My 98 Legacy just had a transmission rebuild...the prev. owner apparently used some sort of transmission conditioner that eventually destroyed the internal seals. Caveat emptor. So far so good, the car has better acceleration and no slippage.

 

Anyway, they also drained the front & rear differentials without checking with me. So much for my fresh Amsoil Series 2k oil. Oh well. They double checked with two dealers (they were a little surprised by the bluish synthetic oil) and refilled the front with 90w gear oil, and the rear with ATF? Is this right?? The repair place only uses the semi-syntheic Mercon V fluid. I thought the rear diff takes 75w-90 gear oil...should I be draining & refilling ASAP?

 

Thanks!

I'm not a differential expert, but that's the first time I hear of ATF fluid in the rear (or front) differential. Gear oil is for gears. I would replace the ATF with 70-90 gear oil ASAP. ATF fluid is more like hydraulic fluid not gear oil.

but some vehicles do use ATF in trannys and rears. My BMW runs it in the transmission (5 speed ZF). It was an old racing tirck to gain a pony or two but on the street you are better off with diff oil in an old diff. No rush to change it, but put it on your list.

Ok, I will drain & fill the front and rear diffs with some synthetic gear oil once it gets a little warmer here in eastern MA...Thanks!

Read what's required in the owners or shop manual. I'm with Frag. Never heard of ATF in a differential. Don't wait to change it.

If you knew anything about hyploid gears, you'd be draining that ATF first thing tomorrow morning. Why take a risk? The only cure for worn hyploid gears is to replace the whole pumpkin. A car can run forever with worn hyploid gears but the LOUD ROARING noise is usually unbearable.

Running ATF as a lubricant in FWD transmissions with an integrated diff is not unheard of. With that said I would drain that diff ASAP, as ATF (~8cSt) is roughly half the viscosity of the recommended lubricant (~15cSt).

drain that crap out of your diff now....

or very soon you will be very very sorry!!!

 

Diffs take gear oil

 

AT trannies and Power Steering = ATF

 

Jamie

I hear you folks loud and clear. A place near my office sells Royal Purple - I will pick up some 80w90 for the front and 75w90 for the rear (as per the owner's manual) and bring it to a garage today to get changed. At -4F, it's a little chilly this morning to crawl under the car to do it myself . It's only a 12 mile drive to work, I think it'll be ok.

 

I'd love to know what the guy at the dealer was thinking when he recommended using the ATF...heck, the 90w in the front was probably chapstick this morning.

My parents lived in Greenville Maine when I was a college kid. I brought my VW up from Augusta to Greenville for Xmas.

It was so cold that I had to adapt a hot plate to the sump to get it started. Once it started the 80 wt. in my diff was so cold it would stall the engine. Then when I got the 80 wt. a bit warmer the car would drive off forward in neutral when you let up the clutch because the oil was pumping like an automatic. I finally got the transaxle warmed enough to drive normally and then the gas line froze.

Perhaps the gentleman had had experience like this. The front transaxle on a Subie will warm up and oil will move fairly quickly. The rear diff is isolated and takes much more time to warm in extreme cold.

The question is what lubes better in extreme cold? Oil that will move or oil that is as you say "chapstick".

I always got by but learned to mix motor oil and diff oil to get my cars to work. No really thin diff oil with crush resistance was available where I was back then.

The real problem with ATF in a diff is that it has less crush resistance.

If you knew anything about hyploid gears, you'd be draining that ATF first thing tomorrow morning. Why take a risk? The only cure for worn hyploid gears is to replace the whole pumpkin. A car can run forever with worn hyploid gears but the LOUD ROARING noise is usually unbearable.

Listen to this ^ guy. It won't take long to toast your diff. Hypoid gear oil is a high preasure lubricant & what your diff needs.

 

Yes some FWD transaxles use ATF, but they contain no hypoid gears. Neither does a BMW transmission.

 

Good luck, you have been warned.

 

Chuck

atf fluid has a ton of detergent in it, change it out ASAP. the inside will be cleaner, thats for sure, but dont go very far on it. gear oil is for gears, and atf fluid is for AT and power steering, what kinda crack was that "mechanic" on when he told you he had atf fluid in the rear diff. almost as bad as jiffy lube putting atf fluid in your crankcase.

i haven't read the owners manual in your car, but this could possibly be one of the dumbest moves i've heard. are you SURE he put ATF in the diff? you didn't get confused by what the mechanic told you?

Anyway, they also drained the front & rear differentials without checking with me. So much for my fresh Amsoil Series 2k oil.

.

