OK, here's the deal. I am overhauling a P'up tranny and found that the last owner had used gear oil in it. And, as far as I know, Isuzu calls for engine oil in all of their trannys. I have two questions:

--- Why do some OEM's call for gear lube while others call
for motor oil?

--- What might be the downside to using gear oil in the P'up tranny?

I ask these questions, not because I want to use gear oil, but because I found that some of the gear teeth and one needle bearing have pits in them as if etched by acid.

Paul

Paul, you are correct the PuP tranny requires engine oil.
I THINK that some gar boxes require the "gear oil" as it is related to the amount of pressure on the teeth of the meshing gears.
But I amnot certain of that however.
No idea why you have pitting.
Eric

Small tight tranny cases with small cavities/passageways/ports require light fluids to allow full circulation. While the motor oil doesn't have the loading capabilities of gear oil, the small loads, relatively speaking, of these four cylinder engines permit the use of it. Plus motor oil will transfer heat a bit better.

Acid is primarily created by moisture in the case, which enters through humid air being drawn in by the cool down process at the end of each use(or it was driven through a creek!). Not a problem if the fluid is changed like it is supposed too and driven frequentlly but if vehicle maint. gets neglected for 10 years and it is driven infrequently during that time, you will see some etching beginning on tranny/differential components. Very common is larger hotter running cases like the tranny cases and diff cases of my tractors.

NCDiesel

HEY PAUL . SPENCER IS RIGHT ON , ON THE GEAR OIL VS ENG OIL IN THE PUP TRANS , SEEING AS HOW YOU HAVE THE TRANS APART, NOTICE THE CENTER AND FRT BEARING ,NOTICE THE SEALS, SOME OF THE BEARING HAVE SEALS ON BOTH SIDES, 90 WEIGHT CANNOT GET IN THE SIDE BEARING TO LUBE IT PROPERLY, MAKE CERTAIN YOUR BEARING HAVE NO VERTICLE PLAY AND USE 5-30-10-30 , ANY STRAIGHT WEIGHT OIL SUCH AS 30-W WILL WORK OK BUT WHEN IT GETS COLD IT WILL BE HARDER TO SHIFT, , 80-W OR HIGHER , IT WILL BE REALLY HARD TO SHIFT WHEN COLD , WE TRIED MANY DIFF OILS HERE IN ATLANTA IN THE WINTER IN THE EARLY 80,S AND COMING OUT OF FIRST INTO SECOND , THEY WOULD NOT SHIFT , THE OIL IS SO THICK THAT THE SYNCHRO RING CANNOT BE FORCED AGAINS THE NEXT GEAR , UNTILL IT GETS HOT , IF YOU PULL ALL THE SEALS FROM ALL THE BEARING S YOU CAN RUN A HEAVIER OIL, BUT THE SHIFT PROB, IS STILL THERE , I HAVE SEEN THE MUA WITH 90 W GO 5000 MILE AND BE MAKING A HORIABLE NOISE , THE BEARING CLEARENCES ARE USUALY PRETTY CLOSE AND THE THICK OIL HAS A TOUGH TIME GETTTING TO THE BEARING SURFACES BEFORE DAMAGE OCCURES, BUT I HAVE ALSO SEEN A FEW OF THE MSG TRANS WHICH IS WHAT YOU HAVE , WHEN THEY GO 70 + THOUS MI, ON THEM CHANGED OVER TO A HEAVY WEIGHT OIL AND THEY SEEM TO RUN FOR A LONG TIME , BUT WITH NEW BEARINGS , I WOULD STAY WITH THE LIGHTER OIL EVEN IN 90 DEGREE WEATHER, THE SHOP MANUAL ONLY CALLS FOR 30. WEIGHT, ON YOUR TRANS WITH A LOT OF MILES I WOULD USE THE 5 OR 10 W 30 AND ADD A BOTTLE OF THE LIMITED SLIP ADDITIVE THAT GM PRODUCES , IT WILL MAKE THE OIL CLING TO THE GEARS AND THE BEARING SURFACES , IT HELPS KEEP THE OIL FROM SLINGING OFF THE SPINING GEARS , THE PT NO FOR THIS OIL IS 10523580 GM NO, ONE BOTTLE IS ALL YOU WILL NEED , IT IS MADE FOR THE LSD UNITS BUT WORKS GOOD AS AN OIL ADDITIVE , I SELL THIS STUFF BY THE BOX LOAD . JERRY

Paul
The Borg-Warner T5 transmission in my truck uses ATF for lube. The first transmission I used had gear oil in it, which was it's demise. The T5 has rather small oil passages to lube the gears, and under cold temps, gear oil doesn't flow well as you know. Hence, lack of lube made the tranny shift like crap, though it never actually failed totally. So the ATF is less viscious, and lubes the T5 better. Besides, if it can take the torture of an automatic transmission, which still has meshing gears and bearings, then a manual should be easy for the oil to handle.
Also, as an aside note, the T5 had a designed max rating of 250 hp, so in theory, with proper maintainance, behind the C223, it should last for just under a million years. <img src="/forums/images/graemlins/notooth.gif" alt="" />
I have no data to prove it, but I believe ATF has all the anti-shearing properties we would need in our applications. It would have less drag and therefore less HP loss. Modern oils are much better then they were, even than 20 years ago.

