More regarding performance from a vintage six

February 1, 2016 | By Staff

Question:

In the November 2014 issue of Auto Restorer you said you wrote a book about building a 235, and set up the truck to go 80 mph turning under 2000 rpm… but you did not mention the name of the book. At the very least, please name the book. I have already invested in Patrick’s 3.55 gears. Is it too late for me?

Answer:

The truck I built uses a 3:90 differential and a Mopar A833 New Process four-speed with overdrive. You need the one with the aluminum case, because the iron case version has the usual one-to-one high gear. This transmission will bolt in using a small input shaft cover, which is available from transmission rebuilders and you will have to get a later fine-splined yoke for the front universal joint so it can mate up to the new transmission. Around town with this gearing you never need to get out of third gear, which is the same as high gear in your stock truck. But when you want to do battle on the freeway, you shift into the overdrive fourth and, assuming you have a classic mid-’50s Chevrolet Pickup with a Blue Flame 235 in it, you can loaf along all day long at 80 mph at around 1900 to 2000 rpm. That is, provided you use the stock diameter tires. If you go to smaller tires you will effectively lower your gearing, which would cause the engine to rev higher at speed, and if you use tires that are bigger around than those that came on the truck you will make your final drive even higher.

Smaller
To use the Mopar New Process A833 fourspeed transmission you will need the smaller input shaft cover.

Patrick’s rear end gear set will make on old Chevrolet perk along at freeway speeds quite nicely too, but I could not tell you exactly what they can do at specific speeds and rpm. In your situation I would install the Patrick’s gear set and see how you like it before going further. If you are happy with the results, you will have saved yourself a lot of expense and effort. Differentials do have to be set up precisely if they are to last and not be noisy, so if you have no experience and don’t have the proper tools, I would suggest you have a pro install the gears and set up the proper lash in them before you install the rebuilt differential. My book is called the “Classic Chevy Truck Handbook” (HP 1534) and is available from Amazon and the big bookstores. ISBN: 978-1-55788-534-0. It is published by:

HP Books Penguin Group (U.S.A.) Inc. 375 Hudson St. New York, NY 10014