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Mack 12 speed Transmission?


sritchhart

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I am looking at a 87 superliner, camelback, 100k miles, with a 12 speed transmission. Would this be a good transmission for hauling grain on short trips (5 to 20 miles)? I had a friend say they can give some trouble. How reliable are they? We will prob. only put 4k miles a year on the truck. Thanks!

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Great transmission, but for short trips, even a 6 speed will suffice. Gears are great for hills or soft ground. But if you don't have to overcome those conditions, it's overkill. Great thing about a 12 speed is that you get 5 gears in reverse, of course, the six speed gets you that too. The Mack 9 speed is fine too. Do you have experience with shifting transmissions with multiple gears? It's an acquired skill that you may not get fully polished on short trips.

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The 12 speed is one of macks best transmissions behind a 300 or 350 motor. You can drive it like a 5 speed on the flats but have the option to split each gear on half. It's overdrive so you can get hone quick.. You also get 5 reverse gears and a low low.. pretty much the best of everything. They did have some scratching issues in the hi low range select..some are worse than others. It's triple countershaft and will hold up to any thing you can throw at it...parts are getting a little harder to get tho...I'm wanting one for my truck.

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Two words about a 12 speed BULLET PROOF! My experience with them is fantastic. I put a 18 speed in my truck just to have some more overdrive. I still have my 12 speed and would go back to it if the occcasion arises.

When I bought my 18 I tried to trade the 12 in on it, but the man was not interested, said he had more 12's than he could sell. The 12's never break and because of this there is very little demand. There are probably a lot of 12's lying around if you know where to look and if they have not gone to the scrap yard.

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Speaking of bullet proof...lots of Mack sled pullers use them behind the v8s. While on topic.. I would like to find a good 12 speed if any one has a line on a reasonable priced one please let me know..

Try Country Boy's Truck Parts in Greenville, KY. Rudy Cundiff. 270-338-6368. Or Winn Rock Truck Parts in Oliver Springs, TN. Bill or John Atterson. 865-435-0032. Both specialize in used Mack parts.

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Thanks Rob. I see another guy started a new thread about his. I have only seen the one I have and maybe one other in a early 50's Mack H cherry picker in person. I guess the guy has one in his B also.

Couple questions , how long did Mack run them in trucks? Why would a person choose the 9 sp duplex over the 10 sp duplex of the same time? Thanks

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Thanks Rob. I see another guy started a new thread about his. I have only seen the one I have and maybe one other in a early 50's Mack H cherry picker in person. I guess the guy has one in his B also.

Couple questions , how long did Mack run them in trucks? Why would a person choose the 9 sp duplex over the 10 sp duplex of the same time? Thanks

Basically the same trans except the overdrive version, (nine speed overgear) is so close between fourth high and fifth low the usage is nil. You can split all five gears on a direct. I think I'm relaying that correctly. A lot depends on the gearing of the axles.

I like the trans in my B67.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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I have it behind a 711, the rear ends been re geared and runs down the road alott faster than it did when new.

Won't hurt anything except low end "grunt" and pulling power. My B67 will run right at 65mph in od with 5.77 rears. Good enough for me cause I can't run that fast unless "Momma" is after my ass again with her butcher knife, (I have nothing left to give).

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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I wish it new what ratio are in the rear end. I run about 65 at 1900 rpm. I think its good enough also. Im passing most OTR trucks and I dont think I can take going much faster.

Prolly a 5.13 ratio with an overgear and 10.00X20 tires. It's easy enough to check if you can get the rears clear of the ground to rotate the tires.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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I absolutely love the 12 speed transmission in My RD. Drive like a 5 speed when empty or even loaded on level or downhill, but you can split every gear on a pull (or if you just wanna grab more gears). They do make a bit of noise when splitting the gears if you dont hit it just right, but once you get the hang of it its a awesome transmission. Mine turns 1800 @65 -Tops out at about 72@1950 I believe I have 417 ratio.

Edited by EWB555
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  • 10 years later...

I have a '90 Mack Superliner Log Truck with the E9 engine. The Mack 10 speed transmission

has finally bitten the dust. Been putting band aids on it for years and this time it's done. I'm looking for a better transmission and don't know what would fit without major modifications.  In reading about the 12 speed that really sounds good as most of my work is short run fully loaded on and off road which the 10 speed didn't like. I need more low range gears instead of almost red lining the engine to get enough speed up to make the next shift. So the question becomes, what will it take to put in a 12 speed in place of the 10 speed.    I'm hoping that there is a 12 speed that will drop in the same space without major modifications. I have no issues with more airlines, and I know I'll need a 12 speed stick but how much more would be required to make this happen. I don't have dimensions or mounting details or input shaft dimensions to indicate that I'll need a new clutch and or flywheel and output shaft info to tell me if I'll need a new driveshaft end to mate with it. Lastly, which 12 speed would come closest to a drop in? Any input on this would be greatly appreciated.

 

 

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Well Dave if your gunna chuck a 12 speed were you had a speed hoping to get more usable gears your gunna be disappointed as the extra gears are at walk pace or slower 

And to the second part of yoiur question, will it bolt straight in, the answer is also no, the 12 speed has  deep reduction gears in a extra section on the front of the box, makes the gearbox maybe 4 or 5 inches longer

They are basically the same transmission except for the 12 speed having deep reduction 

Wish I had some better news, maybe a 18 speed Mack box might give you the extra spread of gears your chasing 

 

Paul  

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Hi Paul, I just looked up an 18 speed and given the choices If I can't find a gear I like in an 18 speed, I might as well give up. Probably have more issues remembering what gear I'm in than anything else. I looked at pricing and there were only a few hundred more than a 10 or 12 speed so that was good. Is shifting this trans with a non-electric engine going to present any issues other than a learning curve? Assuming not, I'm back to the fit issue. Can't tell by looking at pictures but it seems like the 18 speed is longer than my 10 speed, so will this all bolt up ok with just a few more air lines and a new stick? A new clutch would be a given but is this another shorter front drive shaft and yoke to match up to the 18 speed are are there more issues involved? I simply want to go into this with my eyes wide open and come out with a better set up than what I have. If I basically double the bottom half of the gears in the 18 speed for moving around that would be great and have more to go when empty it would solve my problems. All comments good or bad are greatly appreciated!

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