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mboomer 04-02-2010 11:49 PM

Crazy knocking noise
Hopefully somebody can help me out here. Everytime I accelerate or make a left turn there is a crazy knocking noise coming from the rear right side of my YJ. I've heard it since I bought the Jeep and can't see anything wrong. It sounds like sheet metal is banging away on the underside. Any suggestions.

Fweaky 04-02-2010 11:53 PM

Check your motor mounts, exhaust hangers, transmission / transfer case mounts.

Snuffy115 04-03-2010 11:25 AM

Make sure the exhaust hanger by the transmission is in tact.
I had the same problem when mine rusted away.

PaulyNC91YJ 04-03-2010 12:12 PM

Check your tailpipe to see if its hitting the track bar. I had the same issue after getting a new muffler put on.

hammer 04-03-2010 12:39 PM

I agree about the tail pipe mine did the same thing. There
should be a large upside down U going over the rear axle
but most shops arnt used to that.

mboomer 04-03-2010 05:52 PM

Thanks I'll check it out and update.

Pylonpounder 04-03-2010 08:23 PM

If it DOES have that upsidedown u going over the trackbar, check to make sure the end of the tailpipe isn't hitting off the leaf springs, or the gas tank skid plate. (push it and see if you can get it to touch either one) Sometimes the hangers and such can go and allow this to happen. Mine was hitting the leaf spring. I wrapped one of those metal strips with holes in it around the exhaust pipe and used a self-taping sheet metal screw to screw it in to the gas tank skid plate (on the bottom, but about an inch away from where the tank itself starts) and that holds it away. It also has a make-shift hanger that holds it up in general as well, off the original hanger mount. it keeps it from banging.

mboomer 04-05-2010 12:07 AM

the exhaust seems pretty secure. I tried shaking it and moving it around and it doesnt seem to move. I'm gonna try and listen a little more carefully and see if that is what is making the noise. It sounds like its coming from the center more or less so I'm still stumped...

Fweaky 04-05-2010 12:34 AM

Even though your exhaust is solid it could still shift and bang against the frame or other parts if you have a broken motor mount. If the engine flexes to much when you apply torque it will bang usually around the transfer case skid plate area.

mboomer 04-05-2010 01:03 AM

I'll have a look at the motor mounts in the morning. What should i be looking for. Hopefully it's pretty obvious. Or not.

Fweaky 04-05-2010 01:18 AM

If you have someone with you its not hard to tell. Put the jeep in gear and hold the brake. Give it enough gas to make the engine torque against the mounts and see if the engine flexes up too much. The engine should flex in the mounts but still be held firm. On mine it broke the drivers side mount and was lifting hard against the mount on that side while the passenger side was stable. I have broken mounts a couple times over the years and I believe it has always been the drivers side on mine each time.

mboomer 04-05-2010 02:13 AM

Good looking out. I'll try it out and see if that's it. Thanks

Garyk 04-05-2010 01:38 PM

If the motor mounts check out, you might try checking the rear end. You might have broken the pin that sets in the plate the springs sit on on the rear end or you could have a broken spring etc.

mboomer 04-06-2010 04:15 AM

I just put new springs on the rear which lifted it two more inches. Total of 4 inches of lift and this made the noise happen more often. It just sounds like sheet metal banging away when I make a turn or accelerate. Still trying to get a closer look at the motor mounts though.

Fweaky 04-06-2010 06:12 AM

Do you have a transfercase drop installed? Do you see any marks on the rear driveshaft. It could be hitting the skid plate.

mboomer 04-07-2010 02:57 AM

Gonna put the t-case drop in this week asap. No marks on the driveshaft at least that i can see. I was looking at the cover above the muffler, could that cause this noise? It's pretty thin metal and thats the only possible suspect.

mboomer 04-08-2010 04:04 AM

what should i be looking for on the motor mounts? everything looks good from what i can see.

Garyk 04-08-2010 02:50 PM

Don't know what year yours is but on mine the drivers side is easy to check, rubber should be solid and not cracked and tight. One the passenger side the bottom of the motor mount bracket was broken on mine and from looking at it from topside you could not tell and even from underneath it was hard. Use a small pry bar, big screwdriver to check them.

haroldpo6 04-08-2010 03:23 PM

Same noise on mine. Turned out to be the cat convertor. It had a big heavy chunk rolling around in it, took it off, noise gone. Runs so much better now..

benwillis 04-08-2010 04:47 PM

Rear Track Bar???
My performance 4X4 shop told me it was my rear track bar bushings (factory sealed of course). Haven't had time to replace it.

Garyk 04-09-2010 02:33 PM

Usually with lift kits the rear track bar is removed...

mboomer 04-10-2010 03:07 PM

Gonna take the track bar out today and have another look at those motor mounts. Thanks for the info. I'll update when I'm done.

mboomer 04-18-2010 01:43 AM

Well, the noise is gone. I put the t-case drop in and that took care of it. Don't know what was hitting but it's all good now. Thanks everybody for the advice.

distortedtj 04-18-2010 01:48 AM

If you still have the rear trac bar on...remove it with the lift bud.

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