4L80E behavior question

[cuervo]

So I have an 4L80E in a 91 Suburban.

If I put the gear shift lever in 1 at park and then start driving it still shifts into second. Is this normal behavior?

It also seems that at times it wont shift in to OD even at 55 or 65 mph.

I was told it was a recent rebuild and by looking at the tranny from under the truck it does look like it has been pulled not to long ago.

 

[lectric80]

If it still shifts into second while the lever is in first I would think that it would be a shift linkage adjustment. It may be showing 1st on the dash, but actually be in or close to second on the shift cog, thus allowing it to shift up. Have you tried going even higher in speed, if so does it stay in second? If it does then the most likely cause is the shift linkage. If not it may be something in the computer overriding it, but that is pretty unlikely.

If it won't go into overdrive, what RPM's are you running at 55 to 65? This would be important to know.

 

[sweetk30]

1st : yes thats fine. mine does it all the time stock tranny.

2nd : gm trannys with comp control wont lockup in od till 140* temp is reached. this might be what your felling.

 

[cuervo]

I'll have to check the linkage to be sure it is moving all the way down. I thought in all stock transmissions that if you put it on low/first they would never shift up until you moved it to 2nd.

I'm still wondeing about the OD stuff. It seems to shift in OD when the trans is cool and it doesn't feel like it does when hot. I'll need to put a tach in it this weekend and check the RPMs.

 

[nvrenuf]

Like SweetK30 said, the shift is normal. Depending on the transmission either the governer or computer will force an upshift into 2nd, it's to keep parts from dying. Being a 4l80e it should be the computer causing this - perfectly normal.

 

[6.2Blazer]

The 2nd gear upshift is pretty normal on computer controlled transmissions, it's a default in the controls mainly to prevent stupid people from putting the trans in 1 and then taking off down the interstate and wondering why they can't go over 20 mph.

Not sure on the OD thing though. It is a pretty subtle shift once the trans is warmed up. And yes, the controls normally prevent shifting into OD when the fluid is under a certain temp. On my '01 Dodge this was very noticable as I could leave my house, drive to the interstate, and go several miles before the OD whould engage during the winter, it was always like that. On my '03 Chevy w/ 4L80E there has only been one or two times where there was very slight delay before OD engaged when really cold out.

 

[mike reeh]

The trans should not shift into 2nd unless the motor is screaming, when the shift lever is all the way down.. Try slamming the shifter down fast and firmly to engage true 1st gear, and if that fixes it, adjust linkage as necessary. If you are revving the motor to the moon, and it shifts-then this is normal. If it shifts normally like you dont really have it in 1st gear, then its not truely in low.

mike

 

[cuervo]

It seems as though there are several thoughts as to how 4L80E should behave.

 

[Slapperbar]

When I put mine in 1st it stays there. I haven't tried to rev the sheeat out of it to see if it'll force a 1-2 shift thou.