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Thread: diff fluids

  1. #1
    Registered User johnnie27's Avatar
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    diff fluids

    Happy New year boys and girls

    i know some of you do tranny fluids , (as i do too) but has anyone done diff fluids, if so any reccomendations of fluid brands etc

    thanks john
    2004 RS6
    APR, KW, REMUS

  2. #2
    Registered User hahnmgh63's Avatar
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    Redline 75w/90 in the front & rear Diffs & Redline 75W/90NS in the center Diff. Not sure why Audi recommends fluid with a Friction modifier in the Center Diff as it's a Torsen so it should just be work gears. I have used regular Redline 75W90 in other Audi's with the Torsen center diff with no problems before.
    2003 White RS6 2013 Midnight Blue S5
    2013 Daytona RS5 2x944 Turbo's 1974 911 w/'91 3.6ltr motor
    Roy, WA

  3. #3
    Registered User johnnie27's Avatar
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    Quote Originally Posted by hahnmgh63 View Post
    Redline 75w/90 in the front & rear Diffs & Redline 75W/90NS in the center Diff. Not sure why Audi recommends fluid with a Friction modifier in the Center Diff as it's a Torsen so it should just be work gears. I have used regular Redline 75W90 in other Audi's with the Torsen center diff with no problems before.
    thanks man! i gotta say it is so nice having a forum, where people have done stuff that you want to do

    i really appricaite all the tech advice that has been sen back to be, esp being in another land far far away

    i will do this next serivce , as i dont believe or can't see anywhere that is has been done, car is at 45,ooo miles (i assume audi call these fluids life-time)

    john
    2004 RS6
    APR, KW, REMUS

  4. #4
    Registered User johnnie27's Avatar
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    Quote Originally Posted by hahnmgh63 View Post
    Redline 75w/90 in the front & rear Diffs & Redline 75W/90NS in the center Diff. Not sure why Audi recommends fluid with a Friction modifier in the Center Diff as it's a Torsen so it should just be work gears. I have used regular Redline 75W90 in other Audi's with the Torsen center diff with no problems before.
    sorry to nag, do you know where i can get all the tech data from?

    oil qty's and viscosity's etc thanks
    2004 RS6
    APR, KW, REMUS

  5. #5
    Registered User Jimmy Joe's Avatar
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    Quantum Blue lubricants. You can have them mix some gear oil just for your car www.
    check their site at sales@bndautomotive.com

  6. #6
    Registered User johnnie27's Avatar
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    Quote Originally Posted by Jimmy Joe View Post
    Quantum Blue lubricants. You can have them mix some gear oil just for your car www.
    check their site at sales@bndautomotive.com

    thanks mate, but i am in australia , and looking for the tech info

    viscosity / quantities ..for diffs
    2004 RS6
    APR, KW, REMUS

  7. #7
    Registered User 4everRS's Avatar
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    Mark, do you happen to know the capacity of the diff's ?
    Avus Silver RS6 - Viper Stage 2 ECU/TCU - Water/Meth Injection - Frozen Rotors - Hbars - clear corners - Hella smoked tails - gutted precats

  8. #8
    Registered User mdegracia's Avatar
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    Diff volumes are here in this old archive file.:

    http://www.rs6.com/archive/index.php/t-7854.html
    03 RS6 Daytona Grey - EFI Express - 01e - SRM K24 - Aquamist - 495whp/580ft-lbs

  9. #9
    Registered User 4everRS's Avatar
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    Thank you.
    Quote Originally Posted by mdegracia View Post
    Diff volumes are here in this old archive file.:

    http://www.rs6.com/archive/index.php/t-7854.html
    Avus Silver RS6 - Viper Stage 2 ECU/TCU - Water/Meth Injection - Frozen Rotors - Hbars - clear corners - Hella smoked tails - gutted precats

