Best diff/trans oil?
12-14-2014, 12:19 PM
#18
I, recently, had my LSD transaxle rebuilt by Kevin Gross and he recommended Mobil 1 75/90w that can be bought at any parts store not the expensive Delvac product. So far it seems very good. I ran Swepco 201?, Redline 75/90w NS and MT90 prior to getting the transaxle rebuilt and the Redline worked better. The Swepco was too thick making the shifting very stiff.
Last edited by arthropraxis; 12-14-2014 at 10:56 PM.
12-14-2014, 08:37 PM
#20
Nordschleife Master
I check and top off mine every engine oil change, drain and replace it every third engine oil change. Street car Reddline MT90. All I can say is that when I drain and replace with new MT90 it's like I have a new trans again, smoother shifting, quieter 
12-16-2014, 10:20 PM
#23
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In my 968 box I've tried Mobil and ran Amsoil for while. I recently put in Motul 300 LS 75w90, which has been the best oil yet. Mobil didn't shift well until it got warm. I thought the Amsoil GL5 wasn't too bad. The Motul shifts great cold and feels consistent as it heats up. Really nice gear feel, which is quite different to anything else, and the LSD is quiet. Also, Amsoil GL4 worked really well in my 944NA - better than the GL5 version.
Obviously plenty of opinions on this one...
Obviously plenty of opinions on this one...
12-16-2014, 10:39 PM
#24
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I, recently, had my LSD transaxle rebuilt by Kevin Gross and he recommended Mobil 1 75/90w that can be bought at any parts store not the expensive Delvac product. So far it seems very good. I ran Swepco 201?, Redline 75/90w NS and MT90 prior to getting the transaxle rebuilt and the Redline worked better. The Swepco was too thick making the shifting very stiff.
12-16-2014, 10:58 PM
#25
Three Wheelin'
The Swepco 201 does make for stiff shift action when cold, but is OK after driving for a few minutes. Where the Swepco does shine is in LSD-equipped Porsche transaxles that see track use. Remember, transaxles use the same oil for the gearbox and differential, and a clutch-type LSD superheats the oil with aggressive driving. The gear oil needs to be able to stand up to this heat and still do its job.
My shop has used Swepco for decades and the insides of the gearboxes that we take apart look almost brand new after years of track use, and that is good enough for us. Plus the 201 has the requisite LSD additives for chatter-free operation during normal street driving.
If your 951 is normally used on the street without much track use, I'd recommend a "normal" 75W-90 gear oil like the Mobil or Redline mentioned above; Lubri-Moly is also good. The shifting when cold will be much better, and there will still be plenty of protection for spirited street driving, auto-X, and occasional track use.
No matter which gear oil you use, change it AT LEAST once a year if you track your car, otherwise every 30K miles or 5 years is OK.
12-16-2014, 11:22 PM
#26
Rainman
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Thread Starter
Seems to be a toss-up between Swepco and Redline.
My trans is an open diff so I suppose some less heat, and mine has a cooler... Droops you say Swepco is designed for the older style synchro, is there enough functional difference to use a different lube?
I put the current oil in the trans when I first installed it mid-2009 so it's right about that 5 year mark.
My trans is an open diff so I suppose some less heat, and mine has a cooler... Droops you say Swepco is designed for the older style synchro, is there enough functional difference to use a different lube?
I put the current oil in the trans when I first installed it mid-2009 so it's right about that 5 year mark.
12-17-2014, 12:43 AM
#27
Rennlist Member
My understanding is that it's actually hard to get a good oil for our transaxles (or any transaxle). The lubrication requirements of the ring and pinion (high-force / high-shear) are at odds with the lubrication requirements of the gear cluster bearings and the synchros (really blocker rings).
When people are talking about "how it shifts", what's really happening is this: all gear clusters are loose on the pinion shaft on bearings. When the wheels turn, the pinion shaft also turns - the drag from the oil in the gear's bearings try to make the gears spin.
The input shaft has the gears fixed to it (by splines). So, whenever the input shaft spins, the gears are also spinning on the pinion shaft. This is why, when you put the car on a lift or jack up the rear wheels and start the car in neutral, the wheels spin some - the oil drag between the shaft and the gear.
