Fighting a Locked All Wheel Drive System in a Skyline GT-R : ATTESA Troubleshooting

Locked up R33 and R34 GT-R all wheel drive system, ATTESA troubleshooting

This one was a bit of an odd one. We had an R33 GT-R that the all wheel drive system, or ATTESA system was locked. Or in other words, when you were driving it at low speeds, the car felt like it had a welded differential. The wheels would hop and skip about. I have felt this before on a number of cars, but for a different reason than this car. If you run an aftermarket ATTESA controller and turn it up too much, you will find that a car will do something similar. However in this case, everything seemed to be ok. No ATTESA codes. So we started troubleshooting the system. Went into the transfer case, touched it all electrically. And in the end, we really couldn't figure it out.

That is, until Ernie noticed something.

By loosening the lock nut, and adjusting the screw we were able to get the system pressure to relieve. I don't ever remember reading anything about this. We tried to close the screw back down, and at a point the front would lock up again. We tried the car, drove it on the life, everything seemed good. Next step was to take the car on some drives to check operation. Now here is the weird part, Roberto from Rav Peformance and asked me if I ever had an R33 with a locked all wheel drive system... talk about crazy. So I let him know what we had just figured out earlier in the day. He tried it, and saw the same thing I did. So now we are both intrigued, and cautiously optimistic about the fix.

R33 GT-R ATTESA pump assembly. Under the wires is the adjustment nut.

Today we took a spare ATTESA pump assembly apart and I will share some pictures below.

There is that jam nut and adjuster

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The filter/screen in the assembly. This is under the solenoid and valve port section.

Solenoids, spool valve, end cap, and port assembly

End of the solenoid valve. This will press against the spool. This is adjusted by the jam nut/ screw

Jam nut and screw solenoid assembly.

Jam nut and screw on the end of the solenoid. Notice the spring and o ring

Since there isn't a lot of information of why this happens, this is my current speculation. This return spring in the transfer case has gotten weak. That way the spring pressure on in the ATTESA pump is enough to overcome it. That is locking the clutches up partially.