Dextron in transmission

Ok, what I wanted to know is what is the difference between dextron II and Dextron III? Memphis Equipment recommends Dextron II, but all I can ever find is dextron III in the stores? Any ideas on this like what the difference is or if they are basically the same?. Also, does anyone have a source for the transmission output shaft seal or those copper seals that go on all the drain plugs? Thanks.

I was at NAPA today asking the very same question about those crush washers. They sell them in variety packs. However, only one in the package would fit, so I passed on them. I was planning on using teflon tape and the old washer maybe with a little gasket goo. I am trying to get my M135 ready for the road next week. So close now, I can smell it. []

I know this topic was entered back in April but for newer readers I went to google and looked it up on several different web sites, basically they all agree that Dextron II is no longer manufactured and became Dextron III. Dextron III is suited for new and older type gmc transmissions. Best advise, do what I do, go on line and get as many opions and facts as you can, (then flip a coin) ha ha. NO serious just don't go by one web site, go to as many as you can then use all that information to fit your situation.
Steve

Hold on there kids there is a difference. I used to work for an industrial clutch and brake mfg. We had one series of wet clutches. When Dextron III came out we had an increase of failures. Once we researched the specs we found Dex III has a lower hot coefficient of friction. Meaning it can't hold as much. We ended up switching to the old Ford type F. You might be alright if the trans is strong enough to handle the engine. I don't know much about the 135's. If the trans is borderline I'd ask a lube dealer in your area about the differences. I don't know if type F would be a good choice.

You may want to give Memphis equipment a call on this.

Check the spec, you may want to use "Premium Tractor Hydraulic fluid", available at NAPA, Carquest, Farm stores...That's what I'll be using in the 1969 Allison transmission.

hydromatic

When I first installed the Memphis rebuilt tranny in the GMC M215 I used Dexron III. I started to notice the tranning slipping when cold, only in high range forward 1st and 2nd. Once warmed up it worked fine with no slipping. Per Memphis I change the fluid to 30 weight motor oil, reduced the cold start slipping some.

My everyday vehicle is a 2003 Dodge Durango, after about 65,000 miles the torque converter would unlock while on the highway and slip for a moment. My mechanic freind flushed the system and replaced the fluid with a synthetic Dexron type fluid. Solved the Dodge tranny problem with 30,000 miles on the synthetic.

I have concidered changing the GMC hydromatic over to this synthetic fluid, Memphis could not offer any opinion on this idea. Cost is my concern, since the synthetic is $5-6 per quart x 16 quarts

Karl

My 1-cent worth of my opinion.
I rebuilt two of these, one was using 30w oil and the other had ATF. There were no differences in the amount of wear or evidence of ring slippage. Both transmissions had the same problem – no reverse. (Broken reverse forcing cone) due to driver abuse. So my point is this.
If you ever get the chance to rebuild these transmissions, and see how they are made and how basic these things are, this debate would never happen. Three things are going on in the transmission, 1st is the flow of fluid, 2nd is the pressurization of the fluid to activate servos and pressure plates. The 3rd thing is lubrication.
So what are we looking at, 1st we need a oil that flows well and keeps it viscosity with little foaming, 2nd we need an oil that won’t break down under pressure, 3rd the most concerning the lubricating factors. We want an oil that lubricates well but not too well to where the bands start slipping. So what oil has all these three factors, Lets keep it simple for a simple transmission. NON - DETERGENT MOTOR OIL and ATF.
There has always been a debate of what oils to use in these early GMC hyromatic. Remember the internal combustion engine was only developed some 47 years before these came to production. Oil technology and development was at best primitive to today’s standards. Remember they had no computer labs or elaborate testing modules, 90 % of testing was trial and error. Since the oils/lubricants they had at that time were only developed to level of different weights, i.e. 10w, 20w, 30w, and so on, engineers developed a transmission based around the oils available (standard motor oil). Since non-detergent motor oil (doesn’t foam) was it was a perfect choice to use it in these hydromatics, it had all the three good qualities of what a transmission needs. I always approach my M-211 with a keep it simple attitude. They developed these trucks to be simple out in the field.
So if you are having problems with these transmissions, First do the basic inspection to see if the bands are adjusted right, then flush them to see if any engine coolant is getting in them. 50% of problems with these transmissions results from being out of adjustment, or serviced wrong, so check your rigging, and the other 40% of problems is thinking we have a problem.
These trucks will hic-up, slip, burp, or what ever on occasions. We just don’t have the modern day technology such as the control modular (cars computer) or fuel injection, which keeps adjusting our engines and transmissions every half-second to prevent the hic-ups, burps, and so forth. Put it simply, if it starts and the engine sounds relatively smooth, and you put it in gear and it moves without excessive engine rpms, and you put your foot on the brakes without using excess force and it stops. Then you can say life is good!!!!!!, This is all you can except out of these trucks that are 50 plus years old.
Steve

