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Fixes for a Poor-Shifting GM 700R4 Automated Transmission on a Carbureted 383 SBC

Fixes for a Poor-Shifting GM 700R4 Automated Transmission on a Carbureted 383 SBC

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I’ve obtained a 700-R4 in my Chevy C10 pickup behind a typical 383ci small-block Chevy. The engine runs superb with a set of Edelbrock heads and Performer RPM consumption and a Holley 750 vacuum secondary carburetor.

My drawback is the transmission doesn’t appear to be as sturdy on the up shifts accurately. We had been pondering that perhaps the torque converter is just a little too mushy and that’s inflicting the weak shifts. Any ideas?

W.D.

Sure and hopefully you haven’t harm the transmission within the course of. This seems like a traditional case of an incorrectly adjusted TV cable. This can be a complicated difficulty with a ton of different potential causes however we’re going to go together with the best choice of creating certain the TV cable is correctly adjusted as a result of that is typically the place massive issues start.

The time period TV is brief for throttle valve. The TV cable on the 700-R4 and its cousin the 200-4R overdrive transmissions changed the previous vacuum modulator valve because the gadget utilized by the transmission to sense the load utilized to the transmission.

How a Throttle Valve (TV) Works

On the highest of the engine, the TV cable is related to the throttle arm on the carburetor or throttle physique if the engine is EFI. On the opposite finish, the cable is immediately connected to the throttle valve that adjusts line stress within the transmission, very like the vacuum modulator did on earlier automatics. Because the throttle opens, this pulls on the cable which strikes the throttle valve contained in the transmission valve physique and will increase line stress.

All of this works very effectively within the inventory OE configurations as a result of the GM engineers labored out the main points. Issues come up when sizzling rodders begin altering parts like carburetors or consumption manifolds. Aftermarket carburetors like a Holley or an Edelbrock don’t create a correct finding place for the TV cable as a result of these carburetors had been designed and constructed earlier than the TV cable was created.

Correctly Mounting Your TV Cable

It’s vital that the position of the TV cable on the throttle linkage be precisely positioned to duplicate the OE motion of the throttle because it opens. Most frequently this additionally means that we are going to want a mount to place the TV cable meeting subsequent to the carburetor.

To simplify issues, a number of producers like Holley and Edelbrock have provide you with mounting kits. There are completely too many kits to record all of them right here and we frankly don’t have the sources to check them to find out how effectively they work. So we’ve landed on a few merchandise that work for us and likewise might be straightforward so that you can adapt to your specific software of a Holley carb on a twin airplane consumption manifold. The elements we’ll be utilizing are straight from Holley.

First we want a spot to securely mount the TV cable to the manifold and carburetor to create a secure platform from which this cable can function. We’ve discovered a easy bracket by Holley (PN 20-95) works effectively to create a safe place to mount a common TV cable. The subsequent step is to attach the cable to the transmission to verify it’s accurately connected to the transmission TV valve.

Now we want a easy TV adapter that bolts to the aspect of the Holley carburetor major throttle linkage (PN 20-121). This bracket repositions the TV cable throttle linkage level to duplicate the TV cable OE motion required by the 700-R4 transmission throttle valve. That is particularly essential as a result of it’s this cable motion that indicators the transmission that there’s load utilized to the transmission.

Adjusting the TV Cable

If the cable strikes too far too early, the shifts are delayed and are extra aggressive than what is taken into account acceptable. If the cable doesn’t transfer far sufficient with gentle throttle motion, the road stress stays low, the 1-2 and 2-3 shifts happen in a short time and early—these are sometimes known as stacked shifts.

Neither of those conditions are acceptable. Plus, if the cable doesn’t transfer far sufficient, line stress is low and the clutches won’t have interaction rapidly sufficient which causes slippage which can quickly destroy the transmission. This could occur in a matter of some miles. We can’t over-emphasize how rapidly this will occur.

After all, there are different potential issues contained in the transmission that may trigger these points. So one of the best ways to set the TV cable is to do that together with a transmission line stress gauge. All 700-R4 transmissions supply a small 1/8 inch pipe thread becoming on the motive force aspect of the transmission positioned simply over the shift linkage. Our advice is to attach a 300 psi stress gauge to this port and monitor it continuously when establishing and tuning the TV cable. On the backside of this text, we’ve included a stress chart created by TCI, the automated transmission individuals.

The secret is to initially join the TV cable to the Holley linkage on the carb and set the linkage up in order that it’s tight sufficient at idle that as quickly because the throttle linkage strikes previous idle, the road stress instantly will increase. If this doesn’t happen, this will point out there might be inside issues with the transmission which is past the scope of this dialogue. Additionally be certain that your hydraulic pressures are in line with the TCI specs. If they’re excessively low or excessive that would signifies inside issues.

Hopefully this may level you within the correct route towards bettering the shift high quality in your 700-R4 that can guarantee your transmission lives a protracted wholesome life and gives the chance so that you can take pleasure in your truck over many hundreds of miles of enjoyable driving.

On this photograph, the 20-95 Holley bracket is bolted to the rear nook of the 4150 fashion Holley carburetor and the 20-121 bracket is bolted to the throttle linkage. With the TV cable correctly adjusted, the cable needs to be guitar-string tight at wide-open-throttle. (Picture/Jeff Smith)

700-R4 Transmission TV Cable Elements Checklist

  • HLY-20-95 – Holley TV Cable Bracket, Mounts to Carb
  • HLY-20-121 – Holley Transmission Kickdown Bracket, 4150/4160
  • BMM-64511 – B&M Throttle Cable Adapters, Edelbrock Carb
  • EDL-8026 – Edelbrock Throttle Valve Cable Adapter
  • TCI-376800 – TCI Common TV/Kickdown Cable

700-R4 Automated Transmission Shift Factors

Gear Change Shift Level
1 – 2 15 – 20 mph
2 – 3 25 – 30 mph
3 – 4 40 – 45 mph

700-R4 & 200-4R Min./Max. Stress for Every Gear

Gear Place Minimal Stress
(PSI)
Most Stress
(PSI)
Park 90 – 110 190 – 239
Reverse 90 – 120 200 – 300
1st 190 – 230 190 – 230
2nd 190 – 230 190 – 230
third 190 – 230 190 – 230
4th 190 – 230 190 – 230
This chart signifies minimal and most pressures for every gear place in a 700-R4 and 200-4R transmission outfitted with a TCV cable. This chart signifies minimal and most pressures for every gear place in a 700-R4 and 200-4R transmission outfitted with a TCV cable.

Creator:
Jeff Smith has had a ardour for vehicles since he started working at his grandfather’s gasoline station on the age 10. After graduating from Iowa State College with a journalism diploma in 1978, he mixed his two passions: vehicles and writing. Smith started writing for Automobile Craft journal in 1979 and have become editor in 1984. In 1987, he assumed the position of editor for Sizzling Rod journal earlier than returning to his old flame of writing technical tales. Since 2003, Jeff has held numerous positions at Automobile Craft (together with editor), has written books on small block Chevy efficiency, and even cultivated a formidable assortment of 1965 and 1966 Chevelles. Now he serves as a daily contributor to OnAllCylinders.

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