Rusty Bowtie
General Category => Moose's Tech Corner => Topic started by: themoose on December 31, 2012, 08:25:07 PM
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As you might have already guessed if you have read some of my previous posts , if I build a project with an automatic transmission my preference leans toward an overdrive transmission. GM has offered a number of these transmissions over the years including the 2004R, 700R4, 4L60 and the later version 4L60E with the E standing for electronically controlled These transmissions have gotten a bad rap for a couple of reasons. Firstly the very early versions had some engineering issues that were worked out in later versions and secondly and probably the most important cause of failure is the improper adjustment of the TV(Throttle Valve) system. The geometry of the TV cable/ carburetor linkage is quite a bit different than that of the “Kick Down cable on the Turbo 350 and 400. If the cable is not pulled at the correct rate throughout the entire rotation of the carburetor shaft the transmission pressure will not be correctly controlled which could cause excessive heat buildup and severe damage to the clutch packs and other internal components. The best description of how the system works that I have found is in an article from Bow Tie Overdrives http://www.bowtieoverdrives.com/index.shtml (http://www.bowtieoverdrives.com/index.shtml) which I have attached (see PDF File). This is not to promote their products but I will add that they do offer components that will insure that the system will function properly and I have used them with great success. I have also added a short history and description of the transmission below. There‘s a lot to read so grab a beer and sit back relax and hopefully enjoy.
Moose….
The 700R4 Automatic Overdrive Transmission was GM’s answer to the American consumer’s desire for better fuel economy. First introduced in 1982, the 700R4 was met with wide fanfare as the ideal transmission. The transmission featured an impressive 30% overdrive while also offering a low first gear of 3.06. The improved fuel economy added with a low off-road first gear made this transmission an immediately popular choice for conversions. The 700R4 was basically designed to replace the retired TH350 transmission. The 700R4 was used in rear wheel drive passenger vehicles, S-series trucks, Blazers, half ton pickups and even a few three quarter ton trucks. The transmission was offered with the standard V8 90° bolt pattern which also included the 4.3 V6. A smaller 60° bolt pattern was also available for some smaller V6. Engines like the 2.8. The bolt pattern on the rear of the transmission was the same 4-bolt pattern as the TH350 but used metric bolts. The transmission always used a 27 spline output shaft. The 4wd output shaft protruded out of the transmission with a stick out length of 2.75". This stick out was approximately 2" longer than the TH350.Another unique feature to the 700R4 was the lock up torque converter. This feature essentially locked up the torque converter to create a direct mechanical connection similar to a manual clutch transmission. By locking the converter at highway speeds the slip of the converter was eliminated. The results were lower RPMs and significant loss of generated heat. Although the 700R4 is not an "electronically" controlled transmission, this feature was controlled by a PCM. There are any number of ways to control the converter using a simple switch and relay system. The 700R4 also uses a TV cable (or Throttle Valve) to control the shift points and line pressure. It is critical that special attention be used during the adjustment of the T.V. cable. Although GM should be credited with the introduction of such a revolutionary transmission, the transmission did suffer from a few glitches. GM persevered with the development of the 700R4, and to their credit, the transmission received all of the necessary upgrades by 1987. Something else to consider in researching and selecting a 700R4 is the wide aftermarket support available. Automotive aftermarket manufacturers have had over 25 years to master and perfect this transmission. The availability of better clutch packs, shafts and building techniques has allowed this transmission to reach several strength levels. The 700R4 can now be built almost anyone’s needs, which spread a wide spectrum from conservative highway vehicles to extreme competitive racing and rock crawling vehicles.
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Thanks for posting Moose. I'll be setting mine up in the next few weeks. This will help out.
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I have a few of the 700R4's in my barn....my favorite tranny. If anyone ever wants to rebuild one...I have a DVD that you could borrow.
Another reason I like installing TPI in my cars...the ECM controls the trans lock-up.
My 33 Chevy engine.....
Ed
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To be sure you get the better 1987 or newer 700R4 here is an ID chart:
(http://i15.photobucket.com/albums/a383/EdJacobi/TH700-R4_1.jpg)