Planet rebuild kits are readily available from Allison.  I would think Ti or Gama TiAl would be the way to go for the planet carrier. Better fatigue resistance and lighter than the steel. There is one transmission that has a 3.5:1 low gear without being compound. I think it is a MT640.
Dale Davies

If you could get some pictures of those parts I would love it.
Would they sell one planet gear and shaft?

That would cut the cost as the complete planet carrier is expensive.

Paul Lamar

The Allison MT654CR has a 4.17:1 first gear reduction ratio.

Does max input power play a role here?  The MT640 is rated for a maximum 250 HP and 640 lb-ft.  The MT654CR is rated for 300 HP and 780 lb-ft.  A newer Allison HD4070 is rated for 465 HP and 1465 lb-ft of torque.

The parts are far more expensive for older transmissions like the 640 and 653/4.  A modern Allison 2000 P1 gear set from a Chevy Silverado (3.51:1) is $320.11 from my local Allison dealer, vs $880.50 for the same set for the older MT653.  From a junkyard, a Chevy Silverado transmission is $100 if you pull it yourself.

Dave Klingler

Power is a function of RPM. When designing a gear box torque is the main criteria.

Those ratios are not representative of the planet carrier alone. They are combined from
several gear sets. I would need pictures of the parts looking straight down with the
planet carrier sitting on a bench top or on the floor.


Paul Lamar

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