Low pinion pre-load?

[Slabo]

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?

 

[Slabo]

Ok I just read the FRPP gear install instruction and they say to use 8-14 lb-in if using used bearings. 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 per FRPP instructions) then just tighten the pinion nut to that spec. I had missed that when I read through it earlier. Is that what you would do? Is there any way to tell if the crush sleeve was originally overtightened?

 

[railroad]

I like 25 in/lbs on used bearings and a little stiffer on new bearing. If you did not have any in and out movement before disassembly, it probably had no affect on the leak. Just snug it up a little more. You also need to put sealer on the spline of the pinion gear. The lube will migrate up the spline and out from behind the nut if you do not. If you are able to measure the resistance, I guess you have the ring gear out and swapping the sleeve is no problem, unless you count crushing the new sleeve. Also check the seal surface on the back of the pinion yoke. You can clean it up by holding some med to light sandpaper or scotchbrite and twisting the surface against it.

 

[Slabo]

Thx railroad. I did check for in/out movement and it seems solid to me.

I do not have it apart, 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 measurement 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. You use 25 in-lb so now I have another choice..lol I was curious why my pre-load is low? not really wanting to replace the crush sleeve.


Thanks for the tip about the sealer on the spines. Not sure the yolk actually touches the seal as there is some kind of plastic reflector between them but I will check it out.

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.

 

[Slabo]

BTW here is a link to the manual Ford Service Manuals - IN-VEHICLE REPAIR

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. Just want to do this right.

 

[railroad]

You must have some really low drag bearing on the ring gear carrier and the axles. I would think trying to rotate all that, you would have 12 FT/ lbs. Don't sweat the small differences in inch pounds. There should be a flat washer behind the seal on the pinion shaft. This helps deflect lube off the seal and back on the bearing. Use the type rtv that you cannot get off you fingers after wiping it. Put some on the flange of the pinion nut or on the yoke where it seats. The silicone like bathtub sealer is not nearly as good. Tighten the yoke a little tighter than when you broke it down. You should have no movement, and very little drag on the pinion bearings. Definitely no notchiness. Post back if you have any questions.

 

[Slabo]

Thanks railroad,

A mechanic friend is saying the exact same thing. He said to just tighten it up a little until I am between 8-12 in-lbs rotating torque. I can do this since I have a highly accurate dial torque wrench. He said to sneek up on it so I don't go over.

BTW the seal that Shelby used was not a Ford seal. Hopefully I will have better luck with the Ford factory seal.