Vacuum questions

[lepews-me.com (naughtyG)]

So I am having issues with both my rear diff lock and my recently fitted decoupler, so I wondered if anyone here knows much about these systems?

My mechanic tested all the vacuum lines and says they are good, also he says there is vacuum coming up the line to the knobs in the console, but very little - probably not enough - to operate either the rear diff lock or the decoupler.

Does anyone know what the vacuum pressure value should be? Also what is the vacuum pressure needed to actuate a diff lock or a decoupler?

I found the rear diff lock actuator is currently not operating (using a vacuum hand pump) so after just a year fitted (was replaced last year) it seems to have failed.

The decoupler (also fitted last year) operates with the hand pump, but does not seem to operate with the engine vacuum.

Any help or insight appreciated!
Thanks,
Gaetan

[kombi4x427lc (Scott Pitcher)]

The rear lockers and the decoupler push rod shaft needs to operate perfectly straight to ensure good operation.

The rear locker vacuum servo often gets bashed around when removing/ replacing the starter motor as they are so close.

If it gets bent (happened to me) they jam up and wont work.

They do seize up easily too.

Need to be regularly operated to ensure they will work when required.

[lepews-me.com (naughtyG)]

Thanks for the info Scott. Any idea on how much vac pressure is needed for operation?
Anyone? Is there a place I could look to find out vacuum servos specs?

Thanks in advance,
Gaetan

[unclekenz (Ken Garratt)]

Must say I can’t recall anyone ever asking about the vacuum pressure spec. In fact I doubt it’s even officially written down.

Best recourse would be to try a vacuum gauge on the line going to the vacuum storage bottle on a few vans and get an idea what the average or best pressure might be.

Maybe you’ve already read this article on problem solving the difflock system, here goes anyway:
http://www.syncro.org/DiffLock.html

[unclekenz (Ken Garratt)]

Ok a bit more research.
One of these pics will hopefully give you a clue, but not necessarily the exact answer you seek:

Here’s also a forum topic you may glean some info from:
Goto: TheSamba.com :: Vanagon - View topic - Normal Engine Vacuum

Cheers.

[nilsbirkmann]

I checked this out on mine today as I have to replace the rear actuator. The system indeed runs at the same vac as the engine. So you’ll see it float between 15-25 InHg.
The movement of the gauge is quite slow as the T piece from the brake servo has <1mm orifice.

[unclekenz (Ken Garratt)]

Thanks Nils for that, should be the answer that Gaetan was seeking.

I have read elsewhere that it was found someone’s cause of lack of vacuum was due to that T piece being clogged up.