GMC Hydra-matic

Hey SS
After working on the M215 for four years, it finally hit the open road this weekend. I did a couple short 2-5 mile rides and have some shift questions for the other GMC M-seires drivers. My truck is set up with a Memphis REB shift kit as well as a Memphis remanufactured tranny. When shifting into reverse low range (high range reverse is blocked off), I noticed it is necessary to raise the RPMs before it will engage into reverse and makes a whining noise. Also the shift from second into third is very abrupt. Are these normal for these trucks? This is the first one I have ever driven. I did not want to push the new motor and tranny much, but 45mph in fourth was easy to maintain on level road, droping down into third on mild grades. It was a blast to drive, great visibility over the sloping hood compaired to the M35, but much slower than the multifuel.
Thanks, Karl

hey 2nd to 3rd shift on mine is harsh also,changed from dexron atf to 10w non detergent engine oil in tranny now it only does it about 60% of the time after tranny oil change,best it ever shifted or braked was when i had about 4200 pounds of pressure treated wood for a deck loaded on it ,took wood to top of mountain after 60 mile road trip dont know about noise,read tm 9-8024 operators manual it has section on tranny problems,good luck keep posting

Karl,
Do not have my XM211 any longer, but, they are GREAT trucks and just plain superior to the M35.
Regarding the tranny. 2/3 shift in high or low will always be abrupt, IF you just hammer the throttle. Has to do with the complexity of the shift, going from one gear pack and one band to the other pack and the other band all at once. The key is to learn where the sweet spot is for your truck and have the shift occur at that point. Mine was at 17 to 18 MPH, smooth...., but if you hammer it, wow. Low range is even worse. If you have a reman tranny, stay with dextron. The OE-10 was the original, but not as good as dextron, and the seals are different.

Regarding performance, Never encoumtered an M35 that could stay with the XM211 on the road, 55 to 58 MPH for hours on end. That being said, I did loose on the long hill climbs with the multifuels. But again, the M211 is over 1000 pounds heaver than the M35 and your M215 is heaver than that. Superior view (noted), trouble free front axle engagement, bigger cab that is properly designed for human occupant. Many parts available at NAPA etc. (GMC heavy truck stuff, even engine parts.) Parts are even still made for the transmissions! Fantastic off road performance for that class truck.

(Yes I am a major fan of the GMC, currently working on another with a friend at work)

Squirt Truck(er) (Long story about the XM211..)

Thank you for the response!
I do run Dextron 3 in the tranny per Memphis recommendations, but still concerned about the whining noise while in reverse. I have not finished setting up the timing for best perfomance. Points are set at .016 with a feeler gauge and have been trying the distributor at differant positions, it is set a little advanaced now. I do not have access to a tach or a dwell meter to set the timing per the manual. I do use a timing light, but without knowing the RPMs it is kind of a guess. How do you guys set yours up? What happens if you set the timing too advanced?
Thanks, Karl

There is no 't' in the word dexron.

O well oops right chap's.

Good catch on the Dexron, even Chevron that produces the stuff spells it wrong on the official web site. (But they get it correct in the spec sheet....)
BTW, you do not change the torus usage, just the utilization of the stator, the fluid clutch (torque converter) on these trucks has virtually no slip after leaving first gear. The pump (driving member) to turbine (driven member) are very efficient. Ever notice that the trans will kill the engine with a REB kit if you do not return to first gear? But then with an idle speed of 375 RPM it does not take much....

We need pictures of the 215!!!

The following pertains to the transmision only!

