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Low pinion bearing pre-load?


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#1 ONLINE   Slabo

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Posted 15 September 2012 - 11:31 AM

I am in the middle of changing a leaky pinion seal on my '07 GT500 and I am at the point that you measure the pinion bearing pre-load so you can put it back exactly the same and I am only measuring 4-5 in-lbs to rotate the pinion. This is with a very accurate dial torque wrench I use for gun work. This is on a set of 3.73 gears that were installed by SAI during my 40th conversion. Service manual says 16-29 lb-in but I assume that is when you set it up initially with the crush sleave. Does the pinion pre-load drop down after some use? Does this sound low? Do you think this contributed to the seal leaking?

Edited by Slabo, 15 September 2012 - 11:40 AM.

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#2 OFFLINE   Snoopy49

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Posted 15 September 2012 - 12:00 PM

If it uses a crush sleeve, you should replace the crush sleeve and torque to spec, then check preload with the proper torque wrench. I prefer a deflecting beam style.
If it uses a crush sleeve, the crush sleeve collapses when you torque the pinion nut to the specified torque. The crush sleeve sets the proper preload when compressed properly and cannot be reused.

Edited by Snoopy49, 15 September 2012 - 12:08 PM.

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#3 ONLINE   Slabo

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Posted 15 September 2012 - 01:01 PM

Yup I'm sure they used a crush sleeve. I just read the FRPP gears install instructions and they are saying to use a bearing pre-load measurement of 8-14 lb-in with used bearings. Sounds like I am low. Can I replace the crush sleeve and re-set the pre-load without effecting the pinion depth or gear pattern?
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#4 ONLINE   Slabo

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Posted 15 September 2012 - 01:41 PM

Ok I just re-read the Ford service manual and it says that if the measured pre-load torque is lower than specification (which I assume means 8-14 lb-in) then just tighten the pinion nut to that spec. I had missed that when I read through it earlier. It that what you would do?
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#5 OFFLINE   Snoopy49

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Posted 15 September 2012 - 01:48 PM

Are you tightening the pinion nut to 8-14 in lbs? What torque spec are you using to tighten the pinion nut?

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#6 ONLINE   Slabo

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Posted 15 September 2012 - 01:56 PM

I am measuring 4-5 in lbs. So that is low according to the FRPP specs. With my used bearings I should be at 8-14 in lbs. So according to the service manual I should just replace the seal and set the pre-load at the spec (8-14 in lbs). My only concern is why is my measured pre-load low? Did the nut back off? Was the original crush sleeve overtighten and then they just backed off the nut instead of replacing the crush sleeve since you can't go backward without replacing it. Replacing the crush sleeve sounds like a major pain. Is there any way to tell if the crush sleeve has been overtighted?

Edited by Slabo, 16 September 2012 - 11:50 AM.

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#7 OFFLINE   Snoopy49

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Posted 15 September 2012 - 02:08 PM

What torque did you use tighten pinion nut? The 8-14 in lbs is the running torque not the torque required to tighten the pinion nut.
The preload running torque is the torque required to turn the pinion and is usually done without the seal and carrier installed. At least that's the way it is done on the 60's and 70's Chrysler cars that I have worked on. Read your manual and see if it is not the same for your car.

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#8 ONLINE   Slabo

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Posted 15 September 2012 - 02:38 PM

I haven't pulled the nut off yet since I wasn't sure about the pre-load. I am just measuring the load required to rotate the pinion with the brakes and discs removed. So it is roating the axles. This is the way the service manual says to do it. You take this measurement, pull the yolk, replace the seal, then put the pinion yolk and nut back so the measurment is back to the same. Perhaps pinion pre-load isn't technically the correct term for this measurement since I don't have it apart. You can also count nut rotations or threads is another technique. Basically you put the nut back exactly where it was. Except the service manual says that if the measurment is below spec to snug it up to spec. The service manual, however, doesn't have different measurements for used vs new bearings. It just says pre-load (16-29 lb-in) but the FRPP gears manual does and says pre-load (8-14 lb-in) for used bearings. Not really wanting to replace the crush sleeve.

BTW the vent was clear and no fluid was expelled so I don't think it was a pressure thing that caused it to leak.

Edited by Slabo, 15 September 2012 - 02:45 PM.

