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knock in neutral and 5th


cwat

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So I'm working on my new '84 720 4x4. 2.4 z engine with 5 speed. The truck has a knock when the clutch is out (not pressed) in neutral and 5th gear. It is much louder in 5th, you can definitely feel it with your hand on the shifter. I haven't been able to hear it in any other gear and the second the clutch is engaged the noise goes away. Speed of the knock is directly tied to the rpm. I've read the best way to get to the clutch/transmission is to pull the engine but I don't have a shop to support that. I'm hoping its not a throwout bearing... Any advise would be greatly appreciated. Thanks

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Not the release bearing. It isn't moving or being used when the clutch pedal is up.

 

 

You say it makes noise in 5th gear while driving? What about in neutral... is this sitting still or coasting while driving?

 

 

 

Off the top of my head I would say the carrier bearing rubber surround has rotted away. Only know of only one instance of bearing failure so likely the rubber is gone away. The rubber supports the bearing so the driveshaft can spin inside it. Without the rubber support the drive shaft goes off center and vibrates.

 

The 620 has a two part drive shaft the center carrier bearing is at the rear of the front one.

620driveshaft003Large.jpg

 

620driveshaft002Large.jpg

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Then not the drive shaft.

 

 

So I'm working on my new '84 720 4x4. 2.4 z engine with 5 speed. The truck has a knock when the clutch is out (not pressed) in neutral and 5th gear. It is much louder in 5th, you can definitely feel it with your hand on the shifter. I haven't been able to hear it in any other gear and the second the clutch is engaged the noise goes away. Speed of the knock is directly tied to the rpm. I've read the best way to get to the clutch/transmission is to pull the engine but I don't have a shop to support that. I'm hoping its not a throwout bearing... Any advise would be greatly appreciated. Thanks

 

Can I assume that it makes a much lesser noise in all the other gears when driving??? and neutral and 5th is by far the loudest?

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If it makes noise idling in neutral, and you push the clutch in and it goes away, then you have front bearing issues.

You need to stop driving it as if it throws a bearing into the gears or pushes one thru the front cover you are going to have to find another transmission, right now you may just need a new bearing, but it can get a lot worse like oil coming out of the bellhousing drain hole.

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ALL gears 1,2,3,5,rev. use the counter bearing and counter shaft except 4th, which isn't a gear at all but a solid direct line connection through the transmission mainshaft from the clutch to the driveshaft. If fourth is quiet likely it's somewhere in the countershaft.

 

It's troubling that it makes noise in neutral, which is spinning the countershaft, but not under any load.

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If it makes noise in any other gears I can't hear it. It definitely goes away completely when you push in the clutch. Seems a little quieter once warm but that could just be wishful thinking. I changed the oil in the transmission. I got a few metal flakes out, but not much. Also, 5th is MUCH worse than neutral. In 5th you can feel it hit hard with your hand on the shifter. Luckily this is not my daily driver. I haven't moved it much anyway and not any in 5th gear. I'm still having a charging issue as well that I can't quite trace down. I'm thinking a bad ground at this point. 

 

Wayno, I was really hoping that would not be the case, but I fear you are correct. I've never rebuilt a transmission before. First time for everything I guess. Is there any (realistic) way to get at this without pulling the engine? 

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If it is worse in 5th gear rather than neutral, I would suspect the rear cluster gear bearing which is right next to the 5th gear itself.

you are going to have to pull the transmission, as the fluid coming out of it should have been a golden color, and there should not have been any chunks or metal pieces/flakes.

I have never had to change out that bearing in any of my transmissions, but the kid down the street did, he had to pull the whole transmission apart to get to that bearing.

I just know that I lost the front bearing in one of my transmissions, and one of the bearings got between my gears and it broke the cluster gear shaft right at 5th gear.

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If the problem persists in neutral, but then goes away when the clutch pedal is depressed, then it's not likely to be repairable without completely removing both front and rear housings. It could be the needle bearing under 5th gear, in which case, it is possible to repair by removing just the tailhousing, but that's not the likely cause of the noise. Also, when removing one of the housings, it's better to remove the other to make sure the seal is good on reassembly. Since the tailshaft housing bolts also hold the bellhousing, removing them may allow both seals to break.

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