Allison 653 transmission fluid

[Rich Farr]

Due to leaky hose, need to add transmission fluid to our 1979 Newell -6V92 DD with Allison 653 5 speed auto. Allison folks recommended new synthetic ($38.00 per gal), then dropped back to C3/C4 - ??
Don't want to mix synthetic in older unit and uncertain whether should use Dextron III or Type F. What readily available (old red) auto transmission fluid does Newell recommend for this unit? Thanks in advance.

[TechTalk]

Allison 653 transmission fluid Allison recommends Castrol Transynd synthetic ATF as well as Dextron II, Dextron III, or C4 oil. Allison has a service bulletin that goes into detail regarding ATF recommendations. It may be available on the Allison web site. Newell recommends synthetic fluid (we use Mobil Synthetic ATF) and uses it for initial factory fill on new coaches. However, it is more difficult to justify the extra cost of synthetic ATF on a less expensive coach, so our suggestion would be to use a Dextron II or III, or an approved C4 oil.