I bought 2000 Ranger XLT 4x4 with lots of issues about 2 months ago. I fixed most of immediate issues then drove it almost everyday to work.

The weather finally got warm and I had time today and worked on some of remaining issues.

First thing I did was checking rear differential fluid level and when I put my finger in filler hole, there were no oil.
So, I put rolled paper towel down about an inch. It did pickup some oil on the surface, but wasn't completely wet. Meaning there were no oil.

I was not ready to open the differential cover yet, so I put 3/4 qt of gear oil I had laying around. It took all, but still wasn't enough. I checked oil level, and it was about 1/4" below filler hole.

I have 8.8" ring gear, 4.10 ratio differential and I don't know what is the total capacity of this differential, but I believe it will take a little over 2 qt.
So, I'd say it probably had 1qt or less of oil inside.

I drove it like that for little over 1000 miles, mostly on highway.

I plan on opening the cover when I do the motor oil change (probably next month).
How much damage would it have?
I haven't heard any whining or bearing noise yet, but I did feel play in drive train. I feel a soft thump when I step on gas pedal after deceleration on highway.
Also a little clunk going drive to reverse or reverse to drive.

 

Well... lack of oil means lack of boundary lubrication between the gear teeth that slide against each other. This means excessive wear and heat. Also a lack of lubrication in the bearings that hold all the gears in place, which again, wear and heat.

Keep it going very long and you can cause severe damage. You're likely to notice a noise if you're conscientious at all. You'd be likely to hear a whine.

You COULD lock up a diff but I don't think that's likely to happen very quick, with extended driving I think it's possible or it's possible the differential blows rendering the truck inoperable in but still possibly rolls.

Before draining the oil, put a screen or magnet underneath and look for shavings as it drains. If you do, NOT GOOD

Source Citation:
maxamillion2345 (TacomaWorld.com)

 

It's probably fine, look for discoloration(blueing) on the ring gear, if you don't see any it's good given the absence of any other telltale signs.

Check the driveshaft u-joints.. note you have to remove the driveshaft to inspect these joints properly. And while you're under there have a look at the engine and trans mounts and fastening bolts.

 

I doubt you have a problem. The ring gear dips into what oil remains and flings it around in the diff. If there were a problem, the bearings out near the wheels would be the ones most likely to have been dry. I have found that with old trucks, it is best to only fix things that are clearly broken, so now that you have the oil level up about where it should be, move on to other things.

 

I did not hear any whine, but the truck has been loud due to 2 holes on catalytic converter. I just fixed them, so I will listen for the noise again.
As long as I don't see chunks of metal shavings it is ok. Right?
I know there will be fine shavings for sure as is with any old differential.

I did check without removing the driveshaft and did not find any loose u-joints. That is I did not find any that are bad enough to be noticeable by turning it with my hands.
Also tested with transmission in neutral and there is some play between rear axle and drive shaft. (backlash). I think it moved roughly 1/2" or a bit less. I don't know how much backlash it translates to, but since front axle was doing the same, I'm assuming it is within normal (But front can be bad too).

I just realized there was typo on how much oil it took. It took 3/4 qt not 2/4. That still did not fill to the top.
I found total capacity is 2.5 qt. So, whatever was remaining would have been touching bottom of the ring gear, but probably no more than 1/3 to 1/2 of the gear tooth.
Do you think that is still good enough?

If it was not touching at all, I'm pretty sure I'd be hearing very loud noise by now, which is not the case.

 

The thing with U-joints is they dry out first before they get loose so you really need to get the driveshaft out so you can exercise the joint in both axis and feel if it resists articulation(bearings are dry) or is lose which suggest the bearings are worn. The joints in the front driveshaft commonly dry out and seize due to lack of use, I have replaced the U-joints in the front driveshaft and axle on every 4wd truck I have ever purchased shortly after buying it because they are always dry and seized to some point. And it's not uncommon to find the fluid level in the diff a bit low.. that is also something I always check and top up.

 

If it works, don't 'fix' it. Unless you have leaking gaskets or seals, just make sure the lube is at the proper level. If it was damaged, you'd hear howling of the bearings or whining from the ring & pinion. Even if the ring & pinion made noise, they can last a long time before causing any further problems.
I expect the axle bearings, out near the brake backing plates, are sealed, and lubed for life. If this was a 'full floating' axle, the bearings might be adjustable roller bearings, open, and lubed by the differential lube. Given this is a Ranger, you'd have sealed bearings. Pretty sure sealed bearings, pressed onto the axle shafts, were standard in just about every RWD car or trucks in the 1000 lb capacity range. Only larger units had the open bearings, so the sealed kept their lubrication without any effect from the fluid level in the differential.
tom

 

On my ranger, front hub is permanently connected to the axle. So, the axle and drive shaft is always spinning.
If the bearing's grease is dried out, but has not failed yet, it shouldn't cause thump. Is it?

Isn't it still good to drain and fill the differential?

 

Oh yes.. I was thinking of a system with lockabe hubs. In 2wd the front drive is disconnected from the t-case so it shouldn't create noises if there is no play in the joints.


Yes, the axle bearings in the 8.8 rear diff are open and lubricated by the diff fluid, so yes by all means change the fluid.

 

Just changed differential oil and the condition of the differential looks excellent.
Guess it had more oil than I thought. No large metal shavings for flakes. Just very fine metal powders mixed in oil normally seen in differential oil.

 

Looks like you dodged a bullet, my friend!
Hopefully you wiped it out, rinsed it down some, and added a quality gear lube back into it. I'd suggest you re-check the lube level again after 15 miles.

Years ago, I bought a F250. Two weeks later, I was driving 55-60 mpy down a paved road and the DANA rearend locked up! Not a drop of lube in it! The hook truck had to bring me back home! Once home, jacked up and removed the rear cover - the bearings and ring gear turned had blue! I couldn't afford new parts, so I opted for a good but used parts and bolted it all back in........

BarnieTrk

 

I did not bother rinsing, but I did clean up as much oil as possible from bottom of the differential housing.
I did not want to contaminate the differential with lint or fibers from paper towel, and I did not have enough brake parts cleaner to rinse.

I drove the truck on highway about 20 min before draining and the fluid was pretty warm and not much was clinging on to the gears.

Just cleaned mating surface as much as possible.

For the fluid, I just put Walmart's Super Tech 75W-90 Synthetic blend. I don't plan on keeping the truck for long and it was pretty cheap.

 

Byoung Oh,

Sounds like you did a fine job. Yep, you want to keep the towel lint out. I have no problem with using Walmart's Super Tech brand of automotive fluids; I use them too.

Did you obtain a replacement paper gasket for the rear cover or did you just use a bead of silicone RTV?

I would still suggest you re-check the gear lube level after some use....

Good luck & enjoy your Ranger while you have it!

BarnieTrk

 

I used RTV from permatex specifically made for gear oil.

 

You might be experiencing the infamous "driveline thunk" that plagues 4WD Rangers of our vintage.

See: https://www.ford-trucks.com/forums/1...-anything.html

The remedy is to lubricate the slip yoke: Lubricate Your Ranger Driveshaft Slip Yoke