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Hi all......

It's been almost a year since my last confession (I mean post), so I'm kind of rusty. My Question: Has anyone added an overdrive unit to a BorgWarner automatic transmission???

I have a 71 Avanti with the 3sp B/W transmission and at 70mph I'm turning 3000rpm. The engine is not really noisy but I'm sure fuel mileage is suffering from this high steady rpm. This transmission is an AS2-12D manufactured for "Avanti Motors" with a part number of 1700390.

So, is there anyway to add an overdrive unit to this transmission, or am I better off changing to a 200R or 700R transmission?? I bet the Gunslinger has an answer for me. Thanks in advance..........................Rudy RQB-1705

Edited by Rudy Korb
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Rudy...

I can only tell you my experience. When I bought my '70 a few years ago, it had the BW transmission. It was leaking quite badly so I thought it could be rebuilt while the engine was being replaced. I found out that while parts are available, it was more cost effective to get a 700R4 for very little difference in cost. Not only that, the 700R4 has an aluminum case rather than a cast iron case so I was also reducing weight in the car. It did require a different length drive shaft, so I spent about $100 extra over the cost of a cast iron unit for an aluminum shaft to further reduce weight and rotating mass for the engine to turn over.

I've not heard of anyone adding an overdrive to the BW unit but I tend to doubt it would be cost effective compared to a complete swap.

The downside to a swap to a 700- or 200R4 is you will probably have to fabricate new neutral safety and reverse switch mechanisms...I had to as the swap made the original setup too close to the exhaust. I had a 2 1/2" exhaust installed so the bigger diameter pipe could have made that necessary. You'll need your driveshaft modified or replaced, but that might be necessary with an overdrive unit...I simply don't know on that one. Also, some cars seem to need modifications to the transmission tunnel for clearance for a 700R4...mine did not, so it may simply be a car by car thing. A 200R4 likely won't give a problem in that regard.

I've heard that 200R4's have a better spread of gearing than the 700R4 but again, I can't say that from personal knowledge. 200R4's can be built to pretty stout specs, but 700R4's are already built that way. The speed shop that installed the engine and 700R4 in my car used the cam specs, horsepower and torque ratings of the crate engine and the 3.31 spec rear axle ratio of the car to build the transmission to match those characteristics. It turns about 2200-2400 rpm's at 70-75mph. I have P215/70R15 tires mounted on the car.

I agree going to an overdrive unit is a good idea...better gas mileage and less wear on the engine. Being a pioneer by adding overdrive to a BW Powershift might be more trouble than it's worth compared to a swap to a GM unit.

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  • 11 years later...

This is an old post I just happened to notice.....Just adding my two cents that there was an overdrive unit which bolted to the back of the Avanti Powershift. (or any other Borg Warner cast iron case 'model 8' three speed automatic transmission)

I believe it was called the 'Cone Overdrive' (an aftermarket unit) and it apparently worked quite well...I have no idea how many were sold, and probably would not work in an Avanti, as it was a bit bulky and would no doubt clash with the frame 'X' member!

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On 12/20/2020 at 8:13 AM, mfg said:

This is an old post I just happened to notice.....Just adding my two cents that there was an overdrive unit which bolted to the back of the Avanti Powershift. (or any other Borg Warner cast iron case 'model 8' three speed automatic transmission)

I believe it was called the 'Cone Overdrive' (an aftermarket unit) and it apparently worked quite well...I have no idea how many were sold, and probably would not work in an Avanti, as it was a bit bulky and would no doubt clash with the frame 'X' member!

Close, so old stogy instead of new cigar.  The OD was the Hone-O-Drive.

But yes, because of the X-member, there is no overdrive which can be added to the rear of the B-W tranny.

FWIW, if one changes the rear axle ratio to a 3.07 and gets used to shifting the B-W through all three gears, it works OK.

Jack Vines

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My '66 has the 3.07 and with the original B/W taching about 3150 at 70mph, the engine roar was mind numbing.  (I was an audiologist; maybe I have better hearing than Rudy.)  I now have the 700R4 and I could not be happier.   Much less noise, less wear on the engine and better gas mileage.  First gear is a bit low but that transmission was built for a much heavier car.  Shifting from first is at a bit high rpm but, again, that gearing would handle a much heavier car.  Adjustment may tweak some of that out but I've not tried yet.  Other than that, it works great and I'm very happy I made the investment.

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I'm saying Adios to my BW tranny in January, and Hola to a 700r. At 75mph my 383 is turning at 3400rpm...way too fast to last. Plus as that cast iron BW case heats up, you feel it around the center console and shifter. OUCH! Yup, a new driveshaft is in order, as well as other modifications. Nope, I ain't gonna buy that four speed shifter (1-2-3-D-N-R-P) that costs around $500. The transmission will run just fine through the gears and I've never had the occasion to manually put the car in first gear.

Edited by Desert Driver
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If you don't replace the 3-speed quadrant with the 4-speed quadrant you'll find to have it in Drive the stick will not line up exactly with the shifter indicator.  You'll have to learn where Drive is and get used to it.  No big deal but you have to be aware of it.

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