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Transmission issue

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by YaleChevyMan, Jun 24, 2001.

  1. YaleChevyMan

    YaleChevyMan Registered Member

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    I've got a question for you. I have a 1990 full-size Chevy Blazer with the 350 and the stock automatic transmission. A couple weeks ago I installed chrome valve covers and custom gauges on my truck. The next time I drove it, I noticed that the transmission was not locking up properly (it shifted through all 4 gears, but the torque converter seemed not to lock up). This would happen intermittently, and it would often unlock spontaneously. I brought it to a transmission shop, and they replaced the lock-up cylinder, with no improvement. I have since been told that I need a complete transmission rebuild.
    Now, I dont really know how the lock-up works, and I've been wondering if in fighting with parts around the throttle linkage while installing the gauges and valve covers I might have done something to cause this intermittent behavior. Is this possible, and is there anything I can check? Second, I've been told that I can pull a plug on the transmission to disable the lockup entirely so that it will not act so unpredictably. Other than the sure decrease in gas mileage, will I notice any decrease in performance by doing this? If you could give me some pointers, I'd appreciate it.


    P.S. Any idea what the maximum recommended RPM for that engine is? Thanks.
     
  2. bablazer73

    bablazer73 1/2 ton status

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    If you disconnect the plug, you will not have the lock up. BUT. you also should not use overdrive. The problem is when the torque converter is not locked. It generates alot of heat from the slippage. also when the trans is in overdrive, it gets worked harder at lower speeds. Also causing heat. Between these 2, and the problems with these trans burning up, I wouldn't recommend it unless you don't use the overdrive or have a very big cooler added on. I don't think you did anything when you worked on it. At least I can't think of anything. I would bring it to a different tranny shop though. 2nd opinion.

    your right. I don't understand the jeep thing!
     
  3. Thunder

    Thunder 3/4 ton status

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    With all the work you did on the top of the engine you may have knocked the TV cable out of adjustment. It is the cable next to the throttle linkage that goes down to the tranny. If it is out of adjustment it will change the way your tranny performs and shifts. It is important that the TV cable to be adjusted for proper tranny operation. Out of adjustment also cause tranny failure.
     
  4. WOODYJ

    WOODYJ 1/2 ton status

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    I will second the post on the tv cable not being adjusted right. If you were working on your valve covers, that is the perfect time to pull a tv cable out of socket or get it out of adjustment. It is easy for those a__ holes to tell you you need a complete tranny rebuild---who makes any money there. Go back and really check the tv cable and I think you will be surprised at what you will find.

    k5woody I Don't Understand The Jeep Thing Either!!!
     
  5. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Check for vacume leaks also. If the modulator percived a drop in vacume it might think your getting ready to get on it and it's getting ready to down shift. It will unlock the converter. Just never gets the TV cable inpute to do the down shift.

    It's not my damn planet monkey boy!
    Grim-Reaper
     
  6. 84_Chevy_K10

    84_Chevy_K10 Banned

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    That's not a modulator, 700R4s don't have vacuum modulators. It's an electric vacuum switch for your torque converter lockup.

    Look by your washer pump and make sure that vacuum line is hooked up. That switch is what tells your tranny it's time to lock up the torque converter.

    AND check your TV cable, but I'd bet it's the vacuum switch if it won't lock up at all.

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

    YaleChevyMan Registered Member

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    I understand what you guys are telling me, but..... I looked at all the cables near the throttle linkage, and all look to be in their sockets just fine. Also, I have to emphasize that this problem is intermittent, and the transmission sometimes locks just fine, only that it will pop out of lock on its own randomly. Also, all the actual shifts are fine, and i would have to believe that the transmission would not shift right if the cable were out of adjustment. Right?
     
  8. 84_Chevy_K10

    84_Chevy_K10 Banned

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    You're correct. If you messed up the TV cable, it wouldn't shift right.

    I still think you've got the disconnected vacuum line to the vacuum switch by the washer pump. Check that out and tell me what you think.

    Tim
    '84 Chevy K10, lifted, loud, fast, and 3/4 ton axles
     
  9. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    Mine started doing something like what you are describing. After failing to find something external from the tranny, I just drove it. My next symptom was total loss of compression braking. Something (sprag) blew in the tranny.
    At any speed with no throttle I could move the shifter thru all forward gears with no effect. Sucked also cuz I had to go down Mt Ashland summit with only brakes!

    Dave

    BEER: It's not just for breakfast anymore.
     
  10. Wheels

    Wheels 1/2 ton status

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    Have the tranny shop put a gauge on it. You should have 250 lbs + with the shift selector in second with the brakes applied and the engine at 2000 rpm's (just above stall speed on the convertor). If not, you have a line pressure problem and the TV cable could be bound up or the TV valve is stuck or the line bias valve is stuck or wear in the tranny is bleeding pressure. You can bypass the vacuum switch and see if it works. You'll only have lock up when the pressure from the pump is sufficient to allow the lock up signal to apply the voltage to the solenoid. If line pressure is down, then lock up will not occur. The TCC in the convertor could be going out also. Many possibilities here.
     
  11. YaleChevyMan

    YaleChevyMan Registered Member

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    Thanks for the vacuum tips. I'll take a look at that line tomorrow, and maybe thow some tape around the fittings just in case.
     
  12. YaleChevyMan

    YaleChevyMan Registered Member

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    Well, a week ago I taped up the vacuum connections that lead to the wipers, as u guys saiid they might be loose. It worked fine until this morning. What the hell could be going on here? I cannot have my otherwise-working truck have a broken transmission. I'm desperate.
     
  13. jarheadk5

    jarheadk5 1/2 ton status

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    Well, at this point, a second opinion from another tranny shop would probably be a good idea. I wouldn't mention the other shop at all, just act as if you're bringing it to a shop for the first time, and see what they come up with...


    If at first you don't succeed, failure may be your style...
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