Now, to actually shift gears, the lever moves the synchro over - this is kind of a ring gear with teeth on the inside - it's really a "spline coupler". The shaft has a ring with a spine profile machined into it, and the gear has a matching one. When the synchro slides over to capture both at the same time, the gear is "locked" to the shaft and the power is transmitted from the input shaft to the pinion shaft.
If the gear is still spinning when the synchro tries to mate with it, you get that horrible transmission grinding sound and the teeth inside the snchro start to get machined down...
So, there's another component called the blocker ring - this has a little abrasive on it, and is a friction brake. As you start moving the gear lever, the movement of the synchro applies pressure to the blocker which, in turn, slows down the spinning of the gear.
When you car is "shifting slow", it because the blocker cannot slow the gear down quickly enough before the synchro slides up to the gear.
If you've made it all the way through this description, you deserve a video to help you visualize it.
When people are talking about "how it shifts", what's really happening is this: all gear clusters are loose on the pinion shaft on bearings. When the wheels turn, the pinion shaft also turns - the drag from the oil in the gear's bearings try to make the gears spin.
The input shaft has the gears fixed to it (by splines). So, whenever the input shaft spins, the gears are also spinning on the pinion shaft. This is why, when you put the car on a lift or jack up the rear wheels and start the car in neutral, the wheels spin some - the oil drag between the shaft and the gear.
Now, to actually shift gears, the lever moves the synchro over - this is kind of a ring gear with teeth on the inside - it's really a "spline coupler". The shaft has a ring with a spine profile machined into it, and the gear has a matching one. When the synchro slides over to capture both at the same time, the gear is "locked" to the shaft and the power is transmitted from the input shaft to the pinion shaft.
If the gear is still spinning when the synchro tries to mate with it, you get that horrible transmission grinding sound and the teeth inside the snchro start to get machined down...
So, there's another component called the blocker ring - this has a little abrasive on it, and is a friction brake. As you start moving the gear lever, the movement of the synchro applies pressure to the blocker which, in turn, slows down the spinning of the gear.
When you car is "shifting slow", it because the blocker cannot slow the gear down quickly enough before the synchro slides up to the gear.
If you've made it all the way through this description, you deserve a video to help you visualize it.
12-17-2014, 12:45 AM
#28
Three Wheelin'
Seems to be a toss-up between Swepco and Redline.
My trans is an open diff so I suppose some less heat, and mine has a cooler... Droops you say Swepco is designed for the older style synchro, is there enough functional difference to use a different lube?
I put the current oil in the trans when I first installed it mid-2009 so it's right about that 5 year mark.
My trans is an open diff so I suppose some less heat, and mine has a cooler... Droops you say Swepco is designed for the older style synchro, is there enough functional difference to use a different lube?
I put the current oil in the trans when I first installed it mid-2009 so it's right about that 5 year mark.
I did initially use Swepco 201 in the gearbox of my BMW 2002tii (which is a '73 with Borg-Warner synchros; early 2002s used Porsche synchros under license), and shifting wasn't incredibly notchy when cold. I switched to Redline MTL as an experiment, and the shifting when cold is a bit smoother but not the drastic change that I expected. Since this is a BMW with a separate differential and mine has an E21 LSD, Swepco remains back there!
If I were you, I'd go with the Redline MT90, as the shifting will likely be smoother. The Swepco 201 is specifically designed to slow down the old Porsche-style synchros, as is the Redline 75W-90 NS. I might try that for fun when I next change the gear oil in the 951, as that car is a guinea pig for fluids and all types of other stuff.
http://www.redlineoil.com/Products.aspx?pcid=7 This page has good info in the different Redline gear oils.
12-17-2014, 02:05 AM
#30
Three Wheelin'
My understanding is that it's actually hard to get a good oil for our transaxles (or any transaxle). The lubrication requirements of the ring and pinion (high-force / high-shear) are at odds with the lubrication requirements of the gear cluster bearings and the synchros (really blocker rings).
