Isuzu 4x4 on 4x4Wire

4x4Wire Isuzu Minute Mod: Front Wheel Drive Vacuum Shifter Lockout

By: Randy Burleson
First Published 05/2001

House Call
Planning ahead, Michael had the truck up on two ramps when I arrived.
Photo by Randy Burleson
Hoping to minimize the amount of gear oil dripping in my face, I had him back down and use only the driver's side ramp.
Photo by: Randy Burleson
Michael received this house call because I busted the part in the first place. It slipped off a hydraulic jack I was running, and the vehicle's weight mangled the vehicle's FWB vacuum actuator...
Photo by Randy Burleson
that's how I wound up under Michael's trip in Michael's driveway. And no, if you're wondering, nobody has let me live it down yet!
Photo by Randy Burleson
We removed the vacuum assembly for pictures, but you can lock the vacuum assembly in either position without removing it from the vehicle.

Defeating the Vacuum

First defeat the vaccuum. Disconnect the vacuum hose and plug them, or use a barbed vacuum line junction to connect the two lines together, bypassing the vacuum switch entirely. If the hose routing or termination changes, be sure to keep them routed well out of the way of moving parts or hungry four-wheeling obstacles. Zip ties work well for securing vacuum lines.

Photo by Randy Burleson Photo by Randy Burleson
These pictures show the vacuum assembly from a few different angles.

Locking the Shifter Arm

Defeating the vacuum-driven shift mechanism is easy enough, and is a pretty sure way of keeping the longside front axle connected, but it is so easy to lock the shifter, why not take that additional step?

Use an allen key to back out the recessed allen bolt at the bottom of the vacuum shifter mechanism. In ordinary use, this is a drain plug for the shifter chamber and necessary for removing the roll pin that connects the shift fork and shift rod. The 10mm threaded hole offers a better use for 4x4 purposes; a bolt threaded into this hole bottoms on the shift fork within the housing.

Photo by: Randy Burleson
Peek through the threaded hole in the bottom of the vacuum shifter to see the roll pin.

Use a 15mm-long 10mm bolt with a 1.50mm thread pitch, and squirt it with brake cleaner to be sure the threads are clean. Douse the threads in the shifter housing with brake cleaner, then use red Loc-tite or a similar thread-locker to seal the threads as you bottom the fastener against the shifter assembly. Snug it up but don't go overboard; once engaged or disengaged, even with the vacuum still connected, the forces applied against the internal shift fork are very small.


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