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Knocking sound when brakes are on

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Old 10-07-2009, 11:07 PM
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While you have it on the lift, pull the inspection cover off of the trans and check the flexplate for cracks. Mine stated as a very slight tick and soon became a very loud knock. It would be more noticable sitting still either in park or in gear. When under acceleration the broken pieces would lock together and the noise would stop until I let off the accelerator.
Old 10-07-2009, 11:23 PM
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Originally Posted by winston427
While you have it on the lift, pull the inspection cover off of the trans and check the flexplate for cracks. Mine stated as a very slight tick and soon became a very loud knock. It would be more noticable sitting still either in park or in gear. When under acceleration the broken pieces would lock together and the noise would stop until I let off the accelerator.
It doesn't do it when it's just in park or when I come off the gas after accelerating but I'll check it anyway.

I'm grateful for everyone's input especially as I know I'm going to have a few issues with this car (it's got such high km's, 393k, didn't cost much to buy and doesn't have any major body issues) & will be asking for help & information quite a bit.
Old 10-08-2009, 12:29 AM
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Check your trasmission mount. Mine had gotten all worn out and was sagging causing the exhaust to hit the crossmember causing a bad knock especially when stopped and in gear. its a 40 dollar or so fix.
Old 10-08-2009, 08:17 AM
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easiest way to check control arm bushings is while in reverse, tap the brakes enough to get it to knock, and have a buddy look to see if they are visually moving in their mounts.

i also agree that it could be your transmission mount.
but it could also be your brake caliper bolts loose or missing. i've had that happen to myself and seen it twice on other xj's.
Old 10-08-2009, 10:08 AM
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Sounds like something different, but mine has a rattle when engaged in drive and stopped at a light, etc. Someone told me to check the catalytic converter shield, or possible motor mount gone bad?? When I shift into Neutral at the stop, or start driving, the rattle goes away.....for what it's worth--I haven't figured it out yet.
Old 10-08-2009, 10:56 AM
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Originally Posted by Squirrely
Sounds like something different, but mine has a rattle when engaged in drive and stopped at a light, etc. Someone told me to check the catalytic converter shield, or possible motor mount gone bad?? When I shift into Neutral at the stop, or start driving, the rattle goes away.....for what it's worth--I haven't figured it out yet.
Does it sound like its in the dash? Cuz I have that too. Dont know what it is but it bothers me.
Old 10-08-2009, 11:38 AM
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Originally Posted by troy fritz
Does it sound like its in the dash? Cuz I have that too. Dont know what it is but it bothers me.
Did you grab the TC handle and see if it stops?
Try that.
mike
Old 10-08-2009, 11:52 AM
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Originally Posted by Mike1998XJ
Did you grab the TC handle and see if it stops?
Try that.
mike
Ill try it but mines not coming from under. Its coming from the dash behind the heater controls.
Old 10-08-2009, 07:08 PM
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Originally Posted by caged
easiest way to check control arm bushings is while in reverse, tap the brakes enough to get it to knock, and have a buddy look to see if they are visually moving in their mounts.

i also agree that it could be your transmission mount.
but it could also be your brake caliper bolts loose or missing. i've had that happen to myself and seen it twice on other xj's.
Thanks for the tips G.P. & caged - I'm just heading out to my buddys place so we'll see what we can see.
Old 10-08-2009, 08:04 PM
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its probbly that automatic adjusment cable in the rear drum. they snap pretty commonly me and both ma padnas had that problem
Old 10-08-2009, 11:13 PM
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I had a look at the driveshaft u-joints...they seem ok. Of course trying to get the vehicle to replicate the problem in front of my buddy (who is a licensed mechanic) proved impossible (typical, I guess...bets on it doing it again tomorrow??? lol).

The only thing that was different was that it had been in f/t 4wd on the drive over (it snowed here today so was a little slippery out) & we had just changed the CPS.
Old 10-09-2009, 04:59 AM
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Originally Posted by troy fritz
Does it sound like its in the dash? Cuz I have that too. Dont know what it is but it bothers me.
No....mine sounds like it's coming from under the shifter. Shift to neutral at a stop, and no prob. It rattles most of the time--not all I've noticed.
Old 10-09-2009, 07:09 PM
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Originally Posted by UK PONY
I had a look at the driveshaft u-joints...they seem ok. Of course trying to get the vehicle to replicate the problem in front of my buddy (who is a licensed mechanic) proved impossible (typical, I guess...bets on it doing it again tomorrow??? lol).

The only thing that was different was that it had been in f/t 4wd on the drive over (it snowed here today so was a little slippery out) & we had just changed the CPS.
Of course the noise came back this morning...it's definitely less noticeable when in 4wd though.
Old 10-09-2009, 07:23 PM
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i have the same noise while accelerating on my 89 i think it has to be a bushing or a u joint somewhere, never even thought of the trans mount i will check mine tomorrow lol
Old 10-13-2009, 08:41 AM
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After some playing around, my rattle is, in fact, coming from the transfer shift lever. When it "rattles" at a stop, etc., all I have to do is pull it up slightly, and it's good for a while.

What is involved in fixing this permanently (besides holding the lever up constantly! LOL)

Thanks!


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