Ike1990

I have a 1990 XJ 4.0 auto, with 142xxx miles on the clock.

1st issue- when I put the jeep in reverse it gives a sort of lundge as it engages and it makes a kind of clunk noise. I don't know if this a common old age issue or something I need to pay attention to.

2nd issue- My 4x4 isn't engaging, when I put it in 4 high or 4 low it makes a nice clunking noise from the front right and if I'm in 4x4 and go into reverse the right front tire locks up. I'm thinking it's the vacuum engage system not working, all the vacuum lines are connected. But as this is my first 4x4 and jeep at that i don't have to large a knowledge base.

Thanks for any help

BuckB91XJ

1.) this typical of a Jeep with high miles that needs new rear U-joints. Another possible but less likely cause is wear in the rear diff. I'd start with giving your rear driveline a shake at each end near the U-joint. If there is any side to side play at all it needs to be changed out.

2.) You are exactly right about there being an issue with your front axle vacuum actuator. I got so sick of dealing with mine that I got a set of axle shafts out of a 95 XJ with ABS. This got me solid axle shafts on both sides and the bigger (stronger) 297 axle knuckle U-joints. I slung that **** vacuum actuator in the weeds and never looked back. It is a pretty simple device though. Just remove the 4 bolts that hold it in and check it out. If its locking your front wheel up like yo say it should be pretty obvious what is wrong with it.

excess650

The "vacuum motor" may or may not be working. The diaphragms are known to fail, but there are several fixes. Short of replacing the front axles, you could install the $200 kit that converts your front in/out from vacuum to cable operation, or open the cover, pull the C-clip that retains the shifter fork, move the axle locking ring over the axles so they are locked, move the shifter fork to the locked position, and reinstall the C-clip so that it remains captive locked.

If your right front locks up when trying to engage, there may be some broken bits in the works.

Ike1990

yea thats what im worried about

freegdr

heres a write up on how it workshttp://www.pirate4x4.com/forum/showt...php?p=12767839

Ike1990

I think i might do the tractor pto cable mod for now, as i dont have a lot of tools at my disposal here at school. save me some gas millage too.

freegdr

first thing to check is if its getting vacuum at the axle and transfer caese switch and all hoses between

excess650

The write up is on this site with great pictures:

https://www.cherokeeforum.com/f51/fr...ss-91-a-38629/

This will be the quickest, easiest, and least $.