'86 4kq diff locks

[jesse]

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    With the first real snow of the season i was excited to use the diff lo=
cks for the first time in the 2 years i have had the car.
    Problem, the rear diff doesn't show it's engaged, i would assume it's t=
he plunger back there.  But the center lock-up worked, UNTIL i got the revs=
 high.  Then the light would flicker out and *klunk* the diff would unlock.=
  Get off the throttle and it would reengage.  I am assuming it's a vaccuum=
 issue.  Any suggestions for testing the lock-up mechanisms and related vac=
cuum system.  I havn't recieved my Bently manual yet (i swear i'll stop pes=
tering you all so much when i do) so i have no idea where to start.

Thank you all yet again,
Jesse Erickson
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