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Rear clunk or thud noise from 2nd to 3rd gear


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Hey guys,

 

I don’t know if this is a transmission problem but it definitely doesn’t feel like one to me.

 

But if the vehicle coasts into 3rd gear, let’s say going down a hill and it’s gaining speed on its own I get a clunk noise from the rear when it goes into the gear. And that’s between 15 and 20 mph.

 

Or if I’m accelerating and right before it goes into 3rd I pull off the accelerator it makes the noise. Sometimes at 4th or 2nd also if I abruptly take off the accelerator.

 

However, with constant acceleration throughout the gears there is no noise.

 

There is no rough shifting, hesitation going into gears, banging into gears, or slipping. The transmission itself is shifting properly and at its proper points.

 

Even if I were to go down a steep hill and let the vehicle gain its own speed and go through the gears, it changes normally but just get the noise.

 

On highways if I want to rapidly accelerate it drops gears smoothly and changes.

 

Any ideas?

 

 

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7 hours ago, AR97Pathfinder said:

Hey guys,

 

Any ideas?

 

My money's on a busted motor mount, driver's side I think.  Put a floor jack under the oil pan (block of wood between) and lift it up a small amount, maybe 1/2" or so.  Check for separation of the rubber from underneath the truck.

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My money's on a busted motor mount, driver's side I think.  Put a floor jack under the oil pan (block of wood between) and lift it up a small amount, maybe 1/2" or so.  Check for separation of the rubber from underneath the truck.

I’ll check that out. I was planning on changing those motor mounts last summer.

But I’m not sure if I’ll be able to do it myself. I know the passenger side isn’t too bad but the driver side is because of the 4x4?

Have you or anyone changed it?

Thanks Hawairish


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3 hours ago, AR97Pathfinder said:

I’ll check that out. I was planning on changing those motor mounts last summer.

But I’m not sure if I’ll be able to do it myself. I know the passenger side isn’t too bad but the driver side is because of the 4x4?

Have you or anyone changed it?

Thanks Hawairish

 

It's been a few years since I changed one.  It was when I was installing an SFD on a buddy's truck.  IIRC, his driver's side was split because of the engine rotation; stretches the mount on the driver's side, compresses on the passenger side.

 

Installing the SFD is what revealed/confirmed the issue, but we knew going into the install that he was experiencing the same subtle clunk/bump when shifting that you described.  It varied by acceleration but was most prominent when the transmission shifted in either direction.  Sometimes it was a bump, sometimes it was a clunk, depends on how forceful the acceleration/deceleration was.  The mount came out in two pieces...supposed to be one, of course.

 

It's changed in similar fashion to installing a SFD...requires supporting the engine, dropping the front differential, and lowering the subframe a little, just enough to clear the two studs at the bottom of the motor mount.  The diff gets dropped because the snout blocks the motor mount nuts...not much room to work with.  A single nut holds the mount up top, and it can be a pain to reach and requires the airbox and intake plumbing to be removed; a bit tougher on the passenger side, but in all likelihood the mount should be okay.  All things considered, changing one or both is a day's job...kind of one of those things where you change both while you're in there.

 

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1 hour ago, hawairish said:

 

It's been a few years since I changed one.  It was when I was installing an SFD on a buddy's truck.  IIRC, his driver's side was split because of the engine rotation; stretches the mount on the driver's side, compresses on the passenger side.

 

Installing the SFD is what revealed/confirmed the issue, but we knew going into the install that he was experiencing the same subtle clunk/bump when shifting that you described.  It varied by acceleration but was most prominent when the transmission shifted in either direction.  Sometimes it was a bump, sometimes it was a clunk, depends on how forceful the acceleration/deceleration was.  The mount came out in two pieces...supposed to be one, of course.

 

It's changed in similar fashion to installing a SFD...requires supporting the engine, dropping the front differential, and lowering the subframe a little, just enough to clear the two studs at the bottom of the motor mount.  The diff gets dropped because the snout blocks the motor mount nuts...not much room to work with.  A single nut holds the mount up top, and it can be a pain to reach and requires the airbox and intake plumbing to be removed; a bit tougher on the passenger side, but in all likelihood the mount should be okay.  All things considered, changing one or both is a day's job...kind of one of those things where you change both while you're in there.

 

Possible to do this at home? 

 

I do majority of the work on the vehicle in my driveway and garage, but I'm not too sure about this as I've never dropped the diff before or lowered the sub frame. 

 

Based on your experience what do you think?

 

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7 hours ago, AR97Pathfinder said:

Possible to do this at home? 

