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
I do not have photos of the parts. Local Allison distributor should
be accommodating. Just do not mention AC use. The MT654 transmission
is a 5 spd that has an extra planetary assembly bolted to the rear of
the case that gives the 4.17:1 ratio. That is compound through two
planetary assemblies. Not what you want. Some of the Allison
transmissions for the Chevrolet 2500/3500 trucks were designed and I
think manufactured by Allison and then turned over to Chevrolet/GMC
who then looked after parts, service and warranty.
These transmissions may be difficult to obtain individual planetary
components. When you move to the Allison transmissions built and sold
for medium or heavy duty truck applications they handle the parts
themselves. Those you can get individual components. For some of the
newer model transmissions they may have 3.5:1 first gear in one
planetary to go with taller final drives. Most of the new
transmissions also have one or two overdrive ratios.
Dave, have you enquired as to the cost and availability of the HD4070
parts? The MT 654 has essentially the same parts for the planetarium
that give gears 2 to 5 as the components in the MT 640 series
transmissions. The higher power ratings are achieved by having an
extra pair of clutch plates for more friction area.
New long haul engines are 500 to 600 HP. At 2100RPM they may be 1450
ft lbs, but where most are geared to run at 1300RPM they will be
450HP and 1800 ft lbs. That is where the higher cost can come in.
However if you can buy the planet kits as you can for the older
transmissions, the cost would come down. The sun and ring gears are
large and heavy and expensive. But if you want bullet proof high HP
capability that is what is required. When planet kits can be
purchased with the gear and shaft an AL or TiAl Gama planet carrier
can be machined to save weight.
The 2000 series from wrecker would be a good deal with the 3.5:1
ratio. That would allow 10,500RPM for takeoff or racing with a
3,000RPM prop speed. I doubt you could hurt the planetary set with
900ftlbs torque.
Dale Davies
When Paul asked whether the gears and shaft were available
separately, I figured googling and phoning the Allison dealer were
something I could do to help out. I didn’t ask about the 4000
series, but I did ask about the MT640, 654, 1000 and 2000. The 654
wasn’t in the system, but the salesman did show the 653.
It turns out Allison has a tough time looking up anything without the
serial number off an existing transmission. I was going to call the
factory and ask more questions, but I needed to go back to work.
Dave Klingler
There are several wholesale transmission parts suppliers in the US.
They will sell to you if you have a business. They also sell Allison
spare parts.
Make friends with your local auto transmission repair shop and get
them to order the parts you need. Some have a great selection of used
parts in good condition as well. I paid $100 for the Allison 3:1
planetary I have from an autoTX shop.
Paul Lamar
I was thinking about this topic again today. What about integrating
the planetary into the front housing, and running the water pump off
the reduced output? So you’d combine the billet front housing piece
with another milled piece to form the front. The planetary would
share the engine oil. Allison’s approved oil for the 2000 (the one
with the 3.5:1 P1 planetary) is 15w40 for heavy use. I think it’s 5w
for highway, but I need to verify that.
Dave Klingler
Good idea. I'll take a look at that.
The 2000 sounds heavy. The 1000 is already heavy :-)
Paul Lamar
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