almand01

About two years ago i got ford racing 4.10s installed on my 04 GT. There was never any noise or whining from them untill recently. A couple of weeks ago i noticed that i was leaking fluid from my differential, so i took it to the shop and they said that my pinion seal was bad and leaking. ever since that seal was replaced my gears have been whining pretty loud at high RPMs when i let of the gas. is there anything that i can do to make it stop? could it need friction modifier? when i had the gears installed i used royal purple synthetic gear oil, so is it possible that when they added fluid that it could now need FM? any help would be great.
thanks
Reid

jpplaw

They most likely took your pinion flange off to replace the seal and when they put it back on they did not torque it back to what it should be - or maybe they even over-torqued it, which would ruin your collapsible spacer. If you drive it while it is whining it can ruin the gears and the whine will never go away.

cliffyk

^+1, It is very important when replacing the seal to torque the pinion nut to a point at which the force needed to continuously rotate the pinion gear is the same as it was before removing the nut. The procedure is:

1. Pull the drive shaft and use a lb-in torque wrench to rotate the pinion gear through several revolutions--record the torque required to maintain continuous rotation;
   
2. Remove the nut, index mark the pinion flange relative to the pinion shaft and remove the flange;
   
3. Replace the seal;
   
4. Re-install the pinon flange making sure the index marks align;
   
5. Install the pinion nut and incrementally tighten it until the torque required to rotate the pinion equals that recorded in step 1.
   
   If the torque recorded in step 1 was less than the spec for used bearings (8 to 14 lb-in) then tighten the pinion nut until that preload is attained.
   
   If the torque recorded in step 1 was more than the spec for used bearings then tighten the nut so as to obtain the same preload;

Few mechanics know this, even fewer actually do it--most rely on their experience, "feel" and calibrated forearms--they are the "We don't need no stinkin' torque wrenches!" crowd.

Most of the time they get lucky, because of the wide range of the specification; sometimes however, especially when the original preload was too high, things don't work out.

Ask your mechanic what the original preload torque value was, best odds are that he won't even know what you are talking about...

almand01

thanks for the input. i just got of the phone with the shop that replaced the seal and he said that anytime they mess with the pinion flange that they mark the nut to make sure that they can torque it back to the same it was before. the only thing i can think of is that i had 75-140 royal purple synthetic oil in it and the guy said that he had to add about a quart of gear oil because what had leaked from the bad seal and while they were changing it. he said that they used 75-140 but that it wasnt synthetic. do yall think that the mix of oil could be causing the whining?

Stevo86

It's definitely possible. For the price of changing the diff fluid I would do it. While you have the cover off check the backlash of the gears to ensure they were shimmed properly.

almand01

Do you think that i could add some friction modifier to the oil that is in it now? could that take care of the whining?

cliffyk

Problem is that is not the proper way of doing it--see my previous post.

The type of gear oil, mixing or gear oils, etc. would make no difference, they screwed up the preload by not following the proper procedure...

almand01

so at this point i should just take it to a different shop and get them to reset the preload on the pinion? and if i am going to get that done should i just go ahead and get my gear oil changed while they are under the car? are there any negatives in having half synthetic and half non synthetic oil?

cliffyk

The preload torque cannot be set as it "should be" now because they apparently did not test it and record the value before removing the pinion nut. The best that can be done is to pull the driveshaft, see what the rotational torque is, and make a judgement call from there.

It may be that the crush sleeve has been compressed to the point that it needs to be replaced--that will require pulling the differential carrier, the pinion, and putting it all back together--and setting the preload torque for used bearings, 8 to 14 lb-in...

almand01

thank you for all the help Cliffyk. i will take it to the shop on tuesday to get them to look at it. do you have a rough estimate at what i am gonna be looking at price wise for the best and worst case scenario as far as the pinion nut just having to be re torqued, or having to replace the crush sleeve like you mentioned? i have never had to take my car to any shops around here so i hate to go somewhere blind...