The Army originally speced 30 weight motor oil for the M-135 /M-211 for both the engine and the transmision. It will work fine IF you warm up the engine for 30 minutes THEN drive it. The Army changed the oil from 30 weight to (after having many, many trucks burn out clutch packs by the hundreds) 10 weight which allows the truck to move when cold in low range 1st gear only untill it warms up. If it has not been running since last night BUT don't try to shift out of first gear untill the engine hits 180 degrees. The tranny is cooled by a large heat exchanger which is mounted in the tranny. If the coolant freezes and the cooler more often than not will break YOU WILL HAVE COOLANT IN THE TRANNY AND OIL IN THE COOLANT!!!! This is not what GMC designed the tranny to do. KEEP A SHARP EYE ON THE ANTIFREEZE IN YOUR TRUCK WHEN IT GETS TO FREEZING TEMPS!!!. A pocket tester that has five little itty bitty balls with a pocket protector is sold at most auto parts stores for about $3 or $4 dollars and is the easy way to check the freezing point of your antifreeze. All balls floating? Your good to Minus forty below zero. You don't want to tell the Boss "NO EXCUSE SIR!"

There are 2 different clutch packs for the tranny...one for ATF and a entirely different one for motor oil. If you have Memphis Equipment rebuild it it is your choice for oil or ATF. ATF is a lot easier as you can fire it up and drive off quicker than an oil equiped tranny but I would still warm it up. Besides after starting you still have walk around and kick the tires and look for leaks etc.

Remember guys like the add says " You can pay me now or pay me later". I'd rather spend a couple of pennies to warm her up then drive. Gas is cheap compared to a rebuilt tranny.


Yours came with ATF? By all means use ATF and ONLY ATF!!! It came with OIL? Use only oil in the tranny..to convert to ATF from oil you have to R&R the tranny and replace the clutch pack.

My Xm215 also shifts abruptly. It has been off the road a year and I can't remember at which speeds she did it. However, mine still has the oil in the trans. I have always allowed her to warm up- especially in the winter. I changed it before I drove her over 200 miles home. I had absolutely no problems with the trans. The top speed was about 50- 55mph on level and about 15-20 uphill- probably do to the leaking headgasket and incorrect tappet adjustment. The only thing is I couldn't find anyone who sells 10w nondetergent oil so I ended using 10w-30- so far no problems. However, she hasn't gone in low for a awhile without warming it up and going from low reverse to low "level" over and over again until it engages. I think she need the linkage adjusted. I have an operation manual but it says to use a special tool to adjust the linkage to the carb/ trans. Is this a tool that anyone knows where I could buy? It is an L shape. I'll try to post a picture of my truck soon- after I figure out how She doesn't look pretty right now though. Robert

with ref to 10w non det oil vs 30w non det oil, I have 30w non det in mine, I have tryied to locate 10w non det and wiht no luck, does anyone know where to get 10w non det?

When I asked my local Napa they said I couldn't even order it. If someone does still make it it might be pretty costly. Walmart sells the 30w non detergent cheap- at least 2 years ago- 75 cents a quart.
Robert

RE: Re: GMC Hydra-matic

My carquest boys have the 30 wt ND oil. I had them order a couple spare cases and said just let them sit there and collect dust, I'll eventually need it. As to letting it hit 180 degrees; I took it on 2 different road trips and let it just sit and run for a while (like, an hour), and it NEVER got over 150. That's with a new mechanical gauge. I thought maybe it was just being problematic, but even after the 30 mile road trip, I could get out and not have a problem holding eith the to or from colant lines. Guess that monster fan on the front of the engine works a litt too well for a truck that'll never see a load over half a ton...

Tracktor supply stores carry non detergent oil in 30wt. and I think it was 15wt. My xm211 uses 30wt. Tim

I ran an M211 for years - been from southern Alberta to the Beach (Prudhoe Bay), several times. In down shifting from 3rd to 2nd, the engine would over-rev for a second. I learned to back off the throttle @ the shift point. Always thought it would blow, but it never did.

I ran points @ .018. Set the timing by trial & error - advance the distributer till the engine pings when you put your foot in it. Then back it off just a tad, till it won't ping. That is perfect. Be careful no to run it retarded. It sounds better by ear there, but set it as above. If she is retarded too much, it will generate excessive heat in the exhaust manifold and cause it to fail/break.

