[urq] Center diff lock

[urq]

I have to admit that it is not clear to me what your tests indicate ... 

Remember that the purpose of the check valve is to draw air from the
plumbing on the diff lock side of the valve when the manifold pressure is
below atmospheric.  Since you have the system open you might as well test
the check valve ... if you apply suction to the side that hooks up to the
intake you should get air flow.  If you apply vacuum to the diff lock switch
side there should be no flow.  

Were I in your position, I'd just replace the valve ... 

Steve Buchholz

-----Original Message-----

Hi Steve and Keith,

I could not hear the noise because the car only sat for two days so I've
opened the 
console anyway.

Test 1
With the engine running, I can hear your hissing sound switching 'in
between' positions 
from 0 to 1, 1 to 2 etc. Is my switch leaking or is this normal behavior?

Test 2
I've disconnected the check valve from the rubber Y splitter to the switch
and checked 
vacuum (in.HG) with my Mityvac:

IDLE
(+/-15)

THROTTLE
(0 >>> 25+)

THROTTLE RELEASE
(25+ > 15)

With the engine OFF, the check valve side does not hold vacuum.
Q: good or bad?
 
The switch (still disconnected from the valve) does not hold vacuum in
either positions 
( 0 -1 - 2 ).
Q: good or bad?

Test 3
With the check valve and switch now both blocked, the center diff no longer
engages itself 
during aggresive (and long) accelerations.


I'm wondering if I should have checked vacuum 'before' the check valve i.e.
still 
connected to the switch?

So what do you think and thanks again!


Just for the record: Both of my diffs are in the off position on the console
and if I 
accelerate fast, the center diff will lock itself (light goes on briefly).

My rear diff lock actuator is 'jammed' in the off position with a peace of
wire, just in 
case.


Regards,
Maurits

1986 quattro GV (rebuilt)


----- Original Message ----- 
From: "urq" <urq at pacbell.net>
To: <urq at audifans.com>
Sent: Sunday, May 23, 2010 9:01 PM
Subject: Re: [urq] Center diff lock


The symptoms are exactly what I'd expect with a failed check valve ... what
happens is that boost pressurizes the selected side of the actuator, which
is just like applying vacuum to the other section.  I would expect that
you'd have to be on boost for a while for the pressure to build up enough to
move the diff lock, and the actuator should return shortly after the
throttle closes.

I suspect that if the check valve is bad that you will not have any vacuum
stored in the reservoir, so you might be able to do a test without taking
anything apart.  Go to the vehicle after it has been sitting a while (to
give the reservoir time to leak down).  Switch the selector to a different
position and listen for the hissing sound of air being drawn into the open
line.

On my '83 the check valve for the diff lock is in the console, right behind
the lock switch.

Steve Buchholz

-----Original Message-----

My suspicion is your check valves are failing or failed. Although usually
that comes with unlocking on boostm

----- Original Message -----

Lately my center diff lock is getting engaged on agressive accelerations,
mainly above 80 mph. The diff indicator light goes on briefly and you can
feel and hear this very loud thumping noise from the back end, very scary.

This happened many times now and I'm afraid I ruined something.

It's like there is too much vacuum and this actuates the switch or
something.

It's the 'later' style diff lock system with one rotary switch and two
lights.

Any thouhts?

Regards,
Maurits Jonkergouw

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