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Old 06-13-2013, 09:41 AM   #1
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Default 4t60e not down shifting under a load

1995 Bonneville 3.8L II

Well, its time to address the elephant in my car: from dead stop, in 4th gear or 3rd gear, sluggish acceleration. Can down shift into 1st gear and zoom! When starting in 2nd gear is hard to tell but I don't think it is starting in 1st from dead stop; feels slightly sluggish. When going into 4th gear it seems, rpm wise, to be in 3rd gear so I don't think I have 4th gear. Also the gas mileage is lousy: will get 16mpg for awhile and then bang, 24mpg, and then bang, 17mpg. I replace the fuel filter and drained trans fluid and replaced filter. The fluid was almost black! I am going to replace fluid and filter again this summer but I wanted to hear from a trans expert if maybe I should replace shifter solenoids or anything else while under the car.
Any advice would be helpful.


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Old 06-13-2013, 09:35 PM   #2
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Any chance you could get it checked for codes? Even though your CEL isn't on, you could have a pending code that might lead us somewhere.

If your fluid was black, then it was probably burnt and most of your clutch material is in the oil. Which was drained out the last time. And, nothing else besides the filter can be changed out via the bottom pan, all of the other solenoids are in the side pan, which requires dropping the trans halfway out.
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Old 06-14-2013, 08:06 AM   #3
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The CEL is on, forgot to mention that. When the tran is cold it seems to be less sluggish. Is there any problem with flushing? I saw a video on u-tube and thought it might be a good way to go. When the trans is in gear there is no problem other than sluggishness; Is it possible that the electrical connectors to the tran could be corroded?

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Old 06-14-2013, 10:10 PM   #4
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Well, if the CEL is on, then everyone here will suggest to get it scanned for trouble codes. Can't do much more until we get the codes.

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Old 06-15-2013, 12:18 AM   #5
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It would be best to obtain all the codes including engine, body,transmission etc.
Some transmission stores may perform this for free.
How many miles on this vehicle?
When was the last time a full tune up was done including spark plugs etc.
One thing is for sure trans may not shift right if there a vacuum or tune up problems.
Have you serviced the transmission for filter & new fluid lately?
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Old 06-15-2013, 05:27 PM   #6
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The cars are known to stay in lock up for a long time... .. even when accelerating ...ya gotta give the pedal a push to get it out of lock up
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Old 06-16-2013, 12:55 PM   #7
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Thanks everyone! I'll try to answer all the questions:

Trouble codes: this is a 1995 which is equipped with the 16 pin OBD2 style connector but with the OBD1 codes. Every place I have taken it to can not read the codes.
109,000 miles as 12/2012.
Changed sparkplugs (looked great), new OxySensor, new fuel filter.
Tran oil changed and New filter installed.

My Questions:
If the clutches are bad, what are the symptoms? Once it is in gear, 1st, 2nd, 3rd or 4th everything is smooth.
How do I test for low vacuum?

Lock up...so, when starting from a stop in 4th gear I should push the throttle to the floor? I ask because when I gently press down on the gas the engine goes deep throated and the acceleration is slow, labored, as if I am pulling a huge load and if stopped at the bottom of a steep hill, it won't even move until I manually shift into 1st gear. Which brings me to my next question: the trans is shifted electronically by the ECU even when manually shifted?! Since I can Manually shift without a problem shouldn't this eliminate the shift solenoids as the problem?
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