GM3000 Automatic gearbox problems

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Wed 17 Dec 2003 08:59
GM3000 Automatic gearbox problems - VG
Hi,
I have a car with a GM3000 automatic gearbox in it.
It started changing up through the gears very agressively, as though a turbo-charger had been fitted and max. thrust had been asked for! My wife refuses to go in it, it\'s that bad.....
The dealer who sold it to me can\'t solve it. He\'s tried a couple of gearbox specialists & they can\'t solve it either!
Neither I nor the dealer is keen to spend a lot of money on a new gearbox.

I (we!) would be extremely grateful for the input of anyone who has either had this problem before or somthing similar. Or just any ideas at all please!
Many thanks in advance.
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Wed 17 Dec 2003 11:00
GM3000 Automatic gearbox problems - Aprilia
VG

As far as I aware 'GM3000' was the code-name given to the GM-Astra chassis platform (late model). It is not a transmission model code (AFAIK).

What is the car (model/year)?
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Thu 18 Dec 2003 08:34
GM3000 Automatic gearbox problems - VG
Thanks for replying so promptly. (This is my first posting to this site-impressed!)
The car is an old Silver Spirit (B-reg ('85)).
(The dealer/mechanic quoted me the gearbox model....)
No-one seems to know what the problem is, so really grateful for ideas.
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Thu 18 Dec 2003 10:06
GM3000 Automatic gearbox problems - Aprilia
I think you will find that your car has the 'GM400' transmission (also known as THM400). This is a US-made transmission - very rugged.

If the change is very abrupt then I would suggest that the 'line pressure' might be too high. This could be a snapped or poorly adjusted downshift cable (runs from throttle body to transmission).

You really need someone to do a check on hydraulic pressures etc. These are simple transmissions so it should be easy to fix. Maybe try someone who has experience of working on US cars (these boxes were fitted to many US GM cars, Camaro's, Firebirds etc. etc.)
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Thu 18 Dec 2003 16:41
GM3000 Automatic gearbox problems - VG
Hi Aprilia,
Many thanks for that. Turns out you're spot on re type of gearbox.
They've apparently tried what you suggested.

Latest update is:
Another gearbox specialist has looked at it.
Apparently, a "seal kit" was used that only replaced *external* seals.
What this gearbox specialist said was needed was an "overhaul" kit. So, latest suggestion is to "overhaul" gearbox with this kit, presumably replacing *internal* seals (as pressure is being lost (car was road tested with guage of some sort attached) so making gear changes jerky.)

So, "overhauled" (I believe, though not sure how that's defined :-) ) gearbox plus converter is being suggesteed for £900 + VAT incl. labour.
How does that sound to you please?
Appreciate your input. Thanks.
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Thu 18 Dec 2003 18:59
GM3000 Automatic gearbox problems - Aprilia
£900+VAT is about what I would expect. All sounds reasonable. Let us know the outcome.....

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