Picked up a 91 W350 5spd on Thursday and the power brakes don't work on it. The Brake light and the ABS light are on the dash. Checked brake fluid and its full, checked power steering, pretty low so I filled it up. It seemed to help filling that up but maybe I just got used to applying more pressure that I didn't notice. Vacuum lines look good. So my next option is thinking the vacuum pump is dead. Anything else I should look at before replacing?

 

booster, the valve on the booster, and check vacume

 

Check to see if you have vacuum.

 

Whats an easy way to do it? Never done it on one of these trucks.

 

Pull the hose off the booster while the engine is running and see if there's vacuum.

 

If it gives you a hicky than its ok.

 

I ran into some brake issues a few months back. My rig was really hard to stop and needed excessive brake pedal pressure. After checking components and running various tests.......all it ended up being was air in the lines. The bleeding process took a while to "burp" out the air pockets in the system. Before you buy anything of $$$, check to make sure air hasn't entered the system because of previous owners tinking around with the brakes

 

If the brake pedal has been to the floor recently (eg.... A broken brake line), it may have put excessive stress on the old diaphram in the brake booster itself and cracked the diaphram when the pedal was pressed. Even if the engine and pump are creating the vacuum, the vacuum may be leaking out as soon as you pump the pedal.
Common on older vehicles especially if it's had a master cylinder that has previously been leaking at the rear seal at the push rod. The brake fluid running into the brake booster deteriorates the inside of the booster. Seeing a wet stain at the master/booster is a good indicator.

 

Pulled the vacuum line off the booster. No vacuum at all, increased the engine speed a little while holding the line, nothing. if there was any vacuum it was very weak.

 

Dead vacuum pump. Is it the old style with the diaphragm pods? There's a rebuild thread in the sticky for that type.

 

Looking at the stickys I might just convert to hydroboost instead doesn't look that difficult.

 

You could do that.

You still need a vacuum source to run the HVAC doors though.