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12 speed in R model


m16ty
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Years ago I had a 1985 R688 with Mack 10 speed. I never did like the 10 speed so when the range shifter went to acting up, I looked to swap it out. I ended up finding a 12 speed out of a Superliner.

When I went to install the 12 speed in the R, there wasn't enough clearance between the trans and the floorboard. I ended up having to raise the cab 1.5" (the best I remember) to get everything to fit. At the time, I thought maybe the 12 speed was never put into a R is the reason it wouldn't fit but since then I have seen other Rs with the 12 speed.

I wonder now why I had to raise the cab to get it to fit ?

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Would there be a difference between western Mack and typical Mack? A normal R chassis was wider at front so maybe engine sat a little lower? 

However maybe your Mack was on an R model chassis and my therory is debunked already...

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don't know this for sure but, could their have been different trans mount brackets for the 12 sp.? that would drop the back of the engine lower. since we dump trucked all of our trucks had the 12sp. so I never came across this issue but had valueliners thru rd688s to superliners all 12 speed and the cab sat no higher than our mixers with the other vocational trans (cant remember the model now)

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Was it hitting the cab or hitting the cross brace that goes across the cab mounts? When I changed my trans in my Superliner from a 9 speed to a 12 speed, I had to move the cross brace to the other position to clear the trans. The brackets for the cab have two different positions for different trans.

Live every day like it's your last, because one of these days, it will be.

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3 hours ago, MACKTRUCKS4 said:

Was it hitting the cab or hitting the cross brace that goes across the cab mounts? When I changed my trans in my Superliner from a 9 speed to a 12 speed, I had to move the cross brace to the other position to clear the trans. The brackets for the cab have two different positions for different trans.

You know, now that I think about it, I seem to remember putting a steel block under each side of the cross brace to raise the brace.

Or maybe I didn't know there was other bolts to raise the cab. It's probably been 20 years ago. I just happened to think of the project because I was cleaning my shop and ran across the PTO that came off the 10 speed when I pulled it out.

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