Why does my trans drop out of OD? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 01-29-2003, 03:44 PM   #1
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Default Why does my trans drop out of OD?

Posted: Wed Jan 29, 2003 2:42 pm Post subject: why does my trans drop out of overdrive?

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HEY, I'M BACK!!!
Anyhow, I bought a 1994 Bonneville SLE Gold Edition at an auction on January 3rd. Driving it home it rode good except once it warmed up it it dropped out of overdrive. I have driven it out of town 3 times since then it did the same thing all three times.
My friend an identical 1995 Bonneville SLE Gold Edition that doesn't go into overdrive all the time, but when he stops, puts it in park, then back to drive, then takes off under medium to heavy throttle, then shifts into OD manually at 45-50mph then it goes into and stays in OD. I used to have to do this in my old 1993 SSE also. But when I try it in this car it doesn't work.
Is my transmission computer bad ( should I switch comp from my old 1992 SE)? Does it just need a flush of fluid and change of filter? Or is the tranny bad?
P.*. Any Minnesota area Bonneville guys interested in a get-together this summer?
Thanks in advance,
Martin
[email protected]

1994 Bonneville SLE Gold Edition, cone filter on stock air hose, NGK V-power plugs, 9mm wires, XENON blue 80/100w 9006 low beams, XENON blue 100/120w 9005 high beams, XENON blue 55w 893 foglamps, LED taillamps.
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Old 01-29-2003, 04:08 PM   #2
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When you say "overdrive" are you talking about the TCC solenoid engaging the lockup, bypassing the torque convertor? If it'* cutting in and out like that, acting as if it'* downshifting (i.e. like you were tromping on the gas hard), maybe the catalytic convertor is partly clogged. Excess backpressure and loss of manifold vacuum make the car react as if you were accelerating hard, so it kicks down, holds its upshifts longer, etc.

Mine went at about 90K miles. It started downshifting more than it needed to, then got a general loss of power, and finally wouldn't upshift or accelerate at all. Took just a few of weeks of daily driving for things to go from "something slightly weird" to "totally undrivable."
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Old 01-29-2003, 04:11 PM   #3
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Actually it just downshifts to drive and won't go back into OD.
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Old 01-30-2003, 12:53 PM   #4
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Quote:
Originally Posted by OLBlueEyesBonne
Actually it just downshifts to drive and won't go back into OD.
Okay, well, I would measure the intake manifold vacuum level and see if it'* up where it should be. If it isn't, that would indicate excess backpressure and a possibly clogged exhaust.
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