Transmission not shifting correctly - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 11-21-2007, 09:45 AM   #1
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Default Transmission not shifting correctly

Hello all,
It appears that in addition to my fuel economy issue (and probably what'* a good part of it), my transmission is not shifting correctly. This trans has 110k on it, is original, and is currently mated to an L36 that was rebuilt with less than 500 miles on it. There are times when it will not lock the converter on the highway unless I am hardly giving it gas, but recently it has been the opposite. The car does not jump off of the line when you lay your foot into it, it just starts humming around 2k rpm, and the engine finally overcomes the inertia of the car to get the going. The car does not down shift as needed when given gas up to 3/4 throttle, but will operate normally if you floor it. It bogs down and when going up a hill, the trans will not downshift unless it is nearly floored, and the car begins to go really slow with no power due to being stuck in a high gear. It appears there is a certain adjustment that is not correct, anybody know what it is? This thing isn't dead, its just not adjusted right. I will also be getting a flush.
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Old 11-21-2007, 10:03 AM   #2
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With an original tranny with that many miles, I would not suggest getting it flushed, but just a tranny fluid change. Drop the pan, change the filter, see what color the tranny fluid is.

Sometimes, by flushing your tranny completely, you can make things worse.
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Old 11-21-2007, 11:30 AM   #3
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I woudl say change teh fluid and filter. It sounds like it'* not getting pressure. Have you checked your fluid level?
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Old 11-21-2007, 11:36 AM   #4
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No, haven't checked it. This isn't like me, its just that I got this car from my uncle and he just got done putting a brand new engine in it. Normally when I get a new car I give it the works, ALL the fluid gets changed, all wheels are pulled to inspect the brakes, tune up is done, and all filters are changed, problems are tended to, etc. I was under the understanding that this car would be good to go, but I guess we got some bugs to get worked out. I know this trans is electronic, but my uncle said it had a vacuum modulator on it, does this require adjustment? Are there any parameters that can be adjusted?
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Old 11-21-2007, 02:51 PM   #5
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it sounds to me like it'* fluid level, so the torque converter is startgin for fluid and is slipping, I could be wrong, but that'* my first impression.
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Old 11-23-2007, 12:02 PM   #6
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A few days ago I checked it on a flat surface with the engine running. The level read about 2.5 inches higher than the crosshatching . I immediately parked it and have been driving my Z28 until I have time to pop one of the cooler lines to let some of the fluid out. Could this excessive fluid have been causing a "hydrodynamic" drag, costing me fuel economy, bad shifting, and of course possible transmission damage? I am assuming my uncle added too much fluid when he poured it in the converter upon installing the new engine.
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Old 11-23-2007, 12:22 PM   #7
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Too much fluid can cause as many problems as too little. The difference is that too little fluid can cost you your transmission, where too much probably won't.

What did the fluid look and smell like (after driving a short distance to stir it up)? I won't make you taste it.
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Old 11-23-2007, 12:33 PM   #8
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It looked like it could have probably used a fluid change. There were also a few bubbles along the dipstick (not many though), I am assuming that the fluid could have been whipped up by some rotating parts/axles. I was under the impression that too much fluid could submerge some of the valve assemblies and cause some weird things to happen. I checked the fluid right after a decent length drive. As for the smell, it really didn't smell like it was burnt or anything.
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