Th350 vs 700R4 Differences

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TH350 vs 700R4

The TH350 was GM’s go to transmission for light duty vehicles from the late sixties through the early eighties, that is until the 700R4 and 200-4R began to replace it.  When comparing the TH350 vs the 700R4, there are quite a few differences.  The biggest one is going to be overdrive.

It is important to note that for all intents and purposes the 4L60 and 700R4 are the same transmission.  They are not the same as the 4L60E, which is computer controlled.

Related:  TH350 vs. TH400, TH350 vs 4L60E

 

TH350 vs 700R4:  Biggest differences

There are many differences between the TH350 and 700R4 transmissions.  We’ll get into them more below, but the largest ones have to do with how they are controlled, and one having an overdrive gear and the other one not having that gear.

  • Shift control–  The TH350 is controlled by engine vacuum and a kick down cable.  The 700R4 on the other hand is controlled by a TV cable.  The best way to think of the TV cable is as a throttle position sensor.  It controls shifts based on how much throttle is being given at any time.  It is easy to swap transmission control to a TV cable if you are thinking about swapping to a 700R4.  There is more info on what needs to be done in the TV cable article a few sentences back.
  • Overdrive–  The TH350 has three forward gears and no overdrive.  The 700R4 uses an overdrive gear to reduce engine RPM at highway speed.

There are many other differences between the two transmissions that are noteworthy as well.  This is a broad take on these differences.

  • Locking Torque Converter–  The 700R4 has a locking torque converter, which means that a clutch will engage at a high enough speed and allow for a true direct connection between the engine and transmission.  This increases fuel economy and slightly lowers RPM going down the road.  You have to set up wiring to make it work in a car that it was never equipped with.  A car with originally equipped with a TH350 is not going to have the wiring for that built-in.
  • Length–  The TH350 is a shorter than the 700R4, so if you were going to swap one for the other, you’d need to have your driveshaft resized or replaced.
  • Gear Ratios–  The TH350’s gears are placed closer together (despite having less of them).  While a vehicle with 4.11 gearing may scream down the highway with a a TH350, it’s going to keep the engine in the power band longer.  The 700R4 goes from a 3.06 -> 1.62 1-2 shift, which is way more aggressive than the Turbo 350’s 2.74 -> 1.57.  Simply put, the TH350 is going to keep the vehicle in the power band longer.
TH350 vs 700R4 Gearing 1st 2nd 3rd 4th Reverse
700R4 3.06 1.62 1.0 0.70 2.29
TH350 2.52 1.52 1.00 N/A 1.92

700R4 vs TH350:  Conclusion

There are really two major determining factors regarding which transmission is best for you.

  1. What is overdrive worth to you?
  2. Do you want to race or be steerable?

Almost every modern car has an overdrive transmission.  If you didn’t grow up in the time when a TH350 equipped car would be in your daily driver, you may not remember the engine screaming down the highway.  It is not as fun as it sounds.

It’s much nicer to listen to the engine hum down the highway in overdrive sipping, not guzzling, the gas.  Unless you really want to do hardcore racing, you should take a look at the 700R4.