TH400 question

[89wrangler]

I have a Commando with a Buick 350/TH400 combo. On the passenger side towards the front is what looks like a small vacum canister. Mine does not have a vacum line hooked to it. My questions are.. What does it do? and should it have a vacum line hooked to it? Thanks

 

[1-tonmudder]

It's a modualtor valve and controls the shifting of the trans and it should have a vacumn on it.I have saw a TH400 shift without the valve bein hooked up but it was really movin before it changed.