Getting ready to change fluid in FT & RR differentials

[ciaka]

Getting ready to do fluid change on the front and rear differentials on my 05 CTT and just wanted to get final advice on fluid.

Have been searching and found that changing with Mobil 1 synthetic 75W90 gear oil would be good. Just wanted to run by as last sanity checkbefore I get going. Will greatly appreciate this last minute confirmation.

If you can also give me pointers on location of the drain plugsd on the front and rear, it would be great (will look up in manual too but if you already know the location and can share thee info it would be awesome).

Thanks.

Edited October 10, 2012 by ciaka

[Scarpoolla]

I changed mine last weekend to Redline 75w90. Here is a little tip though...The front fill plug is a bear to get to because you have zero clearance to get a normal external torx socket bit in there to unscrew it. So I bought an extra external socket bit, used my 3" high speed cut off wheel and cut the bit where it fits into the socket and then used the closed end of an 8mm wrench with some masking tape wrapped around the bit and wrench to hold the bit in place. This homemade tool was a perfect fit. The drain and fill plug are both the same size. It's either a T-55 or T-50.

[bigbuzuki]

Porsche Technical Service Bulletin 3965 lists all the approved oils and quantities for changing the final drive differentials and transfer case oils.

You can download it from this site if your a contributing member.

[hahnmgh63]

Redline 75w/90 in my front & rear diffs also, '06 CTTS.

[clarksongli]

i chose to stick with the OEM fluids for the diffs....depending on the options, you may have both lockable differentials similar to myself. As best as i can tell, they use a friction disc to provide limited slip ability.

Because of this, you will notice in the sevice bulletin that the lockable differentials require a different oil than the standard differentials....from the VOAs i have done, there is a friction modifier in the fluid....assumingly to provide the lockable function on the friction disc.

Anyways....Burmah is out of business, so you won't find it online anymore.....so i chose to buy OEM fluid for the diffs, really because i tend to require the locking feature when i'm off road.

Either way it's only 3 liters to fill both differentials, so whether you do OEM from suncoast parts, or redline.....it's a cheap and easy maintainence step for the car

[ciaka]

I've been looking at this type of info and i think i will go with the synthetic mobil 1 75W90 fluid. It is for limited slip, hence the LS in the name. It does have friction modifiers in it. I have been reading from other users who went the mobil way and were fine. Just wanted to post as a sanity check. I assume you just undo drain plug, let it all come out, put drain plug back in, open fill plug and top up until drips when car level? Then close fill plug and done. Anything else i am missing here? Thanks.

[hahnmgh63]

You've got it, pretty simple. The book answer is Front Diff approximately 1 liter, rear axle w/out limited slip approx. 1.4 liters (V6 w/M.T. approx 1.25 liters), w/limited slip approx 1.6 liters, Transfer case new filling quantity approx .85 liters (change approx .75liters). Transfer case takes LT71141 Esso spec ATF which most good synthetic ATF's meet or exceed this spec, I use Redline D4 but many others will work also.

Clarksongli is right about the limited slip, it's a conventional clutchpack unit. Many Gear oils will note for use with limited slips as they have friction modifiers. Limited-slip or Positraction units use plates or clutches to provide the proper amount of lock-up to the differential. Slippery lubricants are required to prevent chatter, but too much slipperiness causes excess wheel spin, reducing traction. Sometimes a limited slip will require the friction modifier additive compared to just adding the oil alone even though it claims to be Limited slip compatible. The amount of friction modifier will vary with the type and amount of clutches and will even vary over the age of the differential. My Turbo S has the limited slip option so I use Redline 75/90NS with a bottle of their limited slip friction modifier. Many good autoparts stores will carry some brand of friction modifier, one of the most common is the General Motors stuff.

[deilenberger]

One suggestion - BEFORE removing the drain plug, make sure you can get the fill plug out. More then one person has ended up having to tow a car to a professional to get the fill plug removed after draining the differential (or transmission) and finding the fill plug was not coming out..

[ciaka]

check on that one. I was just thinking the same thing yesterday night: 'what if - i cannot open the fill plug'...lol.

I was also going to pull it to verify the level that the diff. was filled to. I assume it will be to the bottom of fill hole (as in many cars is the case). In case the level is lower than that, I assume having more oil is not going to hurt the diff.

So I will put in:

- Synthetic Mobil 1 75W90 LS into rear and front Differentials

Still a question:

- will this fluid be fine for Transfer case: CLICK HERE

...it is available at advance auto parts and O'Reily auto parts, so I would not have to go out of the way to get some.

Thanks for help.

One suggestion - BEFORE removing the drain plug, make sure you can get the fill plug out. More then one person has ended up having to tow a car to a professional to get the fill plug removed after draining the differential (or transmission) and finding the fill plug was not coming out..

[hahnmgh63]

Mostly likely the Mobil 1 ATF will be fine for the transfer case but I would check the Mobil website to be sure that it meets Esso LT71141 spec. Since Mobil/Esso is the same company it probably does or else they sell another one that does. The ATF for the tranny is JWS3309 ATF so it is a different spec although some of the better Synthetic ATF's can meet both specs.

I'm a Redline Oil fan but here is a good site for those going the Mobil route

http://store.avlube.com/mobilatf3309.html

Edited October 18, 2012 by hahnmgh63

[royxaxa]

I cut the allen key for removing the screw too. very tight there.

[ciaka]

Yup. I plan to have little clearance and already have a volunteer key that will be cut.

[ciaka]

This is a pic from the rear of the car (looking towards the front).

Can you confirm that this is the rear differential, and #2 is the drain plug, and #1 is the fill plug

1 - fill plug

2 - drain plug

Want to confirm before doing the job. Thank you yet again.

Edited October 20, 2012 by ciaka

[Loren]

Click to enlarge...

[ciaka]

OK. I did the rear differential today (will be doing the front soon).

Posting the DIY info for all those who have been asking questions.

Thanks.

[hahnmgh63]

Just for reference, I see it's a '05 Turbo, post your mileage as well as a description of your old fluid if you could. Many, including me found the old rear fluid used but in Ok, shape but the front being much more used up looking compared to the rear stuff?

[ciaka]

Hi. I did that in the dying section. ~67k on Odo. Fluid looked almost black, looking closely had some greenish tinge. Appeared very thin in consistency (almost like water). Take a look at the write up that show pics - in dying section - maintenance section, named rear diff fluid change.