Odd findings during rear diff pinion seal replacement

[Stuw]

I've had my explorer for almost a year now. Its got about 180,000 miles / 290,000 km. I've put probably 10,000 or more Km on it now mostly doing highway trips for a long regular work commute.

I've always had a distinct and sometimes annoying humming/vibration during acceleration between 50 and 65mph 90 to 100 km/h. Only during acceleration at this speed range dropping off immediately as the speed goes beyond this range or if I let off the gas.

Now following a 2400km road trip while hauling a well loaded trailer I noticed oil dripping from my rear differential. Slow but steady drip only during one day right after I dropped off the trailer. No leaks since. Drove maybe 30 miles 50km after that leak.

Went in to replace the pinion seal and noticed that there is a bit of slop perpendicular to the pinion if I press up on the driveshaft. A concerning amount of slop to be honest.

The rearmost U joint does have a very slight give in one plane which I will be replacing. Very very slight and only noticeable once i disconnected the driveshaft from the pinion flange.

By using one driveshaft mounting nut reinstalled on the pinion flange I measured a ~31 inch-pound torque required to turn the pinion. (I didn't have an adapter to fit the torque wrench directly on the pinion nut. )

Upon removing the pinion nut I found only 3 threads exposed and a very low torque required to remove the pinion nut. My estimate is around 30 to 50 foot pounds to break.

The pinion flange then was very easy to remove. Minimal force and no tools required. Basically fumbled it out into my hands.

The splines on the pinion and flange look good. No apparent wear.

The pinion bearing looks/feels fine and the inner race looks/feels smooth. Oil slinger plate is very slightly concave but smooth.

My concern is that the whole thing seemed too loose during removal. Am I right in assuming this?

I am concerned that if I reassemble the differential with the same threads exposed and similar preload that my differential won't be any better off and will end up leaking soon or will cause damage.

My thought is that the very slight looseness in the ujoint may have loosened the pinion nut and/or damaged the seal OR that someone before me did work on the differential and failed to secure or replace the pinion nut thus causing it to slowly loosen.

How should I approach the rebuild of my differential? Definitely new pinion nut and blue loctite...But should I tighten it more and increase my bearing preload?

 

[Stuw]

I should add too that I did not remove the rear tires or brake calipers to do my preload torque measurement.

 

[Stuw]

I am going to get a new pinion nut and crush collar/sleeve from Ford today. 7 bucks for the sleeve and 5 bucks for the nut.

Going to set the preload up properly when I reinstall the flange. Just trying to call around to find out what my preload value should be. Im thinking around 35 to 40 inch pounds with the wheels on?

Upon draining I didn't notice any filings on the magnet so I think the preload was just improperly set from someone before me.

I'm hoping that snugging up the preload this time and replacing the U joint will eliminate the vibration.

 

[imp]

I am going to get a new pinion nut and crush collar/sleeve from Ford today. 7 bucks for the sleeve and 5 bucks for the nut.

Going to set the preload up properly when I reinstall the flange. Just trying to call around to find out what my preload value should be. Im thinking around 35 to 40 inch pounds with the wheels on?

Upon draining I didn't notice any filings on the magnet so I think the preload was just improperly set from someone before me.

I'm hoping that snugging up the preload this time and replacing the U joint will eliminate the vibration.

@Stuw
It's good that you have understanding of pinion bearing preload and how it's controlled by the crush sleeve. Often, if old bearings are kept in use, and the old crush sleeve used, inadequate preload or excessive preload can result. Best deal is use a new crush sleeve, tighten the nut while turning pinion slightly, feeling "wiggle" as the crush comes into play. By then, the torque necessary to further tighten the nut should be substantial, but a small bit of "play" should still be present in the bearings. As that play disappears, begin to measure torque needed to turn the pinion. Ideally, this would be done without the added resisting torque of turning the axles and brakes, but "guesswork" says 30 inch pounds would be insufficient, as 10 or more (I forget the spec) is wanted to turn only the pinion. I'd shoot for 50 inch pounds with both wheels off the ground. I will assume you have or will replace the forward cone and roller assembly. Generally, a slightly higher preload torque is called out with new bearings. Too much preload overheats bearings. Too little can cause catastrophic failure. Choose yer pie!