 

Since you did not authorize them to change the diff fluid, you can legally make them undo the work you did not authorize, without payment, with the Amsoil :-) Just learned about this stuff in class, and if ya don't believe me, or they don't buy it, I'm sure a lawyer could tell them otherwise :-)

Since you did not authorize them to change the diff fluid, you can legally make them undo the work you did not authorize, without payment, with the Amsoil :-) Just learned about this stuff in class, and if ya don't believe me, or they don't buy it, I'm sure a lawyer could tell them otherwise :-)

I agree with this 100%.

My parents lived in Greenville Maine when I was a college kid. I brought my VW up from Augusta to Greenville for Xmas.

It was so cold that I had to adapt a hot plate to the sump to get it started. Once it started the 80 wt. in my diff was so cold it would stall the engine. Then when I got the 80 wt. a bit warmer the car would drive off forward in neutral when you let up the clutch because the oil was pumping like an automatic. I finally got the transaxle warmed enough to drive normally and then the gas line froze.

Perhaps the gentleman had had experience like this. The front transaxle on a Subie will warm up and oil will move fairly quickly. The rear diff is isolated and takes much more time to warm in extreme cold.

The question is what lubes better in extreme cold? Oil that will move or oil that is as you say "chapstick".

I always got by but learned to mix motor oil and diff oil to get my cars to work. No really thin diff oil with crush resistance was available where I was back then.

The real problem with ATF in a diff is that it has less crush resistance.

 

Cookie, here is the ticket for the rear diff: Redline Superlight Shockproof.

http://www.redlineoil.com/products_gearlubricants.asp?subcatID=20&prodID=61

ya make them put back what you had in there man, that is bulls**t. thats why i come to these boards, so i make sure that my car doesnt get treated like a f**king honda. "whats that Mr. Jordan, your car has a total of 3 differentials, there is no way that a car can have 3 differentials, you must be mistaken, we here at (insert crappy auto-chop nationwide chain-name here) have never heard of such a vehicle." " I assure you Mr. Jordan that having ATF fliud in all 3 differentials will cause absolutely no problem to your vehicle, we made sure that your oil was red in color and not tannish-clear like other "inferior" oils."

 

 

 

 

 

~Josh~

that's what the rear in my BMW is running today. She got a nice oil change with Mobil 1 today and anew oil filter. The Subie got some Pennzoil 10-30 and runs all factory reccomended lubes.

For cold weather I would certainly suggest full-synth fluids. I always ran conventional lubricants in my transaxles and diff's until I bought my Legacy. I changed to RedLine synth half-way through the first winter that I owned the car (last winter) and the cold weather shifting performance increased dramatically. Worth every penny!

 

-Heikki

 

(BTW my "Ford" uses ATF in the MT5 tranny)

You guys are really scaring me. ATF fluid should NEVER NEVER NEVER go in the rear diff in ANY car unless SPECIFICALLY requested by the manufacturer. It does not matter what the heck BMW calls for, ATF has NO hypoid component in it (sulfur).

Now for a Chemistry Lesson:

A specific chemical reaction takes place between the steel and the hypoid oil when it is warmed that hardens and strengthens all components involved. For those of you who know your Chemistry, when the temp on certain reactions drops below a certain pt., the reaction "undoes itself" i.e. when your diff cools off. So in very short order your back end will begin (quite literally) to come apart. Beause there is no component in there to harden the gears in it. All the force of the engine has to go through a surface area not much larger than your thumb, it needs all the help it can get.

Change it now.

And yes, some cars (CERTAIN BMW's and other manufacturers - not all). Do require ATF in the GEARCASE, not the diff (I say this as someone who had BMW expierence as well as with a variety of other auto manufacturers). In fact if you read your haynes/FSM/chilton's manual, you will find certain proceedures on FWD trannies to drain/refill the front diff embedded in them.

 

This is perhaps the stupidest mistake for a mechanic to make other than not putting oil in the engine. He should be beaten over the head with a monkey wrench.

 

If you have an LSD (Limited Slip Differential) in the rear then there is a special oil from Subaru that should be used. I don't know if newer subarus have them or not.

Well, the transmission slipped once over the weekend - enough for the engine to rev and bounce off of the rev limiter - so it's back at the transmission shop this morning. They pulled the work order for me, and it stated that there was 90w oil in the front & rear diffs, and of course ATF in the tranny. What they guy had said to me was, quote "We put 90w in the front and ATF in the rear" but apparently he meant the front & rear sections of the differential/transmission unit.

 

Still, the Subaru dealer was still wrong since the 90w oil is only spec'd to 40F, according to the owner's manual. For two weeks in MA we'd had below freezing to below zero weather... Anyway, the tranny shop is going to replace the 90w oil for me (for free) with some Royal Purple 75w90 I picked up on Friday. No harm done, in the end.