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Buckeye

Rear Axle Friction Moment

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About a month ago I decided to tear down rear axle and replace bearings and seals due to some mild wining noise @ 35-45 mph speed. First step with rear axle on the bench was to find out "friction moment" of pinion. Using right tool I was not able to get more than 2-3 Lb-in of drag. 

I have gone thru procedures to determine original shim X is of correct thickness and it is.

815746907_ScreenShot2018-12-26at3_48_49PM.thumb.png.0ab9fce0fd1ca3c04b5319e4f87d3274.png

 

Upon above exercise proceeded with pinion installation with a new bearings, shim X and clamp bush, etc. as followings

520141901_ScreenShot2018-12-26at3_49_39PM.thumb.png.8823ad5163516cf322ecc89038a6e672.png

 

Then proceeded with checking drag with proper tool, which cannot seems getting more than 3-4 Lb-in of drag. Flange nut minimum torque setting 103 Lb-ft has been reached and obviously friction rating of pinion bearing with oil seal of max. 320 Ncm (28 Lb-in) never been exceeded. 

 

So my question is what am I missing or have neglected? Or am I okay with new drag value since that value was so small before disassembly?

 

BTW, there is marking of +8 on pinion shaft, which don't understand meaning nor been able to find.

--Thanks,

Farshid 

155997627_ScreenShot2018-12-26at3_48_03PM.thumb.png.23058cfdfaef6e50cb5ff6e0cd78086e.png

Edited by Buckeye

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There's not a whole lot of preload on the pinion- one of the  big reasons people ditch the

crush sleeve and go to a solid spacer setup is that the oil seal friction  with a new seal and

reused bearings is often almost equal to what the bearing needs,

and the oil seal drag can vary quite a bit.  A solid spacer and shims

lets you set it up without the seal, and then reassemble it with some certainty that it'll repeat.

 

'Just a bit of drag' is about right for a well- worn diff with an old seal. Maybe 5 inch- pounds?  The problems

arise when it's not enough to counteract the distortion that happens inside the diff

under full load.  Then the pinion moves, and things wear, bind, grind, and self- destruct.

By the time it spins freely with no real drag, it's too loose, and has probably damaged itself.

 

I have to say, having done maybe a dozen of these, that I tighten the pinion until it feels

'almost too tight', a number that's entirely subjective.  If there is any unevenness in the drag,

it's 'just a bit too much' and you get to do it all again...  I have erred on the side of too loose

a couple of times, and the second time, it was easy to add a bit more crush.  The first time was...

well...

a learning experience, shall we say?

 

If it's noisy under heavy load, but quiet otherwise, it's probably too loose, but the shims are right, or very close.

If it's noisy in light load and coast, it's in need of reshimming at least, and possibly

the gears have gotten damaged.  And it may still need preload...

 

hth

t

 

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16 hours ago, Buckeye said:

I have gone thru procedures to determine original shim X is of correct thickness and it is.

815746907_ScreenShot2018-12-26at3_48_49PM.thumb.png.0ab9fce0fd1ca3c04b5319e4f87d3274.png

Well is not. Upon reading the instructions again, noticed the value of e I used in my calculation (e = .25) is incorrect. Actual e value of my gear set is engraved on the pinion and is (e = 8+), which is 0.08mm. I will press-out the pinion and existing shim X, will recheck everything and hunt for new shim. According to my calculations I will need to add 0.15mm shim to existing shim X, which make sense to me and why I wasn't able to obtain higher drag value. I will update this post accordingly as progress is being made.

1241305992_ScreenShot2018-12-27at6_29_50AM.thumb.png.4269013b482f82e37e220f81be0109b3.png

 

Edited by Buckeye

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Shim X just sets the pinion depth, or how far into the ring the pinion engages.

I wouldn't think it would mess up your bearing preload if it's wrong.

It WOULD mess up the gear mesh, tho.

 

goot luk,

 

t

 

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Toby’s right. With a crush sleeve, the shims only set pinion depth to get the correct gear mesh. 

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