Bad Clunk in Driveline

[JGrefenstette]

the problem has been there for a while but is now getting worse. heres the deal. this could be in the transmission/clutch, or rear end. i have a considerable about of backlash in the rear diff, 30 degrees give or take. so the when i shift gears between the deceleration of the rear end torque and the accelertation when i start to engage the clutch, if i dont ease it you can feel the surge, but thats not the issue. if i come of the intersate after crusing 65mph+ for any amount of time, and down shift through the gears. say i come to a stop, put it in 2nd, as i begin to engage the clutch and take off, before i start moving, as the clutch contacts the flywheel, i feel/hear and loud, CLUNK!. ive conluded that to be the slop in the rear, am i right? whats worse, since my emergency brake dosent work, i use the transmission to hold the truck. i hate having to park on hills, cause i can feel, after i shut the truck off, put it in 1st, resease the clutch pedal, then slowly let off the break, i feel the transmission take up its slack, then if the hill is steep enough, i feel a second loud, clunk/pop! what the heck, it feels like it could be a transmission mount sleave as the transfer case mounting plate pops above the sleave, or could it be the gears in the rear taking a beating against eachother? i have poly trans mounts, bolts are very tight. new engine mounts too. not poly though. any ideas, thoughts???



ive been wanting a detroit locker for the rear. will this solve the backlash issue/tighten the rear???? also, say this is an issue inside the getrag, main componants. how much does a rebuid kit/parts for it cost?



thanks yall, much apreciated

 

[Makaio]

Jimmy,



Have you checked your u-joints? I've experienced a couple of instances where I thought the ring and pinion backlash was causing the "clunk" when all along it was the u-joint on the transfer case end. I pulled the diff cover and upon inspection everything "felt" tight but when I had someone put it in gear with the parking brake on, I discovered the u-joint had gone bad. Just a suggestion to check the simple things first.

 

[JGrefenstette]

i repalced all 3 rear u-joints, and carrier barring about 12,000 mi. ago. and i keep em pretty well greezed. so i cant imagine they are already shot. do you think its possible? thanks for the advice

 

[PToombs]

It's possible. All it takes is 1 cap not getting grease, and it's junk. Something else to check, the lug nuts. Make sure they're tight! (voice of experience here, the transfer case was ok, after I opened it up. )



Maybe do like Makaio said, get under it and have somebody go from forward to reverse and check for slop. Should be noticable if it's as bad as you say.

 

[Tippin Spotted Cow]

There's also the slip joint or whatever it's actually called that can loosen up. Where your back half of the driveshaft slips into the carrier and into the front half. Those splines wear out and the driveshaft clunks back and forth like with a bad u-joint. Also if your driveshaft is just slightly bent, that could cause your brand new carrier or u-joints to go bad pretty quick... I'd check 'em again.

 

[JGrefenstette]

the drive shaft is tight were it mates at the splined ends, i just was under it yesterday when i changed the oil. and with the truck in gear, i rocked it back and for pretty hard, while under it, to see/listen for the noise. the rear end is VERY loose, but the transmission or transfer case is also pretty loose. and i was hearing some strange noises come out of the t-case. id like to see the internals of that thing and get an idea of whats going on it there.



the np205's are chain driven right? could there be a problem in there? and yes it is full of oil

 

[JGrefenstette]

oh and, yall might like to hear. after just changing my oil, 5,050miles since last change. it had Rotella-T 15w-40 in it with a fleetgaurd filter. (i just changed over to Valvoline Premium Blue)

having worked in a john deere shop, and being around diesels for a while, and now in the heavy trucking side of things, ive seen a fair amount of motor oil, and i mean to tell you, i have yet to see oil come out of an engine with over 275,000 miles on it, as clean as this stuff was. it still had the forest green tint that the rotella had when fresh. i put it on my fingers, couldnt hardly detect any soot, i was very impressed.

 

[foolkiller]

another thing to check... .



the u-bolts that strap your leaf springs to the axle. found those loose on a old bronco one time and it was with the symptoms you describe.



j

 

[PToombs]

Jimmy, you can't check any driveline stuff with it in gear, even if it moves a little. Block the wheels, put it in neutral, and check it again.



I've seen way more bad spline joints on the front shaft than the rear. I don't know why, but they seem to go bad much faster.

 

[Tippin Spotted Cow]

Like Pete said.



I've had some pretty bad u-joints, but you can't even notice them with the truck in gear.



The NP205 is gear driven. That's why it's so hard to shift. The 203's off the gassers were chain driven.

 

[GCroyle]

Another item for your check list.

Jimmy,



Lots of items have been pointed out, but I have not noticed any comments about the clutch disc, specifically the torsion damper.



I cannot diagnosis it from here but IF the (this is based on the original 13" cast iron design clutch system) predamper spring component of the torsion damper is gone, then in the damper itself, you could have a source of lash. External diagnosis could be challenging, but you might try rotating the output shaft with the trans in gear and see how much lash exists. The 13" 1st Gen systems used a set of small external springs to create the predamper or idle damper section. If you have a different clutch, then most but not all of them have a predamper.



Good luck.

 

[JGrefenstette]

hmm, good stuff to check out thanks guys. pete. the truck was in 2nd gear, with the engine off. and i could move the shaft bout 30*. so does that mean the issue is in both transmission and rear end? because it seemed like you were saying that with the truck in gear the drive shaft shouldnt turn much, but it sure does... .



i dont know if this will help yall at all, but sometimes i get a violent launch shudder when i engage the clutch, othertimes its smoother than butter. there is no pattern to it whatsoever. some days its smooth, other its verry rough. who knows?

 

[JLEONARD]

with the truck in gear the drive shaft shouldnt turn much

Mine turned about 10 deg.

 

[Tippin Spotted Cow]

As a side note, the gear driven or chain driven transfer cases refers to just the front end, they're all gear driven to the rear.



Which brings me to my next thought. Try engaging 4wd and turning the front driveshaft, that should help you isolate it to if its the trans/transfer case or if its the driveshaft, or the rear end.



If the front driveshaft also moves roughly 30deg, and the rear moves with it at pretty close to the same amount, I would say the problem is in the transmission/clutch. If the front driveshaft moves 30deg without the rear moving, I'd check out your transfer case. If the front driveshaft doesnt budge, or moves considerably less, I'd say the issue is in the rear driveshaft or rear diff. Don't lock the hubs to do this.

 

[JGrefenstette]

yea matt thats a real good idea. ill do that and let you know what it feels like.



also this should make you laugh, went out to the truck to go to work last week, 5pm, walking to the truck and noticed some golden fluid around the hub lock dial. and it had dripped out and on the wheel then to the ground. first thinking it was a bad axle seal, then imidiatly realizing the front axle dosent have a seal on the outer part of the hub like that, (after i had already touched it and rubbed it between my fingers to check the consitency. it felt to watery to be oil, but slightly thicker than water. ) well yea you probly guessed it. a dog ****** on the hub, and i had just about tasted it to check what it was, before i realized it. hahaha

those dang furry little *****s :-laf