 

I do majority of the work on the vehicle in my driveway and garage, but I'm not too sure about this as I've never dropped the diff before or lowered the sub frame. 

 

Based on your experience what do you think?

 

 

It's doable at home.  At minimum you'll need a good floor jack, 4 jackstands, and a typical set of metric sockets, wrenches, and extensions.  You'll also need a separate means to support the engine, such as an engine support bar, a transmission jack (works fine under the oil pan or transmission), another jackstand supporting the back end of block (use caution), or even a pile of 2x4s (Google "wheel cribs").  It's nice to have another set of hands/eyes, but I've done this sort of work several times by myself to install SFDs, install lockers, etc.  It's tedious job because there's a lot of stuff to disconnect (skids, CVs from axle flanges, front driveshaft, axle from hangers, air box stuff, etc.) and because you have to go pretty slowly checking that things are supported/balanced and that you've slacked things (like the power steering lines).  Plus, limited space next to the motor.  Not a fun job, but doable. 

 

You'll use two jackstands to support the front chassis (use the lift pads under the front of the driver's door).  The other two can be used to assist lowering the front axle...I put the jack under the differential area, a jackstand at the end of the passenger side axle tube, and another jackstand under the pinion flange (to keep the diff from rotating, because it's not balanced at all).  Lower the jack a little, then lower one jackstand a notch, then lower the other jackstand a notch; repeat until it's as low as you can get it, then drag it out with the jack.  When lowering the subframe, it helps to keep the rear-most rear subframe bolt threaded just enough to act as a guide pin for the subframe as you lower it, plus allows the subframe to pivots on the bolt heads so that the front of the subframe can go lower.  The jackstands can then be used to support the subframe when it's lowered enough.

 

Since you live in a rust area, you'll need to see if it's even safe to remove the subframe nuts and hardware, which has probably never been removed before.  If it doesn't look safe, you'll need another approach.  You'll still need to drop the front axle to access the motor mount nuts, and then use an engine hoist or transmission jack to lift the engine enough to clear the mounts from the subframe.  This is tougher because you'll need at least 2" to clear things, which means you'll need to check hoses and wires all over the engine bay, as well as the fan inside the shroud, and tension on the transmission mount (which could stretch the rubber there, too).  To that extent, I'd check the transmission mount too, while you're at it.

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It's doable at home.  At minimum you'll need a good floor jack, 4 jackstands, and a typical set of metric sockets, wrenches, and extensions.  You'll also need a separate means to support the engine, such as an engine support bar, a transmission jack (works fine under the oil pan or transmission), another jackstand supporting the back end of block (use caution), or even a pile of 2x4s (Google "wheel cribs").  It's nice to have another set of hands/eyes, but I've done this sort of work several times by myself to install SFDs, install lockers, etc.  It's tedious job because there's a lot of stuff to disconnect (skids, CVs from axle flanges, front driveshaft, axle from hangers, air box stuff, etc.) and because you have to go pretty slowly checking that things are supported/balanced and that you've slacked things (like the power steering lines).  Plus, limited space next to the motor.  Not a fun job, but doable. 
 
You'll use two jackstands to support the front chassis (use the lift pads under the front of the driver's door).  The other two can be used to assist lowering the front axle...I put the jack under the differential area, a jackstand at the end of the passenger side axle tube, and another jackstand under the pinion flange (to keep the diff from rotating, because it's not balanced at all).  Lower the jack a little, then lower one jackstand a notch, then lower the other jackstand a notch; repeat until it's as low as you can get it, then drag it out with the jack.  When lowering the subframe, it helps to keep the rear-most rear subframe bolt threaded just enough to act as a guide pin for the subframe as you lower it, plus allows the subframe to pivots on the bolt heads so that the front of the subframe can go lower.  The jackstands can then be used to support the subframe when it's lowered enough.
 
Since you live in a rust area, you'll need to see if it's even safe to remove the subframe nuts and hardware, which has probably never been removed before.  If it doesn't look safe, you'll need another approach.  You'll still need to drop the front axle to access the motor mount nuts, and then use an engine hoist or transmission jack to lift the engine enough to clear the mounts from the subframe.  This is tougher because you'll need at least 2" to clear things, which means you'll need to check hoses and wires all over the engine bay, as well as the fan inside the shroud, and tension on the transmission mount (which could stretch the rubber there, too).  To that extent, I'd check the transmission mount too, while you're at it.

Thanks for explaining the process in detail.

Does sound a bit tedious when it comes to the engine, diff and subframe. But I guess an extra set of hands and patience should get the job done.

I’ll probably have to get another jack and some more stands. I don’t have that many.


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