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Discussion Starter #1
Anyone else ever get a bad shudder when towing with the 4bt/nv4500 combo? It feels like bad clutch shudder but I only get it heavily loaded in 4th.
I'm running a Luk single disc clutch rated 350hp/590tq. 3.73's and 33's and I have a good set of traction bars so I can rule out axle wrap. Clutch and u joints were new when I did the swap 4k mi. ago

This is in a 96 k1500 with the factory 10 bolt posi, the trans was out of a 06 Chevy city maintence truck with 30k mi. on it so I hope it it's good. And it can keep up with our 300hp/520tq lb7 d-max so I know I ain't pushing the limits on the clutch.

Ideas anyone??
Thanks, Glendon
 

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This sounds a bit like the old Chevy 4 speed stepvan problem of a clutch disk that has lost a couple of springs in the disk. Luk is a good clutch but can develop this problem when it is abused.
 

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Didn't elaborate on if it shuddered just when shifting ,or all the while in 4th... if it shudders all the while in 4th and loaded, then it could be the driveshaft is binding from the springs being compressed while loaded.....
 

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Yeah, it shudders all the while under boost below 2100 or so rpm and heavily loaded in 4th, 5th is smooth, 3rd can vibrate a little sometimes too but again only when loaded heavy and not a shudder like I get in 4th.
 

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Like I said, check driveshaft. Could be bottoming out ,causing the driveshaft to bind and shudder......would be my first suspect,as I have seen it happen. ..... dirty injector could cause a shudder as well, but could be detected in the exhaust sound.
 

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Check the pilot bearing. A worn pilot bearing causes that exact problem.
 

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Check the pilot bearing. A worn pilot bearing causes that exact problem.
Thanks for that suggestion, it got me thinking and I remembered that when I bolted my trans up the one locating dowel was missing, so I just eyeballed it and bolted it down. So I checked and sure enough it had moved, so I slid the trans back an inch and made a locating dowel to keep it centered. Back together and much improved, the shudder is gone but there is still a harsh vibration. If I roll down the window it sounds like someone taking an air hammer to my aluminum driveshaft.
I also checked the driveshaft and it's not binding and the u-joints seem good.
 

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Discussion Starter #9
Just a thought, could a worn slip yoke cause a vibration like this? Like I said in my previous post it's much improved but still have a harsh vibration loaded and a just a loud rattle empty when you feed it a lot of torque (of which I've got plenty) at 40-45mph. The other day I also noticed a almost imperceptable clanking once when coasting with the engine neither pulling or holding back. Still haven't ruled out the pilot bearing yet but just thought of the slip yoke the other day, wondering if it might be the culprit.
 

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A worn slip yoke wouldn't normally be limited to one gear. OTOH, its easy to check out, so check it out.

A loud rattle in 4th is common with most manual transmissions behind a Cummins, especially a 4BT but the 6 does it also. It's called "gear rollover" noise. Basically, because the countershaft and mainshaft speed gears are unloaded they rattle against one another from the torque impulses of the engine. It shouldn't vibrate though. Well, not much anyway ;-) It's mainly just a loud, annoying growl. The 4.3L gas V6 and 6.5L diesel also did this, and is part of the reason transmissions from those applications have the internal harmonic damper on the mainshaft between 5th gear and the nut.
 
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