Deceleration Moan...what I've done.

[Safado]

So I've been troubleshooting this one for awhile now and have narrowed it down a bit with a recent rear axle service.

Symptoms:

There is a very loud moan/grinding sound when decelerating from ~65 MPH. If I give it a little gas (as to engage the drive line) the moaning stops. Slower speeds either don't have it or aren't audible....I mainly get it when exiting the freeway.

I had the rear torn apart this week to repack the rear bearings as the seal had been compromised and there was a slight wobble in both the tires. So this is all after repacking the rear bearings and eventually putting in new fluid in the rear diff.

Things I've done:

Dropped the front Drive Line, locked CDL...( I did this a few months back) the sound was still there.

Dropped the rear Drive Line, Locked CDL removed both rear axle shafts, NO NOISE.

Put the Axle shafts back in, filled diff with new oil....NO NOISE.

Replaced the Drive Shaft, unlocked CDL....the noise is back.

And for s***s and grins...locked the CDL....NO NOISE!!!!!

WTF is going on here? I didn't want to drive too far with the CDL locked, but from one exit to the other, I didn't get the noise when I normally would.

I need to replace one of the U-joints in the rear driveline...it has a little slop, but not sure if it is enough to really cause that much noise. I packed it full of grease just before going out to test it.

Ok, so this is the point that I rely on all of you for your vast knowledge and experience. Let the questions and ideas flow. Thanks for your help.

 

[Rookie2]

Safado,

Probably not much help but might give you some ideas to run a search on. Seems like I recall decelleration moan being associated with something in the differential.. pinion gear or something to that affect.

Good luck.
Rookie2

 

[Safado]

Thanks Rookie, that's where I though the problem was going to be until I didn't get the moan with the axles put back in place. If I understand things correctly, the wheels would then be turning the gears in the diff and cause the noise on a more regular basis, since the DL was still dropped and there was no way to "engage" the rear pinion.

And the CDL test threw me off that as well.

I'm thinking it's got to be something up in the x-fer case, maybe output bearing, but there's no slop there. Just fishing for ideas.

Thanks

 

[cruiserdan]

FWIW locking the CDL puts an additional load on the drivetrain that would tend to "bias" any slop. I'm not sure WTF that means but it could be that something in the rear transfer output is the offending party and leaving the center locked loads it in such a manner that the slop is taken up.

Purely a wild ass guess...........

 

[RavenTai]

if you have a known bad U-Joint start by replaceing it, and maybe its companion on that drive shaft, it may or may not fix your problem but worth a shot and needs doing so might as well

 

[Rookie2]

Sorry not much help on this, but this is an area I haven't worked in yet. But for the betterment of my understanding, with the rear drive line dropped, why would it matter what's done to the rear dif. and axle. Under this scenario, you aren't getting any power to turn the rear.. no??

Thanks,
Rookie2

 

[Safado]

Thanks Dan...I don't understand the working components of the x-fer case well, and anything helps. Hoping Kurt will chime in soon, didn't he have it all pulled apart and detailed?

RT...it's on the menu...just wanted to mention it for completeness.

Rookie...With the axles in place, the gears in the rear diff will be moved by the wheels as you travel down the road. True there will be no "power" supplied to it from the rear driveline, that's why I did the 2 tests, but the internals will still be spinning.

 

[Beowulf]

Safado,

Is there a chance you have the DS U-joints with incorrect phasing during one of the services? That might account for the noise/vibration.

-B-

 

[Safado]

Ok B, I've read it 4 times and still don't really know what you're talking about...please "stupidfy" your question so that I can understand it.

THanks

 

[cruiserdan]

The Wulf is refering to the relationship between the U-jounts in the driveshaft. That is refered to "phasing". In some cases the U-joint +'s should be lined up (IE pointed in the same direction). Some set-ups prefer that the +'s be "out of phase" meaning that they are shifted 45 degrees off of matching.

Since my FSM's are some distance from my ass and I am a bit lazy to go shag them, I think that the rear shaft should be "out of phase" and the U-joint points should be at 45 degree angles (Memory tainted by a couple Boddingtons, thougthfully provided by a thankfull board member )

 

[MTNRAT]

I have the same thing I think.

