GMC Hydramatic

Hello SS,
Some interesting info and experience with my M215 tranny. During the restoration we put a Memphis rebuilt tranny in the truck, it was over a year after the install before the tranny was ever tested. I quickly realized that the rebuilt tranny had problems, slipped in reverse (low range reverse) when warmed up. After a little arm bending, Memphis agreed to replace the defective tranny (only a 90 day warranty, I owned it for over a year already). Installed the replacement rebuilt tranny and everything was good. After two trips totalling approx 400 miles, noticed the tranny slipping in high range forward from a dead stop when cold. Low range forward / reverse was fine and after warming the truck up it stopped slipping in high range forward. Spoke with the tranny guy at Memphis and was very helpful. These are some of the steps taken

-removed REB shifter and replaced with standard valve body
-adjusted front band
-adjusted shifting linkage
-pressure tested tranny, results were within manual specs. (125 psi forward / 225 psi reverse)

These had no improvement on the cold forward high range slipping. Last suggestion was to drain the recommended Dexon II / III and replace with SAE 30 motor oil. After changing the oil the truck drove and shifted fine but air temps were 60F +

Tonight was the test, air temp 36F, let the truck idle 15 minutes put it in high range / 1st gear on the REB and no noticeable slipping. Drove about 100 feet forward and reverse, felt great!

Just my $.02 on the motor oil / Dexon II debate.

Memphis agreed to work with me if my second tranny is bad also.

Karl

Now I'm really confused! I heard that 30 wt. oil used to be recomended and now they say Dextron is the way to go. I know the manual says warm up the truck before using. But- this oil choice is confusing, I think I am going with the dextron trans oil. I have heard more positives about that than the 30 weight.Thes automatics are supposed to be a good tranny and have the adjustments, but if one doesnt know anything about these automatics, such as myself, I am at the mercy of a trans specialist.How did you know what adjustments to make and where they were? Whats an REB shifter? Was it original to the truck? My truck seems to shift fine ,low or high range .

Cool sae30 it is....Thats what is in mine... It has 22000 on it so I think that is what will go back in ...thanks for your .02....

The REB was a kit that Memphis used to sell. It added a shift lever on the left of the tranny tower. It made it so you could put it in gear and not shift up or down by itself. When you wanted to go higher or lower you moved the lever to change gears. As I remember it with the kit you could not use F2 and reverse on the high side of the tranny. I think you put a bolt in the F2 spot so you couldn't get it or reverse.
For what it's worth I still have the REB plate on the driverside door. I always used ONLY Dexron.
Remember these trannys DO NOT like getting hot. Make sure your radiator is good and free flowing. That the bottom of your tranny is clean in and around the cooler.

Thanks Westfolk! Yes I am with you on the Dexron.I see what you mean about the shifting, sometimes you just want to stay in that one gear without it constantly shifting back and forth. Such as offroading use.The REB shifter sounds good. Thanks for the info. By the way, I like excavating work also. Just bought another track loader today and have a small excavator. Working on a dumper. All old machines but in my budget.

Westfolk , where is Eldred , Pa?

Rich, Old equipment is the best. No computer, elctronics, etc. BS. When something goes it is real easy to figure it out. Try that with a newer machine loaded with "Gizmos". Yeah they run great when everything is working. When it comes to a breakdown. Well that's a whole other story, just like cars these days.
Where am I? I asked you awhile ago if you were in Northeast, PA, as in Erie; or northeast PA as around Scranton. If I-90 is next door....Grab I-86 and run east to Olean, NY. I am 21 miles(by road) southsoutheast of Olean, but in PA. I'm south of town. Closer to Turtlepoint. But I have an Eldred address.

REB shift

I prefer the REB shifter in my M215, it allows you the chose what gear you want and shift as needed. Makes the truck very easy to drive, F2 and high reverse is not used. The tranny guy at Memphis told me they are running out of rebuild parts for the hydramatic. They are no longer making the REB shifter so when existing stock is gone, that will be it!
Karl

10 Wt was recommended for 900 series 5tons to replace DexronII. We put 15w-40 in M113 allison automatics upon filter change or rebuild.

With hearing all about the tranny problems woth the 211 I amconsidering just getting rid of mine beofre i invest the money to put a trans in the tihngs, I ahe to do all that owrk replacing it with a used or reman unit to just have it go out again.

davesgmc I shipped your parts yesterday . I really like my trans mission with the REB I have no slip and shifts smooth I did buy a cckw in case it did not work out and I would swamp out the running gear .

Oh, I'll probably keep the thing. Just have my doubts.

It`s a good solid truck & trany .. You just have tobe smart about how you drive it & maintain it...I don`t have the reb kit though ...sounds cool...

The reb shift kit from Memphis is well worth the cost. We had an M211 at the VFD I used to belong to. We had nothing but trouble with so many different drivers and each one was an "expert" on auto trannys. We finally put in the kit and the troubles were gone. Btw, it had a 1800 gal. tank on it and it handled it full of water.

I have a brand new REB kit in the box for sale on the classified section if anyone wants it. You will have to hurry though because i'm leaving for Basic in 1 week. They are definately nice to have and make the trucks easy to drive. Half of my trucks have engine oil, and my M211 has dextron. I'm planning on putting dextron in all of them someday, but I think that they both will work just fine. Dextron probably is better for the clutch packs though. I think this is one of those questions that will never be answered.

Mixing oils?

Great info!
I drained the Dexon from the tranny, torque converter and two speed unit, all 4 gallons before replacing with SAE30. Would there be any benefit to adding a quart or two of Dexon with the SAE30 (I may of just reveled how little I know of oil)? Would this prolong the clutch paks or is mixing oils bad?
Karl

RE: Mixing oils?

Dont mix the oils.And to DaveGMC, ,This tranny is huge and heavy built.Dont be swayed by a couple of reports of problems. There are more probs with the 5 speeds from what I hear. I am not an expert on this, but from what I have heard, they are good. Just warm them up before you drive them , keep good fluids in them, and if its working well why worry. They do shift hard on one of the speeds, but that is the way they are.I am surprised how well these trucks are built. I have had alot of trucks, but these are overbuilt. You can tell the gov't. didnt want our soldiers having breakdowns. They arent comfortable but they are rugged.

Yes they are... Rugged .........

Different animal but I used to work for a company that made industrial wet clutches. We recommended either Dextron II or Type F. Most of our customers used Dextron II. When Dextron III came out we had an increase in failures. Turns out Dextron III has a lower hot coefficient of friction. Basically it is slipperier which allows a 1990's auto trans to shift like they designed it but it lets older wet clutches slip more. Being your trans is ancient this may have something to do with it. Once we switched to type F everything was fine.

Memphis Equipment reccomends Dextron, original LO says to use 30wt for temps above 32F, 10wt 40F to -10F.
I rebuilt my 211 trans myself with parts from Memphis, these transmissions are very simple inside,(2 clutch pacs,2bands and a valve body). If you can pull a wrench you can fix it. Mine had a Reb kit on it that I took off (yrs ago) they do give better shift control, but if the engine govenor is faulty you could toast your engine,( I know a few guys that did). They do behave better if you let the truck warm-up before heading out. One more hint, because of the way they are designed,( spring pressure on clutch pacs and bands when the engine is off,no oil pressure) always put your tranfer case in neutral when you park and shut down this keeps the load off the trans the next time you start it. I've got 10yrs and probably 2500 miles on mine, most of the miles hauling my MB in the bed, no problems so far