Tranny and shift points

[MisterMan]

I bought my truck 4rm orij owner and well.... to be frank.... he's an lieing.... u know what. the truck was "never messed with".... had spark plug shields on it 4rm so much oil burning, wiring every where, just little things....

QUESTION: 1st revs to hell and then pounds 2nd, revs normal the last of gears.....My truck eaither has a bad cluch, or shift hit. (bangs all the gears) So my question, does ne one elses 70's gmc scream 1st????

I have a 71' gmc LWB v8 350 /w/ TH400

Thanks for reading,
--den

[MisterMan]

no one huh?? no imput? person experences??? common guys!

[Oldtruckfanatic]

Try the vacuum modulator...if it's no good it will cause erratic shifting etc. Before you replace it make sure the vacuum line from the manifold to the modulator is not loose or broken. it should be directly connected to a tee on the back of the intake manifold.

[MisterMan]

cool, ill check it, thanks.
--den

[krue]

Another way to check the modulator is to try to shift it out manually. If it shifts manually but revs too high shifting by itself the modulator vacuum line may have come off.

[MisterMan]

thats prob. it. gonna get greasey tommoro, ill tell ya then. thanks,
--den

[wibilly]

some modulaters are ajustable as well. take off the vacume line, shine a light in the hole where the hose atatches some will have an atusting screw in there to ajust shift points