There is some sort of vacuum canister on the left fender under the hood hinge, with a couple wires hooked to it. The hose from the booster to it was too short and the T fitting and the nipple on the canister were broken off and goo'd back together with some sort of putty. What does that canister do? I have a bolt stuck in the end of the hose to plug it off right now.

 

That little thing is the low vacuum switch, basically turn the brake and ABS lights on when/if your low on vacuum. Though most of use probably figured it out from the hard to stop truck before the light comes on.

 

what wouls cause this? sometimes my truck is really hard to stop and the peddal is super stiff. it also makes a hissing sound when pressed. i was thinking it had something to do with my booster.but now im not sure...could i have a vacuum problem?

 

https://www.dieseltruckresource.com/...ighlight=tweco

 

If you have a hissing sound when you hit the brakes and the pedal is hard I would guess it's the booster. For all the more they cost I wouldn't hesitate to just swap them at the first sign of trouble.

 

thank you sir!