Synthetics = no good for LSD??

[metroplex]

From TracTech (makers of the Detroit TrueTrac - very similar to the Zexel Torsen T-2)

"synthetic oil may well reduce the bias ratio
performance of the Truetrac LSD.
I cannot estimate by how much as we have not
investigated such oils as we consider the
standard oil to be suitable."

They refer to the standard OEM 80W-90 as the standard oil (Whatever Ford recommends, 80W-90 hypoid gear, dino).

What's the reasoning behind this? I know for a fact synthetics outperform dino oils - but how would synthetics hurt the bias ratio performance?

in case you're just tuning in, the Torsen differential uses helical worm gears rather than clutches. It "shifts" torque from a wheel that is slipping to the wheel that grips with a torque bias ratio of 2-3:1 - but if you get one wheel in the air (or with zero traction like on ice or mud) then you're stuck. You need to apply the brakes to apply torque to the spinning wheel, which then the differential applies 2-3 times that onto the gripping wheel.

Now what TracTech is implying is that a synthetic would reduce the bias ratio performance so there's less torque to the gripping wheel, while a dino oil such as the OEM 80W-90 Ford specifies for its RWD passenger cars and some trucks would work better.

I see that Schaeffer's 267 has specs similar to a dino oil (viscosities that exceed that of OEM specs) but with better additives and a slightly lower pour point.

Now why would synthetics hurt the bias ratio performance of a Torsen differential?

Is it because synthetic gear lubes quite often have lower viscosities than dino gear lubes - flowing too quickly and causing premature wheelspin in low traction conditions?

I know my Crown Vic is wheelspin happy in the winter when I used synthetic gear oil but back when I first got it w/ the factory filled 80W-90 (Dino), it was rather tame.

If this is the case, can I use a thicker synthetic such as a 75W-140 or 80W-140 so that I can get the benefits of a synthetic (high thermal stability, low temp flow, better shear and wear protection) while not compromising the performance of a Torsen differential?

 

[MolaKule]

I would think more torque would be available with a synthetic fluid, since it has a lower
friction coefficient, allowing more power and torque to the wheels.

[ January 13, 2003, 01:28 PM: Message edited by: MolaKule ]

 

[metroplex]

The torque bias on the Torsen differentials works based on something like this:

When one wheel slips, you want the wheel that grips to get the torque - so the torsen differential senses this and shifts the torque (times 2-3 depending on the torque bias ratio) to the gripping wheel.

TracTech is saying that the torque biasing is reduced when you use synthetic. I don't understand how this could happen.

 

[Shannow]

The diffs work by balancing the action of backdriving and non-backdriving gears.

The non-backdriving are just on the edge of non-backdriving, so I guess that they're saying that a more slippery lube may allow the gears to drive (and thus slip) where they otherwise wouldn't.

 

[Patman]

When I had my 98 Formula it came from the factory with synthetic 75w90, it was an Auburn limited slip differential. My 95 Formula has the exact same rear end but didn't come originally with synthetic.

Some experts in the f-body world claim the 99+ cars with the Torsen should not use synthetics.

[ January 13, 2003, 07:54 PM: Message edited by: Patman ]

 

[metroplex]

Patman: interesting - why is that???

The Torsen T-2 and T-2R are spitting images of the Detroit TrueTrac w/ minor differences.

 

[Pete2k_Z28]

For what it's worth, I switched to Royal Purple in my 2000 Z28 and the rear promptly blew up a month and a half later. At the time I switched the oil, there was no more than "normal" junk stuck to the magnet, so there was likely no pre-existing condition at that time.

Whether it was the oil or some wheelhop that ultimately did the Torsen rear in I will never know. But I will say this; the week or two before it went (I was doing 25mph, not accelerating oddly enough when it finally let go) it would screech in turns, like a solid spool axle. That tells me that the diff had locked up solid somehow. Ultimately the fate was one of the 4 bolts that holds the carrier assembly together simply snapped a head right off. The car still drove, but the bolt head had torn a hole in the cover. I'm guessing excessive end loading of the carrier from the siezed or partially siezed gears in the Torsen unit were responsable for the breakage.

So I'm more likely to blame it on the oil somehow siezing the carrier than a racing related incident.

Anyway I have a good feeling the synthetic oil was really the culpret.

Hope this makes sense, I'm having a hard time putting it into words.

Pete

 

[MolaKule]

I'm with Metroplex on this one.

The Torsen design has the gears in constant contact, so why would any of them "slip?"

The biasing is all done by reactive loads, whether or not a mineral oil or synthetic oil is used.

 

[metroplex]

One of the helical gears must have jumped a tooth or something - probably not related to the oil at all...

 

[Mike_dup1]

Mt 2002 Pontiac Trans Am WS6 has a Torsen Limited Slip differential. I seem to recall seeing 75W-90 Synthetic Gear Lube recommended in the manual? I will have to double check on that, been about a year since I looked.

 

[Shannow]

quote:

---

Originally posted by MolaKule:
I'm with Metroplex on this one.

The Torsen design has the gears in constant contact, so why would any of them "slip?"

The biasing is all done by reactive loads, whether or not a mineral oil or synthetic oil is used.

---

The "worm" gears have other than a rolling motion, and include some sliding, thus the friction between them should have a bearing on how they behave in general.

 

[OneQuartLow]

Metro, anything is possible but my feeling is that the vendor is being cautious about anything they haven't tested, possibly adopting an old "synthetic paranoia".