The RIGHT way, of course, is to pull off the diff. cover, pull out those little widgets to allow the axle shafts to be pulled back out of the diff gear splines. If axles are left to rest on the seals, they may be damaged! This way, you turn the entire diff. assembly along with the pinion, but eliminate the added interfering torque of the brakes, which can be substantial.

Why can your torque wrench not be used on the socket used on the pinion nut? imp

 

[Stuw]

@Stuw
It's good that you have understanding of pinion bearing preload and how it's controlled by the crush sleeve. Often, if old bearings are kept in use, and the old crush sleeve used, inadequate preload or excessive preload can result. Best deal is use a new crush sleeve, tighten the nut while turning pinion slightly, feeling "wiggle" as the crush comes into play. By then, the torque necessary to further tighten the nut should be substantial, but a small bit of "play" should still be present in the bearings. As that play disappears, begin to measure torque needed to turn the pinion. Ideally, this would be done without the added resisting torque of turning the axles and brakes, but "guesswork" says 30 inch pounds would be insufficient, as 10 or more (I forget the spec) is wanted to turn only the pinion. I'd shoot for 50 inch pounds with both wheels off the ground. I will assume you have or will replace the forward cone and roller assembly. Generally, a slightly higher preload torque is called out with new bearings. Too much preload overheats bearings. Too little can cause catastrophic failure. Choose yer pie!

The RIGHT way, of course, is to pull off the diff. cover, pull out those little widgets to allow the axle shafts to be pulled back out of the diff gear splines. If axles are left to rest on the seals, they may be damaged! This way, you turn the entire diff. assembly along with the pinion, but eliminate the added interfering torque of the brakes, which can be substantial.

Why can your torque wrench not be used on the socket used on the pinion nut? imp

Thanks for your guidance!

I did not have the proper adapter to go from 1/4"M to 3/8"F to fit on my 27mm socket. I do now though.

I am reusing the forward cone bearing for cost reasons and that the rollers look very good as well as the cone bearing race very smooth and no shavings present in the drained fluid. Just almost microscopic flecks in the fluid if you shine a light into it.

I think I'll aim for 40 to 50 inch pounds. The parts guy at Ford printed me out a list of specs but the torque range listed there would almost certainly be for a disconnected differential.

Just hoping that everything works smoothly when everything is buttoned up properly. I will update tomorrow when I reassemble and refill.

New 75 140 gear oil and friction modifier will be going in and I'm excited to see how everything comes together!

 

[Stuw]

The pinion seal replacement was a success!

No more leaking and the vibration seems somewhat lessened. I have heard that these Fords are known to have some vibration in the rear differential no matter what you do but the droning vibration at cruising speed is definitely less now.

Tightening the pinion nut to the proper bearing preload was a PITA under the car on jack stands! I am sore in a couple places today.

I had to use a screwdriver placed through one of the unused holes in the flange to immobilize it during tightening.

Once I tightened it to the point where I was crushing the sleeve I really had to put out on it probably 120 ft/lbs or more. Once I got to this point it didn't take much to get the preload required. 1/8th turns between each measurement would be a good idea to avoid overtightening.

I think the sloppiness may have developed from my dying transmission popping/jolting into reverse all the time.

I imagine that the jolt when shifting would put some force on that nut and might act to loosen it over time.

That or someone had removed the nut and didn't properly reset the nut.

In any case she drives well and I should be good for a bit!

 

[imp]

@Stuw
Great! Happy you are satisfied with it. Yes, such torque applied to a big nut is rough working under a vehicle without a lift. When worst comes to worst, I use a long bar between bolts and bearing against the floor, then have both arms available to tighten. imp