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I Need Info About 5x4 Gears Box


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I need Info about 5x4 gears box,

I just buy a 79-R609 and have the 5x4 gearbox and 673 turbo engine tamden 12-00-R-20.

The top speed is very low only 43 Mph at 2000+ RPM.

Any one knows the gears of this gearbox or were can I found more info Online look like I have a 4.10 or more.

I will like to more info on the 673 engine too.


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oldmacksrus.com has all the info on motors/trannys/etc.

Look on the drivers side of tranny and you'll find the number telling you what it is....TRQ-XXXX (the last digits telling if single/double O/D ) With that road speed I would bet you have 5+ something gears or worse!

One question? What is a '79 doing with a 673/quad box in it?? Seems pretty new for that combo.



1959 B61 Liv'n Large......................

Charter member of the "MACK PACK"


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I dont think quads were options after the late 60s. a BCR could easly have one and if you have a 673 with a quad. it might be an early R model from the late 60s early 70s? the late 70s had numbers like 686,685 etc... Check your vin number on the frame rail near the pass front wheel to see what the truck came with...if its for shure a 79, it very unlikely that the quad came from the factory. My B61 has a quad and 5.73 rears..thats good for about 62 mph


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