  10. #10
    Registered User 4everRS's Avatar
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    When filling diff's, is there a procedure available? Or just fill til it runs out?
    Avus Silver RS6 - Viper Stage 2 ECU/TCU - Water/Meth Injection - Frozen Rotors - Hbars - clear corners - Hella smoked tails - gutted precats

  11. #11
    Registered User hahnmgh63's Avatar
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    All of the drain & fill plugs take a Hex head socket (Allen head). Front Diff takes 1.30ltr, the center is .85ltr, and the rear is the one I'm uncertain about but I believe it is about 2ltrs so 3ltrs total should be enough to do all 3 but if you have 4 on hand your guaranteed to have enough. The front Diff has no drain plug, just a fill plug so the fluid has to be evacuated from the fill plug which is just to the front side (about 2 to 3 O'clock position) on the right side front axle flange. The center diff has a drain plug on the bottom rear of the transmission tailshaft housing about 10cm or so from the axle and the fill plug is on the right side about 1/3rd of the way up the housing above the drain plug. The rear Diff has the drain plug on the bottom and the fill plug I can't remember if it is on the right side (pretty sure), or on the left side. You do have to remove the sheet metal splash pans around the rear diff to get at the fill plug. The fluid is definitely 75w90. The exact fluid recommendation is called: Burmah SAF-AG4 for the front & rear and Burmah Carbon Mod. for the Center Diff (or the SAF-AG4 w/.034 of friction modifier STURACO FM 1992 added). A high quality 75w90 will do the trick although I am partial to Redline as their oils all seem to exceed all oil specs by more than other synthetics. I don't know why they specify the Burmah w/friction modifier for a Torsen diff (knows as a Parallel Axis Torsen) but they do. I have run a couple of Torsen Audi's on regular 75w90 for years (Redline 75w90) with no problems but the closest Redline for the Center Diff would be 75w90NS but when I bought my car in '05 I changed all Diffs with regular Redline, it wasn't until I just reinstalled my engine/tranny last month and refilled the tranny did I actually use the 75w90NS in the center diff and can't tell the difference. And yes all Diff fluids are listed as "fill for life" and only spec'd to be checked & topped off per the shop manual (B.S. is what most people say). Just like the fill for life transmission fluid when even the manufacturer (ZF) specs a fluid change interval every 60K~80K in general for the 5HP-24A tranny whereas I feel the tranny not being beefed up we know enough for the RS6 can use oil changes more frequently so I do my ATF every 40K & Diffs about the same although the Diffs are probably fine going a little longer.
    2003 White RS6 2013 Midnight Blue S5
    2013 Daytona RS5 2x944 Turbo's 1974 911 w/'91 3.6ltr motor
    Roy, WA

  12. #12
    Registered User 4everRS's Avatar
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    Great Mark, thanks!

    As mdegracia posted the link to, the rear look to be 1.6qts. Thanks for letting me know where the drain/fill locations are. So, I will likely just measure what I am putting in. However, for the front diff, after extracting fluid, if I don't get it all, how do i know when it's full? Maybe it just runs out?
    Avus Silver RS6 - Viper Stage 2 ECU/TCU - Water/Meth Injection - Frozen Rotors - Hbars - clear corners - Hella smoked tails - gutted precats

  13. #13
    Registered User speedtrapped's Avatar
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    curious, it seems that changing diff fluid makes sense....every 25k miles? did I read right, lifetime?
    Ebony/Black, DBR Stage 3 race kit, -SOLD :( 996TT Proto 650 basically a sardine can with a rocket attached to the back...11' CTS-V, 540/579RWP hehehehe ;)

