mike8818

Ok i have a chance to get a 1995 gmc jimmy but when you push the 4 wheel drive button you hear a little clunk which in guessing is it engaging but the front tires dont spin so the 4 wheel drive isnt working. It also clunks when you put it in gear wich are the u-joints. Any ideas what it could be?

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1979 pontiac firebird- for sale/trade
1978 Chevy Elcamino- parting out

cbec1999

"Front tires don't spin."

???

So you've disconnected the rear drive shaft, dropped the hammer, and the front wheels don't spin.

I'd say it's a lack of power, not the 4WD workin'...

jdmccright

Not sure how you are testing the 4wd, but the clunking could be a u-joint or excessive driveline lash from wear and tear. Short of taking it off-road or where the road is slippery from rain, putting it up on stands or a lift will let you test the 4wd operation.

If the selector indicator does not flash when you press the button, then the electronics part is functioning. If so, then you'll need to check the encoder motor or the shift control module. The next thing to check would be the vacuum lines and accumulator bulb under the battery that engage the front diff, and then the front diff vacuum relay mounted on the front diff.

If you have it up opn stands, listen carefully where the clunk is coming from. That will help zero in on the problem area. Good luck!

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Current Garage:
NEW 2003 Pontiac Vibe 1.8L AWD
2003 GMC Envoy XL (aka "fat-a$$") - K&N air filter, otherwise stock.
1995 Chevrolet C2500 2wd, 5.7L - K&N air filter, otherwise stock...my weekend hauler.
1992 Toyota Camry LE 2.2L - K&N air filter.

Vehicle History:
2004 4.7L Dakota Quad Cab 4x4
1996 GMC Jimmy 4wd
1992 Chevrolet S10 Ext. Cab 4.3L
1995 Honda ST1100...my first (and only) new vehicle.
1980 Yamaha XS400
1980 Mercury Bobcat...my first car.

terrypg

I would suspect the vacuum switch on top of the transfer case. It has 3 hoses. Remove hoses and remove switch with 7/8" wrench, the button will probably be stuck. While you have the vacuum lines off check for vaccum with engine running, one line will have vacuum.