I have not really come across many 15 speeds in newer trucks. I remember a few with the big gear towards the dash, but mostly with the switch on the dash for deep reduction.
Eaton discontinued the 15 speed because of being able to handle the high torque output of
electronic engines. There was no such thing as a double over 15 spd, never produced. 15
speeds became popular with otr's because a overdrive 15 in top gear with 3.70 drives dropped
the RPM to 1425 running a B model Cat, it was about mileage. It needed the deep reduction
for backing up. The direct 15 was there but it never sold like the 15 OD.
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8,9,10,11,13,15 & 18.
The 11 spd is a super reduction gear box 35.00 to 1, used mainly in spreading material.
It is a super slow gear box.
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Double overdrive, early on there were only three that were double overdrive, RT009513,
RT001113 & RT0014613, with a overdrive of .62. But the RTLO18918B technically is a
double over with 1.00 in seventh and .86-.73 in 8th. Although Eaton does not list it as
being a double overdrive.
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The 9 spd came in a wide variety of configurations, the strangest was the model with
backward shift pattern-like a OD 15 high was forward, 9spd B.
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Really the big change came when the RTLO's came out in early 90's, High Torques with
tapered counter shaft bearings in the rear section. The rear section was the weakest
piece in all because of ball roller bearings and the splitter for high range was at the
rear{back of case on the output shaft}, and it's design was not acceptable with pre-selecting.
When RTLO's were introduced the splitter was moved to the front of the back section and
intersected with a sliding clutch to the auxiliary drive gear {rear output gear on the front
section} which was 8 times stronger. Plus the counter shafts with tapered bearing were
shimmed for preload which took allot of slack out of the gear train.
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The other major change was adding the Halo oiling design. Instead of pressurized drip/spray
oiling of only the auxiliary output gear like on early designs, Eaton added the Halo { called
halo because it's a tube that goes around the input shaft at front of front case sandwiched
between case and bell housing. It is a tube positioned directly over the main shaft gear
cluster and sprays 50wt straight down on the gear sets.
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Not much to talk about with 8LL's, those were designed for mixers/dumps, and that's where
those shine.
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The 9 & 10 are a fleet spec transmission, for two big reasons. First weight-250 lbs less without
the splitter back section, fleets want standardized/simple/light weight trucks. Second there
is no extra air ops to maintain, less to get torn up.
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Torque ratings have increased to over 2,300 ft lbs torque, with 2 1/2" input shafts, clutch
ratings over 2050 Ft Lbs torque.
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Think about this--late 60's early 70's 1693 Cat with the rack screw pulled out, and lowly
RTO9513 hanging on it. That's all there was back then, my old partner in the shop {Gayle}
had 3 Pete's {2 cabovers & 1 conventional} with extremely fueled 3408's. A 12513 spd
would last about 150,000 miles on average before it became toast.
