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Thread: 1993 4L80E NO reverse

  1. #1
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    1993 4L80E NO reverse

    Okay Iam throwing it out there for all to respond for I am at my wits end! After much trail and error and failed attemts to solve my trans problem I purchased a new one from the Chevy dealer. When I installed it I have the same problem. It is in forward all of the time with no reverse. I can shut it off in neutral and it will roll like it should in neutral, but when started again its back to being in forward? Because it is the same problem with the new trans as the old I am thinking there is a problem with the ecm? The gear selector is adjusted properly and it locks up like it should in park but doesnt go out of gear as it should

  2. #2
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    but doesnt go out of gear as it should


    ecm has nothing to do with reverse.
    if it happens with both trannies i would suspect linkage.
    <----just your average 5.3

  3. #3
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    John John John !!!! Why did you not come here first before you got to your wits end and spend all that money??? No its not ECM, and NO you probably did not need a new trans. Depending on how you use your truck, that should be a 150,000 - 200,000 mile trans. ECM controls shift points, and converter lock up, nothing to do with fluid passages, or manual gear selection. It does sound to me there is a linkage issue. You gear selector lever is not matching up with the detents on the manual valve in the trans. Either out of adjustment, and if not adjustable, then likely bent or some bushings are wore which I find it hard to believe they can wear that bad. Usually the most common thing that can bend that linkage is a broken motor or trans mount.
    85 Sierra Classic K1500
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  4. #4
    Senior Member gmctrucks's Avatar
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    JJ are you sure that your truck doesn't have a 4L60E on it? Maybe someone placed a wrong trans on it with a 4L60E trans harness.

  5. #5
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    When I spoke to the dealer and they asked for the VIN it came up as a 4L80. It is a 1 ton. if it was the gear selector then why does it operate like neutral with the motor off and not with the motor running? It shifts and starts only in the park and neutral positions? It may not be starting out in first either, maybe second gear? and I think one servo is first/rerverse? I was thinking the shift servos and the TCC were computor controlled. This all started about 1 year ago and I did came to this site first. its taken a lot out of me to say I am at my wits end. I just wanted to throw it out there one last time before I take it in and pay the piper...

  6. #6
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    Getting that out of the way first, yes its a 4L80-E if its a 1 ton. 1/2 ton would have been 4L60-E. That even more reason to be that it IS shift linkage that it operates like Nuetral with motor OFF, but not when ON. You can take any auto trans car or truck. Put it in first or reverse or any gear you want and its gonna roll because without the motor running , there is no pump pressure to compress cluthes and bands, therefore it actually is kinda in nuetral. True in ONLY starts in P and N, but that is decided by the column gearshift lever selector, so as long as the lever is in the P or N position the starter will turn over the motor. You can even disconnect your trans linkage all together, and as long you put the lever inside the truck in P or N it will start the motor. Servo's are not going to matter in this situation. If you are brave, and have someone you can truely trust not to kill you, chock your wheels, put the E Brake on, have someone hold their foot on the brake, start the motor, Get under it, disconnect your shift linkage, then take your hand on the lever to the trans, and change the gear one notch and you will see you have reverse, go another notch back you will have nuetral, another notch back, you will have Drive. I can not say I am familiar enough with the linkage on your truck to tell you how to fix it, but I am going to stick with your linkage is out of synch with your gear selector lever in the cab.
    Last edited by hotrodpc; 07-06-2009 at 10:35 PM.
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  7. #7
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    I would imagine your linkage has got to be very similar to others, so here is how you can tell for sure. As I had suggested above about chocking wheels and having someone inside with their foot on the brake and E-Brake applied etc. Then #1 start the truck, #2 with your linkage disconnected underneatch, with your hand on the shift lever of the trans, take it back 1 notch, and you feel the truck go into reverse, then one more to N, then one more to D. #3 shut the truck off now. #4 Get in the cab and put your shift lever into D. #5 Get back under the truck, and bring your shift linkage rod to the shift lever of the trans and see if they match up. Both places are in D and you KNOW that since you put both of them there manually. I have a feeling they are not going to match up and that is your problem right there. NOW, if its an adjustable rod or threaded end with a connector, turn or adjust it to fit and match WITHOUT having to move your shift lever of the trans. If there is a bend in the rod, take some of the bend out so it can reach if its to short, add more bend if its to long, and see if you can to make it match up perfect. Hook it back up after you both positions matched up, and I have a feeling your trans is going to work just fine.
    85 Sierra Classic K1500
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    84 Silverado C20

  8. #8
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    Here's the factory book version of that adjust.
    Thumbnails below have the step-by-step.
    If that doesn't get it, pull the codes and
    visually check the harness back to the ECM.

    Attached Images Attached Images       

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    Awesome diag s Crab. So its adjustable at the column under the master cylinder it appears. The method they describe for adjustment is about identical to what I suggested with exception they say to use N instead of D. I agree to use N too, but I always suggest D, so that you can confirm you are in D when you feel it kick in where as N you do not get any confirmation. I also like D because on an OD trans, its more in the center of the spectrum. If you are on target in the center of the spectrum, then you should be on target on both ends of the spectrum too, being P at the top and 1st at the bottom. But, nevertheless, follow the procedures set out by the dudes who designed the vehicle and all should be well.
    85 Sierra Classic K1500
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    84 Silverado C20

  10. #10
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    Thank you all so very much for the bits of encouragement! I will chock the front wheels and jack up the rear end disconnect the linkage and see what happens, first thing this morning. I will write back with the findings. THANKS again. John

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