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4l80e slipping in forward when cold

M

mike Hayes

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Good day all..I've 98silverado z71 with a 6.5 turbo diesel I got it a couple of months ago from the original owner. The truck is basically in unmolested original condition with 381000kms.. my issue was already known when I bought it ,and I have a 98gmc(a twin to it) as a spare truck for parts. The issue is slipping in the forward gears. Some days it's not too bad some days it's more than an inconvenience. I have found that if I drive it for long enough to get it warmed up nice and everything flowing it seems to correct itself?... And shifts like a brand new truck. She's a juicer..minimal surface rust, everything original(even the door handles), and it even has the engine cover still on it. that I've only ever seen in my life once laying in a pile of junk in the corner of a shop long ago. everything as it should be... So when I got it I pulled the pan and changed the element and put it back on. I was leery about the clutches being in the oil so I used probably half of what I took out of it as it wasn't too bad actually added a bottle of Lucas trans.to it and topped it up with new fluid... very little change. So as it is winter here in Saskatchewan it is taking longer to warm up and run normally than in the fall... I have solid reverse but pretty much 1 2&3 are slipping and od is pretty good.. should I just get on replacing it with my donor? Or is it something that I might get with until spring?... The donor is a decent running drivetrain and the only problem with it is the body is rusted off the mounts pretty much sitting on the frame so if anyone has any suggestions as to a better patch or solution I'm all ears.. thank you.
 
The rule of thumb is, if the transmission has NOT been having proper fluid changes, don’t do it until it dies.
But your issue is backwards from the norm.

Absolutely what was suggested above- do a filter change.
But not just filter- you should drain as much fluid as possible. Disconnect the cooler lines and blow them out with shop air to ensure that fluid gets replaced. Then consider a second fluid change after driving it on the new fluid for 25kms.
This is why I wish GM put a drain in the converter.
 
Will L. said:
The rule of thumb is, if the transmission has NOT been having proper fluid changes, don’t do it until it dies.
But your issue is backwards from the norm.

Absolutely what was suggested above- do a filter change.
But not just filter- you should drain as much fluid as possible. Disconnect the cooler lines and blow them out with shop air to ensure that fluid gets replaced. Then consider a second fluid change after driving it on the new fluid for 25kms.
This is why I wish GM put a drain in the converter.
Click to expand...
Ok .. when I did that I changed over half of the fluid but my concern was that I hBe always been taught. That to change the fluid you lose alot of clutch material that's in it ... Maybe these are different. I've never touched transmissions just engines etc... So what about a TCM? It was just suggested this afternoon because there was a new development last night when I turned the key it did nothing.. so I re cycled it and it turned over n started . But it did it again today so I donno what do ya's think
 
Disconnect all the battery cables from the batteries.
Remove the slug from between the two cables connected to the RH battery.
Pry the cable terminal insulators away from the terminals.
Scrub on those terminals and that slug until they are bright and shiny.
Remove all the ground cables from the engine and shine those up too.
Back of engine, right hand side(passenger side) remove the ground cables from the ground lugs back there too and shine them up.
Hook the cables back to the engine.
Get some battery corrosion preventive in an aerosol can and give all the battery terminals a healthy dose of that then hook those cables back to the batteries.
Always disconnect negative cables first and always reconnect negative cables last, on negative ground systems, which our trucks are.
Reply back the results of this experiment.
 
Yeah, sometimes done is done.
Don’t get rid of the other trans for a couple months after the swap. Year to year there are changes and sometimes from one model to another. So there is the possibility you put in a working trans from your donor rig and it won’t work properly.
When it comes to rebuilding- ALWAYS best to rebuild your original than something off the shelf.
 
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