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23 hours ago, mackey58 said:

Even an RD is good i think mine is rare.the built sheet said it was one of 3 that went to chicago mack for a customer but only bought 2

When I was selling Mack's, in the previous century, often our Sales Manager would order extras of a spec if it was mostly typical.  That is if customer "X" ordered 8 he would submit an order for 10 thinking that he might be able to talk the customer into the 2 extra as they would not all arrive at once and sometimes the end of the order might be months out.  The other option was to just add the extras to the floor plan to have new stock.  A long time customer ordered several RD's & RB's every year & we would always add on 3 or more to each order.  There were several other customers who ran the same spec just because they had bought some of these "overages" years earlier. It is a sales advantage to have a common spec on the lot that works well for several customers.

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Can someone tell me what is the difference between an rd686 and an rd 690.  I thought it was just a year thing but now i'am not sure.   Maybe the 686 has only 6 speed and 690 has 7 spd or more Maxitorque gears.

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On 1/3/2019 at 9:06 PM, Maxidyne said:

686 has the engine mounted intercooler, 690 has the chassis mounted intercooler in front of the radiator.

The Mack engine designation 86 represented the use of ENDT676, EM6 285 or EM6 300 engines over the course of the production run.  Early models used the Tip Turbine mounted on the engine for cooling the air charge.  The front mounted charge cooler replaced the Tip Turbine around 1982 on most models.  DM686 models continued longer with the Tip Turbine until 1988, for example.

Engine designation 90 indicates the use of the EM6 300 (early), EM7 250 HP Econodyne or EM7 300.  

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It doesn't cost anything to pay attention.

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