Vacuum system on a diesel syncro question

[Alaskaberrys]

Hi all,

I went to exercise the front and rear lockers on my ‘91 diesel doka (European) as I do every few months (surprised how little I use either front or rear lockers) and this last go around I got nothing. Pull knobs, front, back, both, in, out and no sign of anything happening. Usually get a bit of noise or slight resistance when pulling the knob and then after a bit can feel the lock and light comes on.

Figured I’d check the vacuum lines, the bulbs, tee, check valve underneath and start with the easy stuff - lots muddy rutty roads this winter and easy to see something get plugged off with dirt.

Then I realized I have no idea what produces the vacuum on this diesel in the first place

1.9l AAZ TD (originally 1.6TD)
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'91 Westfalia, Bordeaux Red Pearl 2.1L 2wd Auto
'91 T3 Syncro Doka, Escorial Green 1.9L TD AAZ “Gremian” (to provoke, irritate, exasperate, vex...)

[MarkWard]

There is a vacuum pump on the Diesel engine. Follow the brake booster hose in the engine compartment.
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[Alaskaberrys]

[MarkWard]

I’ve not really paid attention to the 1.9, but the 1.6 had a pump where the distributor would fit the block on a gas engine. My TDI has a vacuum pump driven by the cam shaft on the back of the head.

You really need a vacuum gauge to test the lockers. Each outer nipple should have vacuum when off. On, vacuum is routed to the inner nipples on the servo. I temporarily disconnect the vacuum tank when troubleshooting. It takes too long to fully recover when you are connecting and disconnecting.
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[Alaskaberrys]

I see. So a possibility is having vacuum at the pump, but signal not getting to it to re-route a vacuum to the reservoir?

Sounds like I best route it out to get a better understanding of what lines run to where first. Hadn’t dived into the locker rabbit hole yet.....I guess it’s time
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'91 Westfalia, Bordeaux Red Pearl 2.1L 2wd Auto
'91 T3 Syncro Doka, Escorial Green 1.9L TD AAZ “Gremian” (to provoke, irritate, exasperate, vex...)