Rear diff fluid change 928s auto

[PC-85-928S]

How does one change the fluid in the rear diff on a 928s us auto?

Has anyone tried the synthetic fluids like Amsoil?

[Landseer]

This part is easy.
Conventional (tapered) plugs to remove, 17mm hex.
Use a pump or run about a 1/2 inch hose from the fill hole, through the right rear fender well, and zip tie it to the fuel fill door.

Fill. Am using Mobil 1 LS synthetic, on some, Valvoline inexpensive stuff on others. I think it calls for 75W85 or 75W90. At least 2 qts / check book.

Don't overtighten plugs on reassembly.

[harborman]

Originally Posted by PC-85-928S

How does one change the fluid in the rear diff on a 928s us auto?

Has anyone tried the synthetic fluids like Amsoil?

Make sure you remove the fill plug first. I read this one is sometimes difficult to open, before you drain the case.

[PC-85-928S]

Synthetic from conventional switch on this no problem?

[Pete R]

Originally Posted by harborman

Make sure you remove the fill plug first. I read this one is sometimes difficult to open, before you drain the case.

+1000 I almost totally screwed myself with my wife's CRV by removing the drain plug first. There were several tense moments of sweat and nausea.

[Landseer]

Originally Posted by PC-85-928S

Synthetic from conventional switch on this no problem?

No, it hasn't been for me on engine, trans or diffy, regardless of mileage, 10 different Porsche cars, from a leak perspective. Am using new pan gaskets in engine and transmission on most of the cars. The ones with cork gaskets (944) weren't leaking, so its fine. If your gaskets are already leaking, some say that the synthetic might accentuate it. Don't know.

On the automatic transmissions, though, am now using Valvoline High Mileage ( red container ) these days because the Mobile 1 trans fluid doesn't shift as firmly on a couple of my cars as the Valvoline. The Valvoline might not be synthetic. I think the issue is the friction modifier package as opposed to the origination of the oil portion.

[Maleficio]

I'm running Amsoil in mine, plus a dose of Tufoil. Works great.

[harborman]

Originally Posted by Landseer

No, it hasn't been for me on engine, trans or diffy, regardless of mileage, 10 different Porsche cars, from a leak perspective. Am using new pan gaskets in engine and transmission on most of the cars. The ones with cork gaskets (944) weren't leaking, so its fine. If your gaskets are already leaking, some say that the synthetic might accentuate it. Don't know.

On the automatic transmissions, though, am now using Valvoline High Mileage ( red container ) these days because the Mobile 1 trans fluid doesn't shift as firmly on a couple of my cars as the Valvoline. The Valvoline might not be synthetic. I think the issue is the friction modifier package as opposed to the origination of the oil portion.

Not to confuse the original question, but he was wondering about the differential not the trans fluid. I also used the Valvoline in my Auto-trans and I think it said good for 75K miles. I have never used synthetic oils. Now they seem to be changing the time frame on engine oil changes too, no longer every 3K miles.

I do remember Mrmerlin saying to open that fill plug on differential first before draining as some were hard to get off. I might tackle that job as well.

[Landseer]

Yes, you are right, I got that totally sideways!

But he and I were corresponding separately a few days ago on the trans fluid, so it must have gotten tangled up in my mind. Good call, bad communication on my part.



The 5 speed has the diffy open to the trans, so they fill as-one with gear oil.

The auto uses gear oil in the back, and trans fluid in front.


Valvoline and Mobil 1 are brands of both gear and trans fluid --- am using all permutations right now, gets confusing sorry.

[harborman]

Originally Posted by Landseer

Yes, you are right, I got that totally sideways!

But he and I were corresponding separately a few days ago on the trans fluid, so it must have gotten tangled up in my mind. Good call, bad communication on my part.





The 5 speed has the diffy open to the trans, so they fill as-one with gear oil.

The auto uses gear oil in the back, and trans fluid in front.





Valvoline and Mobil 1 are brands of both gear and trans fluid --- am using all permutations right now, gets confusing sorry.

Hi, no problem Signor!! I was just hoping he would not put auto trans fluid in his differential, that's all. Your advise as always is right on! You certainly helped me a number of times.

[PC-85-928S]

I am going to try amsoil trans fluid and amsoil gear box fluid just waiting for new trans filter

[harborman]

Originally Posted by PC-85-928S

I am going to try amsoil trans fluid and amsoil gear box fluid just waiting for new trans filter

Are you also going to drain the torc converter?? Otherwise you leave a lot of old fluid in the trans. There is a drain plug on the converter but you need to position the plug by rotating the crank by hand. They also suggest getting new plug seal washers. I just did this job a few months ago.

[PC-85-928S]

yes will drain convertor as well

[Maleficio]

Originally Posted by PC-85-928S

I am going to try amsoil trans fluid and amsoil gear box fluid just waiting for new trans filter

You will feel the difference immediately.

[harborman]

I just did my Differential fluid change today. Got a 17MM hex allen 1/2 drive socket at Autozone for $11, actually a 3 pack. The plugs came out easy on mine. I put some anti-seize on them before reinstalling them. My old fluid was actually not too bad looking but this car was well kept! As was the trans fluid when I did that. The pan was clean. Anyway, now I know it's all new.

[Landseer]

Changing all the fluids, at least once at beginning of ownership, seems like a very positive thing to do.

We've begun disecting filters for clues to condition. Messy but revealing.