Seems to me if there was a problem with synth, they would be much louder warning about various gear oil FMs. The friction characteristics of different base oils should be a minor player with the other variables in a gear lube.

In any case, the worst you might have to do is change it out an extra time. What make are the gears? Are you doing the install?

David

 

[metroplex]

I'm doing the install.

It's on a 2000 Ford Crown Vic.

The stock rear end is an open Visteon 8.8" carrier, with stock 3.55s

I'm keeping the stock 3.55s and just swapping in the Detroit TrueTrac. Dyneer (Titan Wheel) manufactures the TrueTrac.

My friend has a 2000 Mercury Grand Marquis w/ open 3.55s and swapped in a Detroit TrueTrac last year. His car is basically the same as mine.
He used to use Valvoline SynPower 75W-90 and now switched to Royal Purple Max Gear 75W-90. He said he noticed the torque bias performance to be much better with the RP than w/ the valvoline.

The main difference between the two are the viscosity ratings at 40C and 100C!
With the RP being thicker.

Now - would a thicker oil like a synthetic 75W-140 or 80W-140 protect the helical worm gears or simply help with torque bias performance? Or would it do both?

 

[DABEAR95]

quote:

---

Originally posted by Mike:
Here's what Eaton told me just last month.

quote:

---

Mike,
We do recommend you use synthetic lube. In fact, we recommend you use either of these 2 oils:

1. Texaco 2276 GM Synthetic Gear Oil 75W-90
2. Shell 59433 Synthetic Fuel Efficient GL 75W-90

Have a great Holiday season!!

Kind regards,

David M. Beller
Sales Manager
Eaton Corporation

---

quote:

---

So I'm more likely to blame it on the oil somehow siezing the carrier than a racing related incident. Anyway I have a good feeling the synthetic oil was really the culpret.

---

Pete2k_Z28

so you figure it was the oil, racing had nothing do with it.

I vote for the racing!

---

I'm sorry, I should have been more clear. For my applicaiton Eaton did not recommend synthetic fluid because of the clutch material.

Your best bet is to call the manufacturer and find out why they are saying not to use synthetic. (IMO)

 

[OneQuartLow]

quote:

---

Originally posted by OneQuartLow:
Metro, are you sure your version doesn't have 3 side gears? ...

---

Never mind... Guess they have anywhere from 2-4 depending on model & duty.

 

[metroplex]

quote:

---

140 should hold up better but will also run hotter. How often are you really racing/towing? As for the 8.8, if that unit is is similar to the solid models you might want to upgrade the cover. One 8.8 weakness is the tendency of their housings to deform under shock loads which leads to bearing failure. Plenty of aftermarket covers available.

---

I bought 4 quarts of Redline 80W-140 for the Dana 60 in my Ford E-250 (3.73 limited slip) - I'm not sure how it'd run but its very close to SAE 90 dino oil.

The aftermarket covers are $140+
I don't drag race my Crown Vic, and I have an auto transmission - I heard the shock loads were less with a slush box than with stick? I'm not sure - I've contemplated getting one becuase they have drain and fill plugs, VERY VERY neat!

 

[OneQuartLow]

quote:

---

Originally posted by metroplex:
I bought 4 quarts of Redline 80W-140 for the Dana 60 in my Ford E-250 (3.73 limited slip)...

---

That'll work. I've used plenty of it in different diffs.

quote:

---

The aftermarket covers are $140+
I don't drag race my Crown Vic, and I have an auto transmission - I heard the shock loads were less with a slush box than with stick? I'm not sure - I've contemplated getting one becuase they have drain and fill plugs, VERY VERY neat!

---

Yep, they're getting silly money for those replacement covers. Looks better than what I'd make though.

The two gearsets I've ruined happened far from home which was not convenient, which is why I always think of reinforcements.

Racing was all I was thinking of. Sounded like you were going there. Auto's can be harsh too. Borrowing a buddy's slicks, wheel-hop, or a high stall converter are usually what leads to "surprise" breaks.

With a stock converter and normal tires you're fine.

I'm sort of religiously against diff drain plugs. I like to see the metal in the bottom and check wear patterns, then flush things out before adding new. Adds 15 minutes per diff but I sleep better.

Sounds like a fun car, BTW. I need something to work on besides these offroad abortions!

 

[OneQuartLow]

Bob, that 30min edit timer needs to start when the beers wear off.

 

[DABEAR95]

I upgraded the differential in my 95 Camaro this past spring with an Eaton unit. Eaton expressly states to use only conventional fluid, not synthetic. It actually voids the warranty. When I spoke to them, they said it was due to the clutch material.

The said something along the lines of -

"The use of synthetic fluid would degrade the carriers ability to "lock-up" and would result in premature clutch wear"

Jason

 

[Mike_dup1]

Here's what Eaton told me just last month.

quote:

---

Mike,
We do recommend you use synthetic lube. In fact, we recommend you use either of these 2 oils:

1. Texaco 2276 GM Synthetic Gear Oil 75W-90
2. Shell 59433 Synthetic Fuel Efficient GL 75W-90

Have a great Holiday season!!

Kind regards,

David M. Beller
Sales Manager
Eaton Corporation

---

quote:

---

So I'm more likely to blame it on the oil somehow siezing the carrier than a racing related incident. Anyway I have a good feeling the synthetic oil was really the culpret.

---

Pete2k_Z28

so you figure it was the oil, racing had nothing do with it.

I vote for the racing!

[ January 14, 2003, 12:45 PM: Message edited by: Mike ]