96 GMC Sierra shifts but nothing happens - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 09-28-2016, 01:08 PM   #1
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Default 96 GMC Sierra shifts but nothing happens

Hello to all. I really need some help. My 1996 GMC Sierra Truck (4.3l Vortec) just all of a sudden just decided to not shift. The shift lever (This is an automatic) shifts fine when the brakes are depressed, no problem. But while shifting to any gear, nothing happens. The engine sound does not change and I can tell that the transmission is not at all engaging. So it seems that the problem is happening before the transmission since the transmission is not being told to shift. Again, no difference in engine noise and no sounds are heard when shifting, and the idle speed does not change. I checked the cable connected to the transmission and it is fine and all electrical connectors are connected. By the way, the cable that I saw coming out of the transmission is actually feeding to the back of the truck. Am I missing any other cables. I checked the transmission fluid level and it is fine. What else can it be that would be causing this issue to happen. Are there any fuses that could cause this to happen if blown. It drove fine when it was last parked and now it does not. Any help would be greatly appreciated and I would like to thank you in advance. Stacey
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Old 09-28-2016, 03:37 PM   #2
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If the truck has been sitting for several hours(cold), go out and check the trans level WITHOUT starting it. Notice the precise location of the oil level on the stick. Now wipe the stick clean and put it back into the tube. Next, start the engine and let it run for about 30 seconds. With it running, pull the dipstick out and note the oil level again. If its still at the same level, the pump is not working pulling the oil level down. If the oil level did go down from the first measurement, then the pump is working and the fault lies somewhere else.
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Old 09-28-2016, 04:50 PM   #3
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OK, so I have had a chance to look at it further. With my son at the wheel and shifting the shift lever, the part on the transmission with the cable attached is moving and shifting (from what I can tell) the way that it is suppose to. That is with the engine running and not running. Also, while it is in park, I cannot move the truck. If it is in any other gear, regardless of which gear it is in, I can easily push the truck forward (with the shift lever in reverse) and backwards (with the truck in drive). I don't think I like where this is heading. I will check the transmission level next the way that you explained and let you know what it is doing. Thanks for your response.
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Old 09-28-2016, 04:57 PM   #4
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OK, the oil level is exactly the same sitting cold without the engine running as well as the engine running after about a minute of sitting at idle speed. Is there a fuse or anything that I can check that be be the culprit if it is the pump that is not working?
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Old 09-28-2016, 10:25 PM   #5
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The pump is driven mechanically by the engine....there is nothing electrical to do with it....
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Old 09-29-2016, 03:16 PM   #6
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OK, so I am guessing that I can go with a bad fluid pump in the transmission. Can I assume that this transmission is a 4L60E transmission with a 298mm shaft? How hard will this be to remove and install the transmission, and are there any tricks or problems that I may encounter while I am doing this? I talked with a local transmission shop and he said it has been years since he has had to replace a pump. I am assuming that these do not go bad very often. Also, do you think anything else in my transmission may be messed up that I would need to replace or check. Thanks greatly for your help. Stacey
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Old 09-29-2016, 03:30 PM   #7
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I have heard of pump shafts breaking.

This is a far fetched possibility, but not that far out. Slide under the truck, remove the flywheel/torque converter inspection cover on the bellhousing and see if the flywheel is spinning the torque converter.
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Old 10-01-2016, 10:02 PM   #8
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Mike, thanks for that suggestion. As it turns out, the flywheel was not spinning the torque converter. The 3 bolts holding the torque converter to the flywheel was not attached. One was missing (backed out), one was sitting in the bottom of the bell housing (backed out), and one bolt sheared and was left in the torque converter. No telling where the head of the bolt is. It looked like the flex plate walked about a 1/4" around the torque converter. I would guess from the looks of it it has been pretty loose for quit a while to have done this damage. Has anyone ever seen this before. And there has been no work done on the transmission or torque converter.
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Old 10-02-2016, 07:49 AM   #9
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I've seen a couple mentions of this on other forums. Usually you can hear some racket while the engine is running from the flexplate vibrating against the TQ. At any rate, judging by the flexplate, you need a new one. This will require dropping the trans or pulling the engine out. While you have it dropped out, tis the best time to replace the rear main seal also. Kill 2 birds with one stone.
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Old 10-04-2016, 10:43 PM   #10
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Like Mike said, there should have been one heck of a noise as this was happening...surprised the flex plate didn't crack and really make some noise....
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