Changing trans diff oil, any tips?

[ckelly78z]

I have somewhat of a whine in my differential while driving after sitting idle for the Winter, and want to change the rear diff/ trans fluid out on my 5 speed 85.5 944.

I already have 3 quarts of Redline MT-90 and have a long hose and funnel set up to make filling more easy. I'll already have the car jacked up and on jack stands for better angle of attack for a 50 year old that doesn't bend so well, and I was wondering if you guys remove your driver's side rear tire/wheel for better access to the drain/fill holes. Also, I have to find a 17 mm hex head/allen head bit, or wrench to loosen the drain, any idea where to get it....Advance Auto or other parts store, or should I hit up a tool store.

Do I fill the case until it runs out or drips, or do I fill it just below the upper hole ?

[jpk]

First off, don't drain anything untill you have gotten the fill plug off.

For the fill plug wrench, getting a 17mm allen socket up there is pretty tight if not impossible. I ended up getting a 17mm allen wrench and cutting off about 1" with a cut-off wheel in my grinder. I put that into the plug, and used a 17mm box wrench to turn it.

[pdxfj]

Check NAPA. I picked up a 17mm 1/2" drive impact rated for about $8. P/N: NPT 615317.

[ckelly78z]

Getting the fill plug out first will help the flow of the oil out the other plug because the air can equalize ?

[jpk]

No, its about being able to get new oil in... If you cant get the fill plug out after you've drained the tranny, you have an empty tranny with no way to fill it...

[kevingross]

Do *not* use a power tool (impact wrench) on the plugs. They go on to 18 ftlb / 24 Nm torque. I have seen cracked cases from overtightening, and even more plugs with cammed out sockets.

[pdxfj]

The fill plug in mine was cammed out and we had to tack weld a bolt in just to get the plug out.

Only suggested the impact rated one since it's half the price of the regular one and is a tool you won't use very often so why spend $16+ when an $8 one will do... Gotta save a few bucks someplace working on these cars...

[thomasryan]

Yes....three attempts at the fill plug before I won.

I used a marine lower unit pump to fill mine back up with the car sitting on its tires (so it would be level) tight but doable.

[mytrplseven]

I ordered a manual hand pump on amazon and it was cheap. You just stick it in the bottle and the other end in the transaxle and pump until you see the oil come out of the tranny. It's a cheap pump but it works great and it's not like I'm planning on using it again any time soon. I replaced the Turbo coiled oil cooler so after I run the car a bit, I'll recheck the oil level and add more as necessary.

[John_AZ]

The drain plug will come out easier next time if you wrap some Teflon tape around it...credit to "samba"



J_AZ

[ckelly78z]

I may "flush" the tranny/diff with some cheap store brand 80/90 weight oil for 100 miles and then drain to put the Redline in. I'm just trying to ensure that I get any gunk and flakes out without putting the expensive stuff in on top of particles and gunk. I'll do the Teflon tape thing too, makes sense so no leaks, and easier to remove.

[BobFitz]

You can flush with a few quarts of diesel, run in neutral for 5 minutes and drain, then fill with Red Line. DO NOT DRIVE With diesel.

Bob

[pfarah]

I used some 75/90W Valvoline from Wally World for 200 miles then the MT90.

[ckelly78z]

If I use the diesel fuel as a cleaner, should I rotate the wheels manually to get it throughout the gears, or just more of a fill and drain ?

[BobFitz]

Originally Posted by ckelly78z

If I use the diesel fuel as a cleaner, should I rotate the wheels manually to get it throughout the gears, or just more of a fill and drain ?

I put the trans in neutral and let the engine idle for 5 min. or so. Been doing it for 50 years with no ill effects.

Bob