1994 F-350 1 ton dually.
PSD 5spd.

The brakes are only working sometimes.
When you step on the brake pedal its "hard" and very little brakes.
Other times they work fine.
Fairly new pads and shoes , lots of brake fluid.
Could it be that vacuum pump?
Whats the proper name I looked on Ebay and couldnt find anything.

 

That sounds just like a lack of vacuum. now i am not sure that it is the vacuum pump because when mine failed it just quit all out. its the only thing i could think of.

 

Is it just called a "vacuum pump"?

 

Yes!

I found two on there:

eBay Motors: FORD 7.3L DIESEL MECHANICAL VACUUM PUMP (item 140265324978 end time Sep-13-08 05:01:40 PDT)

eBay Motors: 96 97 98 Ford F450 7.3L Diesel Vacuum Pump (item 180286250614 end time Sep-12-08 13:15:10 PDT)

 

I wonder if they would fit a 94.5?

 

So the brakes are rock hard and barley slowing down the truck.
I took the pump off it seems to be pumping , when I turn it by hand?
Any ideas?

 

check you vacuum lines for a cut or hole maybe a bad connection somewhere.

 

You need a vacuum gauge to know if the pump is doing it job well enough. It will still pull a vacuum just not enough. It should be able to pull 18 in hg. If not check it right off the pump. If that is good then you have a leak else where like mklemin said

 

Once you figure out the problem with the vacuum or booster, fix the problem with the vacuum gauge. If you don't have vacuum, the brake light should come on.

 

Brake light didnt come on.

 

If you can't get one on flebay they are a stock item at Autozone, replaced mine about 2 months ago I think it was 89.00 plus 20.00 core charge. They will loan you the puller to remove the pulley. Dont forget the bolts go in the pump flange before you install the pulley. You probly get enough vacuum to operate a/c and heater valves but not enough for brakes like TJ said you need at least 18" for brakes to work properly. JEEP1947

 

Cheapest one in stock in my town is $240
I ordered a used one from a autowrecker for $150.