Can we replace the gear lubricant in the front and rear differential like what the title says? I was draining my rear differential earlier and couldn't find 75W90 Mobil 1 Full Synthetic Gear Lubricant at Walmart but did find something in the form of 75W140 and I almost bought it to put in both differentials of my car but somehow I backed out from buying it due to uncertainty. Can someone please tell me if it is okay or not? Both say Gear Lubricant so why not?

Can we replace the gear lubricant in the front and rear differential like what the title says?

The difference is the thickness. Even though they both start with 75, the 75W140 will in general be thicker overall. Thicker oil doesn't lubricate bearings quite as well, but it won't hurt in the short term, expecially since it's still summer - at least it is here in Southern California. When the weather gets colder, especially in cold climates, you'd want to go back to the thinner oil for sure.

Mailman, I disagree. The thicker oil should have a higher film strength and therefore be much better at protecting the gear teeth from scuffing eachother.

 

It's just a question of 75W-90 being plenty already. A worn diff or gearbox might be made to last - silenced a bit - by 75W-140.

 

I would not worry about about using 75W-140 instead of 75W-90. In principal the 140 will increase fuel consumption, but only marginally. The "75W" in both oils should mean that they perform near identical in cold weather. The 140 will handle higher temps better.

The thing you need to remember is that the transmission uses this gear oil as well as the differential gears. Each requires a different set of needs for lubrication. If you put the 75w140 in there, shifting will probably become more difficult since the gear oil is thicker.

 

I'd stick with what the manufacturer recommends.

Josh: unless he drives an automatic. where the front dif is 75/90 and then ATF in the trans. But you're right, if he's got a manual...

 

I work in a lube shop. General rule of thumb is to always use the reccomended weights. in the case of older EA subies, i've heard of redline 75/140 doing miracles in worn out syncros... but, in our EJ awd subies, I'm not too sure. I don't think I would want to risk it. I say that as long as you've been up on your fluid changes and haven't extended the periods too long (as so therefor built up your varnish) put in some full synthetic 75/90.

Can we replace the gear lubricant in the front and rear differential like what the title says? I was draining my rear differential earlier and couldn't find 75W90 Mobil 1 Full Synthetic Gear Lubricant at Walmart but did find something in the form of 75W140 and I almost bought it to put in both differentials of my car but somehow I backed out from buying it due to uncertainty. Can someone please tell me if it is okay or not? Both say Gear Lubricant so why not?

 

looks like he is up in the Twin Cities!! It gets REAL cold up there pal, I would not want 140 weight in the pumpkins!! I know it is 75 at start-up but 140 is what heavy-duty trucks use!!

Mailman, I disagree. The thicker oil should have a higher film strength and therefore be much better at protecting the gear teeth from scuffing eachother.

I agree with you about the gear teeth. But you misread what I originally wrote because I mentioned the affect of "bearings", not teeth. Thinner oil flows into bearings better.

Yes sir! Sometimes I just read want I want to read :-)

75w-140 is usually specified for towing. If you are going to be towing it may be an option (depending on owner's manual recommendations), otherwise stick to a 75w-90.

75w-140 is usually specified for towing. If you are going to be towing it may be an option (depending on owner's manual recommendations), otherwise stick to a 75w-90.

yea, you use thinner oil when its cold

and ticker oil is usually associated with heavy duty uses as well ie towing...

Stick with a 'real syn' 75W90

I went with Durablend (Valvoline) for cost issue due to me being broke at this time. The front diff. looks clean and not muddy at all. It's always that way. Am I seeing the wrong lubricant or what? The rear got dirty and muddy that was why I changed it. But on the dipstick on the front diff., the fluid looks clear, and light, not discoloration at all. Is this normal?

 

Anyway, that means I now have Durablend (semi synthetic) in my rear diff. while the front diff. still has the full synthetic fluid. Would this cause any complication on the tranny?

 

Thanks for the huge replies!

you'll be fine