Rearend Whine

[Gauthier]

MWilliams:



Who is the DC rep you met with convcerning your axle whine? I have a DC rep scheduled to look at my truck in two weeks.

 

[JHardwick]

Originally posted by MWilliams

He said that the AAM 11. 5" rearends have a 'whine' in them by design. "I don't think so!"

I'm sure they didn't design a whine in them, but the design has a whine.



Any gear box is gonna make some noise. The bigger the parts, the looser the tolerance, the more noise ... ... ... period.



By looser tolerance, let me give you an example ... ... .



If you want a 1/2" pin to "slip fit" in a 1/2" hole ... ..... . 0003" to . 0005" is sufficient with good surface finishes.



If you want a 3" pin to "slip fit" in a 3" hole, now your talking . 002" to . 003".



This is not a 40K luxury car with lighter parts and better noise dampening ... ... ... ... ... ..... it's a truck with big, heavy moving parts.



I'm prolly gonna get flamed, but if you want a luxury car, buy a luxury car ... ... ... ... . for me, DC has made a 1 ton dually so soft and quiet that I can pick apart the progressive suspension that rides nice, but wheel hops!!!!!

 

[JHardwick]

as a post script ... ... ... ... ...



Ride beside a commercial truck with your window down someday ... ... ... the bigger they get the more noise they make!

 

[Gauthier]

There is definitely a problem with the rear end in the Dodge trucks. The 11. 5" rear end uses the same gears and bearing as the Chevy, yet the Chevy trucks do not have the noise. The center section casting is, however, different than the Dodge. I'm thinking there is or was an error in the machining or setup tolerances for the gears. I removed the rear cover to look at the wear pattern and gears have the worst setup I've ever seen on a factory rear axle.



On my truck, if you listen closely, the noise goes up in multiplies of 25 mph with the worst at 50 mph. This makes me think there may be a harmonic element to the problem. The counter to this is that I think DC engineering must have modeled the trucks during the stress analysis and at least conducted a modal analysis. However, judging by the primitive and goofy vibration controls, a full vibration analysis was not completed.

 

[MWilliams]

Gauthier,

I'm sorry but I didn't get the Rep's name. I had to leave my truck at the dealer because they could not give me a time that the Rep would be there. I only spoke with him on the phone. And, I did tell him that I disagreed with his decision.







JHardwick,

I do understand what you are saying, however, I believe if you heard the noise My Truck was making, I'm sure you would understand my concern. The noise is beyond normal!



Thanks for the replies!





Michael

 

[GDouglas]

I was noticing the whine in my 11. 5" rear (between 65 and70 on slight pull) the other week and I decided to take the cover off and do a gear pattern check with some white lithium grease brushed on 3 or 4 of the teeth. The contact pattern on the pull side of the teeth was textbook perfect. The pattern on the coast side was slightly toward the tip of the teeth but not running off the tip edge of the tooth.



If I were to change anything, I might change the pinion shim to about . 003" deeper to try to get the pattern on the coast side a little deeper in the tooth, but since my whine is on a slight pull and not on coast, I decided not to worry about it and just change the fluid for now. If I ever have to replace a bearing someday, I will pursue a little better pattern then. For now, if I play the radio where the volume usually stays (1/3 scale), I can barely notice my whine at all.



Since I have an acceptable contact pattern, I am comfortable that it isn't going to leave me on the side of the road in BFE with ring and pinion failure.

 

[JHardwick]

Originally posted by GDouglas

If I ever have to replace a bearing someday, I will pursue a little better pattern then.

From what I know (which may be very little), changing the mesh pattern on broke in gears could be detrimental.



-Jeff

 

[GDouglas]

I kind of see it as a judgement call on changing the mesh on a set of "broken in" gears. Most rear gears that I have come across have such a high suface hardness that it seems to take a lot of beating to create a pattern in which you may be able to hang a scribe point across. If I don't see/feel a difference in tooth surface quality, then I would feel comfortable with a little adjustment of the pattern.



Of course, like others on this forum, I am not in favor of a noisey rearend either. Mine has a very slight whine within a 5 MPH range and only seems to do it after pulling the trailer for a while. I feel comfortable for now to leave things as they are now since my mesh pattern is acceptable. Other than that, I will run it like I stole it! Hell, if it makes it through the 7/70 powertrain warranty, I guess it will have earned its keep enough for me to feel comfortable with it.

 

[catoiler]

Mine had a whine from the day i got it. At 700 miles i put a Mag Hytec cover on and the oil was grey in color,Thought it was just break in, told dealer and they said nothing wrong, fast foward to 10000 miles checking oil before going to races pulled the stick and the magnet was full of metal!Fines and lots of splinters!It scraped some of it off comming out of the hole it was so big. After next weekend back to the dealer with a long list. 2nd time on some of it hope this don't have to go to a Lawyer.

 

[Johnstra]

Rebuilt rear diff... now MPGs are way down

Mine had a coast-side whine and the dealer rebuilt my rear diff. My problem now is I'm hearing more noise than I was before the rebuild and, much more disturbing to me, my mileage is down about 3 MPG. I was consistenty getting 19. 5-20 MPG empty - even in winter - now I've seen 2 consecutive tanks at 17. No reflashes were performed.



I don't know if this is expected with a rebuilt rear-end. Do I need to give it a couple thousand miles to breakin or should my mileage not have been significantly affected.



Thanks for any info.



-john

 

[hotram03]

I know this does not pertain to the whine, but where are you guys getting the mag-hytec covers for 3rd GENs at? Mine has had a slight whine since new, about 70 mph on a long trip it gets a little loud not annoying though. I have 31,236 on it now and its nothing I can't live with.

 

[Big Wheel]

I think D. C. is trying to keep this rear end noise thing from becoming a recall issue on the

trucks. If they had to recall all the 2003-2004. 5

trucks for rear end noise and replace them thay wouldn't have time to make any for the plants.

 

[GDouglas]

Johnstra,



If you are loosing 3 MPG after rebuild, I would be looking at the possibility of the rear end lube being a whole lot warmer than it was before. If your loss in mileage is in fact due to possible extra "drag" in the rear end, then the extra energy that is using up the 3 MPG has to be dissipated as heat. Just something simple you may want to check first.

 

[Johnstra]

I don't have a scientific way to measure the difference since I don't know what the temp was like before the rebuild. I felt the diff after a drive yesterday just to see if it seemed abnormally hot. It was pretty warm, but nothing alarming.



Like I said in my earlier post, I don't know how much breakin takes place in a diff.