I'd appreciate some feedback on the direction to take with this vac pump rebuild.
My brother's 1985 300D was only making about 5 Hg vac and not shutting off, no power assist brakes etc.

I pulled the pump, sure enough one of the check valves was cracked.
I installed the parts from the rebuild kit and I think I did it right but put back the pump and still no suction. Pulled the pump back off, checked installation of the check valves. The main check valve at the hose inlet was tested by blowing and sucking. It passed that test by not allowing suction but I was able to blow air through it in the direction of vacuum.

I don't see what could cause it not to produce vacuum. Is it possible that the rings that go around the piston were pinched or compromised on installation?

In perusing the threads, I see that an argument can be made for just putting on a new pump because of the possible devastation caused by the pump arm bearings.
I'm leaning towards that as the car has 275K.

But, I'm just curious as to what would cause my rebuild job to fail.

Thanks

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63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

The valve seals supplied in some overhaul kits are too thin. If that was the case with yours, the check valves won't function properly.

After paying about $2500 for the engine damage resulting from a vacuum pump failure, I replace the entire pump the first time it looks like its considering thinking about maybe failing. I just replaced one after about 60K miles due to a slight click that could be heard with a stethoscope.

Tangofox you nailed it.
The new seals were 1mm thick, the old 2.5mm. Quite a difference. Fortunately the old seals were still soft and pliable so I reused them which solved the problem.

I couldn't see anything to my untrained eye that would cause me to think the bearing was going to fail. I've heard they give fair warning so for now, it's going to be the old pump.

I guess moral of the story is don't throw away anything until the job is done and carefully compare ALL parts from new to old. This is the second kit (first one was power steering pump) with wrong sized seals. Fortunately my mechanic knew about the ps seals which undoubtedly saved me hours of pain.

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63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

So now that I have read this thread and already have rebuilt the pump with no luck. Where might one get the right size o rings if I not longer have them?

Damn, I did a rebuild and it didn't work so I pulled it off and threw on a used one I had. I should dig out my rebuilt one and check the O ring. Thanks Tango

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

They sell an other kit that completely replaces everything on the on the drive side of the vacuum pump; are, pins, bearing and ect. The catch is that if you buy both rebuild kits it will cost almost as much as a new vacuum pump and the new pupm would come with a warranty.
Here is an example of a place that sells the Arm assembly. But some places sell the Arm kit for close to $300.
http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2FE00V9U72FH147MEK&yearid=1984%40%401984&makeid=MB%40%40MB%40%40X&modelid=300%2DDT%2D001%40%40300D++Turbo&keyword=vacuum&mode=PA&subcatid=D3010@@Vacuum+Pump+Repair+Kit

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84 300D, 82 Volvo 244Gl Diesel