1992 auto transmission problem

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lvjetboy - 03 Oct 2005 02:32 GMT

Step on the gas and the transmission doesn't seem to want to downshift
smoothly. It "vibrates" as if the transmission is rapidly shifting back and
forth between gears before finally engaging the lower gear. Happens more
during loading conditions, sometimes finally downshifting other times not.
Been doing this since 40,000 miles but getting worse now. Has anyone heard
of this? I'm sure the shop will just tell me time for a new transmission. :
( Any thoughts?

jer

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PJ - 03 Oct 2005 14:44 GMT

> Step on the gas and the transmission doesn't seem to want to downshift
> smoothly. It "vibrates" as if the transmission is rapidly shifting back and
[quoted text clipped - 5 lines]
>
> jer

Likely suspects are pressure regulation problem, crud in the valve body
passageways (the jitter between gears or servo chatter) or slippage.
The 'during loading' makes me think excess slippage. First, some
slippage is normal--makes for smooth. Cadillac's have more, trucks have
less and Corvette's have it just right! Excess slippage may cause the
transmission to switch into the 'git home' mode, raising servo pressure
upward to produce a 'hard shift.'

Do the low-cost and easiest thing first. Change the fluid and replace
the filter. If there's any improvement, repeat both in a couple of
hundred miles. If symptoms of slippage continue, get it adjusted soon
before you cook some parts. Above all, don't let just any transmission
guy swap out the transmission--there are dozens of THM versions that
will "fit." Get to a Corvette specialist--stay with something that
shifts smoothly, performs well and will handle the torque.
PJ

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lvjetboy - 07 Oct 2005 08:20 GMT

Thanks for the ideas PJ. I didn't know slippage could cause that strong
vibration I'm feeling in between gears. I start with the oil and filter.
Wish I knew a good vette mechanic in Vegas :( I've always had dealer gm
mechanics work on it, but they don't seem very good and not nearly worth what
they charge.

jer

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PJ - 08 Oct 2005 00:29 GMT

> Thanks for the ideas PJ. I didn't know slippage could cause that strong
> vibration I'm feeling in between gears. I start with the oil and filter.
[quoted text clipped - 3 lines]
>
> jer

Check here: << http://www.vegasvettes.com/ >>

PJ

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lvjetboy - 08 Oct 2005 10:53 GMT

Thanks for the LV vette link PJ. I checked that forum, not much going on...
but I'll give it a shot. Driving to work yesterday I was thinking...slippage?
As in a clutch? Is automatic transmission slippage caused by excessive
"clutch" clearance or other facters and if so wouldn't that slippage also
occur with a manual downshift? With manual downshift I get immediate
response. No vibration, etc. Same also from a stop. If I floor it in 1st
gear then manually shift to second, then manually shift to third...etc...I
get no slip. Yet if I'm cruisin' in drive or overdrive up an incline at say
50 or 60 or 70 mph, then give more throttle w/o manually downshifting? The
transmission sometimes vibrates before automatically downshifting.

Has anyone else experienced this? Is there a tech bulletin? Like I posted,
this has happened to me since the transmission (and engine) had 40,000 miles
on it. Not much. 40k is not enough for normal wear and tear to start
acting like this.

It's almost like the transmission is rapidly switching from high to low
quickly and causing a vibration before finally deciding to go to the lower
gear.

jer

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