Medium and Heavy Trucks
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Hi, Welcome to JA! my name is ***** ***** I Will try to Assist you with this.
The first Thing that we need to do is to get the number off of the serial plate on your transmission.
The number usually starts out with FRO or RTO, RTLO, something like that, this number is ***** important in choosing what transmission to go with, secondly I would like to know what is the ratio of the rear.
Just so You know, before we go any further, you will have to cut your driveshaft down to make this work. The 9 speed is a shorter trans and the 13 speed is about 9 inches longer which means that your drive shaft will have to be shorter to accommodate a larger trans.
there is a kit available to convert a 9 to a 13 but only on 1 specific model trans made by eaton fuller.
This is why I was curious about your trans number.
The Fuller Convertible manual transmission operates as a simple 9-speed transmission, and can then easily be converted to a 13-speed to increase vehicle versatility and resale value at trade-in time
Depending upon your diff ratio, average cruise speed lets say 50 mph you would probably be at about 13 to 1400 rpm?
The 13 would bring you down to about 1150 to bring in fuel $$ savings.
you would loose a little bit of torque on the low side, but have plenty of top end in hills and pulls