When people are talking about "how it shifts", what's really happening is this: all gear clusters are loose on the pinion shaft on bearings. When the wheels turn, the pinion shaft also turns - the drag from the oil in the gear's bearings try to make the gears spin.
The input shaft has the gears fixed to it (by splines). So, whenever the input shaft spins, the gears are also spinning on the pinion shaft. This is why, when you put the car on a lift or jack up the rear wheels and start the car in neutral, the wheels spin some - the oil drag between the shaft and the gear.
Now, to actually shift gears, the lever moves the synchro over - this is kind of a ring gear with teeth on the inside - it's really a "spline coupler". The shaft has a ring with a spine profile machined into it, and the gear has a matching one. When the synchro slides over to capture both at the same time, the gear is "locked" to the shaft and the power is transmitted from the input shaft to the pinion shaft.
If the gear is still spinning when the synchro tries to mate with it, you get that horrible transmission grinding sound and the teeth inside the snchro start to get machined down...
So, there's another component called the blocker ring - this has a little abrasive on it, and is a friction brake. As you start moving the gear lever, the movement of the synchro applies pressure to the blocker which, in turn, slows down the spinning of the gear.
When you car is "shifting slow", it because the blocker cannot slow the gear down quickly enough before the synchro slides up to the gear.
If you've made it all the way through this description, you deserve a video to help you visualize it.
What's inside a Corvette (T56) transmission - YouTube
When people are talking about "how it shifts", what's really happening is this: all gear clusters are loose on the pinion shaft on bearings. When the wheels turn, the pinion shaft also turns - the drag from the oil in the gear's bearings try to make the gears spin.
The input shaft has the gears fixed to it (by splines). So, whenever the input shaft spins, the gears are also spinning on the pinion shaft. This is why, when you put the car on a lift or jack up the rear wheels and start the car in neutral, the wheels spin some - the oil drag between the shaft and the gear.
Now, to actually shift gears, the lever moves the synchro over - this is kind of a ring gear with teeth on the inside - it's really a "spline coupler". The shaft has a ring with a spine profile machined into it, and the gear has a matching one. When the synchro slides over to capture both at the same time, the gear is "locked" to the shaft and the power is transmitted from the input shaft to the pinion shaft.
If the gear is still spinning when the synchro tries to mate with it, you get that horrible transmission grinding sound and the teeth inside the snchro start to get machined down...
So, there's another component called the blocker ring - this has a little abrasive on it, and is a friction brake. As you start moving the gear lever, the movement of the synchro applies pressure to the blocker which, in turn, slows down the spinning of the gear.
When you car is "shifting slow", it because the blocker cannot slow the gear down quickly enough before the synchro slides up to the gear.
If you've made it all the way through this description, you deserve a video to help you visualize it.
What's inside a Corvette (T56) transmission - YouTube
However, my point about the type of synchronizer in question and its gear oil in question remains true. The old-school Porsche baulk-ring synchros need to be slowed down even more than the newer style (as shown in your video) to work effectively. This a lot of the reason the old Porsche transaxles (especially the 915) get a bad rap; shifts simply should be be rushed with them.
Swepco 201 and Redline 75W-90 NS are specifically designed for use with the old-style Porsche synchros, which were also used in Ferrari gearboxes for many years.
Both also happen to be GL5 rated for use in transaxles. Now this is where the discussion gets sticky, as there are a lot of warnings out there admonishing that GL5 gear oils should never be used in gearboxes with brass cone-type synchronizers, as used in the 944 transaxle (Redline states this in the link that I posted above). Contact the gear oil manufacturer for specific recommendations if in doubt.
Now I am by no means any type of engineer, but I do have 10+ years of hands-on experience as a Porsche/BMW mechanic. My shop uses GL5 rated Lubri-Moly or Swepco in all Porsche transaxles, and we have never seen unusual brass synchro wear due to EP additives. Maybe the Germans use better brass than their Japanese or American counterparts.
All of this said, my initial recommendation stands: Swepco 201 for heavy track use, maybe something a bit more slippery for street use! And changing the gear oil regularly is possibly more important than the brand used, as the additives wear out and synchro (and LSD clutch material) build up.