M998 3L80 TRANSMISSION DOES NOT SHIFT INTO GEAR

[Iambiig]

It is a 1993/1994 M998 with a 3L80 trans that will not shift into any gear. It used to sometimes take a minute after start up to shift, now it does not go into any gear at all. Almost felt like it had to build up pressure or vacuum when first started.

Fluid is a pretty pink, no leaks underneath. Filter was changed last year, had a little sludge, but nothing extreme.

Is this the symptom of failed modulator?

Any help would be appreciated.

 

[Mogman]

Sounds like a failed pump, modulator would not give those symptoms.
The 3l80 is an all mechanical transmission, so this is not a good sign.

 

[Hummer Guy]

Never knew a 3l80 exist

 

[Mogman]

Never knew a 3l80 exist

Yep! another name for the TH-400 The TH-400 was still in production when GM went to the speed/position/load rating designations for their transmissions.
3 speed, longitudinal mounted, load class 80 (this does not mean 8,000lb as some believe)

 

[Hummer Guy]

Yep! another name for the TH-400 The TH-400 was still in production when GM went to the speed/position/load rating designation for their transmissions.

Ohh, so its just a term for the TH-400, for a second I thought that was another 3 speed

 

[Iambiig]

Yep! another name for the TH-400 The TH-400 was still in production when GM went to the speed/position/load rating designation for their transmissions.

Ok, so decided to try again. This time mashed the gas pedal before starting. Started it up and went right into reverse. Drove it around. Trans shifted nice, no problem at all. Made it kickdown, multiple times, no problem.

Maybe something to do with the kickdown?

 

[Mogman]

Ok, so decided to try again. This time mashed the gas pedal before starting. Started it up and went right into reverse. Drove it around. Trans shifted nice, no problem at all. Made it kickdown, multiple times, no problem.

Maybe something to do with the kickdown?

Interesting! I would think the kickdown circuit would do that, but I am only Youtube certified on transmissions