Rd Models

[Mack2]

What is the differnce in the Mack RD688s and the RD690s?

[HK Trucking]

What is the differnce in the Mack RD688s and the RD690s?

The 690 would have a Maxidyne engine and the 688 would have the Econodyne engine.

[Mack2]

Ok but we have both RD690s and RD688s and they both have the same moter.

[HK Trucking]

Ok but we have both RD690s and RD688s and they both have the same moter.

When you say that "they both have the same motor", do you mean they externally appear to be the same, or does the ID info on top of the valve covers indicate that they are the same engine model?

If the engines are indeed the same model in both the RD690 and the RD688, then someone has done a transplant, because as I said, the 690 would have a Maxidyne such as "EM7300", or "EM7300L", while the 688 would have an Econodyne such as "E7350", or "E7400" etc.

The Maxidyne engines were made to work with the T2050, T2060, T2070, and T2080 Mack transmissions which were 5, 6, 7, and 8 speeds respectively.

The Econodyne engines were made to be used with T2090, TRTXL1070B, T2130, and T2180 Mack transmissions which were 9, 12, 13, and 18 speeds respectively, and some of the Econodyne equipped trucks were set up with Eaton Fuller 8LL, 9, 10, 13, and 18 speed transmissions.

[storkmack]

I have a 94' RD690, and it had an EM7 300. It can from the factory witha fuller 9 speed which we later changed to a fuller 13

[HK Trucking]

I have a 94' RD690, and it had an EM7 300. It can from the factory witha fuller 9 speed which we later changed to a fuller 13

Are you sure it came from the factory with a Fuller 9 speed?

A 690 with an EM7 300 and a 9 speed doesn't sound to me like a factory set up.

[granitefan713]

I was told by a retired Mack engineer that Mack would put whatever you want in a Mack if you requested it. He said they would build a Mack with a Cat engine for you if you wanted. He said he knows they built alot of Macks with Detroit engines for Roadway freight.

[convoyduel]

Officially from Mack:

The 690 refers to RD's with factory HP of 300 hp or less. The 688 refers to 350 HP or more. EXCEPT....if you custom ordered a non-catalog engine in an RD, it got the 690 designation regardless of horsepower. Such was the case in 2002 when we ordered the 355/380 MaxiCruise in our RD, it sent the specs to engineering and forced an RD690S model number.