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Signifigant "clunk" from the the front, only on REV Launch


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Ok... this is going to be vague and you smart guys will have to help walk me though what I should be checking...

 

When I'm parked, drop into Reverse and start backing up, I hear a noticeable "clunk/chunk". It's in the front half of the vehicle, and sounds like more central, like on the passanger side of the tranny tunnel or maybe just a little forward (I'm guessing).

 

There is NO noise as I'm moving forward at a slow, normal or fast pace. I have a somewhat steep driveway and the "clunk is more noticeable" when pulling out of it.

 

I'm thinking if it were Ball Joint (which were new less than 2 years ago), wheel hub, it would be happening all the time FW and REV. Also the Axle Shafts (if it were a little further forward than it sounds like) were the D30 shafts out of my TJ when I had the Vacuum CAD thing blocked off (I know I'm killing terminology here), with good and greased u-Joints with less than 30K miles on them. I have checked torque on Lower Control Arm Bolts on both sides (which were replaced with WJ Lower Control arms with good bushings) and have check Steering (Tie/Rod/Drag Link,etc) which was also a swap from my TJ. No wheel/tire rub anywhere that I can tell...

 

Could my Tranny be making this noise? There have been times of "hard"'ish shifting but nothing horrible and nothing really recently.

 

Thoughts, what else could I/should I check?

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Could be a slightly compressed tranny mount allowing the exhast pipe to hit the crossmember. More likely is a worn bushing in the right lower control arm.

 

I thought about the Tranny Mount but wasn't familiar with how it was setup, and hadn't yet taken the time to unbolt the mount and look.

 

The bushing on the LCA was good when Installed the WJ LCA's a few months ago...

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i would check the u joints, all of them even on the front axle. If any of the seals are bad on the non greasable one and havent be change for years they can be dry and would need replacing. Clunck clunck goes the u joint!

 

The front U-Joints were on the TJ Axle Shafts and I had them....they are barely 10 years old, upgraded, stronger 297x u Joints and had barely 30K miles on them (less than 1000 since installed on my MJ). Vistually they appear fine and I get no rattle or shake in the ujoint upon poking and prodding with a big screwdriver.

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get a helper to listen for you since it does it at slow speeds.... narrow down the location of the noise for us

 

Stick my head under the MJ while the wife pulls it out of the garage...sound like a death wish!! :cheers:

get in-FRONT of it and make sure she hits R not D

 

plus if you tell her you cancelled the life ins. she will be less likely to squish you on purpose :idea:

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lol funny stuff :fool: anyway my problem may not help you but its a thought look at "fyi control arm knock", this is a problem that i had, and that I'm fixing at the moment. It was a knocking sound in the front that i felt under my feet. I couldnt find what it was for a while i just over looked the upper control arms. I pryed on them and they seemed ok, i didnt see how bad they got until i remove them.

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I thought about the Tranny Mount but wasn't familiar with how it was setup, and hadn't yet taken the time to unbolt the mount and look.

You don't have to unbolt anything. Just crawl under and eyeball it.

 

Try a test: Keep your foot on the brake, put it in reverse, and touch the gas, forcing the engine to twist under torque. Listen for the clunk. If you hear it, repeat the procedure but have an assistant do the goosing the gas while you lie on the ground and watch where the exhaust pipe runs over the cross member.

 

What can happen is that the resilient cushions in the tranny mount compress due to age, allowing the space between the exhaust pipe and the cross member to be reduced. When the engine twists, that can result in contact and a clunk or rattle.

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I thought about the Tranny Mount but wasn't familiar with how it was setup, and hadn't yet taken the time to unbolt the mount and look.

You don't have to unbolt anything. Just crawl under and eyeball it.

 

Try a test: Keep your foot on the brake, put it in reverse, and touch the gas, forcing the engine to twist under torque. Listen for the clunk. If you hear it, repeat the procedure but have an assistant do the goosing the gas while you lie on the ground and watch where the exhaust pipe runs over the cross member.

 

What can happen is that the resilient cushions in the tranny mount compress due to age, allowing the space between the exhaust pipe and the cross member to be reduced. When the engine twists, that can result in contact and a clunk or rattle.

if it is this you may also be able to find a shiny mark where the exhaust is rubbing on the member. :dunno:

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I thought about the Tranny Mount but wasn't familiar with how it was setup, and hadn't yet taken the time to unbolt the mount and look.

You don't have to unbolt anything. Just crawl under and eyeball it.

 

Try a test: Keep your foot on the brake, put it in reverse, and touch the gas, forcing the engine to twist under torque. Listen for the clunk. If you hear it, repeat the procedure but have an assistant do the goosing the gas while you lie on the ground and watch where the exhaust pipe runs over the cross member.

 

What can happen is that the resilient cushions in the tranny mount compress due to age, allowing the space between the exhaust pipe and the cross member to be reduced. When the engine twists, that can result in contact and a clunk or rattle.

 

I'll pull it into the Garage tomorrow and take a closer look...it cold (for CA), Dark and I have "kid duty" tonight

 

BTW, I only have 2 feet....how do I keep a foot on the brake, one on the clutch and one on the gas at the same time (have I mentioned that I wish this was an AUTO recently?).

 

Wade

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stick shift changes things, i was thinking automatic... don't forget to check for axlewrap in the rear-end and worn out bushings back there.

 

for some reason (volvo experience here) only stick shift cars wear out the bushings in the rear-end and the tell-tale signs are clunks (again... RWD solid axle volvo here) but the same principle applies.. check the rear end too.

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stick shift changes things, i was thinking automatic... don't forget to check for axlewrap in the rear-end and worn out bushings back there.

 

for some reason (volvo experience here) only stick shift cars wear out the bushings in the rear-end and the tell-tale signs are clunks (again... RWD solid axle volvo here) but the same principle applies.. check the rear end too.

 

i have the Chevy Drop shackles that are basically new, so I know those bushings are good...but I can "feel/hear" the clunk and its for sure in the front 1/2 of the truck.

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:hmm: To check something simple, how about a motor mount? :dunno: I've found many of my takeoff front end clunks to be a worn out and busted motor mount, causing the whole engine and tranny to hop around, and depending on which one is bad, thats why it would do it in reverse, and not drive, or vise-versa.?.

 

-James

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:hmm: To check something simple, how about a motor mount? :dunno: I've found many of my takeoff front end clunks to be a worn out and busted motor mount, causing the whole engine and tranny to hop around, and depending on which one is bad, thats why it would do it in reverse, and not drive, or vise-versa.?.

 

-James

 

I didn't think about the motor mounts.... I actually have a brand new set sitting in a box somewhere...

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BTW, I only have 2 feet....how do I keep a foot on the brake, one on the clutch and one on the gas at the same time (have I mentioned that I wish this was an AUTO recently?).

My bad ... so many members have auto I fell into the trap of assuming.

 

I guess let the gas take care of itself. Hold the brake, and let the clutch up partially just enough to torque the engine and slow the RPMs, but not enough to fully engage the clutch. You don't need to hold it there, you only want to "bump" it momentarily to see if the pipe will hit the cross member.

 

As an alternate -- slip a thin piece of wood or something that's not "readily" combustible/meltable between the pipe and the cross member and try driving it. If the noise isn't there, you'll have a clue.

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I only have 2 feet....how do I keep a foot on the brake, one on the clutch and one on the gas at the same time (have I mentioned that I wish this was an AUTO recently?). Wade

 

A little heel and toe action jamminz.gif Although I doubt even the some of the best race car drivers could could do it very well in reverse on an incline. :brows:

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