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.........--- G-Force 101A Transmission Information---

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Some years back we decided on a G-Force 101A for Hooley's Studebaker and have been very happy with the choice. It offered the ability to run a lot of HP, a multitude of gear ratios that could be changed with the needs of the car and was fairly affordable, especially for a transmission that will do so many things.

I'd like to share the versatility of running the G-Force 101A where internal gear changes are fairly easy to accomplish and reasonably priced.

Please note that the 101 has had a number of versions over the year starting with the Tex 101. Some parts will interchange and some won't. To keep it simple what follows applies to the 101A (note the "A"). Always make sure you are buying parts that will work with the 101 you actually own. Also on that note as you will see I'd recommend buying the 101A and not the previous versions if you are running higher HP numbers. That will be explained further on.

First we will look at using one of the spreadsheets that you can find on this site ( HERE ) in conjunction with using the 101A and picking gears for your situation. If you just need more info about the transmission skip down the page a ways.

Why the 101A is such a versatile transmission for a Land Speed Car:

Above is one part of the spreadsheet I use. To the right under the double red arrows is a table of the different ratios available for the 101 (top right) for the drive gears (the gears that drive the countershaft off the input end of the main shaft--Input Drive & Cluster Drive). Also shown there to the left of the Input Cluster drive gears are the ratios for 1st, 2nd and 3rd (which can also be an overdrive 4th). Down to the right in that area are the Drive Sets we have and the 1-2-3 gear sets we have bought used for our two 101's (Stude & Lakester) that we can choose from.

Underneath the double purple arrows is where you input the gears you are using for the Input/Cluster and 1st, 2nd and 3rd. Those inputs will then automatically be posted to the left as 1st, 2nd, 3rd and 4th gears. So you input the gears, rearend ratio and the tire diameter and the spreadsheet does the rest for you. The area between the 2 middle blue lines gives you a quick idea of speed in gears and you can input any rpm's you want there for your combination.

The top left arrow shows that we have the present Ford 2.47 rear selected and that at 7000 in the overdrive 4th (yellow arrow) the car should be running 270 mph. These are the gears we are going back with for Speed Week but we will have the other gear sets with us. With the transmission out of the car you can change any of the gears in less than an hour. Getting it out of the Stude is not a fun job. I hope to make that much easier with the lakester.

The quick speed in gears at different rpms by the 2 blue arrows is nice but we need to look further down the chart for the telling information and this is something that most of the speed calculators don't give you...

Above we can pick any rpm we want for shift points and see the rpm there and the drop in rpm during the shift and the new rpm in the next gear after the shift. This can help to make sure you stay where you want in your torque/HP curve if you have that info.

Above we will shift at around 7000 for this example. 135 is 6982 rpm in 1st. We loose 2155 on the shift and end up at 4827 in 2nd. In second we would be shifting at 195 and end up at 5827 in the 1:1 3rd. The final shift would be at 230 and we now only loose 925 rpm with the .865 overdrive 4th dropping to 5947. Further down the sheet we would see that 7000 is about 270 mph, our immediate goal.

If that works then we could re-gear the transmission, staying with the 2.47 rear...

...with the gears we have on hand ending up with a .829 overdrive 4th where 7000 is 282 mph and 290 would be 7250. Notice we left the cluster drive gears as they were and only changed the 4th gear set.

The better plan though would be to build the 2.26 rearend we have talked about in this thread.

With it in the car we could again change the gears in the 101 from the ones we have and end up with a better 4th overdrive of .90 which would only give us a 10% rpm drop between 3rd and 4th instead of the 17% we had with the 2.47 rear gears. A 700 rpm drop on the shift to 6300 rpm. Now we have changed the 4th gear set and also the Input/Cluster Drive gears.

The G-force 101 is a great fairly low budget transmission for the salt and since it was used by NASCAR and now isn't finding barely used gear sets right now is a pretty easy and inexpensive deal compared to other transmissions out there and the spreadsheet makes it very quick and easy to do 'what-if' scenarios for different combinations of drive gears and gear sets along with rear gear ratios and tire sizes.

One last one.... the dream situation :-)

...changing 4th and the input/cluster gears. We have the gears for all of the above situations and more on hand. They cost anywhere from $50 to $100 per set used but hard to tell they were used.

In the lakester I'll run a combination for the 3 mile course, working on gearing for 175 at the 2 1/4 that hopefully will get the car qualified for the long course and then change to long course gears.

Other Info & Sources for G-Force Transmissions and Used Gear Sets:

New Transmissions -- G-Force North in PA and G-Force South in NC. We have mainly dealt with G-Force north but for no particular reason.

