Curbside Classic: GMC TDH-5105 Old Look Transit Bus – GM’s Greatest Hit #9 Despite Being the Agent of a GM Deadly Sin

(first posted 4/3/2012; updated 6/28/2020)

The GMC “Old Look” bus was first made in 1940, and was phased out when the “New Look” buses arrived in 1959. They utterly dominated the bus market with their advanced features and superb ruggedness, and rightly earned them a Greatest Hits designation. Unfortunately, part of their dominance was the result of GM’s concerted efforts to wipe out hundreds of electric street cars and light rail systems throughout the country and replace them with buses, as well as to monopolize existing bus systems. A Deadly Sin, one for which GM was convicted in 1949. By that time it was too late anyway; the damage was done, and the ultimate outcome may well have played out the same without GM’s meddling.  But even without that blemish, these buses were by far the best of their kind. And having had the pleasure to drive them allows me to give a comparison with the newer ones.

Yellow Coach, a subsidiary of GM before it was fully absorbed into the GM Truck and Coach Division, was a pioneer in modern bus design. Their Model 719 highway bus of 1936 set the template for all buses since, being the first to have aluminum monocoque (unibody) construction and a transverse diesel in the rear. (See CC here).

Yellow/GM adapted these significant design principles to their transit buses, the result being the 1940 transit bus series that came to be known as “old look” buses. There were a bewildering array of sizes and variations in this range of these buses, and the last was not built until 1968. In the very first two years, they had flat front windshields, like this 1940 TH 4502.

But the reflections at night on the windshields were bothersome to the drivers, resulting in the familiar slanted windshields of all the subsequent versions.

They ranged from 25′ (this is a 28′ TG-3205) to a few rare 41.5′ long models, but the two most popular sizes were the 35 and 40 footers, in either 96″ or 102″ width. Our featured bus is a 40′, 102″ wide TDH-5105. Their naming system starts with T for transit, then either D for diesel, or G for gas, and after the automatic transmission came along, an H for hydraulic, or M for manual. The first two numbers stand for the nominal seating capacity. Now you’re an expert.

Since buses are just buses for most folks, let’s take a look at some of the distinctive features that made these so successful and legendary. The first stop is in the engine compartment.

Since this bus has a split rear door, we can’t see the Detroit Diesel 6-71 engine in its entirety. For a more detailed description of its history and operation, I refer you back to the GM Coach Silverside” CC. Suffice it to say, this family of engines, which first appeared in 1938, operates on the two-stroke cycle, but with exhaust valves in the head, in what is called the “Uniflow” system. That requires a blower to fill the cylinders with fresh air and exhaust the old. These engines have the reputation of being “screamers” because they sound like they’re revving so high. That’s just because like all two-strokes, they have twice as many power strokes per revolution. These engines develop maximum power at between 1900 and 2300 rpm. But the sound is unmistakable.

The shorter diesel transit buses used the four-cylinder 4-71 engine. And there was a related family of GM buses that were designed for lighter use, and had GMC six-cylinder gas engines and Hydramatic transmissions.

Here’s the right side, or output end of the engine, and a limited view of the Allison V-Drive automatic transmission, which is angled in relation to the engine and bus.

Its configuration was based on the Austin angle-drive patent of 1932.

Here’s another view of the V-Drive, but still partly hidden. The actuator that engages Forward and Reverse is prominent here. Anyway, the Allison V-Drive was a huge step forward for transit buses. Most transit buses before its arrival in 1949 still used a manual four-speed transmission, which highway coaches kept for several more decades, due to its much greater efficiency. But the shifting of the non-synchronized transmission was grueling, especially given the 40′ linkage that it entailed. It’s hard to imagine now, the endless double-clutching and shifting, given the stop-and-go cycles of inner-city transit bus operation.

The Allison V-Drive has a wide-range torque convertor, which allowed the engine to spool up to almost maximum rpm on full-throttle take off (almost the only kind). Depending on gearing (and to some degree on the whims of the particular transmission), at somewhere between 25 and 35 mph came a powerful clunk/lurch into direct drive. The reason it was so noticeable, is because top gear was a direct mechanical connection; the torque converter was locked-up or bypassed, for efficiency. That meant that the engine dropped quite a bit in the rpm band, and any further acceleration was leisurely, to say the least. Top speed on transit buses was roughly 45 – 50 mph.