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#9 OFFLINE   Snoopy49

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Posted 15 September 2012 - 03:09 PM

I suggest waiting for an answer from someone who has first hand experience with this axle.
I would think that it would take a lot more than 4-5 in lbs of torque at the pinion nut to rotate the axles. It's to bad I don't have access to a service manual, I would really like to read about the entire procedure.
Good luck and you were wise to wait on the repair until you get all the answers to your questions.

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#10 ONLINE   Slabo

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Posted 15 September 2012 - 03:24 PM

Thanks Snoopy. Here is the link to the manual. http://iihs.net/fsm/...Pinion Seal.pdf

Here is the part I am hung up on:

If the original recorded drive pinion bearing
preload is lower than specifications, tighten
to the appropriate specifications for used
drive pinion bearings. If the drive pinion
bearing preload is higher than specification,
tighten the pinion nut to the original
reading as recorded. For additional
information, refer to the Specifications
portion of this section.

The manual doesn't say what specs to use for used vs new bearings that I can find. Just says 16-29 in-lbs. That is why I was looking at the FRPP gear install manual. I am with you, just want to do this right.
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#11 OFFLINE   Albino500

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Posted 15 September 2012 - 04:24 PM

Slabo,
You can go to 8-12 in/lbs rotating torque with used bearings Just got home so I have not looked up the torque setting for the pinion nut which I believe is 70-90 ft/lbs . If you replace the crush sleeve you will have to reset gear pattern and backlash along with the rotating torque. The drag with the new seal maybe enough to bring your rotating torque back up to where it needs to be so - take off the nut , pull off the yoke , and replace the seal , slide the yoke back on , put on a new nut or locktite the old and torque down to spec , check your rotating torque reading and check to make sure that backlash is staying the same. You are safe if your rotating torque is low and coming into range but , if you go too tight -your hosed . KP
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#12 ONLINE   Slabo

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Posted 15 September 2012 - 04:40 PM

Thanks for the reply and PM Kevin,

I will proceed with replacing the seal and putting the nut back to the same spot using the measured rotating torque and counting the exposed threads technique. I will then work my way up to the rotating torque of 8-12 in/lbs using my dial torque wrench for measurements.

BTW I ordered one of Bob's axle reservoirs just to make sure I have maximum venting.
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#13 OFFLINE   Snoopy49

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Posted 15 September 2012 - 05:36 PM

From the 2011 repair manual in your link, it appears the the pinion nut is color coded and needs to be replaced with a nut with the same markings.
Kevin, have you found this to be true?

This note is from the 2011 Manual and may not apply to your axle, but I thought it was worth mentioning.

NOTICE:

This operation disturbs the pinion bearing preload. Install a new pinion nut with the same color as the original if not replacing the collapsible spacer. If a new collapsible spacer is installed, install the pinion nut in the kit or damage to the component may occur.


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#14 OFFLINE   Albino500

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Posted 15 September 2012 - 06:24 PM

From the 2011 repair manual in your link, it appears the the pinion nut is color coded and needs to be replaced with a nut with the same markings.
Kevin, have you found this to be true?

This note is from the 2011 Manual and may not apply to your axle, but I thought it was worth mentioning.

NOTICE:

This operation disturbs the pinion bearing preload. Install a new pinion nut with the same color as the original if not replacing the collapsible spacer. If a new collapsible spacer is installed, install the pinion nut in the kit or damage to the component may occur.

Snoop - this is correct however I have seen and done (or I should say gotten away with) using locktite on the old one .
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#15 ONLINE   Slabo

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Posted 16 September 2012 - 11:41 AM

The service manual does say to use a new pinion nut but I was going to reuse the old one because I have marked it so I could put it back in the same spot. But since I am increasing my rotating torque a bit I will go ahead and replace the nut. Also it looks like Shelby might have reused the nut once already.

BTW I pulled the seal and it is not a Ford seal. Shelby definately used an aftermarket seal. Hopefully I will have better luck with the Ford seal. You can see how the Ford factory seal has a silicon bead around the outside to keep it from leaking between the diff and the seal. Also the inner seal is cupped outward instead of inward. New Ford seal on the left.

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Here is pic of my highly accurate torque wrench.

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