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Identifying running gear on '83 MCR Mack


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Hi folks,

I'm new to Mack trucks and have just picked up an '83 MCR with a Maxidyne 237 hi-torque engine and 5-speed with air shifter on the knob. I'm trying to identify all the model numbers so I can buy the right service manuals and am a bit bewildered by the range of different boxes and engines that came out in these trucks.

The truck has a splitter type airshift on the gear shift knob, effectively giving me 10 foward and 5 reverse ratios, with a neutral position that must be used when engaging the PTO. To engage the PTO, the transmission must be put into gear, typically 2nd or 3rd.

If anyone could give me clues on the following questions, I would be most appreciative:

1) What is the gearbox in my truck and is it specified as a five speed with the airshift splitter as a separate casing or does the whole core/splitter combo have it's own designation as one unit? From what I've been able to gather it must be either a TRL-107/107x or TRDL-1070/107x

2) How can I identify if the engine has 2V or 4V heads?

3) How is this PTO arrangement described in the service manuals?

I have included a couple of pics of the truck and airshifter for reference.

With thanks.


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The 237 was a 2 valve engine,and it's most likely a 6 speed,Lo split in first gear only,you'd have to check numbers on the case to see which one as there were a few different versions depending on the lo gear ratio.Mack used that knob on several different versions of the old Maxitorque transmissions,6,7,10 and 12 speeds.

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if the injectors heads can be seen from the passenger side its a 2V

If you can only see where the fuel lines enter at the side of the heads its a 4V

are you sure its a 10 speed? Many of those were just 6 speeds. But as said it could be a 7-8 or 12 speed as well. You use low "L" just in 1st and then split it into direct "D" then shift 2-3-4-5 giving you 6 total forward gears and 5 reverse gears.

IIRC there were the standard 6 and 8 bolt pto mounts on the 6 speed case. many also had the option for Macks rear mount PTO that ran off the lower contershaft via a splined coupling.

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Thanks for the input everyone - Lmackattack, if by "passenger side" you mean the left hand side when viewed from the rear (here in Oz we are not just Down Under, but also Ass About), then yes I can definitely see what look like injector heads.

I also read elsewhere in the forums that the greenish blue paint is a 2V giveaway.

I reckon you're right about it being a 6 speed with a split only in 1st on the main - I can actually drive it like a splitter all the way to top (and back) without gnashing any teeth, but the timing is so critical to flick the split with revs and clutch all lined up I can't see the idea being sellable to any but the most enthusiastic knob jockey.

Kudos to a newbie with only 15 hrs experience on a crash box I guess.

The PTO also looks like it comes off the lower countershaft at the back of the box just like you said.

Once again thanks for all your help.

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Sorry "mate" LOL I

I was noting the Starboard side of the engine...you know the side the Turbo hangs from :tease:

if its a 6 speed you only can get 6 progressive up shifts. the 6 speed is just a basic 5 speed but it gives you that one extra low low gear. You can start in 1st low "L" and shift all the way up into 5th then split it into direct "D". doesent matter where you make the split from L into D but you only have 6 forward speeds. on the older 2 stick 6 speeds I Often I started out with Low, up shift 1-2-3 then split into 3rd Direct then continued the upshift 4th-5th (total of 6 speeds) reason for this is many times when you use low 1st you had to stay in that gear untill you reached hard level ground. if not when you tried to make the split you were just going to slow and the truck stopped before you can grab the next higher gear.

there was also 12 speed that was real nice. most times you drive it like it was a 6 speed but you could split each gear giving you a total of 12 speeds. the top gears were over drive and the bottom were very slow. it was the perfect trans for macks that ran the on/off roads.

you have a good rear mount PTO! it runs off the front box so it turns off engine RPM so long as the clutch is engaged. the side mount pto ran off the transmission gearing and you had to put the aux in nutral and main in 1st or 2nd to properly operate it at a safe speed.

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