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  Topic Review (Newest First)
06-15-2019 07:50 AM
Alfar7
Diffs

Option 3!

Don`t try to rebuild a worn differential. Replace it in it`s entirety.
06-15-2019 07:45 AM
mthomas2911 I'm resurrecting this post because I was finally able to get the car into the shop for this aliment. When they opened up the differential on the bench they found 0 pre load on the pinion nut. They were unable to find the correct setting but left it at 13 in. lb. After re-installing the rear axle and test driving the noise was still there and occurred under the same conditions previous to the tightening of the pinion nut. After discussion with the mechanic and some reading I'm thinking there are 3 options to pursue.

1. Have the shop change the thickness of the shims.
2. Replace the bearings, even though the mechanic said he does not think they are the culprit.
3. Replace the rear axle & differential.

Any input or advice is most welcome.

Also, do you think the tourque setting on the pinion nut should be greater than 13 in. lb.?

Thanks.

Mark
10-06-2017 04:46 PM
goats Same exact list. Its a bit of 'mystery' on exact pinpoint causes for these whines, but they all relate to incorrect pinion-to-crown gear relationship. Only two adjustments are possible though -- pinion to crown depth (how far radially the pinion is located relative to crown wheel center) and pinion-to-crown wheel clearance (how much gap there is between the pinion hypoid gear and the crown wheel 'teeth'). Pinion yaw and attack angle are NOT adjustable at all (for me at least).

I tend to look at lash as the very first thing to see where it is, lash is absolutely needed but can not be excessive. CHapter ?17? of the service manual gives all the specs and test methods.

You could try swapping the diff oil to something else like mineral oil or other. The experts on this forum on this is Alfar7 (RJ) and little Italian (bud) for sure.
10-06-2017 04:36 PM
alphil [QUOTE

It occurs when you unload the drivetrain by cutting back on the gas or giving no gas and coasting. It does not happen during acceleration.

From a mechanical stand point what is going on inside the differential to cause the growling noise?

Mark[/QUOTE]

Hijack!! What causes a diff to whine under load,no noise coasting,just the opposite of Marks problem?
10-06-2017 12:58 PM
Alfajay
Quote:
Originally Posted by goats View Post
My point was removing the AXLE TUBE (not the diff side case cover) , the one on the other side small diameter one, has no influence at all on anything other than spline engagement. Without a doubt, removing diff side case with bearing as you point out and adding a gasket will change crown wheel preload
Since I was the one who flagged mthomas2911's comment that "the differential gaskets were changed", I guess I started this portion of the debate. goats, thanks for expanding on it. Yea, a gasket on the small diameter side won't have any effect on the crown wheel's position. But put a gasket on on the large side - what he calls the "side case" - and the side-to-side play of the crown wheel will be off.

Although mthomas2911 typed "gaskets", he probably meant seals. My guess is that the shop incorrectly installed the pinion nut when replacing the pinion seal.
10-06-2017 12:41 PM
goats "Sorry, incorrect, but there are factors involved. If you remove the axle tube that contains the diff side bearing and add a gasket then reinstall without adding shims behind the bearing cup (the same thickness as the gasket) you will have altered the diff side bearing preload. BUT if you rebuild the differential and set the preload based on the thickness of a gasket then yeah no affect as you say, but that is not how 99% of Alfa diffs are setup and in this case they were trying to remedy a leaky diff, not rebuild, so if there is now a gasket or thick gasket goo we have a problem that needs to be fixed immediately."

Pete this is correct as well. My point was removing the AXLE TUBE (not the diff side case cover) , the one on the other side small diameter one, has no influence at all on anything other than spline engagement. Without a doubt, removing diff side case with bearing as you point out and adding a gasket
will change crown wheel preload
10-06-2017 12:34 PM
PSk
Quote:
Originally Posted by BrundleFly View Post
See this post by Papajam for an explanation of why pinion nut torque changes over time, and how to find a good setting when you aren't able to restore the original:

http://www.alfabb.com/bb/forums/1038599-post6.html
Quote:
Originally Posted by Papajam
What happens over time as the bearings and races wear, the torque on the nut gradually gets less and less. If one now retorques the nut, or tightens it good and tight, the bearing pre-load can be so high as to prevent the pinion from even spinning!
The trick to replacing the pinion seal is to first note the torque on the nut before removing the nut. After seal replacement, torque the nut to the previous value (disregarding the torque spec in the book).
I have a lot of respect for Papajam but the pinion shaft has solid spacers all the way so again I cannot see how the pinion nut can affect bearing preload no matter how worn the pinion bearings are. It is vital that the pinion nut is sufficiently tight that the spacers are doing there job. If the pinion preload was set with gaps between the solid spacers then yes the pinion nut torque will alter the preload, but then the diff rebuilder should be fired.

