Shifting delays by my 1996 3T40 125 transmission.

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Jul 25, 2019
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#1
Make
Chevy
Model
Beretta
Year
1996
Miles
32400
Engine
3.1L L82 V6
My 1996 3T40 125 is having delayed shifting issues. It tends to shift a bit sooner when warmed up though. It down shifts just fine and doesn't kill the engine. But my engine is running hot because the delayed shifting. I don't have a Tach, but I'd guess it doesn't shift until around 6000rpm and sometimes it won't even shift into OD/3rd. Right now it first shifts at about 30mph and second shift is at about 50mph. I'm hoping it just needs some fine tuning or adjustments made, so it will shift properly.
 

grcauto

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#2
Going to need pressure tests to narrow down area of problem.
 
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#3
@6000 RPM ? WTF are you thinking.

Is there a chance the CEL or SES (Service Engine soon) light is on?

A PLAN -
I would suggest you start by getting the system checked for codes.
 

bp042665

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#4
ok all I see in all data for this in 96 with 3100 is a 4T60 witch still had vaccum module that was a common problem on delayed shifts but 4T30 Had a governor and throttle valve cable it could be either one of them
 
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#6
Our electronically controlled automatic transmission problem were mainly caused by electrical connectivity problems between the PCM and the transmission. Mainly in what they use to call the neutral safety switches that has a bunch of contacts for the various gears, switches on the brake pedal, and the connector itself on the transmission.

Sure doesn't help to live in road salt area melts the ices, creates salt water, highly corrosive and splashes all over the place. Use to have a separate AT module, what, an extra box, wires, put it in with the PCM that way if it goes back, can hit them with over a 1000 bucks for a new one. 1996 was the year that code was not stored in permanent memory, using all flashram like in a USB stick where one little tiny glitch can wipe out the code. Marketing, engineers were against this, but flashram with the advent of the internet could send new code at little cost to the company. Rather than replacing a ROM chip that cost the company 89 cents for making corrections. In 1957 working for Plymouth was able to buy a Fury for $1,800.00 brand new loaded, today, looking over $25K for a compact, $50K for something full size. So worried about spending 89 cents.
 
Last edited:

billr

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#7
Wow, I haven't already touted using live-data??? Use live-data to quickly move past wonderment about switches and sensors. Specifically, look at "gear commanded". If the PCM is commanding a shift and it isn't happening we look in one direction; but if the gear shift isn't being commanded, then we focus elsewhere. Let's start paring the problem down in size.
 
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#9
AT's use to be self-contained units. vacuum module with a mechanical governor, and a very sophisticated control valve for gear selection. Recall even in the 70's could pick up a rebuilt TH-400 for around 150 bucks.

Today just clutches and control solenoid fluid valves, all the brains is done by an 89 cent microcontroler, speed is a tiny bar magnet with a few turns of wire on it, but want a small fortune for a replacement transmission.

Kid was toled by a shop needed a rebuilt transmission, 4000 bucks for a vehicle not even worth 2000. Can you get it home? Sure, just dirty switch contacts, polished them, good to go again.