Have Your Cake and Eat it Too – Bowtie Overdrive’s TH-700R4

By Tony Bonafide

Okay, so you just installed a set of 3.90s or more in your ride and took it out for a spin 15 minutes later you were refilling the tank because you discovered that your 462 is now getting 5 MPG and it’s running hot as Hades. Of course, when you finally got to the drag strip (4 tanks of gas later) you really liked the dig those new gears gave you.

What if I told you that you could have both – reasonable gas mileage and even better dig than your current TH350 or TH-400 AND those nasty big gears?

The problem that most of us face is that when we install big gears in an Auto trans car, we are stuck with three speeds and no overdrive. Those of you with 83-88 G-Bodies may have the TH-200 4R, but we all know that that’s a good solution until we make over 300 HP, then we are in trouble.

Well, I am here to tell you that a TH-400 level of sturdiness and overdrive is available, and on top of that the solution also offers a 3.06:1 super low first gear which launches your car like a Saturn Rocket – or is it an Olds Rocket. The answer is Bowtie Overdrive’s TH-700R4.

One of the big problems with TH cases is that there has been a BOP case and a Chevy case, meaning that all the research that Chevy racers have brought to the transmission table was usually lost because getting those guts in a BOP case meant tough luck. Bowtie fixed the problem by using a universal bolt pattern case, provided by Ultrabell, letting all GM people get on the Bowtie Bandwagon. Best, they removed the ears from the case which required one to tilt the trans when removing it from the car. Hooray!

And I can speak from experience about this transmission because I have installed the Bowtie TH-765R4 in my 1969 455 Cutlass flattop wagon and wow, this is the best thing since canned beer.

The TH-700R4 Described

Bowtie Overdrive supplies the 700-R4 and 200-4R transmissions reworked for performance use. For our discussion, we will be talking about the 700 and 765R, but much here applies to the 200; for those of you with G-Bodies with a small block, the 200 is more than enough transmission for you.

The 700 is supplied in level 1-4 makeup, with level one being the mildest and four being a full race piece. Contact Bowtie and they will recommend the right unit for you. Prices range from about $1000 to $1900 for the unit, a very reasonable price since you are buying the trans outright, with no core.

Level one is basically stock, but fully rebuilt transmission, and Levels three and four are race transmissions. The level two trans will handle a steady diet of around 450/500 hp and 400/450 ft/lbs. of torque, while level three is likely best for Big block Oldsmobiles. They will handle 650 hp and 650 ft/lbs. of torque. Level four will handle the same HP/Torque but are for extreme-duty high-stall converters in the 2600 to 3500 rpm range. As I said, talk to the people at Bowtie and give them your car info, and they will recommend the right unit for you.

Features I like:

  • “Ultra Bellhousing”. The Ultrabell housing is not as wide as the standard bell housing and will slide right up between headers and any exhaust system. The stock bell housing on a TH-400 or TH-350 has ears on the sides that hit headers and make it almost impossible to remove the trans without turning it on its side, as it will not fit between the headers.
  • The Bowtie Supplied Crossmember. When using their cross-member, you don’t have to pull the exhaust down to pull the trans if you ever have to. If you use the stock cross-member and modify it, you will have to pull the exhaust. The supplied cross-member has ends that bolt to your existing frame in the rearmost trans-cross-member holes and then they have center cross bar bolts to them. You can unbolt the center bar and remove it without pulling the exhaust. (See Pictures).
  • Ultra-low First Gear Ratio. Transmission builders say that it’s great to have the lower 1st gear of a 700R4 and use rear gears in the neighborhood of 3.08- 3.42 to get a good launch and great mileage, but the newer Camaro and Corvettes use the 700R and have 3.73 rear gears. They still cruise the highways at a lower rpm, so why not do the same in your muscle car and use a 3.73 or better rear gear ratio? The 700R’s 1st gear is 21% lower than the first gear a TH-350 and 23% lower than a TH-400. But with a 0.70:1 4th gear, (overdrive) with 3.91 gears, your final drive ratio in overdrive will be 2.73!

Installing the TH-700R4

I chose the Bowtie 765R which is the guts of a GM TH 4L65-E in a TH-700R case. This trans has more beef than the 700R. I got a great deal on it or I would have purchased a 700R level 3 trans. (See description of the levels below).

