Front driveline clunk

I have recently noticed a noise that sounds like someone is lightly tapping my front diff with a hammer. I only notice the noise when moving forward in two-wheel drive. The noise is not present while in four wheel hi or lo. This makes me think that maybe the four-wheel is not completely dis-engaging. The noise gets more frequent the faster i go and is present whether i am on or off the gas. I understand this is a very broad description of a problem, but was wondering if there is any obvious diagnosis before i start ripping the driveline apart.

Thanks,

ECGTECH

Just guessing here (no year/engine/transmission/transfer case/axle info), but if you have a D30 CAD front axle the vacuum motor could be failing, you have insufficient vacuum, the transfer case vacuum switch could be failing, all of those could cause the axle to fail to disengage.

sorry about not listing info. '89 4.0 with D30 and np231. would the vacuum failure be due to poor vacuum pressure throughout the system, or just in the 4 wheel motor? is there an easy way to check the vacuum for the 4 wheel? I haven't had any problems getting to engage or dis-engage other than the suspected problem listed above. any more info about this problem would be helpful

Yes, could be not enough pressure or the side of the motor that disengages is failing.

Test for steady vacuum supply, about 17 lbs I think. Then test the motor with a vacuum pump.

I have to leave but will be back in a couple hours, can post test procedure then or try a search, I posted a detailed description here some months back.

Joe_peters
i did disconnect the coupling from the motor and there was suction on one of the lines, but it didn't feel strong enough to be 17 lbs. I have very little experience with testing vacuum components, and was wondering if you could walk me through testing the amount of pressure being pulled by this line. Also, is there a way that i can fully dis-engage the axle manually until i get the vacuum figured out? I just don't want any potentially dangerous contact to continue while the vacuum is out.

Thanks,

ECGTECH

In this thread I posted the full test procedure with all test values:

http://www.naxja.org/forum/showthread.php?t=980642&highlight=vacuum+motor

You need a vacuum gauge and a manual vacuum pump with gauge, both should be available for loan/rent at your chain parts stores.

Yes, can remove the vacuum motor with cover and simply shove the locking collar all the way to the right (pass. side). When you remove the cover you might lose just a little gear oil so you need a small pan for that. Can't remember if you have to remove the little shield, but it is only two bolts. Once you have moved the collar over you simply align the shift fork with the collar and bolt the cover back on. If you are going to leave it like that for awhile plug the vacuum lines so you don't have strange effects on the engine.