I get the growling moan on deceleration. Remove front drive, use rear only and CDL locked, still there. Remove rear driveshaft, use front only, CDL locked still there. Thought it may be an exhaust rattle but, full OEM exhaust replacement from manifold to tailpipe, still there. Removed rear under back tire carrier that was not in use. Still there. Removed, cleaned and reinstalled all heat shields, still there. Upon futher retrospection, I believe it started very quietly after I regeared to 4.88s. First thought it was when I put on Ice radials as their rubber is very soft and can make noise. Put on those tires just after I had the 4.88s installed. It is getting louder and happens more often now. It is more pronounced with both driveshafts in, and even moreso with both driveshfts in and CDL locked. I have done so much stuff to my truck lately I cannot pin it down to any one modification???????? Next tuesday I am going on a business trip for a few days so I am going to leave the beast with my mechanic to give him a little time to drive it, and see if he can figure it out. Any leads would be helpful.
Cheers,
Sean

 

[cruiserdan]

Sean,

In your case I would lean toward the Gearsets. It may not necessarily be a durability problem, just a by-product of the aftermarket gearsets.

 

[MTNRAT]

Gears?

Well, if it is the gear sets, can they be shimmed to get rid of the noise. It is really loud going down long mountain passes and is driving me nuts. i think it is only making noise from the rear of the vehicle.
Cheers,
Sean

 

[cruiserdan]

I do not know if it can be "adjusted out" it may be a case where you just need to live with the noise or replace the gearset. It is indeed possible that a noisy gearset will last many, many miles and it is not necessarily a "bad" gearset.

 

[Safado]

Ok Dan, that makes more sense. I read teh whole PROPELLER SHAFT section in the FSM and didn't read the word "phasing" once in there. They rely heavily on match marks before removing any part. All the pics however show the +'s in phase at all times. Let me know if you find out differently. I just checked mine and they all seemed in phase.
The problem is that I know both shafts have been toyed with so I'm really not sure if they're where they should be, ie if matchmarks were set and followed from factory. The front has been re-tubed and a CV joint added, and I had the rear retubed about 5 months ago ( the sound has been around longer than that...truck came used this way ). And depending on how bad this is or not...I've NEVER set a match mark each time I've dropped them. I just never knew it to be that important. Can it cause problems? Or just bad form?

Thanks for the ideas...keep em coming.

 

[Beowulf]

Safado,

"The front shaft unis (on 80s) are 90 degrees out of phase, while the rear shaft unis are in phase. Correct assembly will see all grease nipples on either shaft roughly in line (if assemblies are as from Toyota)."

and

"Universal joints by their nature are NOT constant velocity joints when working through an angle. A smooth/constant rotational force is converted to a jerky 4 movement affair. The greater the angle, the greater the jerking. Try driving a 4WD with uni joint steering knuckles and you will feel this through the steering. The idea of having unis on either end of a shaft 'in phase' is to allow them to 'cancel' each other. This of course necessitates that they be working through roughly (actually closely) the same angle. The 80s front unis being out of phase contradicts this practice. I don't know why they are out of phase."

-Norm Needham-

-B-

 

[Safado]

Wouldn't 90 degrees out of phase put them back in phase...or did he mean 45?

Kinda like a + and an X What would be recommended for a CV joint configuration?


My current configuration...

My front driveline with the CV joint had all 3 in phase...the rear 2 were in phase as well.

 

[RavenTai]

I saw a explanation about this in one of the manuals but I cannot find it now

The FSM assembly drawing shows the front shaft 90* out of phase and the rear in phase, the high pinion front 3rd member with its reduced shaft angle (at stock height) may have something to do with the difference

Safado, you say you have 3 front shaft joints? Did you add a double cardan to that shaft?

 

[MTNRAT]

Thanks, Cdan. The thing is if it is a noisy gearst, I won't be able to live with it. I hate noises. I am going to change out the gear oil bact to dino to see if there is any difference. If it does indeed prove to be the gearset I will be changeing that out. It sounded very much like an exhaust rattle, but i changed that and no diff at all, so I am beginning to think it is in the moving parts.
Cheers,
Sean

 

[Safado]

UPDATE: PLEASE READ IF YOU'RE FOLLOWING THIS

I went to bed last night thinking a lot about what B wrote in his second quote. As visions of U-joints danced in my head, I could envision what Norm was talking about and want to improve the description of the sound I'm getting. The moan could more accuratly be described as a very fast pulsation...or a wobble. This could very well be the problem, especially if there is any slop in the u-joint (which I know there is) and the angles at which the x-fer case and rear diff are pointed.

Thanks for the quote B!!!