Looking for some thoughts from the community.

My ‘69 has 115k and I have no knowledge of any previous servicing on the rear diff: it’s running well with no issues but I don’t know the quality or level of the existing fluid. My only concern about replacing the gear fluid is, will I potentially cause leaks through the axel seals due to the new oil.

 

The new lube will have additives to help prevent leaks at the seals. Absolutely, definitely change the lube.

 

If you have no knowledge of any previous differential fluid changes @ 115K miles, you should change fluid. Certainly w/o question you should evaluate the level of the differential fluid. Optimally, rear differential fluid should be changed every ~50K - 60K miles.

 

Completely agree with Run to Rund and Vintage Chief, change the fluid. If new oil causes a leak which it very likely won't, the newly leaking seal was toast from the beginning. New oil will better protect the bearings.

 

I will change the fluid

thank you for the advise

 

Spray/Saturate the differential fill bolt w/ your favorite penetrating fluid the night/day before you plan to remove the bolt to give it some time to penetrate. Will/Should loosen it up nicely so you're not fighting w/ it just in case.

 

^ Don't pull the cover and drain the fluid until you are able to get the fill plug out. Get the fill plug out first.

 

LOL Yes, good point on that one, Jeff.

Don't go all Magilla Gorilla & decide you'll remove the cover first before removing the fill plug bolt. Ensure that fill plug bolt can be removed - FIRST.

 

You can always put a fill plug in the cover. GM Mopar Dana did it on many rears.

 

I intend to change the oil in the diff of my starfire.
Taking into account the information on the thread which is awesome.
Only question does the diff take standard gear oil?
The diff is not LSD.

 

It should take standard gear oil (i.e. no additive needed) if not a a posi/limited slip. I would use a full synthetic oil.

Also, I'd get in there with your hands (rubber gloves suggested) and scoop out whatever old oil is sitting all the way at the back of your open differential - you'd be surprised at how much still remains even after the fluid drains from an open cover

 

Most lubes these days have some posi additive in them already. However, you don't need it with a conventional differential. I suggest 75-90 synthetic from Mobil or Valvoline. Top fuelers etc race with Torco 85-140 dino lube (not syn) because it seems to be (or was when I checked) the only lube that would keep gears alive in such a violent situation. When it was available, I liked (and still use) LE 607 dino 90 weight in the Ford 9" for racing. The steep hypoid angle of the 9" diff causes more friction and is why the GL6 spec was developed.

 

Well I decided to check out the filler plug on the diff tonight.
Replies on the thread recommend removing the filler plug before
taking the diff cover of.
Only problem I cant find the plug.
Where the heck is that thing!!!

 

Changing diff fluid

 

Thanks Vintage Chief
I was feeling around on top of the diff obviously
I wasnt going to find the filler there.
Cheers

 

Yes, it isn't on the top - it's located "near" the top but on the side.