So I changed to Royal purple 75w-90 trans fluid about two weeks ago.

I think the car sounds a little quieter now and most shifts feel a bit smoother. BUT, to shift from first to second smoothly, I need to shift really slowly. If I go quickly, I either feel resistance or get a small grind. And long term, it's probably good I learn how big the jump is from 1st to 2nd and unless I need to, I'll shift slower from now on.

I guess, this could be some kind of clutch thing? It's not releasing fully so I have to have better shift timing. But my fluid reservoir has not dropped at all, so it's not a leak. I suppose there could be no external leak but the master cylinder could be pushing fluid up into the reservoir if there were some problem internally.

But since the problem arose hand in hand with the fluid change, I'm guessing that the old fluid whether due to age or maybe debri was creating more friction with the Syncro. I tried searching and I don't know, lots of varying information.

So I'm thinking
1. Figure out if I have an LSD.
2. If I do, I don't know what to do.
3. If I don't, try the Redline NS fluid that has some syncro friendly magic in it.

Any input from you guys?

I wish a snail shell swap were easy as there is a 1980 931 sitting in the local wrecker with the trans available but as I understand almost everything is different in that rear end.

 

Where do you live? I'd love to get my hands on that 931 trans.

 

If it were me, I'd drain that stuff out and replace it with Redline 75-90. Some lubes don't work well with Porsche synchros.

 

Red Line 75W90NS doesn't have friction modifier so it'll be the Red Line product you want to try to get better synchro engagement. If you do have a LSD then you can still mix 75W90 and 75W90NS so you don't have any LSD "chatter".

 

What I have found works on both track and street , ( as well as most of my friends running vintage 944s and 911s ) is a switch to SWEPCO 201.

Southwestern Petroleum Company makes a very highly refined product which is just loved by Porsche transaxles or transmissions. There is no need for a friction modifier in using this product in LSD transaxles.... it's all I have continuously used since the mid 80's. No grinds, no missed shifts, no adverse wear on synchros or LSD componentry. No noise as in whine or chatter, and NO forced/hard shifts.

Just like slicing warm butter with a warm knife, but with rifle bolt accuracy and precision.

 

Both of my 944 transmissions dislike fast shifts from 1st to 2nd, especially when cold.

 

944 transaxles work best with GL-4 rated gear oils, and don't do so good with GL-5 fluids. Every GL-5 fluid I've used has caused rough shifting, including redline 75w90ns, mobil1 75w-90, and a couple of synthetics I got from my FLAPS.

I use Brad Penn GL-4 80w-90 in the 944 and it works great for me.

(I don't know if Swepco 201 is GL-5, I have it in my 968 and it works great there, but I've never tried it in a 944.)

 

I have Mobil Delvac full synthetic 75W-90 in my 200k+ NA trans I swapped in a few years ago. Even in cold weather it still shifts pretty well. I ran Lucas GL-5 in my old trans and it was very reluctant to shift in cold weather (15-35* F which is about as low as we get in this part of TX).

 

I agree that these trannies like their GL4 per Porsche. I also run Swepco in mine and it performs well, but I am in a warm climate. Change to GL4 and I bet it feels better.

 

Noah - yeah, I think long term learning to take it easy on the 1-2 shift will probably be better for my trans. But I think it could be a little more forgiving.

Thanks for the input everyone(though this is a common theme in trans fluid threads, is that it starts one way and then recommendations start scattering). Royal purple says it's good for gl4 and gl5 but in researching apparently it's common for gl5 to just also tag in gl4 comparability and there is a difference in gl4 only fluid.

 

Put Porsche approved Mobil 1 PTX and be done. It has magic juice in it.

 

You can check for LSD in the 944 (not all 968) in the usual way, jack up the back end of the car, trans in neutral and spin one wheel Note the direction that the other wheel spins. Obviously chock the front wheels. A clutch-type LSD should make both rear wheels to spin in the same direction. If this happens, block one rear wheel and note the torque it requires to turn the other. Maybe 20-40lb-ft or so.

It's also not surprising that your transaxle oil might be too slippery for your old synchros. I'd find some GL-4 or maybe Redline 75W90 NS which is supposed to be OK for clutch-type LSDs as well as less 'slick' to promote synchro function. I'm not sure how that elfin magic works, friction modifiers for clutch LSD would IMO make synchros work less well.

-Joel.

 

Not to muddy the water, but I have had good luck with Amsoil transaxle 75w90. Two more good reads below. The second is gear oil related, but I included it to show that Royal Purple will corrode your brass syncros.

http://www.widman.biz/uploads/Transaxle_oil.pdf

http://www.lastgreatroadtrip.com/wp-...comparison.pdf

 

When I tried the LSD test, the other wheel didn't spin. Ha! Either too much drag in the wheel bearing or a dragging brake caliper I guess. They didn't feel hard to spin but... Must be some kind of resistance there. And the option code sticker is missing.

I ordered the Redline MT 90 GL4 fluid before I saw some of the more recent responses(and just so everyone is clear, redline has 3 75w90 fluids, a trans gl-5(NS), a differential gl-5, and mt90 which is for gl-4.

I think one reason for lots of confusion in these trans threads is all of the different types of oils. But based on everything I read I think amsoil, swepco, lucas or I'm hoping redline mt90 are good bets.

 

Or Mobil 1.