[200q20v] Diff Lox Mod - Long term test report

QSHIPQ at aol.com QSHIPQ at aol.com
Wed Feb 7 11:04:08 EST 2001

Well, here's the skinny on the diff lock mods after the Steamboat test.

2 UrS4 diff lock controllers and switches mounted into 83 Urq

Thermal shutoff
Vacuum actuation character
ease of use

Thermal shutoff
NONE.  16hours from Chicago to Denver center diff engaged the whole time.

Vacuum actuation character
Similar to the knob type, push button, usually a second or so to engage the 
actual diff.  That said, I passed on the replacing the 3X30USD vacuum ck 
valves.  That will cost me about 10 times that much to fix the LF fender...  
At the private track session on MON I was running 13psi of boost for about 
25seconds prior to entering turn 8 (off camber down hill).   As I entered 8 
under fulll throttle load, both diffs disengaged, which sent me into a rear 
out attitude, throttle lifted, both diffs *engaged* again, just in enough 
time to send me straight up a 5 foot snowbank on the exit of 8.  So much for 
my 7 year record of no tows!  The LF fender suffered a minor bend, but the 
facia and other assorted pieces parts came out unscathed.  

One thing I hadn't counted on was the altitude effects of the vacuum 
actuators and engine vacuum.  I found in bench tests in Chicago, that about 
15Hg was necessary to pull the center diff (about 10Hg or less for the rear). 
 I had little concern of that because I was getting 20 some Hg on decel here 
in Chicago.  At steamboat I would get maybe 15Hg on decel, and since the 
course was icey, not much braking torque as I had hoped.  I think I figured a 
way to eliminate the engine vacuum and run an aux vacuum system for the 
lockers, which also means I won't need any ck valves at all.

Much easier to use than either the pull knob or the rotary knob.  I left the 
center locked the whole time, and used the rear to exit the apexes, until it 
got really slippery, then I used the rear diff and center diff on all the 
time.  The nice thing about this mod is that you can mount as many 12v+ feed 
switches as you want, and just interrupt the line from the audi switch on the 
dash.  I have an extra 12v+ feed source wire under my ashtray that I intended 
to use for a switch on the shifter.  I really wish I had done this for 
Steamboat, but alas, time ran out.  Certainly a mod I plan on adding soon.

Great upgrade for *all* gen 1 quattros with differential locks.  Very 
transparent in operation to the rotory knobs, with great freedom to make the 
access to activation more "advantageous".  Thermal shutoff was not a concern 
in the mounting location I used (behind glove box).

Full Steamboat trip report to follow.

'83 Urq - Amazon with diff lock mod 

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