Figure8king

Having problems with my 4L80 transmission. Mechanic friend said to disconnect the modulator and shift it manual.
I concerned that this will not work or will damage my transmission.
Any input will be appreciated.

mrvedit

I don't believe there is such as thing as a 4L80, they are all electronically controlled 4L80E.
If you have a "modulator" that means the electronic valve body was replaced with an aftermarket vacuum controlled one for manual shifting. Since it appears you have automatic shifting, you don't have a "modulator". However I might be missing or misunderstanding something.

Therefore, why not tell us exactly what you have - vehicle, year, and mods, etc.

braiden1

You can add a vacuum 48-mod kit to any 4l80E and still retain electronic automatic shifts. To have manual control on a 4l80e, you can wire it up internally to do so or, you can buy an external manual control box to achieve this.

joecar

If you disconnect the vacuum modulator, line pressure will be maximum always... your shifts will be full hard regardless of throttle and/or vacuum.

mrvedit

I suspected that, but it seems the OP doesn't have anything so exotic, or the OP would have know and mentioned it.
The OP really needs to document what he/she has.