Lee in Alaska

I know this is an old thread, but do to the latest responses I had to say something here.
Please do not adjust your timing or any other adjustments to compensate the shifting jolt you get from 2nd to 3rd. Here's why,

The two torus halves (drive torus) and (driven torus) separate the main shaft and the input shaft or what I call the (driven torus shaft) in the transmission. Or the easiest way to remember this is when ever the REAR planetary reduction unit is in reduction, (Band On) the transmission is in ( full fliud coupling). The first thing we have to understand that the main shaft will always be truning, either in reduction 1.55 to 1 or in direct drive 1 to 1, when the clutch piston squeeze the clutch plates plates and stators together. This locks the engine input shaft to the main shaft in the planetary gear unit, this is called direct drive.

OK now that we see this, let's look at the main shaft. The main shaft has two ends. On the forward end, the drive torus is connected to it and on the rear end, the rear planetary gear unit clutch plate gear hub. Which means this The clutch plates are connected to the main shaft and the stator plates are connected to the drum and the drum is the ring gear to the planetary gears then to the transmission output shaft.

So when the rear planetary unit is in reduction for 1st, 2nd and in reverse, the clutch plates are turning but the drum and stators are not. Which means engine power can not reach the transmission output shaft going this way.

So the only way we can get the engine to turn the transmission output shaft is by the main shaft turning the drive torus on the front end of the main shaft. Then by fluid pressure the drive torus drives the driven torus which turns the driven torus shaft sun gear which turns the rear planetary gears which turn the transmission output shaft.

So it goes like this, engine power goes into the front of the transmission, into the front planetary gear unit, to the main shaft, out the front of the transmission, to the drive torus, THROUGH THE OIL, to the driven torus, back into the front of the transmission by the driven torus shaft, to the rear of the rear planetary unit, through the sun gear, planetary gears and stationary ring gear then and only then can output shaft turn.

Now when we go from 2nd to 3rd, we assist the torus halves and the transmission goes into direct drive by assisting the torus halves.

When we select 3rd we release the band on the rear drum and activate the rear clutch pistons, this squeezes the main shaft clutch plates which turn the drum and it's ring gear. Since the ring gear is turning 1.55 to 1 the planetary gears (connected to the output shaft) driven by driven torus shaft sun gear turns the output shaft to the same ratio. Due to the pressure on the driven torus shaft sun gear from the drive torus, it acts like a rotating locked sun gear.

When this happens, the planetary gears can't turn because the drum is locked to the main shaft. At the same time and the drive torus is supplying constant pressure to the driven torus and the driven torus shaft sun gear locking it from turning in the opposite direction, which in this case would be required for the planetary gears to rotate. This shows the main shaft and the drum’s ring gear are supplying the majority of the force to turn the output shaft.


If you are feeling a severe jolt, look at you throttle adjustment going into your transmission, make sure it's dead on. If it's out by an by a fraction, the shifting can jar your teeth out. When its adjusted properly, you can take the jolt out by lifting your foot off the gas pedal at the moment you feel it going to shift up. Then if it's going to down shift, apply a little more gas at the moment you feel it's going to shift.

By now I hope everyone is starting to understand the basics here.

Anyone who has been following my explanations on this transmission Please let me know if I'm getting the information out so every can understand it? If I need to do something different please let me know.

Steve
Of all the miles that I drove my two trucks (still have them), I never could find anyone that knew much about the transmission. I didn't figure out how to adjust the transmission throttle linkabe either. Your obiviously well versed in the transmissions functions.

Lee in Alaska

Sorry guys

I miss read a couple of threads and thought some of you were trying to adjust the timing to smooth out the shifting jerk you get going from 2nd to 3rd. BUT when ever you do adjust the timing, make sure to check your engine rpm and shift chart to make sure you are still with in the limits. Believe or not this will have a slight effect at what RPM the truck will shift at and you might need to adjust the throttle linkage.

I just posted a thread about trannies that includes info relative to this problem under "Hydramatic Heaven". Check your oil pressure. This sounds like a classic problem. The engine is revving up because you do not have enough pressure to engage reverse. The associated whining noise is the reverse cones slipping and destroying themselves. I think you have a bad tranny.

WOW.......my head is spinning like a top...........But I am leraning.......