Noah930

I have a new-to-me 1990 964 C2 (manual, but sadly no LSD). I haven't done any maintenance to it yet, but through reading up I'm finding that it's similar but different than the 930 I've had for many years. Holy smokes, is everything different? Jacking up the car, oil change, heck even swapping out the hood shocks those things have different attachments than the ones used in my G body.

So I'm planning a transmission fluid exchange. Even though the car had its clutch done about 25K miles ago, and the motor rebuilt 12K miles ago, I cannot find in the old receipts any documentation of a transmission fluid change. Because the shifting is even notchier than my 930 with its 915-based box, I thought I might as well swap out the transmission fluid FWIW. (I've read all the threads on Swepco 201 vs Mobil 1 vs Redline--I'm gonna go out on a limb and try the Swepco 202 and see how it works). But my question is: is the procedure the same as that on 915 and G50 boxes? The threads/pages I've read seem to be more about the 993 than the 964, but it still seems like the fill hole is on the left/driver's side of the gearbox, and the drain hole is on the bottom. PO has already removed the underbody cladding, so that's one less step for me. Otherwise, is the procedure the same as in earlier gearboxes? Torque spec should be 30 Nm (22 ft-lb) as in the G body G50? I've done this before in my 930. Is the procedure the same for the 964? Sorry for the newbie question. I just wanted to make sure I wasn't doing something blatantly wrong.

John McM

Just did my C4. Undo fill plug, undo drain plug and leave to drain for a while. Refit drain plug with new washer (same as engine). Pump new oil into fill until it starts to drip out. Refit fill plug with new washer. Torque to 30Nm.

Re oil choice. Notchiness could be worn synchros or an oil that isn’t allowing them to work as intended. I’ve just researched this as well. I can’t recall seeing Swepco as the preferred fill for a G50. It’s a difficult box for an oil. GL5 to keep the hypoid gear happy and a less slippery oil to allow the synchros to work. Redline 75W 90 NS is my third go at getting a less notchy shift and my box is rebuilt.

rotorheadcase

How have you found the Redline John? I used the Penrite 75W 90 on my last service but it hasn't improved shift feel. I anything it's a little more notchy that previous. Was considering LiquiMoly as a replacement.

Neil

John McM

Hi Neil, it seems better. I have a spare gear set, slider and syncro so had a play to see how they work. It’s quite complex. To get a smooth shift the syncro has to smoothly bring the gear to the right speed. The oil slipperiness will definitely have an impact as it lubricates the gear and syncro interface.

newsboy

Redline improved the smoothness of my shifting. Didn't have a pump, so I ran a tube from the fill hole out through and above the wheel well, and added fluid from there.

r-mm

That is a nice style of pump. I have the hand pump with loose hose for input/output and its fond of coming out of the jug while filling and or not getting to the bottom of the jug. For what its worth I used the Redline 75W90NS and shifting felt very nice even in CT winter temps but I only have a few miles on it.

John McM

The difference in the oil is the friction modifier level, apparently. Non slippery oil allows the synchros to grab the gear more easily.

The pump was a cheapie from a local auto parts retailer.

Noah930

Did the deed yesterday. I greatly appreciate the advice given on this thread. I kinda wish I had invested in even a cheapo pump like above, as it took almost an hour for my even cheaper funnel-and-tubing method.

Not sure what gear oil was in the car before, other than it was grayish-black (not blue). But even just taking the car around the block, I think the Swepco 202 is an improvement. Shifts used to be especially balky when everything was cold--now, no longer. And now upshifts are quicker. I used to have to shift slowly, otherwise I'd feel a little snickt as I moved the gear lever from one cog to another. That's clearly improved now with the 202 in the box. The synchos may still be worn (that was my fear originally, and still is), but the fluid change was definitely an improvement.

Laker

gravity is all you need

John McM

How does the air enter the container to allow the oil to flow?

Noah930

I was wondering the same thing. Maybe make a pinhole at the top of the handle?

But with my luck I'd have to stand the container up again for some stupid reason, and then gear oil would come spilling out of the hole I just made.

Laker

^^^ Pinhole at top point of handle :-)

Rocket Rob

I've used a variety of methods over the years, but have found that the Motiv PowerFill to be very easy to use and its my current favorite.

PS: I'm running Swepco 201 in both of my cars. Shifting is very good but note that I don't drive the cars in the winter (road salt season).

https://www.motiveproducts.com/colle...-5-gallon-tank

Tsmith5150

So far I hear the following recommendations for Trans fluid to help with the crunch of the shift.
1 Liquimoly
2 PTX
3 Redline 75w90

I currently run PTX and that did not help. It was pricey, My mechanic mentioned REDLINE and was pretty adamant when he said it.
So I may drain my PTX from 8 month ago and check for and metal fragments as I do it. Then I will try RED LINE. Thats my plan to get my smooth back.

Tsmith5150

So your RED LINE made a difference in Shifting?