Transformation

Adapting Contemporary Transmissions to Vintage Engines

Author: Ron Ceridondo

There's a lot to be said for building a custom rod with an original engine. First and foremost, it beats yet another small-block Chevy swap. But there's another big reason that many of these engines don't need to be given the heave-ho--there's nothing wrong with them in the first place. Most can be made reliable as an anvil, and many have excellent performance potential to boot. Vintage powerplants such as Hemis, Cads, Olds, Buicks, and yes, even the venerable Ford Flathead V-8s and inliners (such as Buick straight-eights and Chevy sixes) can provide all the motive power a custom rod will require. The real problem with the running gear in most custom rods isn't the engine; it's what's behind it.

Early automatics were often referred to as slush boxes, and phrases coined in the day, like "slip and slide with Power Glide" and monikers like "Dynaslow" were not terms of endearment. For the most part, '50s and '60s automatics offered disappointing performance, and they haven't improved with age. The only thing that's changed is they've become much more expensive to rebuild.

Of course all custom rods aren't equipped with automatics; on the other side of the fence are the manual transmissions of the era. And in some respects they're not any better than the auto-boxes of the time. Back then, standard-shift boxes generally had just three forward speeds, with syncromesh on the top two cogs only. And it you think parts for vintage automatics are expensive and tough to find, try coming up with some of the more rare stick shift components. But look at the bright side--keeping that vintage engine doesn't mean you have to be stuck with a lousy transmission. Today, there are a variety of options. Transmission swaps have always been a part of the automotive hobby, but now it's easier than ever with the wide range of adapters available.

When selecting an adapter, there are a host of considerations to be made. First off is space; is there room for the transmission you want to use? With manual transmissions, the location of the shifter has to be considered. On some five- and six-speeds, the shifter will end up under the seat unless the stick can be moved forward. For automatic transmissions, a custom flexplate may be required, while manuals may require a custom flywheel. In addition, stick shift adaptations may require pilot bushing adapters, combining clutch components, as well as special throwout arms and bearings (a hydraulic throwout bearing often solves a variety of problems). And, of course, there is the starter to be concerned with. In some cases the stock starter will work; in others a substitute will be required. All these items should be addressed when selecting an adapter. Let the transformation begin.

ADAPTER ADVICE
By Pat McGuire (Wilcap Company)
The biggest thing to keep in mind about adapting an engine to a transmission is that it's a big project. In a lot of adaptations, everything from the radiator to the driveline has to be changed. If you're building from the ground up, then you're ahead of the game as long as you start out with the engine/trans assembly and work from there.

Although many builders prefer to use the same make engine and transmission, from my point of view, the transmission should enhance the engine just like the induction system or exhaust. That means bolt in the best transmission for your application, and that often means adapting a contemporary overdrive automatic. The most popular adaptations are the various GM automatics, with the 700-R4 being the most common. (However, for the purpose of bolting the engine to the transmission, there is no difference between the 350 or 400 transmissions and the 700-R4.)

Another option is one of the modern four-, five-, or six-speed manual transmissions. Whichever one you pick, keep this in mind--the adaptation of the engine to transmission just got twice as complex when you go to a manual transmission. The reason is that if it's done wrong, a manual transmission adaptation is downright dangerous. I strongly urge anyone who is doing a manual adaptation to do two things: 1. Never use a spacer between the crankshaft and the flywheel. 2. Buy an "explosion resistant" (no such thing as explosion proof) bellhousing or, at the minimum, a scatter blanket. Why the caution? The first time you miss a shift and the tach goes off the scale, you're going to find out one of two things: 1. You did a good job on buying, assembling, and installing your adapter, flywheel, clutch, and transmission. 2. You might get to find out what 30 lbs of steel sounds like exiting the bellhousing at an equivalent speed of about 290 mph. An automatic transmission is a safer design. The front hub of the torque converter rests in the end of the crankshaft or in the hub spacer if it is an adapted assembly, and this "captures" the torque converter. If a failure does occur, it is not likely that the torque converter is going to escape the bellhousing.

If the adapter is a "plate" type adapter, then the flywheel needs to be fabricated for that particular adaptation. The extra length that the plate adds between the crankshaft and the input shaft should be made up by the thickness of the flywheel. This doesn't mean that the flywheel is heavier than stock, just that the contact surface of the flywheel is closer to the input shaft. The other factor with a manual transmission adapter is the transmission-to-bellhousing alignment. If the input shaft of the transmission and the crankshaft are not in line or concentric, the resulting "bind" will cause the input shaft to continue to rotate with the clutch engaged, the transmission will be difficult to shift, and the syncros will wear prematurely. More importantly, the resulting bind on the friction disk will cause it to drag and wear at its outer edge prematurely and could cause a failure to the hub (center plate) of the friction disk.