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Old 02-07-2018, 04:42 PM
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Knocking while driving in higher gears

I'm at a loss of what is causing the following problem. I have a 92 2.5l yj it has a new tranny, clutch(sound was there before) and the engine was rebuilt about a year and a half ago.

a few months ago I noticed a knocking sound, the problem is, there is nothing at idle, or even first gear, yet when I hit 3+ I get a loud knocking that gets faster as the rpm's go up, yet if I let off the gas an any of those gears, the knocking goes away. I've also checked(as well as I could see) if there was any cracks in my exhaust manifold, and didn't find any. any idea's on what to check would be greatly appreciated, as well as any fixes or diagnostic thoughts. I would like to repeat, this only happens when driving and not parked or at idle.

cheer's

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Old 02-07-2018, 06:00 PM   #2
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First thing I'd check is the U-joints on the rear driveshaft.

After that if I found nothing, I'd support the Jeep on 4 jackstands (on a good solid surface-not blacktop on a warm day) and start the Jeep and let the clutch out in 3rd or 4th gear. Set the idle around 2000RPM to 2500RPM and climb under and look & listen.

Be certain to observe all prudent safety precautions.

Let us know what you find.

Good Luck, L.M.
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Old 02-10-2018, 03:55 PM   #3
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Quote:
Originally Posted by Luckymac View Post
First thing I'd check is the U-joints on the rear driveshaft.

After that if I found nothing, I'd support the Jeep on 4 jackstands (on a good solid surface-not blacktop on a warm day) and start the Jeep and let the clutch out in 3rd or 4th gear. Set the idle around 2000RPM to 2500RPM and climb under and look & listen.

Be certain to observe all prudent safety precautions.

Let us know what you find.

Good Luck, L.M.
Another U-joint check to do is find a steep-ish hill. Roll it down with the jeep off (to eliminate engine noise) !key on so your steering wheel isnt locked!. If you hear a clock-clock-clock-clock noise that increases with wheel speed its probably a u joint.
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Old 02-11-2018, 07:10 PM   #4
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May just be a Carbon knock, [maybe you don't rev. the engine very high when you drive it], buy a can of SeaFoam an do the soak overnight where you drown the engine out by pouring the SeaFoam in the TB till it dies, let it set overnight, then the next day start it and run the Shize out of it, this will clean the carbon off the pistons and valves.
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Old 02-15-2018, 12:21 AM   #5
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Originally Posted by scaramoche View Post
I'm at a loss of what is causing the following problem. I have a 92 2.5l yj it has a new tranny, clutch(sound was there before) and the engine was rebuilt about a year and a half ago.

a few months ago I noticed a knocking sound, the problem is, there is nothing at idle, or even first gear, yet when I hit 3+ I get a loud knocking that gets faster as the rpm's go up, yet if I let off the gas an any of those gears, the knocking goes away. I've also checked(as well as I could see) if there was any cracks in my exhaust manifold, and didn't find any. any idea's on what to check would be greatly appreciated, as well as any fixes or diagnostic thoughts. I would like to repeat, this only happens when driving and not parked or at idle.

cheer's
Now you say it gets faster with RPMs... Are you sure? We need to know if it's following RPMs or wheel speed. A driveline issue won't follow RPMs, It's wheel speed and load. Re-test and report back.
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Old 04-20-2018, 05:28 PM
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Im almost certain that its wheel speed. In 1 there is no sound, some times in 2nd its very soft or or not there at all, in 3rd and higher it becomes very noticeable. in lower gears and high rpm, there is no sound, it only exists in higher gears, even in low rpm. Now the thing that has me puzzled is if I let off the gas, the sound stops. things I have done are new tranny(rebuilt), new u-joints on drive lines, new clutch.
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Old 04-20-2018, 09:30 PM   #7
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If it only happens in 3rd or higher gears, I suspect the rebuilt transmission.

Have you done as I suggested in the #2 post? A mechanics stethoscope is only a few $s at harbor freight or a buck or two more at your local auto parts store. At least you'll be able to locate the general source, if not the exact cause.

Good Luck, L M.
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"Wrangler....It's not just a vehicle, It's a lifestyle".
.................................................. ........................
1987 YJ-4.2L-Standard Shift- Re-manufactured Carter Carb-2" body Lift-31X10.5X15 BFG KOs-190K Miles No back seat.
HEI distributor with computer and all related relays and wiring removed.
12K Badlands winch with dual batteries.
Warn front bumper. Matching imitation Warn bumper on the rear.
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Old 04-21-2018, 06:29 PM   #8
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I'm wondering if you might be experiencing spark knock. It usually occurs at lower rpms with the engine under load. You could fill up with premium or add octane booster to the tank and drive it and see if there's any change.
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Old 10-20-2019, 12:09 AM   #9
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Did you ever figure this out?? Just tonight my Jeep started doing the exact same thing your describing like to a T
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Old 11-12-2019, 01:01 AM   #10
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Any updates? Anyone?

Here is my issue:
https://www.wranglerforum.com/f202/2...h-2382133.html
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Old 11-12-2019, 06:03 PM   #11
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I'm gonna guess u-joint. LMK if i win.

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