Differential

Part of what a gear oil does is 'cushion' rounded surfaces from each other. This is done with viscosity. All else pretty much equal, synthetic ATF has a lighter viscosity. You have rounded surfaces coming/leaving contact between the ring/pinion gears, more so the spider gears, and the tapered carrier bearings. Am not a fan of using light viscosity oils in this application. Synthetic ATF has an advantage in sliding surfaces applications like power steering pumps and bands / clutchs and where the lubricant is subject to greater oxidation.

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~Philip

"Liberalism is a mental disease!"
                      -Michael Savage

Phil, my understanding is the viscosity is the same but the anti friction additives make it just more slippery- less friction. Viscosity is thickness or the ability to pour through a certain sized hole at a specified temp measured for volume and time.

There is a difference in the viscosity vs temp curve for synthetic oils. I tried a 5-50 synth in place of a conventional 20-50 in a old tech V8. In theory both oils should have had similar viscosities approaching 100c or at the engine operating temp of approx 80c, but they didn't seem to have the same 'film-strength'. The synth oil allowed channeling to occur at the rod-bearings which could be heard.

The same conditions, but at a lower temp exist in an automatic transaxle. The gear teeth meshing in the final drive, especialy the side-gears as Phil mentioned, present a similar channeling opportunity.

Jason

The PRIMARY difference distinguishing the various ATFs is the friction coefficient (friction modifier additives). This is determined by the transmission manufacturer based on their objectives to get smooth shifts and compromises to improve final drive gear life. Therefore any ATF (synthetic or conventional) must meet the friction coefficients for the designation. The synthetic would have longer life, improved viscosity stability across the operating temperature range, and have a viscosity on the thin end of tolerance compared to a conventional ATF. Viscosity is as you described

*and* has a value quite distinct from slipperyness.

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- Philip @ Maximum Torque RPM

Yes. The synthetic ATF will substitute for standard ATF.

Personally, I use Mobil i synthetic ATF in the automatic transmission, differential and power steering reservoir, plus Lucas Transmission Fix in the following proportions (from my service notes):

100,230, drained differential and replaced with Mobil 1 synthetic ATF and Lucas Transmission Fix at 5%, ie., 3 oz. to 1.7 qts.

also upgrade P.S. reservoir to 1.5 oz., 3 tablespoons, equivalent to

12.5% concentration

according to factory manual, total transmission capacity for the A140E is 5.9 qts., so orig. 24 oz. was 12.7% concentration. to maintain

12.5% would be 10 oz. in 80 oz (2.5qts.)

For the differential, why not use fully synthetic ATF? The old fluid looked like chocolate milk when drained out - milky brown color rather than clear bright red. Plus I noticed an improvement in power within the first fifteen minutes test drive, while accelerating up a slight grade on to a freeway. Had tried 10% Lucas in the differential, but felt it bogged down too much, so drained out and replaced with the 5% solution. I also use Lucas and Mobil 1 in the transmission. One bottle, and then replacement quantities at drain intervals to maintain concentration. Added the Lucas in the transmission to quiet the hydraulics and extend transmission life. There are no solvents to swell or damage seals. Added Lucas power steering fix with Mobil 1 to the power steering (flushed by the Dealer at 85,000 miles) as preventative measures against steering rack leaks, which are not unknown with this model and also quite costly to repair. Noticed unexpected improvement in power steering response when turning quickly at slow speed. Belt was already in good condition and tensioned correctly so I credit the Lucas.

99,996, Lucas at 20% (.75 qts [3 cups]) plus Mobil 1 10W30 oil change (engine), added to minimize potential for leakage at rear main bearing seal after seeing the tiniest hint of seepage beginning. Major job to replace that bearing seal. Unexpected side benefit, blue smoke on cold start up from slight seepage at valve guide seals over night - gone - no more smoke on cold start up for the last 20,000 miles, and I no longer see the beginnings of a drop of oil where the transmission joins the engine block. I use synthetic oil in the engine because the 4 cylinder often downshifts under acceleration, instantly kicking the RPM range up - and I like having the extra film strength of synthetic - also useful when idling with A/C on in hot weather because synthetic is more stable a higher temperatures, plus synthetic is known for promoting internal engine cleanliness. Since I've gone this far, I also use a power bleeder to bleed the brake fluid. The power bleeder makes it easy enough I've bled them three times over the last 15,000 miles and the brake fluid is now staying light amber color. I also keep the coolant fresh with factory fill plus distilled water. Everyone seems to be saying use 50% mixture, but I use 60% coolant as recommended by my factory service manual. I also use RedLine complete fuel system cleaner, apx. 2 oz. per gas tank fill up, and run the 14" tires at 31 psi front and 26 psi rear. (Figure I'm going to catch criticism for Lucas with Mobil 1, may as well list all my maintenance idiosyncrasies simultaneously - but ... the 2.2 liter 4 cyl. has ample power, runs smoothly and quietly, and when I occasionally take corners at speeds which seem way too fast, it just handles the corners effortlessly.)

Oh this is going to be fun.

As you have described your final drive fluid suggests water contamination. This can happed when driving thru very deep flooding over roads. There is an air vent on the differential ya know. Also I doubt very much you can distinguish oil grades in the differential. A double blind test would likely bear this out. These a low rpm gears with the ring bear turning at the same rpm as the *tires*.

Talk about a load of BS. You're a "believer." The ONLY component in any automatic that might possibly produce a sound that you can hear is the oil pump. Now, if your pump is making noises that any additive can silence, you've got *much* bigger problem in the works.

With 85k on the original PS fluid, the seal damage to the steering rack is already accelerated. PS has a very small volume of fluid compared to a transmission and should be replaced as often as the transmission fluid. Fluid in a power steering rack should also have more anti-stiction additive that ... in a transmission ... would promote softer/sliding shifts. Dexron can be used in PS systems but is not the optimum until such time as ATFs are formulated similarly. You'll notice Honda has had a special PS fluid spec for many years (very low stiction). What you've accomplished with Lucas in your PS fluid is to lower the fluid's friction coefficient. This is a good thing for this system.

more

Unless you're maintaining the RPM up above 4,000 rpm a lot and in hot ambient temperatures, there's little benefit except to your beliefs.

WHAT? No Lucas magic goo in the brake fluid?

water.

It's rarely beneficial to mix that strongly (unless the car is subjected to sitting in 40 below zero weather). Mixing the coolant strongly *interferes* with water's ability to absorb and release heat. Remember .... the thermostat regulates the temperature of the coolant only. If you compromise water's ability to absorb/release heat, the engine block will run hotter in spite of the coolant temperature as regulated by the thermostat. If the car were *never* exposed to freezing, you can run something like Redline's Water Wetter with only 10% antifreeze and experience no corrosion. At the high temperature end, water / coolant's boil point is determined mostly by pressurizing the cooling system.

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- Philip @ Maximum Torque RPM

In none of my manuals can i find a power steering fluid replacement length

replacement

That's because that particular service is not listed. LOL It's another one of those things you LEARN when you've been in the business for years. One starts to see the correlaton between rancid fluid and leaking steering racks and blown hoses. :^)

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- Philip @ Maximum Torque RPM

So what else isnt listed for maintenance that should be. Wheel bearings are one thing I can think of.

60% coolant

I'm sure that's all true, nonetheless, Toyota factory manual for my year under "Engine - Coolant Checking and Refill" "recommends_more than 50%_ethylene - glycol . . . but not more than 70%."

There are numerous services that should be done that Toyota (not uniquely so) does not mention and other services that are recommended but barely often enough when your anticipated ownership is more than three years.

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- Philip @ Maximum Torque RPM