[gumby79]

Originally Posted by slowmover

The expense of an automatic is why I’d still choose a manual. New, used or a rebuild.

Can’t remember why you have an auto. I’ve probably asked and you’ve probably replied.

AFAIK, it’s only the later 6-speed Autos that are trouble-free as to normal power-handling. They’re not cheap and probably require computer control.

The G56 Manual has been used in the CTD since about 2007. The NV5600 in mine is well-liked, but now long out of production. A crapshoot on a core plus parts.

My truck is 3.73-geared. With a junkyard axle swap it could be the current 3.42. That’s one long pair of legs.

With 3.42, stock tire height and the .73 OD, 60-mph is a hair above 1,500-rpm on mine with the 5600. Redline is 2,900. Room to grow.

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why? It was the original trans from 91.5 and has a higher .69 OD 2.44 final(gear X OD= final engine to tire ratio) than the NV 4500 w/ .75, and the 5600's were hens teeth of solid gold when I got the truck + a clutch can cost more than a auto rebuild , dropping to a .74/ .79 OD and further below peek TQ. Is your 56 the .74OD 2.76 or the .79OD 2.94 final single OD? Slow can saves fuel but has PTSD side effects for me (I ran the rear gun truck /emergency MacGyver in Iraq) and safety are trump cards for me. when in heavy traffic slow can be extremely dangerous. Not my fault if they were not paying attention but driving 20-40 mph off the pace can get me and them killed. 26.xmpg 1 tank @70 ~1846 rpm +- TQ slip from Albacurky, NM to Las Vegas, NV on I40 is respectable and can be improved upon.

06+ Allison 6 speeds have a 500+TQ rating would be my preference for auto or Tremac Magnum XL 700TQ w/.74 2nd OD.50 but sourcing a bellhousing for either is difficult. Called Tremac they said they would be interested in buying the custom designed bell housing blueprints if I could make it work. as of that phone call none had been successful in mating there product on a B-series , but assured me it could handle any thing my ve pump could throw at it at max load or on the salt . ive heard of a tremac behind the v10 viper the skuttle but was that it had nearow gears that wouldn't handle the diesel TQ.

The allison SAE 2/3(gota mesure after its out of the doner) bell is getting sorced from a 97 MT-45 Freightliner motor home chassis with melted pistons 160/400 p-pump Cummins (timing cover is coming as well for a later p-pump swap) it is coming with a mt545 4 speed direct. Means going from 2.44 final(96 max 2500 red line) to 3.55:1 (65.01 max 50@2000) not accounting for the demonstrated 6% loss from non-lockup on the 46RH. With plans for the $3-6k trans +$2k controler+$1.2k TQ converter 6 speed($6.2k-9.2k). after the family emergency is handled .

My dad an OLD school trucker, over 45 years behind the wheel, is convinced:1)he can get a set of 2.44 or 1.95:1 gears for my rear end that will be tow worthy. will require 2)that tall gears and a direct box is the best combo for MPG . He said this was proven by Swift that the extra drag from the OD gear set consumed more than the tall rear , the best I have found was 3.23 or 3.08 with a rear swap to a early 1st gen or custom 9"dana 60. He said less than a .75 OD brownie from Gear Venders. or the OD shaft X2 for the 2 US Gear under/over boxes I got from Sky king. Gear Venders rep did some calculations and said that 2 boxes in OD + internal OD on an empty truck would brake stuff at my current power(this was before the dyno said the #'s are bigger and at different places).