My Isuzu manual calls for 2.7 pints of SAE #30 motor oil in the gearbox.

Thanks all for your inputs. I have been running Mobil 1 synthetic 15-50 in my trannys but now think I will go even lighter to say, 0-40. Anybody know what the weight numbers would be for ATF?

The tranny I am working on has been sitting for years, so moisture may well be the reason for the pitting.

Jerry, thanks for the LSD additive p/n. I will get some and check it out. Can you tell me if it will affect the shift quality?

Another question. Why do the replacement bearings come with either a seal or a shield? I would think that a free flow of oil over and thru these bearings would be the the best deal.

Zack, I like the 'million year' number. So far,I have been able to get only 100k +/- out of the Isuzu bearings. The gears are always good unless driven too long on bad bearings.

Regards--

Paul

HI PAUL , ON THE OIL, THE ATF WILL WORK FINE IN THE ISUZU TRANS ALLSO , I HAD A N ENGINEER FROM ISUZU (JAPAN) TELL ME THE ONLY REASON THEY DIDN,T USE ATF OIL IN THE TRANS , IT DOESN,T HAVE THE SOUND DEADING ABILITY OF THE ENG OIL ESP THE HEAVIER STUFF, SO THEY JUST USED 5-30 LIGHT VISC, AND LUBED EVERYTHING FINE , AND ALL THE ISUZUS THAT CAME WITH THE BORGWARNER T5 DID IN FACT USE ATF,, UP THRU 97, THEY ONLY CAME IN THE 4CYL RODEOS HERE IN THE U.S. , SHARP EYE ON THE BEARINGS, I HAVE ASSEMBLED DOZENS OF THOSE TRANNIES OVER THE YEARS , AND GUESS WHAT I HAVE ALLWAYS REMOVED THE INTERNAL SEALS , AND HAVE NEVER HAD A BEARING FAILURE, ESP THE CENTER BEARING, EVEN THE FRT MAIN SHAFT BEARING, I HAVE LEFT THE SEALS OUT AS THE OIL CAN FLOW THRU THE BEARING AND IT GOES BACK DOWN INTO THE CASE THRU A PASSAGE IN THE FRONT BEARING RETAINER , MY BELIEFE WAS IN THE EARLY 80,S WHEN WE WERE HAVING A BUNCH OF FAILURES OF THE FRT INPUT SHAFT BEARING , LET THE OIL FLOW THRU , IF ANYTHING IT WOULD WASH SMALL PARTICLES OF WHATEVER THRU THE BEARING INSTEAD OF TRAPPING THEM, ON THE ONES THAT HAD HAD PREVIOUS FAILURES ,WE STARTED LEAVING THE SEALS OUT AND MONITERED THE VEH, FOR QUITE A WHILE AT THE DLSHIPS AND THOSE TRANNIES NEVER CAME BACK WITH BAD BEARINGS , AND THESE WERE ALL IN FLA, IN THE JACKSON VILLE AND ORLANDO AREA WHERE IT IS HOT MOST ALL THE TIME , NEVER HAD A NOTHER FAILURE, SOOOO I LEAVE EM OUT JERRY

Jerry--

Thanks for the input. Yes, I have found that the input shaft bearing fails the most. Think I will leave the seals out too.

Paul

I believe that the spec for many Isuzu transmissions is 5W30. Why use anything else?

If spec were straight 30W (like the Pup in question here) I'd use dino SAE30. I could see using a multi-viscosity synthetic but I'd chose the least variable I could get--liekly 10W30. AFAIK, you can't get SAE30 synthetic.

Tom--

If all else fails one should follow the instructions. So, maybe I should do what they say.

But, the reason I have been using Mobil 1 is because it is supposed to be more stable vs temperature & time and should have superior oxidation resistance, maybe superior lubrication. I don't know if any of this is true.

The reason I am thinking of going to Mobil 1, 0-40 is because it should have a more stable viscosity versus temperature than the 15-50 I was using and will be slightly lighter. This will make it easier to shift at low temperatures while maintaining enough viscosity for adequate lubrication at high temperatures.

I checked my manual for my '84 P'up and it calls for 10-30 or 30 or 40 weight oil depending on the ambient temperature.

Regards--

Paul