transfer case/A4WD problem
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transfer case/A4WD problem
Have a 99 Expy, 4x4 w/63k miles. During a long highway trip, (14+ hours stopping only for gas) noticed that during some stop and go traffic (i.e., doing 70mph, then slow to stop quickly for rush hour bumper to bumper, then accelerate quickly again from a stop) I would experience some serious 'clunking' during initial take-off coming from what felt like the front underneath, like something trying to engage over and over again but not quite engaging. Once it got up past 30mph no problem, only seemed to occur between 15-30mph during aggressive acceleration.
The problem went away if the vehicle sat for more than 5-10 minutes.... Would recur after more prolonged highway speeds. Highway driving seems to amplify this problem, and leaving the vehicle set seems to help it go away.
Did some research and found a new TSB on uncommanded shifts into 4H and 4L occurring.... Tested this theory, sure enough the problem occurs in A4WD where the x-fer case must decide between 2/4wd, but did *not* occur in 4H. The TSB recommends among other things replacing the shift motor with a new one that has improved 'sensing' components and new terminal design. This seems to be a costly fix.
Is this a matter that perhaps could be helped by replacing the x-fer case fluid? i.e., internal clutches not working correctly (I'm not familiar with this component unfortunately...) Maintenance schedule says to do it at 60k, but in looking over my receipt for 60k service, I don't see that they changed out that fluid.
Also, I'm told there is a GEM reprogram available for 4x4 shudder at take-off... Any info on any part of this stuff?
Thanks for any input.
The problem went away if the vehicle sat for more than 5-10 minutes.... Would recur after more prolonged highway speeds. Highway driving seems to amplify this problem, and leaving the vehicle set seems to help it go away.
Did some research and found a new TSB on uncommanded shifts into 4H and 4L occurring.... Tested this theory, sure enough the problem occurs in A4WD where the x-fer case must decide between 2/4wd, but did *not* occur in 4H. The TSB recommends among other things replacing the shift motor with a new one that has improved 'sensing' components and new terminal design. This seems to be a costly fix.
Is this a matter that perhaps could be helped by replacing the x-fer case fluid? i.e., internal clutches not working correctly (I'm not familiar with this component unfortunately...) Maintenance schedule says to do it at 60k, but in looking over my receipt for 60k service, I don't see that they changed out that fluid.
Also, I'm told there is a GEM reprogram available for 4x4 shudder at take-off... Any info on any part of this stuff?
Thanks for any input.
Thread Starter
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Joined: Mar 2002
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Did more research and I'm thinking more along the lines of a slipping clutch within the xfer case... From what I can tell power is actually applied a bit to the front wheels during aggressive acceleration in A4WD mode. Beyond 30-35 mph or thereabouts this is no longer the case.
Perhaps that clutch is slipping during the power application step while accelerating hard, causing the clunkity-clunk from 15-30 mph and seems worse as the case heats up (i.e., immed. after highway driving and/or during hot days)? Any transfer case wizards out there? Thanks.
Perhaps that clutch is slipping during the power application step while accelerating hard, causing the clunkity-clunk from 15-30 mph and seems worse as the case heats up (i.e., immed. after highway driving and/or during hot days)? Any transfer case wizards out there? Thanks.