Tom R.

My car is at the mechanic with instructions to change the transmission oil with synthetic.

He drained the old oil and called me to tell me he just read in a journal that changing to synthetic may screw up shifting if the synchros are worn. The synchros rely on friction, and synthetic is more slippery.

Anyone have any experience with this?

I'm going to synthetic because cold shifting into first is a real bear when the outside temp drops. We are implementing the other suggestions from my earlier post regarding the stiff shifting when cold.

Thanks again in advance.

Bryan

For a non-LSD transaxle, Redline 75W-90NS is your oil. The NS stands for non-slippery which addresses this concern exactly. I've put Swepco or Redline in many varieties of cars and the results have ranged from slight improvement to quite substantial improvement. It's never made anything worse.

Bryan

Lemon Yellow 87 n/a

So would you recommend redline over swepco?

Michael Stephenson

For what its worth, I have had Castrol Synthetic in my gear box for about a year and I have noticed that my shifter has gotten notchier across all of the gears.

Are the two related?? I do not know.

To be on the safe side, I am going to switch to Swepco or Redline in the near future.

Tom R.

Michael,
I don't know what brand I'm getting. I will update with the brand in a few days and tell you if the notchiness appears.

If it does appear then I will speicify Redline or Swepco.

With the car on jack stands it's a little difficult to request special order fluids.

Skip

Yet another performance Catch-22. You want smoother shifts, but your syncros want friction (somewhat). Synthetics by nature are considered *more slippery* than dino fluid (molecule shape and additives). Good thing for you, Swepco, Redline, and many other synthetic lubricant makers know this... and are bound by industry quality measures to provide a suitable fluid for syncronized transaxles. 80% of all new cars use transaxles = combined transmission and differential... and ALL of these cars use syncro'd transmissions. So, are synthetic gear oils okay for syncro'd trannies... YES. Now comes the choice you really have... GL4 or GL5? GL4 is recommended, but GL5 is the *new* spec (like Dextron I - II - III for auto trannies, or our power steering systems). This is all personal choice... there's no real concensus that I've been able to see as to which is better. Redline will tell you GL4 because that is what is recommended by the manufacturer, and they have liabilities to maintain. Sales and history of GL5 use in our transaxles tell a slightly different story.

So, why synthetic? Because it works better when cold, maintains a steady and predictable usefullness throughout heat ranges better, and does not break down as quickly as organic/dino oils. PLUS, it's more expensive... so it MUST be better!

Just an FYI, Redline comes in both GL4 and GL5 for your application (and if you have an LSD).

Good Luck!

Bryan

Redline versus Swepco - I'd just go with what's convenient. I don't think there's much to differentiate them personally. Swepco comes in a gallon jug where I've only seen Redline in quarts. But I've seen Redline for sale locally and would have to mail order Swepco. Whatever's easiest to get hold off I guess.

Bryan

Riff

As a data point, I have had Mobil 1 in my tranny for the past year and the shifting has remained smooth across all gears in all temps. Car is daily driven in non-snow weather and sees AX and DE duty. The tranny is a non-LSD unit and has approx. 145K on it.

Cheers

Weasel.

I use Redline MT90 in my 86 951 and have had no problems. It did help a bit when cold going into 2nd gear so that's nice. Shifts seem a bit smoother but the tranny still acts better once warmed up.

belz

Is Swepco synthetic?

Skip

Nope, Swepco is most times referred to as "highly refined", but does use synthetic additives (lubium). So, I guess it falls in the synthetic blend category. Definitely a favorite among pre-G50 911, 914, and 356 folks.

Skip

Tabor

I use Redline MTL (GL4) and love it. I met someone who put the GL5 rated Redline stuff in and proptly fsk'ed his 951 transaxle.

DB944T

So what is recommended for a LSD application(in a 951)?

My second gear is a bit stiff, and I plan to change the fluid this winter to see if it helps

Skip

For LSD's there are some more choices to make. First, is it the standard lockup or modified? When talking Redline: the 75W90 (GL5) has Friction Modifier (slippery stuff that prevents premature lockup of LSD)... MT90 (GL4) has a little FM, the 75W90NS (GL5) has none (designed for non-LSD cars). Some folks like to mix-n-match to get the correct LSD feel... to do this, you start with either MT90 or 75W90NS and manually add the FM to the case, then test the driving conditions on your favorite corners. FM is the stuff that keep your LSD from lurching on lockup... which would cause some drivability problems while cornering. The idea is to get the LSD to lockup smooth and consistent when cornering. The two people who might do this are racers with modified LSD's, or folks who think their clutches may be well worn... requiring less FM. Redline FM can be purchased separately, and can be added to any brand gear oil.

Clear as mud?

Good Luck!

Tom R.

I've just been told by my mechanic there now is fresh Mobil1 75w90 in the transmission.

I'll let you know if it eliminated/alleviated the near impossible cold start shifting.

Also, the boot on the rear cv joing is torn, any experience with aftermarket boots anyone?