Unwanted Noise

Scoutboy74

Scoutboy74

Moderator
Alright yawl. The fat white boys got us a sitsheeyashun with one of our fleet rigs. This be johnboy's '77 sii with 304, 727, d20, 3.54 open diffs sitting on stock suspension and small tires. This rig was a dead dawg reskew about 14 months ago. Now it's a solid driver. Ever since we've been able to drive it, we've noticed a steady growling noise once a certain speed is reached. The rear wheel bearings and brakes were done a couple months ago with no change to the noise. There is no slop in the rear drive shaft at either end. There is no u-joint clunk when the transmission is engaged. When moving slowly in either forward or reverse, the thing is church-mouse quiet. The noise only rears it's ugly head once a certain speed has been reached, and then it is steady and related to some rotational speed. Coasting has no effect. Neither does shifting the trans from d to n at speed.
Earlier today in an attempt to isolate the noise, we removed the rear shaft so that we could run on the front axle. Immediately I noticed the shaft was about 45 degrees out of phase. Naturally johnny and I were quite excited thinking perhaps we had found he culprit. We went ahead and test drove it on the front axle only. The noise was gone. When we got back, john removed the slip joint which was one spline off and re-installed it in phase. We then put the shaft back in and went for a drive fully expecting to share high fives, only to be disappointed, as the noise was back. So what does all this tell us? Tia

couple more things...yes we've had the diff cover off and did not notice any obvious issues. Yes the diff is full of gear lube. The t-case is full of 50wt. Motor oil.
 
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I would have to say u-joints...

U-joints only "clunk" when the needle bearings have been ground to dust / almost dust.
 
Rc- u-joints would at least be a fairly painless thing to eliminate and I've dun tolt johnboy he orta change 'em. The ones in the rear shaft now are of unknown vintage, but the needles are definitely not ground to rust. They look pretty good still.

Rk- with the shaft in place, there is no slop. I realize now that I shud have jerked on the t-case output and the rear input yokes individually while the shaft was removed to observe slop also...dammit my retardid hyde!
 
No need to yank the drive shaft, just stick the trans in neutral with the ebrake on. Crawl back under the thing and see. Should be able to distinguish the pinion rotating within the gear lash.
 
Okay, thanks rk. Will do and report back with observations. May be a bit before that happens. Happy easter, yawl!
 
Time fer sum foller up on this'n. The other nite, cambo and johnboy got after swappin' out the u-joints for sum newbeez. As yoojooull, jerry and I took care of the stoopidvisjun. While john was thoroughly enjoying his time underneath the rig, he did sum jerkin' and twistin':yikes: and then when he wuz all dun playin', he tested the rear diff yolk for slop. His report was no up/down or lateral travel, however he wuz able to git the yolk to rotate just a small amount. This was with all fours on the ground, driveline connected, transmission in n, and brake set. Changing out the joints definitely improved things. The growling noise that we've been chasing now seems to be coming primarily from the t-case region, which is to be expected from a unit that has probably never been overhauled and is due for sum luvin.:ihih:
 
Slop in the azzend axle overall is most likely from wore-out spiders and side gear shit in the rear diff. The pin is worn out and possibly the diff case holes are toast. The diff case holes are not elongated, then a diff rebuild kit can be installed.

It's also very common regarding a d44 that one or both of the carrier bearing inner races have "spun" on the differential case and the shims have been eaten up resulting in excessive side play when the gear train is loaded and un-loaded.

Is the rear diff a trac-loc or open?

Any possible excessive wear/damage can be easily seen if the pumpkin cover is removed.
 
John did remove the rear cover months ago to bilge out the old goop and replenish with fresh gear lube. I did not get a chance to examine the internals, but I know he looked it over with an equally untrained eye and didn't discover anything blatantly obvious like metal chuncks or broken teeth. There does seem to be far less noise emanating from the rear axle region now with the new ujoints installed. The guys did find at least one joint cap with fubared needle bearings, so it was a much needed service.
 
I have no doubt that u-joints were the issue currently, the driveshaft simply amplifies all kinds of noise and vibration due to it's hollow construction. The out-of-phase just adds to that amplification.

The noise created by the wore-out differential case/components is also amplified by the driveshaft when it "loads" and un-loads when power is applied. That is what makes driveline noise diagnosis a bitch! It's normally a process of elimination just like you boyz are doin'. At least ya don't have to deal with the center/carrier bearing shit like you will have when dealing with mongo! Ya can't blame that on the fresh tranny!
 
Well johnboy bit the bullet and took blue thunder down to a qualified driveline/gear shop. The noise seemed to be getting pretty bad and once again sounding like it was coming from the back and not the t-case. Damned elusive noises anyway! When he explained the symptoms, diagnostic tests and items replaced, shop dude was quite convinced the problem would be in the rear diff. We should know for sure pdq.
 
Just a belated foller up tuh put this'n to bed. Gear dude found that the carrier bearings were badly pitted due to moisture contamination and an extended period of non-roto. The gears were fine thankfully. New bearings installed and the dam thingz as kwyit as a church mouse now!
 
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