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Old 02-23-2010, 10:49 PM
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TH4l80e MT1 weird shift

I have a 96 c3500 SRW with a l-29-7.4L with the th4L80e ( series MT1) thats doing a goofy thing , when its cold out ( below 30 degrees which is warm for Canadians ) if i start and let it warm up alittle ( 2min or so ) or start of cold , it will go but the first stop I come to it will act like I am spinning the wheels then go into 1st gear ( like its slipping internally ) and it bangs into gear , it has 115K miles , fluid changed out at 60K miles with convertor flush ) level good when cold or hot . it only does this on days when its below freezing , and if I let it sit and warm up to 80 degrees on water temp it stops otherwise when warmer than freezing it shifts normal ( checked for water in fluid too ) . whats going on ??selinoid problem or ecm problem , No codes thrown when scanned at dealer .
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Old 02-24-2010, 12:52 AM
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I had a problem with the exact same symptoms except it was a 96 dodge dynasty. I changed the fluid and filter and added a can of lucas trans tune. The problem went away immediately.
I was amazed because it was the first time a tranny additive had ever worked for me. That was my first and last attempt for an easy fix before either a new trans. or junk yard jewel to replace it. Drove the car another 50K before I sold it at 158K mi. still running good!
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Old 02-24-2010, 05:22 AM
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Internal seals getting hard
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Old 02-24-2010, 08:31 AM
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Note that the 4L80E has a pulse width modulated valve that controls internal hydraulic pressure. It also has input and output shaft speed sensors. If the computer senses slippage between the input and output shafts, it increases the line pressure up to the max allowable. This is why after the slippage, you feel a very hard shift.
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Old 02-25-2010, 12:25 AM
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So Joe ,basically I have a low line pressure, Like Pump going south??? or could it be the valve acting up ?? I want to try to make this thing last a while as I don't have $2500 handy to get a complete R&R'd unit and convertor ( built to towing specs )
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Old 02-25-2010, 05:15 AM
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The PWM ( pulse width modulated) system in the 4L80E is used only on converter clutch apply. It is not part of the main line pressure control. Two different items.

The bang into gear is simply the fluid and seals making contact when the trans is cold, the internals of the trans are spinning and it bangs into gear. That most likely is all that is happening.

Internal seals are getting hard and the cold temps you mention here are the cause..

To add one other thought here in the cold temps; check the fluid level and when was the last fluid service on the trans? Trans Filter changed?
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Last edited by Crosley; 02-25-2010 at 05:37 AM. Reason: other thoughts
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Old 02-25-2010, 06:36 AM
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1st Post says (Fluid changed, converter flushed @60K) 115K now so it's due for another service. They may not have changed the Filter the 1st service & only flushed the Trans.
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Old 02-25-2010, 06:02 PM
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Quote:
Originally Posted by SSedan64
1st Post says (Fluid changed, converter flushed @60K) 115K now so it's due for another service. They may not have changed the Filter the 1st service & only flushed the Trans.

that is why I asked... 60k miles is too long for fluid service.

depend on vehicle and fluid type, 30k to 40k miles is my preference
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Old 02-25-2010, 06:53 PM
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filter was changed out when service was done , its dextron III , I should get a whole sevice and band adjustment done , trans service was done 5 years ago . fluid still red and not burn't , I'm going to lengthen warm up times for now .
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Old 02-25-2010, 07:36 PM
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Quote:
Originally Posted by stimpy
filter was changed out when service was done , its dextron III , I should get a whole sevice and band adjustment done , trans service was done 5 years ago . fluid still red and not burn't , I'm going to lengthen warm up times for now .

no band adjustments in the 4l80e trans as a maintenance item , clearance is set when the trans is built
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Old 02-26-2010, 06:38 AM
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I'd try a can of Lucas Trans Fix, it can't hurt. I've had numerous transmission problems that chemicals have cured, or made better, at least for a while,
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