On Pinions & Gear Sets: The Thunderjet “Drag Pack”

It seems clear to me that there was some sort of relationship between Aurora and Ford, at least in the early years of the Thunderjets. The very name of the slot car platform was used by Ford as a nickname for one of their 429 engines (of course, both likely cribbed the name from the F-84 post-war jet fighter). We also know that a large number of the early T-jet bodies were models of Ford cars: they made a Mustang, a Falcon, a Fairlane, a Galaxie, and a Thunderbird, all in those early years.

In 1969, FoMoCo offered a discrete option, rarely discussed, for those “in the know” who wanted race track performance in a street car. If you were buying a Mustang Boss or Mach 1, a Torino Cobra, or a Mercury Cougar Eliminator, whether you wanted a manual or an automatic transmission, you could check a little box for an option called the “Drag Pack.” This little box got you a tire smoking rear gear ratio (from 3.91 all the way down to a stump-pulling 4.30 if you also checked the box for the Detroit Locker axle), but unbeknownst even to some enthusiasts at the time, it did a lot more than that. If you were ordering a big block-powered car, checking that little box essentially got you a whole different engine! Because, ordering the “Drag Pack” option automatically turned your Cobra Jet into a Super Cobra Jet, which included, amongst other things: four-bolt main bearings, forged aluminum pistons on heavy-duty connecting rods, a solid-lifter camshaft with an aggressive profile, a Holley 780 cfm carb, an oil cooler, and header-style exhaust manifolds. WOW! All that for only an extra $155??? What a deal!

All of this makes me wonder if some of the marketing guys at Ford were racing slot cars in their free time, because before Ford offered the “Drag Pack,” Aurora offered the “Hop Up,” and, later, the “Tuff Ones.” So, what’s the connection between the toys and the real thing? It’s all about the gears, baby!

This post started with my own observations as I acquired and built these Aurora chassis, and then went to our brave new world’s sum of all knowledge: from that, I’ve learned that there were 3 gear ratios available “from the factory” for original T-jets; the original standard 9-tooth pinion, the “Hop Up” with 12 teeth, and the ultra-low 15 tooth pinion of the Tuff Ones. Each of the 3 came with a matching ring gear-or “crown gear,” as they are commonly called. Contrary to what I instinctively thought, the crown gears were not different in either tooth count or diameter; the difference was in the depth of the “collar” on the back of the gear, which influenced its position on the axle: obviously the bigger pinion needed more clearance.

Aside from the obvious-the vastly improved acceleration of the lower gearing, changing these gear ratios affects the car’s performance in other ways as well. Principally, I’ve found the lower gear makes a tremendous difference in braking ability; the cars slow much more quickly when letting off the juice, a huge performance advantage. In the case of the Tuff Ones, this braking ability is almost too extreme, although, once mastered with practice, it can be utilized to make a Tuff One almost unbeatable. When it comes to speed, however, it makes sense that it is the stock pinion-the smallest one-that seems to offer the highest top end speed on long straights.

So far in my limited experience with these older cars, I like the middle size-the 12-tooth “Hop Up” Pinion-the best, which gives the best blend of performance; you get better standing pick up and braking and, it seems to me from the cars I’ve built so far, more controllable torque when accelerating out of a turn. The “hop-Up” was a really cool package from back in the day when really cool things like this were not uncommon: sold in a small cardbox box, it consisted of some decals, a little jar of oil, and some replacement parts, but the most significant part of the kit was a larger rear drive gear pinion and crown gear to match; unlike the decals, this made a real difference in a T-jet’s performance.

Fortunately all these parts are still around, although some are definitely harder to find than others-and thus more expensive. The Auto World Ultra G’s, for instance, have a crown gear almost identical to the Tuff Ones in terms of backspacing, and these can be easily bought brand new right from Auto World. The pinion gears are more difficult to find, but they do show up frequently enough on ePay. It is the crown gear for the Hop Up pinion that seems to be the hardest part to come by, at least for now, but you never know when someone might start making them, especially the way these vintage slot cars are selling now!

As to how to install different pinion gears so that you can alter the ratio of your existing motor, well, that requires some skill and at least 2 rather specialized tools. But working on cars often does! That is a story of its own, which will be the subject of another post at some point in the future!