IrishLegend

Me again, the slowly learning 928 owner. I'm going to change my manual transmission fluid and was advised to change the differential fluid as well. Is there a write up anywhere on how to do these basic jobs? Hell, I don't even know where to fill these fluids!

Thanks guys for putting up with my ignorance to some of the most basic jobs.

I appreciate the help.

Maleficio

I just changed my diff fluid the other day. It's easy.

You've got a drain plug, and a fill plug.

Open the fill plug first just to make sure you actually can. If you open the drain plug first, let all the old fluid run out, then find you cannot open the fill plug, you're screwed.

Once the fill plug is out, open the drain plug and drain out the old fluid. Then reinstall plug.

Then use the fluid pump you can buy at any parts house to pump in the new fluid into the fill hole until it just begins to run out. When it starts to run out the hole as you pump it in, you know it's full. Reinstall plug. You're done. Enjoy.

Manual tranny's are the same.

I installed Amsoil gear oil along with a healthy dose of Lucas Oil Stabilizer and a healthy dose of Tufoil oil additive. This three-way is a magical combination that equates to removing 300 lbs from your trunk. It's awesome. Do the same in your gear box. Unless your gear box and diff are one and the same unit. I have an auto.

If you install Tufoil in your manual tranny, your shifter will turn into silk. Nothing more smooth.

Maleficio

By the way, you'll need a 17 mm hex-head to fit into the plugs. Like a big Allen wrench. You can buy them anywhere. A socket-style to fit onto your 1/2" drive ratchet works best and takes up less space in your tool box. You may need a long breaker bar to get the plugs loose.

Rob Edwards

On early cars there are 3 plugs to deal with, 2 drain plugs on the front and rear of the tranny/diff, and 1 fill plug on the rear. You need a 17mm hex socket. THE FIRST PLUG TO UNDO IS THE FILL PLUG, half way up the rear diff cover. You'll be sad if you drain the trans and then can't get the fill plug out...

Here's the rear drain (lower) and fill plugs (upper) on a GT box (which have the 10mm hex plugs, not 17)



Filling can be done either by snaking a hose from above (thru the battery box?) or pumped up from below like so:



16 ft lbs torque on the drain/fill plugs, add ~4 quarts of 75W90 GL5 gear oil. Brand is your choice, this ain't politics and religion.

IrishLegend

I was told to put Redline: Heavy Shock Proof 3qts and Redline: MTL 1qt will do the same.

IrishLegend

Thanks guys.

Maleficio

All I know is what I've tried, and it's worked like a champ for me since 1996.

Redline is good stuff.

mark kibort

Its always nice to have another spot to run the filler hose so that you can use gravity. The race car makes this easy as I use a plugged hole above the transmission and just hang a funnel from rear hatch.

NoVector

I used Tony's page as a reference for my transmission and differential change.

http://members.rennlist.com/v1uhoh/

FWIW - My differential didn't leak until I used synthetic fluid ... Just say'n.

Good luck and hope to see you at a future 928 GTG! / Bruce

GlenL

No. Who told you that?

I did that and drained it out after reading the specs more.

You want the 75w90NS.

Vilhuer

On all manual gearboxes there are two drain plugs, one at front and another at rear plate below fill plug. It is important that both drains are opened. If not, all old oil will not come out unless car is in serious angle.

Maleficio

Where did it leak from? The axle seals? The input seal?

Rob Edwards

Erkka is, as always , right. Oops, my bad. Here's the front drain hole on a later tranny as well:

NoVector

It's the big seal that goes around the back cover in the bottom area. Don't get me wrong--it's not really a leak. It's more of a weaping. / Bruce

Maleficio

Sounds like the old-school problem of switching to synthetic: oil molecules are very small, and easily slip past older seals.