Transaxle Fluid

General Information

Info - manual transaxles

"What kind of fluid does my transaxle use? Some people say 5W30, others say Dexron ATF (Automatic Trans Fluid)."

Today I researched the transaxle mystery. After calling 2 dealerships, 2 transmission shops, 1-800-pm-cares, and talking to the builder of my transaxle. I discovered that Dexron II was replaced due to the newer transmissions having solenoids and the like. Dexron III is used in cars that have devices such as solenoids because it doesn't harm electrical parts. Dexron III is a sutiable replacement for Dexron II.

I also discovered that Dexron III and 5W-30 are interchangable. GM switiched to 5W-30 because it had superior high pressure tolerance. Which ment that 5W-30 kept the actual gears from touching each other by making a thin layer of lubricant seprate them, thus lowering wear. I was also told that GM experimented with different fluids to try for higher gas milage from thinner fluids.

We went further to see that the Muncie-282(I believe) has composite blocking rings. As transmissions started using different composite materials; in my case brass rings to composite, some vehicles such as the S-10 switched to a fluid called Syncromesch or Syncro lube or its equivlent. It is a high dollar synthetic that has all the benifits of Dexron and 5W-30 with an even better hi-pressure tollerance additive. It should also be interchangable with the Dexron. I am going to switch today.

The bottom line on the stuff is that either fluid is ok. I'm personally going with syncromesch. I believe that it is better, and I don't think it was avaliable in 86, that would explain why it is not recommend. This is not ment to convince you to switch, but to take a look at new and better lubrication.

From: James Hamilton

It is amazing how many different responses came in regarding the correct fluid for the 88 Getrag. I specifically say "88 Getrag" as the factory recommended fluid for my 88 GT Getrag is different than what was recommended for my 84 4 speed. Let me share a recent experience I had while shopping for a used Formula at a Pontiac dealer.The Getrag was low on fluid so they took it over to the shop to top it off.When they brought it back I asked what did they put in it. The salesman called the service manager and he said they put in motor oil "that is what they are supposed to use". I told him he was incorrect and he decided to call over his "transmission expert" to verify that he did the right thing.His transmission expert said "no it just uses regular automatic transmission fluid". I asked them to show me in the factory manual what fluid was specified. They were both surprised to find out that the factory manual specified a special synthetic gear oil. I passed on the car. The following is factual from the 88 factory manual regarding the Getrag:

  1. fluid required: GM part no.12345349 (note this is the only lubricant that is in bold type in the complete lubricant list-I think they want us to notice it)
  2. Getrag fluid does not require replacement
  3. capacity is 1.9l (4.1 pts.)

As an engineer myself I put a lot of faith in factory recommendations since I know how much testing is behind these recommendations. Anyone can give you his opinion but if the factory recommendations are incorrect they are legally liable. I am not saying that other fluids might not work, it's just that until the factory changes its recommendation I will only use GM p/n 12345349 @ $7/qt. in my Getrag. The risk reward just isn't worth a couple of bucks a qt.

From: John Austin

The Getrag transmission, other than for a small vent hole, is a sealed component. There is no combustion in the transmission, or possibility of contamination from fuel. Therefore, the oil in the transmission is not subject to the same problems the oil in an engine experiences.

Unlike an automatic transmission, there are no clutches in a Getrag transmission. There is also no filter, pump or valve body. Internal oil temperatures are kept very low in the Getrag. Therefore, the manual getrag is not subject to the trash components or temperature degradation the oil in an automatic experiences.

Over time (a long time) some minute particles of metal from normal wear and gear scraping may settle in the bottom of the transmission. Since there is no pump, these particles usually stay out of the way and do little, if any, damage.

Over time (still a long time) some dust and moisture may collect inside the transmission via the vent hole. Some of this may be kept in suspension in the oil. Oddly, moisture may be the more serious problem. Condensation in transmissions and transaxles is not uncommon as humidity and temperatures change. The transaxle's lower operating temperatures also mean evaporation of the moisture is slower than in an engine. Moisture collection may be the compelling reason to change manual transmission oil.

GM recomends 5W-30 engine oil in the Getrag transmission [before changing their reccomendation to Syncromesh during '88], just as the engine. This is a detergent based, non-varnishing lubricant capable of providing adequate lubrication to the bearings and gears under a wide range of temperatures. Since the transaxle never sees the high temperatures oil in an engine will, there is absolutely NO advantage in using a higher viscosity oil. In colder climates, a higher viscosity oil will possibly make shifting harder and accelerate wear.

Dextron III is also an acceptable lubricant for the Getrag transmission. The bearings, gears and seals in the Getrag are made of the same type of materials as the automatic and will receive adequate lubrication and protection from Dextron III - but there is NO advantage to be gained by changing to Dextron. Again, the Getrag does not have a valve body, torque converter, wet clutches and metering valves found in an automatic and therefore does not need the weting and flow properties associated with the different types of automatic transmission fluid.

There is no advantage to using Synthetic oil in a Getrag, unless you live in Minnesota, Canada, Alaska or some place where sub zero temperatures are common. Under those conditions, a synthetic may stay more fluid and provide better lubrication and easier shifting. Remember, the oil in the transaxle is warmed by conduction from the engine block, convection from the exhaust and a small amount of internal friction. Therefore, it will take longer for transaxle oil to warm up enough to flow freely in extremely cold temperatures.

As for changing the transaxle oil? I see the $2.50 cost of annually draining and refilling the transaxle to assure clean, moisture, dirt and particle free lubricant inside a very expensive and labor intensive component to replace or repair a worthwhile preventive maintenance item. NO DAMAGE WILL COME TO THE TRANSAXLE BY CHANGING THE OIL (how could it?).

Bottom line - It ain't no big deal one way or the other. Do what makes you sleep better.

From: Randy T. Agee

[Top] | Online Service Guide Main Page