I have a 81 240d my ? is how do you tst it and can it be rebuilt..thanks

With a Mity-Vac. Yes.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

These are the 2 do it yourself (DIY) areas below.
I am not sure what is available on Vacuum Pump rebuilding.
http://www.peachparts.com/shopforum/forumdisplay.php?f=82

http://www.peachparts.com/Wikka/DoItYourSelf

There are several types of Vacuum Pumps. Double Diaphragm, Single Diaphragm and Piston type.

The thing on the Piston type Vacuum Pumps is how much do you want to rebuild.

There is 2 rebuild kits for the Piston type. 1 Kit around $60 is for piston itself and the pump Valves. The other kit replaces the driving mechanism that operates the Vacuum Pump and is over $200.

The 2 kits added together cost almost as much as a new Vacuum Pump and you get no warranty if you rebuild it yourself.

The problem here is that when the driving mechanism Bearing or other parts go bad the come apart and drop into your Timing Chain Drive stuff and can cause serious Engine Damage.

I recommend that before you decide to rebuild your Vacuum Pump you take an extremely close look at the Driving Mechanism to see if it looks like it can be reused.

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84 300D, 82 Volvo 244Gl Diesel

what kind or readings are normal for vacuum you say with minvac,do I tap in on the line to master cyl to get these reading?/

In what year did the piston pump replace the diaphragm pump?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Depends on your elevation, but typically between 18-22 inches. That main vacuum line can be brittle. I'd tap in downstream initially.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

And, on which Engines?

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84 300D, 82 Volvo 244Gl Diesel

I got 18 on the main run to the brke mastercyl, 20 when I reb it up a little , i got like 5 going to the tran andegr value.. I 'm going to get the pump to do more tst to see if I have a leak,, what fun..Norm