Picked up a 1973 Kenworth tractor not to long ago with a fresh big cam cummins and a 13 speed rto 1213. Problem is that I,m cranking along at 18-1900 rpm at around 55mph. I tried looking up tranny specs for ratios but seems to me that rpm and road speed combined with 24.5r11 and 4.33 would give me a 1.00 ratio. If I try a .85 It shows 65 at same engine speed? I really would like to find another transmission that would allow me to do 65 or so at same or less engine speed and looking for pointers? Found a rebuilt rto 14613 on local cl just want to avoid being in the same boat.
Sounds more like a 5.38 rear gear. I don't know which transmissions had an OD top gear, so I'm no help at all, but I'm guessing that truck was built for logging or as a dump truck in mountainous ground.
If the truck pulls good enough that you don't need the low hole you could always turn it around to give you a higher final gear. Don't know exactly how it's done but I've driven before and after and it would probably get you where you want to be on the final ratio.
That rto is an overdrive tranny. The "o" in the model means overdrive. It must have some crazy low gears in it. Sent from my SPH-L710 using Tapatalk 2
tag on rear end says 4.33
I don't think that is what the "o" means...... If it was a overdrive it would have a B at the end ? Pj
I thought the 0 ment overdrive also. :beatsme
Roadranger nomenclature: RT: Roadranger, Twin countershaft RTO: Roadranger, Twin countershaft, Overdrive RTLO: Roadranger, Twin countershaft, Low inertia, Overdrive RTAO: Roadranger, Twin countershaft, Automated, Overdrive.
Almost sounds like you have a Direct 13 speed transmission or the rear end ratio on the tag is wrong.Like other membors have stated the"O" in RTO means overdrive. I had a customer with an 1982 Frieghtliner with RTO9513 and 4.88 rears on 24.5 rubber and the governor bumped out at 60MPH.Thats pretty close to where your at roadrunner81. Might double check rear end ratios. A helpful formula I have used to figure engine rpm............. MPH X axil ratio X 336 and divide by tire diameter= RPM'S . That formula works for a direct drive transmission .
Jack up one corner and count number of turns on the driveline to make one turn of the wheel.
You need a whole axle jacked up and wheels turning evenly to figure it like that. One wheel up will spin the spiders. Sent from my SPH-L710 using Tapatalk 2
R is for roadranger, T is for twin countershafts, O is for overdrive. Sent from my SPH-L710 using Tapatalk 2
You're right, my bad.
check those tags on drive axles-- I calc. 1900 rpm, with .87 o.d. (early 70's RTO 12513) x 4.88 = 56 mph 2100= 62 mph road speed calc. http://big-rig-road-speed-calculator.blogspot.com/2011/03/semi-truck-road-speed-calculator.html ISX
If you want more road speed i would find a nice air ride cut off from a late model truck with better gearing. dont know what your using the truck for but a set of 4.10's or 3.73's would be good for normal every day running down the highway use
No, it still works, you just have to divide by two.
Or this ^^ Sent from my SPH-L710 using Tapatalk 2
I'm running 4.42 gears with a .78 OD and 11R-22.5 tires and get the following: 55mph=1600rpm 60mph=1740rpm 65mph=1875rpm I think it is your transmission - having a .87 or .89 OD and not a "double" OD
I will try to jack up today, but did verify that both axle tags say 4.33 and dated 2001
With one wheel jacked up, turn the wheel TWO complete revolutions and count the driveshaft revs. We have a truck in our fleet with 4.56 rears and an 18 speed, runs about 1950 rpms at 65 mph.
Your transmission has a .87 overdrive ratio. The RTO 14613 has the same ratio. You need to find a late style RTLO 13 speed, or RTLO 18 speed, or any 9 or 10speed with an overdrive from from the 2000's or newer they will all have a .73 top gear ratio which will allow you to run 65 at around 1650 rpm.
update: after replacing tachometer and drive cable I'm running 1850rpm at 60mph, atleast according to speedometer. Tach kept creeping higher and higher, original cable was somehow to long for outer sheath putting load on tach. I guess i'm doing fine now, thanks everyone.