As I mentioned, you should use the Bowtie� transmission crossmember, mostly because it is two-piece and makes it easier to remove the transmission, however, you do not have to do that, but you will have to move the existing crossmember forward five inches, which may be impractical – especially if you are running headers.

Since the 700R4 is longer than a TH-400, you will have to shorten your existing driveshaft about 2.5″. If your driveshaft has one of those rubber insulators in the rear of it, you will have to have a driveshaft made. If you don’t, the first hard WOT shift will spin the driveshaft inside of itself.

The Uni-bellhousing eliminates the need for an adapter plate, so bolting the trans to the block is a no brainer. All other components are similar and in about the same location so things like the cooling lines can be made to fit, thou, as I did, you may want to purchase new lines.

A trans cooler is also a must. The combination of higher stall and the lock-up in the Bowtie converters will make the trans run hotter and can cook the trans fluid and the trans. You should use the largest auxiliary cooler you can fit to insure the trans runs as cool as possible. The one I used is from Jegs, and it has an external 1250 CFM fan built into it. My thoughts were that the fan will double as a cooling fan for the A/C condenser and radiator if I ever get into summer traffic with the A/C on. It may be overkill but I’d rather be safe than sorry.

Fluid pressure in these transmissions are important. Pressure is adjusted by the “TTV cable” (Transmission Throttle Valve cable), which is absent in older TH transmissions. The TTV controls the trans hydraulic pump – it provides clamping pressure, and fluid pressure to control the shift timing and feel, lubrication, and transmission temperature control. The TV cable systems operation is critical to longevity and proper operation.

The TTV cable system cannot be set up correctly without a pressure gauge. The TTV cable requires an additional attachment point for your carb (Quadrajet example shown in picture at right) and does require adjustment at the transmission end. It is important to have the cable and the pressure adjusted within the proper range or the trans could slip between shifts from lack of pressure.

With too much pressure, it will make the engine rpm’s very high between shifts. The trans has a cap on the driver’s side just above the shift shaft. This is for the external pressure gauge hookup needed to adjust the TTV for your shift points.

Getting the TTV work correctly does require some setup and trial and error, but it is no more difficult than adjusting your carb. Just make sure you follow their instructions and install a pressure gauge (the housing boss is supplied, you merely need to install and line and purchase a gauge of your choice.

Last, you must wire up the torque converter for electric lock-up. This is called “TCC” (Torque Converter Control) for 4th gear. This system should be checked frequently and immediately fixed if it malfunctions. Failure of the converter to lock up is a major cause of failure with these transmissions. Bowtie provides you with a simple wiring diagram that easily lets you set up this function. Again, test it after you have completed the install.

Obviously, you have to have your driveshaft cut. Bowtie provides excellent diagrams and instructions for this measurement. Please take my advice and have your driveshaft done by a professional, as any out of balance or out of alignment situation can ruin the transmission.

Last, Bowtie adds a new shifter detent for your shifter and console indicator that is specific to Olds, which looks stock. This will show the proper gear placement. These indicator bezels are supplied by Shiftworks www.shiftworks.com . Shiftworks has both standard Olds console, Dual Gate, and column shift indicators if Bowtie is not aware of your application.

Let me also say that I would suggest buying a complete kit from Bowtie. In the long run, you will spend more time and money fabricating the necessary pieces, and from my experience in the installation, save you from a ton of frustration. I bought the complete trans conversion kit that they were advertising last fall to generate some sales. It came with the 765R4 trans and everything I needed for the installation except the trans cooling lines which I made new.

I am very satisfied with the installation and have yet to go to the strip to see what the result will be there. I can tell you that the lower first gear can be felt at hard throttle – in a good way – but it is imperceptible at part throttle starts.

The biggest thing I can already see is the huge drop in RPMs at cruise and the lockup feature. Highway driving is now a pleasure and adding modern transmission controls means you feel like your ride has entered the 21st Century.




Bowtie Overdrive: Supplies 765, 700R4 and 2004R conversions for stock and modified vehicles. Includes all parts and pieces for a complete installation. www.bowtieoverdrives.com

Shiftworks: Supplies shifters, bezels and other components to alter your shifter for the extra detent when converting from 2-speed to three speed and 4-speed overdrive units. Looks factory!

Eric White Digital Library

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