I've got a 1985 CUCV Blazer with the 6.2 and the Turbo 400 transmission. I have an odd problem. Truck started shifting late, and finally stopped shifting at all except for the stock hard shifts. Points towards a vacuum problem, right? Checked vacuum on the pump, no vaccum. Replaced the pump, still no vacuum! looked down in the hole to see if gear was damaged. No damage to gear. Stuck my finger in hole and I can turn the gear with my finger. I am sure that this is not right.

haynes manual is no help, does not cover the 6.2. The ARMY manual diagrams leave a little to be desired.

So, what drives the vacuum pump? I do have good oil pressure, truck starts and runs fine.

I'm stumped.

 

Got my finger further down the vacuum pump hole, gear is not loose, thank goodness. Found a better diagram at the public library, showed the pump drive gear on the camshaft.

Took the replacement pump into the garage and cobbled up a drive for it, and it was not producing any vacuum.
Looks like a bad rebuilt pump. Taking it back to the parts store for return. We'll see how it goes tomorrow.

 

Vacuum pumps are very problematic on these gm diesels, but it somthing we have to live with cause you need vacuum, or put a electric pump like ford uses on their diesels.....