My Quest for a 700R4, there are loads and loads of information out there about the swap and all the possible down falls to being happy with the end results. So I’ve gathered together my thoughts and logic of all the information and will lay them out hear for others to see. If any one sees a flaw or pit fall with the plan please let me know I think I got it right but it’s always easer to correct a problem before I build it.
The engine is a stock GM 350 crate engine with no performance mods made to the cam, compression, or intake manifold to change the horse power or torque curves of a stock carbureted engine. Looking at the torque curve for the stock motor the majority of the torque is obtained by 1700 RPM. The primary area the truck will be used is at sea level and very little towing so corrections for altitude or weight should not be required, there for my RPM at highway speed should be above 1700 RPM.
I did a comparison between the stock truck TH350 trany and the 700R4 with different deferential ratios and the same tire diameter (27 inch) that I will be using, for speeds at 60 – 70 MPH to determine operating RPM. Found a very good online calculator for this comparison at Mark Willams Enterprises (
http://www.markwilliams.com/calculators.aspx ) and took some screen shots and with a little manipulation in Photoshop generated the comparison below. When I rebuild the deferential it will be with 3.42 to 1 gear ratio for 1800 – 2100 RPM at highway speeds.
With so many different places to get a 700R4 transmission from and all the different versions I decided go with a TCI Maximizer RV & Towing Transmission Package 371002P1, TCI 700R4 slip yoke 967300 and Sonnax TV cable corrector AS3-03K to correct the TV cable pull geometry at the carburetor. Note per TCI there aperies to be a difference between the TH350 yoke (Fully splined) and 700R4 yoke (Counter bore in end of barrel) what this exactly means I’m not sure but to be on the safe side I decided to use the TCI 700R4 yoke rather than reuse the TH350 yoke from the truck.
Will be using the torque converter cover from the TH350 trans. I Did have to trim the aft edge of the cover about 1/16 to 1/8 of an inch to clear the 700R4 trans pan.
The Trans mount cross member support will have to be moved approximately 3 inches aft I see no problem there. Except there might be a clearance problem with the Trans oil pan if so I will just fabricate a new one that will clear.
The driveshaft will have to be shortened approximately 3 inches. Plan on retaining the 2 peace driveshaft configuration, just take the new yoke and old driveshaft with the exact dimensions down and have it made and balanced. The 2 peace drive shaft configuration works well with the coil spring swing arm set up and no need to play around with pinion angle for a one peace drive shaft.
Speedometer calibration is being accomplished with 34 to 39 tooth gear housing, 15 tooth (gray) drive gear and 38 tooth driven gear. Found P.A.T.C Speed Shop (
http://www.transmissioncenter.net/highperf700r4.htm ) on the web and ordered the housing and gears, good price, fast shipping and they have a speedometer calculator to figure out what to order. I may have to get a longer speedometer cable for this installation, I don’t know now. Just a thought do you think any one would be interested in a “how to” with pictures on changing the drive gear on a 700R4 for speedometer calibration. If so let me know and I will generate one. I’m going to be changing mine shortly.
Converting the shifter from a column to the floor and wanted kind of a truck 4 speed look so I went with a Lokar Auto Trans 23 inch Shifter ATS6700AB and Lokar Back-up Light Switch BL-1400U. I will say that installing the main shifter mount bracket with the Trans on the bench is a lot easer than it would be in the close confines of the truck tunnel. I did have to bend the shifter arm outboard about ½ inch to clear the trans and vacuum switch. That changed the geometry between the gates in the shifter and the trans lever detents. To bring it all into sink again I moved the shifter rod hole lower on the trans lever.
I wanted to be able to lock up the torque converter in other gears than the 4th gear automatic lock up the trans provides, so I will be adding a switch to do this. I made a switch bracket out of aluminum, sandblasted and clear coated to be mounted to the shifter shaft. Kind of reminds me of larger trucks that have an over and under (two speed rear-end) switch on the shifter.
I have rebuilt the steering column removing the shifter handle and filling the holes plus removing the lever and detent in the lower end of the shaft.
On to the electrical, I find it easer for me if I draw out wiring modifications to figure out where to tap into the stock wiring. So with a little work and Photoshop manipulation I generated the one below that shows the Trans wiring plus all the other electrical items that will be added to the truck.
Well that’s all I can think of on my quest for a 700R4 post except to figure out what pictures that will be posted.
