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Hello. Recently, someone showed me a local advertisement for a mid-70's U686ST...the seller included the following statement in the advertisement: "...this U686ST is basically a short version of the R686ST just with an off-set cab. It has a 237 Mack engine and 10 speed transmission." I'm guessing the "237 Mack engine" he's referring to is the ENDT-675. I don't know a lot about the U models (aside from the off-set cab, short bumper to B.O.C. length, and lighter frame/axles as compared to the R model) so I am just wondering if the comparison statement with the R686ST is accurate. Also, I did not know that a 10 speed transmission would work well with the 237....was installing a 10 speed transmission a good move by the previous owner? I had just always assumed that the 5 spd or two-stick 6 spd transmissions were more common with that particular engine.

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Neither a U or R model 686 would have a 237 engine. A truck equipped with the ENDT-675 (237 HP) would be a 685 truck designation.

Both truck designation 685 and 686 (ENDT-676 285 HP) feature a Maxidyne series engine and utilize 5 or 6 speed transmissions.

The specs between an R/U 685 or 686 (beside the engine spec) could be identical with the exception of the U models offset cab and a shorter chassis wheelbase to take advantage of the shorter BBC dimension.

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It doesn't cost anything to pay attention.

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