steve, im not a early deuce person but your post was a great post on this subject, thanks

tranny fluid

couldnt have said it better,have used both dexron and nd 30 wt oil,tranny performs and shifts better with nd 30 wt oil,just say no to dexron,33k miles on my truck with no tranny problems using oil,drive it by the book,service it by the book,and the lube order in the book calls for 30wt oil,i use PEP BOYS brand NON DETERGENT 30 WT OIL, just got through changing oil in my m211 tranny this week,the old oil still looks and smells like it was new,

RE: tranny fluid

Great post Steve!! Love the common sense !!! Randy

RE: tranny fluid

Am new to all this but am trying to come up to speed. Haven't had any experience with the M series till last winter, but I restore old GMC trucks and am being called on to work on these trucks now too. I notice there is little consensus on oil types for the Hydro-Matic (of which I am still not very familiar). I have a GMC shop manual from 1954 that stipulates that ONLY ATF be used in Hydro-Matics. In an emergency #10 engine oil series DG MIL-L-2104A may be used. It recomends that it be drained and replaced with ATF as soon as possible. I also have a GMC shop manual from 1957 that stipulates that engine oil series DG or MS MIL-L-2104A of the same viscosity used in the engine be used in the Hydro-Matic. It says that in exteme and extended cold weather, ATF may be used as long as the two are not mixed. Some technilogical change must have taken place between these years. Does anyone know the scoop here? The M 135 and 211s we have have a tag on the dash put there by the military (manufacturer) that stipulates #10 engine oil in the transmittion. I am told by others that the military wanted to standardize all oils so that someone did not dump gear lube or the like in it. Caterpillar still recomends engine oil in ALL of its functions (even the hydraulic systems) the same wt. as used in the engine. Some large truck transmittions (such as Roadrangers) specify engine oil, one Spicer 16 spd. called for #10. Anybody have any data that will shed light on these questions?
Frank

RE: tranny fluid

Frank this debate is an ongoing debate and will never be solved, the easiest way to determine what type of oil you need is to answer one question. Does my transmission work properly? If you answered yes, your tramsmission does not slip, shifts properly and does not make an adnormal amount of noise. Then keep the same oil that's in it. Memphis Equipment when rebuilding these transmissions used a newr type of clutch plate materal. and using ATF the transmission slippage was minimiml compared to 30w non-detergent motor oil. The orginal clutch plate materal made back in the 50's could use 30wt motor just fine with no slippage.
So what really matters here is again, if your transmission is working perfectly, keep what you got, use the same oil that you drained out of it. now 10wt motor was used in weather below freezing (32 degrees) above ambient temperatures of 32 degrees use 30wt oil.
I hope this cleared up your confusion, if it did then your the only one who knows the real answer. Me, I rebuilt three of these and daily I could swing in either direction of ATF or non-detergent motor oil.

RE: tranny fluid

The military became involved with the Hydramatic transmission during WWII, using them in the M5A1 and M24 tanks. Tests were conducted at Aberdeen Proving Ground utilizing the Hydramatic in the CCKW.

