Popping in the front...

[96 XJ Sport]

I tried searching, but there can be so many reasons for popping sounds. So let me describe mine...when I put it in reverse, and ONLY with my foot on the brake I get one good POP! Then I can continue backing up putting foot on and off the brake with no more popping. After I get the one pop in reverse, if I stop and go into D with foot on the brake, it sometimes makes a pop in that direction, too, but not quite as loud. With foot off the brake, I go between R and D with no pops at all.

So here's the kicker...I first assumed that I had a worn caliper and even inspected them both and found that the driver's side could be wiggled pretty good by hand compared to the pass side which was pretty tight. Tried new caliper pins to no avail. So I did a full front brake job with calipers, rotors and pads. NO CHANGE!!! Now I'm scratching my head. What else could this be?

Eric
96 4.0 AW4 D30 open 8.25 open RE 3.5" 31s

[kastein]

maybe worn/loose U-joints? Can you have someone else listen from outside while you do this and maybe localize the source of the sound a bit more?

[96 XJ Sport]

You know, I had kind of ruled out u-joints because it only happens with the brakes engaged, but perhaps I did so prematurely. I guess I can see how putting it in gear with the brakes disengaged is possibly just not enough pressure on the joint to make it pop. I will lay under it tonight and let my wife put it in R

Eric

[AIbandit]

This is a sign that your drive shaft ujoints are bad. If they have alot of slop it alows the driveshaft to spin slightly before hitting. being that forward and reverse will put the ujoint at exact oposite ends of its limit. It gives it the most distance to speed up and pop on the other side.

Grab your read drive shaft and rotate it back and forth if there movement... tada

Edit: I wouldn' suggest getting under the vehicle when she puts it in reverse thats asking for trouble nothing you cant hear squating from the side.

[Timber]

Originally Posted by 96 XJ Sport

I will lay under it tonight and let my wife put it in R

Eric

I hope you haven't pissed her off lately. Kidding aside, the suggestion for the driveshaft u-joints is a good one. Have you ruled out control arm bushings? I don't mean to start you on a wild goose chase, but depending on how the "pop" sounds, that might be a possibility.

[Joshooha]

I would definetly not rule out U-joints...check your transmission/trans case and motor mounts too.

[96 XJ Sport]

Thanks for the suggestions guys. I will check the rear DS although it really sounds like it's coming from the front. And the rear DS is new (2,000 miles ago) double-cardan from DPG that I installed with the lift and RE HnT SYE.

Assuming that it is coming from the front, which I will confirm 100% tonight, then it shouldn't be front DS u-joints or axle u-joints, correct? ...because they don't have any stress on them in 2WD. I had not thought of the control arms...I also installed them with the lift. They are the RE superflex fixed length arms and I torqued to something like 110 or 120 ft lbs, but they certainly could have worked loose.

Eric

[AIbandit]

I would think your front ujoints would only vibe in 2wd at speed. If they popped like that they would have to be insanely bad. which you could probably feel by hand.

I still recomend trying to spin the ds with your hand. A jeep I bought with a SYE had bad slop in the tcase. In the least your just narrowing things down with 10 seconds of effort.

[96 XJ Sport]

Originally Posted by MpSlayer

In the least your just narrowing things down with 10 seconds of effort.

Yep. Def will do.

Eric

[96 XJ Sport]

Well, she had her chance, but she didn't run over me I laid underneath and she went between R and D several times, but the pop was just not distinct like it is sitting in the jeep. Actually, I could hardly hear anything. Then I said, move and let me try, and I hopped up there and POP, there it is. So now I'm totally confused, lol. It's like it transmits through the floor inside the cabin.

I did check the rear DS by twisting it back and forth by hand and it's tight. Control arms did not appear to have any slack in them either. I did notice that the transfer case had a fair amount of flex in it when either R or D was engaged. Is that normal? And does that have anything to do with the tranny mount being bad possibly? I'm at 142K and I'm sure it's original as well as the motor mounts, but I don't just want to replace things willy nilly.

Eric

[Timber]

Loose front shock bolts?

[96 XJ Sport]

Originally Posted by Timber

Loose front shock bolts?

Don't know, but I can check. I'm not getting any noise going down the road with suspension flex, though.

[AIbandit]

With the brakes on? nothings moving except drivetrain

[96 XJ Sport]

Originally Posted by MpSlayer

With the brakes on? nothings moving except drivetrain

Yes, with the brakes on, so I had ruled out suspension, too. I guess in 2WD, even with the brakes on, the REAR suspension has some load on it as the DS tries to twist on the axle. So I guess I should double check the leaf spring bolts. If nothing else, I am learning to not rule out anything on a jeep!

What does anyone think about the TC flex and tranny mount question that I asked a few posts up?

[jrowell]

How do the Motor mounts look? Did you watch them with the hood open when you hit the gas? They are pretty close to your feet when your driving and can transmit the pop pretty good.

My guess is Control Arm or Motor Mount.