Refurbished Transmissions -- Also try G-Force North and South. Hooley's was a refurbished one from them and mine was one they were selling on E-bay which they do from time to time. If you see a 101 being sold by tt3rotor on e-bay he is one of the head guys at G-Force north and is how I bought the 101 for the lakester. He set it up with the gear sets I wanted and it was shipped right from G-Force north.

Both of our transmissions looked new when we got them and since they will install the gear sets of your choice that can save a lot of money vs. buying a used transmission and then having to buy individual gear sets and also wondering about the condition of the other parts. You will find that a lot of the used ones don't have the gear sets we want to run the salt. They are setup for road racing or drag racing.

If you get a transmission like we did the shifter will probably also be included in the price, ask for sure. They are not cheap if you have to buy them separately. Hooley's came with the Long H pattern shifter (Long Industries actually owns G-Force) and ....

.....I got mine with the V-gate (vertical gate) shown above. I'd recommend the V-gate as once it is in 1st it is just back and forth on the lever, no H pattern. This is for sure going to be better in the lakester since the transmission is way behind the driver. Hooley and I have both missed shifts with the H pattern. It is not a bad shifter it just you don't get a lot of practice at the salt and with the cage the way it is around the driver you also don't have the freedom of movement you would have in a more open car.

Used Gear Sets (all of the guys below are pretty knowledgeable about the 101 especially Daniel and Rick):

Oval Speed on E-bay -- 919-533-3246 Rick Boyd

Muscle Motorsports -- 704-948-1040

Daniel Powell -- 864-617-5483

Other Info: I'd for sure get the newer 101A's that have what is call the "full cuff" between the main shaft and cluster shaft as it is stronger than the older 101's with no cuff or a half cuff. From what I understand G-Force made the gears and some other parts for the older Tex 101 transmissions and then bought Tex out so now there is just G-Force. They have also made improvements to the transmissions like the full cuff. Daniel knows all the changes and I can help to make sure you are getting the right one.

One other item to consider is that the cluster shaft/countershaft can either be a splined shaft where 1st slides on the shaft or 1st gear is integral to the shaft. Try and get the transmission with a splined cluster shaft/countershaft where 1st gear slides onto it. That way you can run a 'taller' first gear than what is available if you are looking for a 1st that is integral to the shaft.

You can find the available gear sets ( HERE ). Notice you can set the transmission up with different input/cluster drive gears (top of the chart). To then see available ratios look down the chart under whichever input/cluster drive gears you have selected. The gear sets are then to the left side and show the teeth count on the gears with the gear that is on the main shaft to the left and the gear that is on the countershaft to the right..

The chart shows ratios for 1st gear. Those are the ratios you have a choice of when 1st is integral to the cluster shaft. If you get the splined shaft where 1st slides on you can go below that line and use the gears below there as a first gear. For instance you could run a M/S 33s -- C/S 21s gear with a Input 25 --Cluster 31 for a 1.949 first gear (what Hooley's 101A came with originally).

Andrews also made gear sets for the 101. The teeth are narrower but the hub part is the right thickness and one source told me that even though the teeth face is narrower that they are as strong or stronger than the G-Force gears. The teeth have a different shape and you have to use them as a set and determine the ratio by the tooth count on each gear. We have one set of these but haven't used them yet.

Gears with a "s" after them: Looking at the gear chart for the 101 ....

...you will see that some gears have a "s" after the tooth count. For instance above there is a 21 C/S and a 21s C/S gear available. You cannot mix these. You need to use the 27 C/S with the 29 M/S gear, bottom blue arrow, and the 27s C/S with the 28 M/S gear. The "s" gears are a special design to make sure they are the right diameter to work with the M/S gear. When you look at used sets they should come as a matched set. Be sure you are dealing with someone who knows that. The same for the Input drive gears at the top of the chart. They also need to be matched sets. Do not use for instance the 24s Input Drive gear with the 32 Cluster Drive gear.

HP Levels: G-Force rates the 101A at about 1000 HP on pavement so on the salt you could figure quite a bit more than that. We hope to find out how it works with HP levels up to 1500 HP in the Stude with the new twin turbo 572 BBC. More about the 101A ( HERE ). If you need more HP or more gears take a look at their 5-speed transmission. It is rated to 1300 on pavement but is quite a bit more money. I would of liked to bought one of these but it just wasn't in the budget. If I had the money my next big purchase would be a Winters Extremeliner quick change rear from Joe at Deleware Chassis Works.


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