Rear Differential Fluid

[VTAudiA4]

My rear diff. seals have been leaking for some time. Today I will jack the car up to see how much fluid there is in the diff. since I will be going on a 300 mile trip.

How do I know if I need to fill it up?

I read one way was to stick your pinky finger in there and if its near the bottom of the plug opening that it should be fine.

Also, is it ok just to add fluid or do I need to bleed it and replace all of it?

I am planning to replace the seals eventually but since they are leaking slowly I am not in a rush. Plus Im in college and soon to be broke after I buy books.

[VTAudiA4]

One more thing, can someone check their manual since I do not have one as to which fluid is needed. Haynes says SAE 90 synthetic but after a little search this comes into conflict since others say 75W90.

Can anyone shed some light on this?

[VTAudiA4]

Ok so I checked shopkey and this is what they say but Im still a little bit confused. Front and center diff's use 75W90 synthetic.

Rear differential
Initial Fill (SAE 90)
A4 Quattro
Fluid Change (SAE 90)
A4 Quattro
Manual Transmission (75W-90 Synthetic)
A4



So does that mean that when chaning the trans fluid you put in 75w-90 or does it mean when you are changing rear diff fluid on a manual transmission A4 that you add 75W-90 instead of 90 SAE Synthetic?


I feel like Im talking to myself. lol

[ghost6303]

ive used mobil1 75w90 in the rear. its GL-5 which is what you need in the rear. there isnt a dipstick or anything to tell you how much oil to put in, you basicly just pump it in until its level with the fill hole (car has to be on a level surface). if i remember correctly its 1.75 quarts. theres a write up on how to change it on audidiy.com

edit: ive read mobil1 wasnt the best for your transmission fluid, i used redline MT90 in there, and mobil1 75w90 in the rear.

[VTAudiA4]

cool, thanks

[djwimbo]

Yea, GL5 fluid in the rear. so just about any 75W90 will work. I topped mine off with Lucas until I fixed my axle seals, and put Mobil1 in after the repair.

SAE 90 would be fine if you don't have to deal with <45*F, but for people in the midwest of similar climates the viscosity range is beneficial.

[k0mpresd]

i used motul gear300. gearbox and rear diff. helped with vibrations from the diff mounts.

[VTAudiA4]

What is the allen tool size for that plug? Its really big and I don't have the appropriate size. Is it 17mm?

[kjgarreau]

Whatever you do, make sure you can get the fill plug off BEFORE you remove the drain plug. IIRC the fill and drain plugs are 10mm on the diff. 17mm is for the fill plug on the gear box.

[O2VW1.8T]

Whatever you do, make sure you can get the fill plug off BEFORE you remove the drain plug. IIRC the fill and drain plugs are 10mm on the diff. 17mm is for the fill plug on the gear box.

That would suck lol....

[lotusgardener]

Its a triple square tool not allen key, you don't want to strip that bitch. Make sure you PB-Blast that thing too since you're way up north.

And it takes 1.9L. Just fill it up with a bottle and lower your car down on level ground. If some comes out of the fill plug, then you're full. If not give it some more, and repeat.

I just did my seals yesterday, and let me tell you, it does take all of the 5-6 hours that the shop is going to charge you, but it's money well spent. Just make sure to do it with a friend so you don't have to climb from underneath the car a bazillion times.

[kjgarreau]

The triple square is to drain the transmission.. not sure if he's planning on doing that.

[VTAudiA4]

Well, I just spent 3 hours trying to get that bitch to move. I have two broken wrenches (3/8, 1/2) bunch of scratches and bruises. I made pipes, used a hammer, Pb'd the shit out of it, and muscled it to the max. I am calling quits because I need to get some new tools. haha


My little angry rant. Another day tomorrow.

[xqwizit]

I just changed out my rear diff fluid today too. It is indeed a 10mm allen socket. Most of our cars will probably have some dirt and grime inside the bolt head so to clean it out, hammer the allen socket in there and take it out and then blow on it. The debris caught in there will keep the socket from going in and getting a snug fit. Otherwise if you don't put it in all the way, you risk stripping it and that's not good news. So be patient and it will come out but take care to ensure that the socket is deep in the plug bolt.

As for the triple square, I assume that you guys meant Torx bit. I didn't need a torx bit on my 98 1.8T. For the transmission, I had the big 17mm allen plug for the fill, then I believe a standard 13mm bolt for the drain. For the rear diff, it's two identical 10mm allen plugs. And I used 75W90 Mobil1. A fluid guidebook at Kragen said that it was 75W90 and at $8.99 a quart it wasn't too bad. Good luck VtA4. BTW, I know it may sound dumb but I know that sometimes some bolts are reversed but this one is normal (lefty loosy, righty tighty). Just make sure that you are spinning in the right way (in this case counterclockwise). Oh and tighten with 26lb/ft.

[VTAudiA4]

Thank you for all the help guys. It is greatly appreciated. I woke up today, bought myself another 1/2 drive breaker bar and went at it. I let the bolt soak over night in PB blaster and it was cake getting out this morning. I refilled the diff with 75w90 SAE synthetic. I think I might have overfilled it a little bit because the car was not exactly even. I hope I will not have any problems. Finally, now I can go on my road trip, come back and then do the seal. YES!!!!! (sarcasm) lol

[B5A4Kevin]

its better to have a little more than full rather than a little less, especially since your seals are leaking. just remember almost every repair you do to your car will have at least 1 bastard bolt (or nut) especially on northern cars. sometimes you have to talk dirty to it, maybe make up a few new cuss-words, but eventually you will get it. another good technique (esp for big bolts) is to heat the area (not the bolt) with a torch for about 5-10 min, then cold shock the bolt with pb blaster or a similar product that has a cooling agent like liquid nitrogen (i have rust-off ice at my shop). might take a couple cycles but its the ultimate solution. it has never failed in my experience.

[lotusgardener]

The triple square is to drain the transmission.. not sure if he's planning on doing that.

My apologies, I meant Torx.

[VTAudiA4]

its better to have a little more than full rather than a little less, especially since your seals are leaking. just remember almost every repair you do to your car will have at least 1 bastard bolt (or nut) especially on northern cars. sometimes you have to talk dirty to it, maybe make up a few new cuss-words, but eventually you will get it. another good technique (esp for big bolts) is to heat the area (not the bolt) with a torch for about 5-10 min, then cold shock the bolt with pb blaster or a similar product that has a cooling agent like liquid nitrogen (i have rust-off ice at my shop). might take a couple cycles but its the ultimate solution. it has never failed in my experience.

Cool, thanks for the tip. I will keep that in mind next time I have a similar problem.