Hi,

 When I turn hard to the left in 4WD I can hear and feel a loud banging sound. I think one or both of the hubs are unlocking/relocking. I'm guessing that one or both of the lines that leads to the locking mechanism on the hubs is getting pinched. Am I on the right track? Is there anything else that I should consider? I'm going to crawl under the truck this weekend and take a good look at the lines. Any advice is more than welcome.

Thanks,
Al

I don't have your answer, but I can tell you you're on the wrong track.  If it's stock, your hubs are always "locked" and both half-shafts are always turning.  The shift-on-the-fly only affects the differential; there is only one vacuum line.

Ok. Cool. Thank for the feedback. At least that variable is eliminated. Maybe I should check the line the line that runs to the diff???

Al

Are you driving on loose ground/mud/snow, or is it on hard/firm surface?  If it's the latter, there's your explanation.  If you turn corners on a firm surface in 4WD, you get transmission wind-up as the front wheels cover more ground than the rear.  The wind-up is relieved in jerks as the front wheels "hop" to relieve the stress.

The answer is not to use 4WD on firm surface.

I was on hardpacked dirt and a little mud.

http://www.suzuki-forums.com/1g-1999-2005-vitara-grand-vitara/18777-transfer-case-wrecked-2.html

That link should answer your questions.  I have the same problem.  Here's the text in case the link goes dead sometime in the future:

File In Section: 04 Driveline Axle

Bulletin No.: 01-04-19-003

Date: April, 2001

TECHNICAL

Subject:
Harsh Clunk Noise From Front Axle While in 4WD and During Turning Maneuvers (Replace Front Differential Case, Actuator and Side Bearings)

Models:
1999 Chevrolet Tracker with Four-Wheel Drive

Condition

Some customers may comment on a harsh clunk or popping noise coming from the front axle. This condition is most apparent while driving in 4WD at low speeds on loose traction surfaces such as gravel or snow and turning right or left.

Cause

Inside the front differential case, the teeth of the free wheel axle hub may jump a tooth resulting in the noise.

Correction

A modification was made to the design of the front differential case, which should reduce the likelihood of the free wheel hub teeth from jumping.

Replace the front axle differential case, actuator and side bearings using the service procedure and part numbers as shown.

Important: With the new design differential case, the teeth may still jump under extreme torque load conditions, such as making tight turn maneuvers in 4WD on hard dry surfaces resulting in a similar noise. This noise is now considered to be a normal vehicle operating characteristic. Driving on high traction surfaces in 4WD is not necessary and contributes to excessive torque load on the front axle. Customers should be advised to shift into 2WD when driving on such surfaces.

Yeah I get the same thing, a clunk/bang/ping, I always thought it sounded like a spline slipping a tooth.  Anyway it really only happens when cornering downhill at low speeds, sounds like that is considered a normal operating characteristic under those conditions so I'll worry a little less now.