66 Suburban - Transmission Woes!

[burban66]

My suburban has a 350 transmission and all of a sudden while I was driving it last night, it stopped shifting. As long as I eased on the gas pedal it would slowly gain speed topping out at about 25 mph. As I gave it gas, all the engine did was turn high rpms and the tranny did nothing, but when I let up off the gas the truck seemed to gain a bit more speed. Any ideas on why the transmission would just all of a sudden stop working?

[awbrown]

as you increase engine rpm and shift it manually does it shift ?? if so you lost your vacuum to the modulator or the modulator went bad.. they are also known for governor problems , both easy to try before giving up on it .. also make sure the detent cable isnt broke or stuck wot......

[burban66]

It won't shift manually either. Would the fact that I still have reverse make the prognoses any easier?

[neto]

Like awbrown said I would check your vacuum line at the modulator first. Make sure it's not collapsing from being soft or disconnected.

[awbrown]

with it running pull the line off the modulator and see if you have vacuum.. if you do replace the modulator ... the govenor is an easy swap , I have seen them stick or come apart before...

[burban66]

Don't mean to sound simple, but where might the modulator be located?

[neto]

http://67-72chevytrucks.com/vboard/a...1&d=1167592572

[burban66]

Looking at the pic, could you point out the modulator?

[bama63]

the modulator is on the passenger side rear of the trans and has the vacuum line going to it, but in my honest opinion it sounds like you lost your 2-3 clutch pack and need a rebuild. the statement "As I gave it gas, all the engine did was turn high rpms and the tranny did nothing, but when I let up off the gas the truck seemed to gain a bit more speed" is a definite sign your clutches are slipping the modulator only controls the shift points at low rpms before the Governor takes over hope this helps