Will keep thinking about this ...
Pete
10-06-2017 12:26 PM
BrundleFly See this post by Papajam for an explanation of why pinion nut torque changes over time, and how to find a good setting when you aren't able to restore the original:

http://www.alfabb.com/bb/forums/1038599-post6.html
10-06-2017 12:16 PM
PSk
Quote:
Originally Posted by goats View Post
Lots of misinformation out there.
Correct but ...
Quote:
a. Pinion preload is not set by nut torque to an appreciable degree. It is set by the collar and shims on the pinion shaft behind the rear pinion bearing.
b. Pinion position is set by shims behind the bearing shells.
100% correct and the torque of the pinion nut will never affect pinion preload or position. A myth ...
Quote:
c. Putting gaskets on the axle tubes has no effect on crown preload or pinion alignment at all. It only effects the depth of penetration of the axle splines into the spider
Sorry, incorrect, but there are factors involved. If you remove the axle tube that contains the diff side bearing and add a gasket then reinstall without adding shims behind the bearing cup (the same thickness as the gasket) you will have altered the diff side bearing preload. BUT if you rebuild the differential and set the preload based on the thickness of a gasket then yeah no affect as you say, but that is not how 99% of Alfa diffs are setup and in this case they were trying to remedy a leaky diff, not rebuild, so if there is now a gasket or thick gasket goo we have a problem that needs to be fixed immediately.
Quote:
d. I agree 100% that if the seal is replaced, it is best to return the nut to the previous position.
Yes while contradictory to your point A, it is good practice to return anything removed back to exactly where it was.
Quote:
e. You might try redline 90-140 NS gear oil to see if that helps. it might
f. Don't rebuild a diff unless you have the right tools, and a lot or patience.
g. Lash is a factor in diff noise as well as pinion position relative to crown gear.
Pinion position relative to crown gear was set by the factory and never needs to be altered. Just ensure the shims under the pinion to the first pinion bearing remain the same. New bearings are made more accurately made than we mechanics can measure, so just leave everything as Alfa set it and just set preload and backlash. This is where most screw up a diff rebuild and confuse themselves with pinion position relative to the crown wheel where you actually don't have to worry about it at all
Pete
10-06-2017 12:04 PM
goats Tom I agree with you that D is 'best practice'. I believe "A" is factually correct as worded except that the tube/shim is in FRONT of the rear bearing (ie between the front and rear!)
I also 100% agree that I sure as heck wouldn't arbitrarily tighten that pinion nut either!!!!

I just finished complete rebuild of three 4:10 LSD diffs. Complete rebuild including all bearings. It was a BEAR!!! I wont do it again unless under extreme duress. The thread is somewhere probably in the gearbox/trans/diff forum
10-06-2017 11:55 AM
Gubi Goats, your “a” and “d” are in conflict. While “a” may be true in theory, practice has shown that “d” is important when working on a not-new diff.

I sure as heck wouldn’t arbitrarily tighten the nut on a diff that didn’t have problems.
10-06-2017 09:41 AM
goats Lots of misinformation out there.

a. Pinion preload is not set by nut torque to an appreciable degree. It is set by the collar and shims on the pinion shaft behind the rear pinion bearing.
b. Pinion position is set by shims behind the bearing shells.
c. Putting gaskets on the axle tubes has no effect on crown preload or pinion alignment at all. It only effects the depth of penetration of the axle splines into the spider (EDIT -- only the "small diameter" axle tube, NOT the diff side case axle tube)
d. I agree 100% that if the seal is replaced, it is best to return the nut to the previous position.
e. You might try redline 90-140 NS gear oil to see if that helps. it might (edit -- its probably 75-140NS!!)
f. Don't rebuild a diff unless you have the right tools, and a lot or patience. (Edit -- read item f twice then once again if you have a doubt)
g. Lash is a factor in diff noise as well as pinion position relative to crown gear.
10-06-2017 09:29 AM
alfaparticle The position of the pinion is set by shims, not by torque. That is why the factory torque requirement is so broad, 60 to 100 ft-lb. I tighten the nut with an impact wrench and I have seen a respected Alfa mechanic use a hammer and punch to tighten one on a race car. I believe that the advice offered by roadtrip originated when folks were unable to lock the flange and use a torque wrench.
10-06-2017 07:08 AM
Alfajay
Quote:
Originally Posted by mthomas2911 View Post
From the responses received it sounds like pinion alignment is something that should be investigated. How do you check for it and how do you correct it?
To give you slightly flippant answers:

- The way you check for proper pinion alignment is to listen to the differential. If a howl occurs when you unload the drivetrain by cutting back on the gas or giving no gas and coasting, but does not happen during acceleration, then you have an alignment problem.

- To correct it, you put it back to the way it was when it left the factory. Repair manuals give some specifications.

As an aside, a slight amount of misalignment won't cause damage, but will drive you nuts. With significant misalignment and enough miles, the differential gears will wear prematurely. Not having heard your differential, it's tough to say where you are on this scale.

Quote:
Originally Posted by Roadtrip View Post
When replacing the pinion seal, you DO NOT tighten the pinion nut back to new specification torque settings. You tighten it back to the same as it was taken off.
I think what Roadtrip is saying is that the nut needs to be returned to the same position the factory tightened it to; not set to a specific torque value. Finding that position isn't too hard, as the factory staked the U-joint flange to lock the nut. You can see the old stake marks, and set the nut to there.

So perhaps the problem is as simple as the shop over-tightening the nut, and the remedy is backing it off to where the factory had put it. (admittedly this may be hard to understand without photos/diagrams).

Hmm - or is there a "crush washer" on the pinion shaft, and once it's over-torqued, the washer can't recover?
10-06-2017 05:20 AM
mthomas2911 From the responses received it sounds like pinion alignment is something that should be investigated. How do you check for it and how do you correct it?

Also, thank you all for responding.

Mark
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