  14. #14
    Registered User hahnmgh63's Avatar
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    The manual calls for level ground and room temperature to fill to the bottom edge of the filler plug for all three diffs. The front not having a drain plug is a PIA. I just used a mighty vac extracter and moved the hose around a little so I think I pretty much got it all. Factory calls for lifetime fill for everything with top off & refill procedures in the manual for checking level and Mx work done. And if you haven't done this before you will see right away that the lifetime fluid definitely doesn't look fresh anymore after years and miles of use but it will last through the new vehicle warranty period
    2003 White RS6 2013 Midnight Blue S5
    2013 Daytona RS5 2x944 Turbo's 1974 911 w/'91 3.6ltr motor
    Roy, WA

  15. #15
    Registered User speedtrapped's Avatar
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    ahh...I have some amsoil 75/90....sounds like a week end job
    Ebony/Black, DBR Stage 3 race kit, -SOLD :( 996TT Proto 650 basically a sardine can with a rocket attached to the back...11' CTS-V, 540/579RWP hehehehe ;)

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    Quote Originally Posted by hahnmgh63 View Post
    All of the drain & fill plugs take a Hex head socket (Allen head). Front Diff takes 1.30ltr, the center is .85ltr, and the rear is the one I'm uncertain about but I believe it is about 2ltrs so 3ltrs total should be enough to do all 3 but if you have 4 on hand your guaranteed to have enough. The front Diff has no drain plug, just a fill plug so the fluid has to be evacuated from the fill plug which is just to the front side (about 2 to 3 O'clock position) on the right side front axle flange. The center diff has a drain plug on the bottom rear of the transmission tailshaft housing about 10cm or so from the axle and the fill plug is on the right side about 1/3rd of the way up the housing above the drain plug. The rear Diff has the drain plug on the bottom and the fill plug I can't remember if it is on the right side (pretty sure), or on the left side. You do have to remove the sheet metal splash pans around the rear diff to get at the fill plug. The fluid is definitely 75w90. The exact fluid recommendation is called: Burmah SAF-AG4 for the front & rear and Burmah Carbon Mod. for the Center Diff (or the SAF-AG4 w/.034 of friction modifier STURACO FM 1992 added). A high quality 75w90 will do the trick although I am partial to Redline as their oils all seem to exceed all oil specs by more than other synthetics. I don't know why they specify the Burmah w/friction modifier for a Torsen diff (knows as a Parallel Axis Torsen) but they do. I have run a couple of Torsen Audi's on regular 75w90 for years (Redline 75w90) with no problems but the closest Redline for the Center Diff would be 75w90NS but when I bought my car in '05 I changed all Diffs with regular Redline, it wasn't until I just reinstalled my engine/tranny last month and refilled the tranny did I actually use the 75w90NS in the center diff and can't tell the difference. And yes all Diff fluids are listed as "fill for life" and only spec'd to be checked & topped off per the shop manual (B.S. is what most people say). Just like the fill for life transmission fluid when even the manufacturer (ZF) specs a fluid change interval every 60K~80K in general for the 5HP-24A tranny whereas I feel the tranny not being beefed up we know enough for the RS6 can use oil changes more frequently so I do my ATF every 40K & Diffs about the same although the Diffs are probably fine going a little longer.
    Hey Mark, finally getting around to doing this. Do you know what size the hex heads are for the differential fill and drain plugs off hand? I thought I remember seeing 5mm somwhere. I don't have one down to 5mm and just want to make sure.

  17. #17
    Registered User hahnmgh63's Avatar
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    That's easy, only because the car is on the lift, engine & tranny are out sitting on separate stands. Front Diff is 8mm fill Hex/Allen (no drain plug so it has to be evacuated, fill is on the right side at the 3 o'clock position on the axle flange), center Diff is 8mm fill, 6mm drain (Audi, what were they thinking?), Rear Diff is 10mm drain & fill.
    2003 White RS6 2013 Midnight Blue S5
    2013 Daytona RS5 2x944 Turbo's 1974 911 w/'91 3.6ltr motor
    Roy, WA

  18. #18
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    That's awesome! As usual, thanks for your help. Bought a kit that has some stubby socket style of each of those sizes. I really appreciate it Mark.

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