Allison Transmission Talk

[Benjamin]

Do you know much about the HT-746? I've only seen a video of a Phantom school bus and someone said it had an HT-746 and it shifted like a Voith.

No, not much.

There are indeed, however, some HT740 series transmissions that are tuned to have second-gear start, which is why you hear what you describe on that Phantom schoolie. This 1986 01.508 operated by YRT (6V92TA MUI engine) also has its HT747 with the second gear start:

~Ben

Edited February 2, 2015 by Benjamin

[Detroit Diesel 6V92TA]

No, not much.

There are indeed, however, some HT740 series transmissions that are tuned to have second-gear start, which is why you hear what you describe on that Phantom schoolie. This 1986 01.508 operated by YRT (6V92TA MUI engine) also has its HT747 with the second gear start:

~Ben

Oh okay.

Wow, it sounds odd to hear it do that. It's like it skipped the first gear. I'm not exactly sure if SamTrans' 2003 Gillig Advanatges' Allison B400Rs are set like that, because I hear the B400R shift, but the Series 50 keeps on a high govern until it shifts a second time.

[Detroit Diesel 6V92TA]

Was the Allison VH the only transmission available for all models of GMC Old Looks and even the Yellow Coach Old Looks?

[tomsbuspage]

Was the Allison VH the only transmission available for all models of GMC Old Looks and even the Yellow Coach Old Looks?

Far from it.

While the Allison VH transmission was the standard automatic transmission offered on heavy-duty (32 seats or more) starting in 1949, and to the best of my knowledge it was the only option, earlier buses were offered with a Spicer Model 90 or 91 angle-drive torque converter. In fact, transversely-mounted engines with angled transmissions were first offered on the Yellow Coach 718 starting in 1934.

Light-duty buses (27- and 31-seat versions) used GM's exclusive Hydra-matic transmission, while the later 35-seat Old Looks of the 1960s used an Allison T-drive automatic transmission.

Finally, bus companies who specified manual transmissions, largely due to cost during the Yellow Coach era and speed limitations after the Second World War, received buses equipped with Spicer Model 7141 4-speed mechanical transmissions, though light-duty city buses were offered with 3-speed transmissions during the early years of Old Look production.

[Detroit Diesel 6V92TA]

Far from it.

While the Allison VH transmission was the standard automatic transmission offered on heavy-duty (32 seats or more) starting in 1949, and to the best of my knowledge it was the only option, earlier buses were offered with a Spicer Model 90 or 91 angle-drive torque converter. In fact, transversely-mounted engines with angled transmissions were first offered on the Yellow Coach 718 starting in 1934.

Light-duty buses (27- and 31-seat versions) used GM's exclusive Hydra-matic transmission, while the later 35-seat Old Looks of the 1960s used an Allison T-drive automatic transmission.

Finally, bus companies who specified manual transmissions, largely due to cost during the Yellow Coach era and speed limitations after the Second World War, received buses equipped with Spicer Model 7141 4-speed mechanical transmissions, though light-duty city buses were offered with 3-speed transmissions during the early years of Old Look production.

Wow thanks. So from 1949 it was standard while pre-1949 it was the Spicers.

I did forget about the Allison AT series and hydramatics.

Maunals were all Spicers?

Also, do you know the engines used for diesel models outside of the Detroit Diesel 6-71? I know the 4-71 was used in certain models, but which ones? As for gas models, (TGM and TGH) do you know which engines were available?

Sorry for asking so many questions, but I wanted to take note of this info to add to the wiki for GMC/Yellow Coach Old Look specs. Thank you for the info from before.

[Benjamin]

Wow thanks. So from 1949 it was standard while pre-1949 it was the Spicers.

I did forget about the Allison AT series and hydramatics.

Maunals were all Spicers?

Also, do you know the engines used for diesel models outside of the Detroit Diesel 6-71? I know the 4-71 was used in certain models, but which ones? As for gas models, (TGM and TGH) do you know which engines were available?

Sorry for asking so many questions, but I wanted to take note of this info to add to the wiki for GMC/Yellow Coach Old Look specs. Thank you for the info from before.

The 4-71 was used in the 3610, 3612, 3714 and 4008 models. I suspect the 3-71 was used in the 3207 and 3209.

~Ben

Edited April 28, 2015 by Benjamin

[tomsbuspage]

I forgot to mention the General Electric propulsion motors installed on the Yellow Coach TDE-4001, 4002, and 4005 buses ordered by PSCT of New Jersey between 1940 and 1942. Also, the first Old Look buses to be equipped with the VH torque converters were the TDH-5502 buses for the Chicago Motor Coach Co., followed by the TDH-4510 buses for the New York City Board of Transportation. After that, the VH was installed in the TDH-3209, 3612, 4010, and 4509 buses.

I got almost all of my information out of Old Look Buses: Yellow Coach and GM in the '40s and '50s by William A. Luke and Linda L. Metler, and Welcome Aboard the GM New Look Bus by John M. McKane and Gerald L. Squier. According to those two books, the smaller diesel-powered buses used 4-71 engines, while the larger buses used 6-71 engines. The smallest of the Yellow Coach buses, the 24, 25, and 27 series non-Old Look buses, would have used 3-71 engines, or even 2-71 in the case of the tiny TD-2401. These buses all had mechanical transmissions, with the automatic transmission being available on the monocoque-style buses starting with the TD/TG-3201.

Gasoline-powered buses used 270 cubic inch engines in the 27 and 31 series Old Look buses, 451 ci engines in the 32 and 36 series, and 529 ci engines in the 40 and 45 series buses. These are described as a "variety of GM six-cylinder gasoline engines [...] chosen on the basis of coach size and customer preference." GM stopped offering gasoline engines in its heavy-duty buses in 1948, though they were the only engines available in the light-duty buses between 1949 and 1963, after which the Toro Flow diesel engine began being offered in the TDH-3501.

As for the mechanical transmissions, the Spicer 7141 was the predominant transmission after the Second World War, and it was the same transmission that was used in the highway coaches of the time. The tables in the books didn't specify which company made the 3-speed transmissions, nor did they specify which models had this option. Lastly, mechanical transmissions were not available on the 27, 31 and 35 series light-duty buses.

[Benjamin]

T-drive transmissions in heavy duty buses didn't really take off until the Orion I and Gillig Phantom were success stories in the late 1970s and early 1980s respectively. In late 1982 Orion followed Gillig in cataloging the heavier-duty Detroit Diesel 6V92TA engine and Allison HT740 (HT747 in 1983) transmission.

~Ben

[Detroit Diesel 6V92TA]

T-drive transmissions in heavy duty buses didn't really take off until the Orion I and Gillig Phantom were success stories in the late 1970s and early 1980s respectively. In late 1982 Orion followed Gillig in cataloging the heavier-duty Detroit Diesel 6V92TA engine and Allison HT740 (HT747 in 1983) transmission.

~Ben

Seems like the only place you could find an HT-740 before the Phantom was in those 8V71N MCI MC-Series buses. Other than those, I haven't seen any HT-740 usage in buses before the Phantom.

[Benjamin]

It would appear the Allison ATEC electronic controls was originally exclusively a feature for the V731 and VR731 V-drive transmissions when the feature was introduced in 1983 (as 1984 models). The HT & MT series didn't have ATEC until 1984 (1985 model) and 1986 (1987 model) respectively.

~Ben