Along came the G-749 (M135/M211) at a time when the Army arguably had more experience running automatics than did the civilian sector. Army logistics is a massive undertaking, including POL. One of the key reasons the army shunned diesel-powered vehicles during WWII was the lack of desire to add a new liquid to the supply system (diesel) - by the same token, the Marines commonly used diesel-powered tanks because they burned the same fuel as the landing craft - simplifying logistics.

Anyhow, the non-detergent engine oil was used in the military hydramatics from WWII forward for the same reason - to avoid adding another petroleum product to the supply chain. This is documented extensively in the Aberdeen Proving Ground test reports.

In later years, the army adopted silicone brake fluid (despite it being VERY expensive) because it allowed the use of a single automotive brake fluid rather than the three previously used fluids, resulting in millions of dollars in reduced logistical expense.

BTW - the lube data plate on the GMC's only tell part of the story - the TM and Lube Order have the accurate info.

HTH,
David Doyle

RE: tranny fluid

I'm glad you responded David, you have great access to Aberdeen, but again the question arises.

Even though the Army went with the non detergent motor to ease the POL supply problem. According to the reports you have on hand from Aberdeen, how did the two different oils compare? or did both oils perform the same with no difference?
David here is an example, when I first went into Air Force, the standard fuel for the C-130 was JP-4, well the t56 engine worked well with this fuel. in the late 80s early 90s as you are well aware of the the whole military went to JP-8, this was for everything from humvees to bombers and from aircraft carriers to captian"s boat, use the same fuel. JP8 has a higher kerosene content and made the t56 engine smoke and also there was a slight power loss. (noticeable only by the engine calculator.) So even though the A.F T.O. today will state service the aircraft with JP8, JP4 was the better of the two fuels.

So which is the better of the two oils.? I think this is what this whole debate is about.

thanks again for you earlier response, I never seen it in writing about the availability oil due to the POL supply issue, I heard of it, but did not see it. Thank you again for sharing that with us. Please, if you have any information of the performance test, please tell us, I for one would like to see this debate end!!!!!!!!!!!

Steve

RE: tranny fluid

Caterpillar still recomends engine oil in ALL of its functions (even the hydraulic systems) the same wt. as used in the engine.
The above statement is not true. Let me elaborate on this Please. Cat says use of one fluid is ACCEPTABLE if it meets the necessary requirements. We discourage the use of engine oil in transmissions, way to many earl hour clutch failures. Mind you that when this info was new, engine oil was a lot different than it is today. also when used as hydraulic oil, the oil tends to drop out its zinc additive package. This leaves a calcium like deposit on the inside of cylinders, tanks, pumps etc. People using engine oil instead of hyd oil also have a higher rate of cylinders that drift and leak from the head seals. Just two cents from someone who works for Cat?

RE: tranny fluid

For your information, if you look for oil emergency replacements, refer to manual TM 9-2320-356-BD, Table D-3 .

RE: tranny fluid

I never had a problem of getting Dexron II from autoquest!!!!

RE: tranny fluid

Gee, I just saw this after it came up again. To answer the question asked in December......the lower viscosity oil (10W) was supposed to be used in very cold conditions. Under normal conditions, the 30W non-detergent was to be used. The 30W did not flow well in arctic conditions, and the 10W did not provide enough lubrication in normal condition.

Keep in mind that these trucks were designed and built by GM, who also built the transmissions, and also had to warrant both. Remember too that this trucks were created wholly by GM - not in response to a bid request - GM could have used any transmission or transmission components they chose. GM would not have risked the huge financial exposure the warranty would have posed if they were not VERY comfortable using the non-detergent motor oil.

Best wishes,
David

RE: tranny fluid

I always used straight non detergent engine oil in mine and never had any real problems...Was told to steer clear of tranny fluids by oldtimers that worked on these when they were new...For what its worth