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Power Divider In A 77 R Model


77rmack
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I've got a '77 R-600 that I bought not to long ago, that although it is retired I would like to have it play on a dump trailer once in a while. It does not have a power divider air valve in the cab, which leads me to believe it does not have a power divider, but a friend tells me that Macks did not need dividers, they are always locked in (???) Right or wrong?

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77mack,I have not had one apart in about 30 yrs. any Macks I ever bought new I always put a power divider lock out dash mounted, but if I remember correctly the rears are not locked all the time. Now if my memory serves me Macks unit allows traction onto the axle with the most resistance as the truck rolls down the road. How that works is inside the rear thers these inner & outer cams that work on centrifical force, so as one axle rotates faster then the other, this (miss match) allows a small wedge (PEANUTS) to engage to the other cam locking up the axle ONLY WHEN MOVING NOT STANDING STILL. Now thats where a power divider inter axle what ever you you wana call it differs. If your on ice or slippery pavement you just put the dash switch in lock an you can pull away with both rears locked. BULLHUSK PS you can do it with a Mack I'v never done it but some of the guys on this site could tell ya

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Macks of that era likely had a automatic power divider. the dash switch operated was a option as well.

the auto power divider has its good and bad.

the good is if its not worn out it kicks in automaticly before you know you need it.

the bad is if you do get stuck you wont know for sure if its giveing you the power transfer you need.

the old trick if you got stuck in slick mud or snow with the auto PD...was to lightly tap the brake pedal as you were spinning the wheels. ( dont stand on the pedal!) this may help the power to transfer from the spinning wheel to a stopped wheel and help you get out.all your doing is resisting the free wheels from spinning in hopes the stopped ones grab and get you out.

Remember most trucks have open diffs so in reality we only have one wheel drive. All the power divider does is sends power to both axels giving you 2 wheel drive when more traction is needed. all depending on the weight thats over an axel and how slick the ground is will depend if you can spin 1-2-3-or all 4 wheels at the same time. hard to explain without showing someone in person with parts in hand.

Regardless you can buy an air operated PD and install it. should be easy to find parts.

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