Zero10

I searched and didn't come across anything terribly relevant, so I thought I would ask....

*puts on flame suit*
So, my 951 has a terribly notchy transmission. When it's cold I cannot grab reverse at all, and have had to push it out of parking spaces before. I have big problems getting first at a light when the transmission is cold as well. Once the transmission has warmed up, shifting is significantly better, but not perfect.

When I bought the car, it had swepco 80W90 with LSD additive in the transaxle, and I replaced it with Redline 75W90 in an attempt to fix the notchy shifting. If anything, this fluid made it worse.

Looking at the kinematic viscosities of these fluids, it seems that the Redline is a much thicker fluid.
So, I am thinking that a much thinner fluid would allow for better shifting, and I've seen lots of threads for other makes and models (lots where 75W90 or 80W90 gear oil are reccomended) stating that GM synchromesh worked miracles, and that their notchy transmissions are just like new again. This seems to go hand in hand with my previous thoughts.....
On to my question which required the aforementioned flame suit:

Has anybody put GM synchromesh in their transaxle, and if so, what are your impressions?

On a side note, before somebody starts spouting that a thinner oil will cause more wear, look at the case of the 505.01 VW certified oils vs the 506.01 cerfieid oils..... 505.01 is a 5W40, 506.01 is a 0W30, and yet wear rates are roughly cut in half by switching to the 506.01, as well as fuel economy is increased. Thinner does not necessarily mean more wear.

The particular synchromesh oil I have in mind is the Amsoil synchromesh replacement product.


On a related topic, I have a guard limited slip differential in my transaxle. Do I require a LSD additive for it? I don't know if it's a torsen type, clutch pack type, etc.

hacker-pschorr

FWIW Royal Purple trans fluid took away some clunkyness in my 928.

Zero10

Wow, holy thick fluid batman!

Kinematic viscosity at 40*C of over 200!
GM synchromesh is like 50. Most 75W90 gear oils are ~90-120.
I can't imagine my transmission gets much hotter than 50-55*C, so the kinetmatic viscosity at 100*C is almost irrelevant.
The Redline that is in there has a viscosity at 40*C of ~165, which is definately far too thick. The swepco was around 130.

AR10

I would be looking at possibly a clutch problem.
Sounds like it is not releasing completley or there
is a problem with the pilot bearing or an alignment
problem in the clutch, bell housing or drive shaft.

Just my .02c

horsepowerfarm

I think AR10 is a smart guy, I agree with him and was thinking the same thing when I read your (Zero10) first post.

Zero10

Just did the clutch. This happened before and after replacing the clutch. I know for certain that the clutch is releasing. In order to get first or reverse, I have to press the clutch in, wait 1-1.5 seconds then try to grab a gear. Any sooner and I can hear it grind, any later and the input shaft has stopped, and for whatever reason, the teeth never line up.

I don't know a better way to explain it, but it happens both at a stop, and when shifting, when rev matching or when not, etc.
I am pretty sure it's the transmission, but am most definately open to other suggestions.

Any input on my original question? Is the guard unit a torsen type differential?...

nickg

vw makes a nice tranny fluid too...it works well in these cars

944CS

It sounds like you or a previous owner have worn out the first gear and reverse gear synchros. I do not know if any fluid can save you at this point. Next time you are in the car and coming to a stop, push the clutch in, put the car in neutral, and release the clutch. When you are completely stopped, push the clutch in again and then try first gear. See if it will go into gear easier. If it does, then you can almost be certain it is a worn out synchro.

Zero10

VW G52 is what you're talking about?
Sorry, but I'm not paying $35/L...

That's what I do when I pull up to a light. It's terrible for the thrust bearing on the crank to hold the clutch in at lights


I know it's indicative of a worn-out transmission, but given how far gone it is, I am just trying to get some more life out of it. If it eventually dies, I'll pull the guard differential, and install it in another transmission

mnypit944

I have direct experiance with this. Not on a Porsche, but the Triumph TR7 and TR8 with the 5 speed transmission came from the factory with GL5 gear oil. They were warrantying out one after another before they found that it was the fluid. They started putting in ATF to solve the notchiness and hard shift problem. Then when GM started making the syncromesh someone tried it. It worked miraculously.

So yes, it should work. Cant hurt to try. Now that you mention this, I think I will give it a try too. I just tried putting in the recommended fluid and it made mine worse too.

Good luck, let us know how it goes.

John Peacock
Deland FL
83 944
99 328iC convertible

Zero10

Well, that makes me feel better about my hunch.
It has a very high film strength (at least the Amsoil stuff does), and shows very promising wear test results, so I'm not concerned about grinding my gears to dust because it's too thin (technically it's a 5W30 with additives to make it act like an 80W when warm). My biggest concern is it won't provide enough friction for the synchro's to work properly, at least what's left of mine. I will be trying it in just a couple weeks. First auto-x is the 14th, going to try to have my 951 going the weekend before

formerGMguy

Let us know how it goes. I'm very interested in how it works out. My car is starting to have problems with the second gear synchro. Its no where near as bad as your problems, but it can still take a second or so for the synchro's to engage when going from 1st to second gear. Annoying, but not devastating.

Zero10

I will be picking the fluid up this weekend if nobody objects by then, hoping to re-fill my transmission next weekend when I re-assemble the intake.

AR10

Try jacking up one or both rear wheels and with
engine OFF see if it will shift. If it does there is
something dragging in the clutch.

bader$

I would not use gm Syncromesh in our transaxles. It is too thin to properly lubricate the final drive.
It is more the viscosity of thick motor oil than gear lube.