How to tell if a rear diff is toast?

[dashhho]

I had some noise from my rear brakes and after inspection the rear diff axle seal on the passenger axle had been leaking. When I took off the drums the insides were pretty coated. And when I took out the fill plug from the rear diff I could not feel fluid as far as I could stick my finger in.

I am going to take the cover off the rear diff tomorrow and inspect for damage. Is there anything I should look for in terms of damage? I am hoping I did not toast it running it lower with fluid.

 

[85_Ranger4x4]

Metal in the oil.

Or no oil...

If it otherwise runs quiet you are probably ok though.

 

[MaicoDoug]

I take it that the leaking axle seal leaked all the diff oil out. Maybe not all of it. The pinion/ring gear assy is the stoutest thing in that truck. There is a decent chance that with a small amount of oil still inside, it's safe, but I would certainly re-fill it after you have those axle seals replaced including a brake job to clean & replace those brake parts.

 

[Curious Hound]

Probably fine. Leaky axle seal won’t leak all the oil out unless you park with that side down on a very steep slope. I would drain, inspect and refill the diff and plan on replacing the axle seal and wheel bearing on the other side, since it’s high enough to possibly be starved if oil.

 

[lil_Blue_Ford]

You have to pull the diff cover to get the axle shafts out to replace the bearing and seal for the shafts, so it’s easy enough to take a look around in the diff for damage. I’ve driven for a couple years on a leak with no ill effects. Replace both bearings and seals. If you elect to use the “repair” bearing and seal assembly, if it has a seal on the differential side of the assembly, rip that thing off or the bearing will never get oil and you’ll be doing it again in about a year.

 

[dashhho]

Thanks all. Do you folks recommend using the "repair" seal/bearing assembly? I am a bit confused on which part number is correct. I have 4.10 gear ratio and the tag on my diff says 8.8.

The National assembly says one fits both 7.5 and 8.8. And the other says only 8.8 (depending on splines). The Timken has no mention of splines and has different parts for 8.8 vs 7.5

 

[4x4junkie]

The one that "fits both 7.5 and 8.8" is the one you want for your 28-spline axle (the other one would be for Explorers/F-150s which have larger bearing journals and 31 spline axles).

 

[dashhho]

OK I found some info https://www.therangerstation.com/tech/ford-8-8-inch-rear-axle-history-and-specs/#gsc.tab=0
So since mine is a B4000 I am thinking it is a 8.8 with 28 splines. So the national RP5707 should be correct.

It would seem that would make the Timken bearing assemblys incorrect...unless you have the "rare" 8.8 with 31 splines.

 

[dashhho]

A side quesiton. I have some 75W140 left over. Think it is OK to use in the rear? Seems to call for 75W80 or 80W90

 

[4x4junkie]

Should work, though it might ding your MPG more than 75w90 would in cold Canadian winters.

 

[lil_Blue_Ford]

Yeah, there’s a lot of confusion on the bearings and seals. Autozone’s computer has been wrong forever on this so I’m sure a lot of other places have bad information. Years ago, I never gave it a thought and bought bearings and seals for an 8.8 for my green Ranger but they didn’t fit (way too big). Got into an argument at the parts store when the guy behind the counter insisted that the computer was right and I just must not know what I was doing. Fast forward to more recently… I did bearings and seals on the 8.8 in my F-150 and then a couple months later had to do them in a Ranger 8.8 and again not thinking I just ordered for an 8.8 again not thinking the computer would still be wrong. When I got the new ones, I thought the part number looked familiar and sure enough, they were too big for the Ranger 8.8, but when I looked up what my F-150 took, well, I suddenly knew why the part numbers looked familiar. Parts stores are selling F-150 8.8 parts as Ranger 8.8 parts.

Unless there’s damage to your axle shaft or heavy wear, you don’t really need the repair assembly, but you can use it anyway if you desire. Most of them come with a seal on both sides though, which is counterproductive because it will keep the gear oil from reaching the bearing to lube and cool it, so if it has an inner seal, you have to remove the inner seal so the oil gets where it needs to. Otherwise you just trash the repair assembly fairly quickly.

You will need a slide hammer and the axle bearing and seal puller. Some parts stores loan them. Sometimes I’ve had very reluctant bearings (I blew them to pieces trying to get them out and the outer piece was still stuck). Best way to handle that is to run a bead of weld inside the junk bearing then it will come out easy.

 

[dashhho]

May the slide hammer gods be with me.

 

[dashhho]

So opinons on when I put the diff cover back on. I do have a fel-pro gasket for it. Should I gasket or use black RTV?

 

[Curious Hound]

I use Permatex ultra black or ultra gray. Haven't bought a gasket in years. But if you want to use it go ahead.

 

[lil_Blue_Ford]

I use Permatex ultra black or ultra gray. Haven't bought a gasket in years. But if you want to use it go ahead.

Ultra black has been my go-to for years. My green Ranger got sealed with something that was green or grey, it was some new stuff that was specifically for diff covers. I dunno if it’s really any different. I know a lot of guys use that Right Stuff in the caulking gun tubes. If I had a garage up I might do it that way.