Packard Forum Index » Post-War (1946-54)

Back in the day did people put overdrive on their cars with Ultramatics? Was there an overdrive designed to work with the Ultramatic? Curious more than anything.

I don't remember ever reading of any kind of overdrive that could be offered for use with a standard automatic from any mfg. Not because you could not install some kind of add on unit to the drive shaft but more because most if not all automatics have functions that depend to a large extent on speed or governor dependent hydraulic pressures for proper operation. There is probably someone who tried but I would think adding a separate overdrive that would change car or engine speed after the point where that carefully calibrated hydraulic pressure was produced could cause all kinds of shifting problems. Don't believe there was an overrunning or OD gear available on an automatic until the advent of the Automatic OverDrive transmissions in the 1970s or 80s.

An overdrive would mostly work with an Ultramatic. Engaging a 0.707 overdrive at, say, 70 MPH would make the transmission "think" that you were climbing a slight hill at 50 MPH. No big deal.

There are two problems though:
- The driver would have to be careful to disengage the overdrive when driving at demanding, moderate speeds. For example, in a manual car if you were driving up a long, moderate hill at 55 MPH, you might be OK in overdrive, and in an Ultramatic, you would stay in direct. But if you left the overdrive engaged, the Ultramatic would see the 40 MPH car speed and heavy throttle as a reason to go into converter drive. This will heat up the transmission resulting in more wear and poor fuel economy, as the the transmission and OD are working "against" each other (the converter drops the ratio and the OD then raises it) instead of both being in direct.
- Traditionally an overdrive will kick down if you floor it. But an Ultramatic will do that too. The Ultramatic engineers purposefully set the kickdown limit at about 50 MPH to keep things from getting too crazy, but this value would change to 70 MPH in overdrive. So let's say you're on the freeway in OD and you hit a huge hill so you floor the gas to get up it, keeping up with traffic. Congrats, you went from 0.707 direct to 1:1 converter drive at 70 MPH. And in a Twin-Ultra, now you are in 1.82:1 converter drive at 70 MPH which will surely test the limits of your engine regarding angular velocity. Probably would get a fair amount of low range band slippage in there too just for fun, since the torque application to the band would briefly oppose the servo direction.

So such an installation would have to accompany a knowledgeable driver, and the kickdown feature on the OD would have to be disabled.

Overdrive is not used with automatic transmissions of the 1940s/50s/60s/70s. Automatic-equipped cars of that era were equipped with "high speed" rear axle gears, and they depended on the torque converter for snappy take-off. Transmission gear ratios were adjusted also, in order to allow for a "passing gear". Adding an overdrive unit would offer little or no benefit and would defeat the engineering that went into the original installation.
Cars originally equipped with a manual transmission and overdrive usually had a lower geared axle than was used with the manual only.

Thanks guys for the replies! What got me thinking about this is listening to guys that want to swap out their transmission, or rear-end, so they can cruise a little faster. (I think there is a Chrysler transmission that is a popular choice.) Or they have had troubles with their Ultramatic, got frustrated and swapped it out for something else.

My 53 Cavalier feels pretty comfortable around 60 mph, and I'm never in a hurry to get anywhere if I'm driving my Cavalier! Not to mention I'm not interested in modifying my car to fit a non-original/non-Packard transmission.

What I have found with my car is, it's best to not deviate too far from Packard's original engineering.

I think going to one of the late 70s to early 90s GM V8 automatic overdrive transmissions such as the 700R4 or comparable later series is about the only commercial option now. Bendtsen makes the adapters for both straight 8 and V8 cars. A Chrysler TorqueFlite was the first available conversion and choice for several years but AFAIK, no one makes adapters anymore and finding the proper year trans is also getting hard.

The problem with the first-generation 727 adapters made by Sierra Grove Packards in California (which were the most common ones) was that the adapter plate did not have eccentric locators to allow for runout between the 727 and the engine. Since there is also essentially a spline adapter between the engine and input shaft, the runout gets magnified over distance.

The 727s used eccentric locators on the Chrysler engines.

Sierra Grove released a later version of the adapter plate with eccentrics, but it was only available for a short time before they stopped offering the conversion kit altogether.

You can calculate your engine RPM in high at 60 MPH pretty easily. I think you'll find that it is moderate, and well within the engine's operating range. If you were to remove to the automatic and replace it with a manual/overdrive transmission and appropriate rear axle ratio, you'd get better MPG under most conditions, but the '53 with an automatic ought to have pretty good gearing for highway operation as-is, assuming it has the standard axle ratio for the engine/transmission it was originally built with. I don't think it would be worthwhile to change the automatic for an OD/manual unless the automatic is in bad condition, or unless you just prefer a manual. I'd avoid putting undersize tires on any older car. I'd stay with the correct original tire's overall diameter, or just a little more, never less.

I'd want to be sure the original auto trans was in good working order with clean filters and the correct fluid level. Some transmissions are very sensitive to improper fluid level or incorrect fluid level checks procedures.

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A lot of people like the 288 engines since they rev higher and don't mind the interstate. Downside is a bit more shifting at lower speeds because you can't lug them, compared to the 327 in a Cavalier.

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I saw recently that the tooling for that is for sale. Think it was in one of the news bulletins.

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True. On the V8 cars the rear end ratio made it where Ultramatic direct lined up with being "3-1/2"th gear on an OD car. In other words, the driveline ratio was right in between 3rd and OD.