawdaddy Epic Member Staff Member 5+ Years 1000 Posts Platinum Contributor

    OK, after it raining so much for the past 3 days, I finally had time and decent weather to get something done on the truck. I went and readjusted the cable at the throttle body. Well, it seems to drive and shift about as well as when I first replaced the transmission, so that's good. It just still doesn't quite seem to be right yet though. I'm following the adjustment procedure to a Tee as far as I know. I'm considering pulling the motor since it's got near 200K on it and it seems like it's on the decline ever since the tranny died. If I pull the motor, the tranny's coming out with it. Judging from the results I got with the TV cable, I think it's still an adjustment issue. Should I just ignore it for now till I rebuild, or should I fix it now? Any ideas on how to get it right? It seems like it's sooo close, but far enough out to be a pain.... Thanks as always guys!

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