Like the later “new look” buses, these also came in “Suburban” versions, used for longer routes and highway use. They lacked a rear door, had larger windows, and coach-type seating throughout. They had a higher highway top speed (60-65 mph), as they used the VS2 version of the Allison, which had a planetary overdrive on the input shaft that engaged automatically above a certain speed. A manual transmission was also still offered on these.


The other huge step forward was GM’s air suspension, which arrived on these buses in 1953 or so. The transformation was quite startling, in terms of ride quality. In order to carry such heavy loads, the leaf springs on the previous buses had to be very stiff, and unless well loaded, the ride was quite harsh.

Here’s a look at the rear suspension (looking forward); the air bags are very visible, as is the drive shaft.

And here’s the front end. The trailing control arms (two sets) are visible. Like most air suspensions, they leak. When I used to start my bus up in the morning, it would magically rise from its low-rider position, like an inflatable toy.

During my short bus-driving career at Iowa City Transit (1975-1976), the system had all new look buses except for one ancient 1948 40′ bus like this one, as an emergency backup if one of the newer ones broke down. As such, it had the leaf springs and a bone-jarring ride when empty. And during the winter months, the system rented a handful of 40′ air-ride “old-look” buses to handle the crush of passengers on the busiest routes by switching to higher-frequency service.

I’ll never forget my first drive: it was downtown, and I was relieving a driver for the afternoon shift. Compared to the picture-window “fish-bowl” buses, this thing was like climbing into a submarine. The visibility was drastically reduced, especially if one was tall. I’d have to hunch way over and peer up to see traffic lights.

And although they were supposedly made of alloy like the newer buses, the old ones felt much heavier, more ponderous, and sluggish. Well, the 35 foot New Look buses were smaller, lighter and more powerful, so it’s not surprising that they felt almost “sporty” in comparison. But I got used to the old tanks, and before long, was whipping them around, although that expression seems a bit of a stretch. More like it was whipping me around; these U boats were a handful.

This bus has been converted into a mobile restaurant of some sort, but wasn’t open. Let’s see, what would be the appropriate food to serve in a bus? Seems like a french fryer would have to be on board.

Here’s how it would have looked back in its day hauling passengers.

And haul they did. I used to ride these quite a lot in Baltimore when I’d hook school. The #8, went right from the courthouse in Towson down York Road into downtown. I have some colorful and zesty memories of those rides.

I was a bit surprised to see them still serving the main lines in Los Angeles, probably right into the early eighties. Must have been the climate. Most of these buses served at least twenty years in front line duty, up to thirty or more, testament to their structural integrity, which was probably never surpassed.

the past and the future; or vice versa?

Speaking of Southern California, it was one of the more contentious areas where GM (and some other “partners”) played a role in the downfall of the high-speed regional Red and Yellow Line light rail systems that were once the envy of the world, as well as the transit planners of today (part of the Red Line has been rebuilt at great expense).

I’m not going to go into the whole story here, as it’s complex and can’t be done justice in this space. And there’s no question that GM doesn’t deserve full credit for the whole huge transition away from the electric trams that once served almost every city and even smaller towns. But there is no question that GM deliberately undertook and participated in a number of schemes to convert rail systems, and monopolize existing bus systems, with the goal of selling more buses.

The more nefarious theory is that GM really wanted to sell more cars, as the buses increasingly were swallowed up in the rapidly congesting surface streets, instead of the dedicated rights-of-way most regional rail systems enjoyed. This was particularly so the case in Southern California. Obviously, it wasn’t as simple as that, as folks were spreading out rapidly after WWII, and the still-private and declining rails systems lacked the required capital to expand, since no public funds were then involved, for the most part. Bus service, even a mediocre one, was relatively cheap to implement, wherever the new roads were built. Wiki has a story on it here.

Agent of change or faithful servant, the old look GM buses did what was asked of them, and then some.

Related reading:

 GMC Coach “New Look” transit bus

GMC 3501-3502 “Old Look” Lighter Duty Transit Buses

GMC “Old Look” Trolley Buses

Many more in CC’s Bus Archives