Questions and Answers

Jimmy 4WD Q. I recently bought a 1971 GMC S-15 Jimmy. I can't seem to get it engage into 4 wheel drive. The transfer case seems to be engaging but the front hubs don't lock. Someone told me that there is a vacuum switch or vacuum lines that might be the problem. Is this true?

A. Are you sure it's a 1971? That's the old style that could have manual locking hubs or automatic locking hubs. If it's a mis-print and you have a 1991 there is a vacuum switch mounted on the transfer case that activates the front axle by vacuum. The switches are prone to sticking on which would cause the front axle to stay engaged all the time with no 4x4 until the transfer case is put into 4 high or 4 lo. Yours is not going into 4x4 so I would look for a vacuum hose rotted somewhere between the transfer case and front axle actuator under the battery tray.

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