The Stovebolt Site Forums The Shop Area Engine Shop Converting over to a 700r4

Hi, I have a 53 3100 1/2 ton that my Dad and I are restoring. It has the original pumpkin axle with 4.11 gears and 3 speed column transmission with a 235 motor. I plan to swap out the axle for a open drivetrain from a 55-60 truck.

Now I need to decide about the transmission. I would really prefer to have an automatic and was thinking about a 700r4 that a friend has. It has the OD and would work better with the 3:91 gears that I would gain from the axle swap. we have never done anything this and I'm nervous about getting in over my head in time and $. Will this bolt up directly to my 235? What is involved in the swap? Appreciate any help. Thanks.

700R4 would be a good one. I changed my 350 automatic out to a 700R4 and I love the R4. I can't help you with bolting it up as I am running a 350 engine. But I do love the R4.

On the rear end change out..... I did this on my 52 panel. Dumped the torque tube and installed a 55/56 pumpkin. Later I found out that SOME of the later model trucks, say maybe 60-62 I think it is, had a higher gear ratio. Now I wish I had kept looking for a higher gear as I am running a V8 in my panel. All things considered the 3.90 may be the right thing for your 235 engine especially if you can figure out hooking a tranny with OD to it.
Keep us posted. I'm interested just so I'll know for the future.

I am putting a th350 behind my 235 from a 1959 Apache and I can tell you that you will need an adapter plate and a custom flexplate to make this swap work. I have found several venders for these adapter plates and flexplates , but they are expensive. They range from $350 to $700 depending on who you call and what day of the week it is. The swap itself seems like a pretty easy swap once you find the parts you need. STOVEBOLT ENGINE Co. was the cheapest on the parts (http://www.stoveboltengineco.com/).The inline-six 235 never had a flexplate for that engine, so there are none that will bolt up it needs to be made. You can search my threads on this subject and see some of the answers i was given. If you want more or more detailed info let me know and I can share the info i have gotten tryin to do my swap. Good luck and let me know how it turns out.

You will have to cut the crossmember out also. It would be a lot easier to but a manual o-drive in it like a T-5. or a later model 6 like a 250.

You will need to fab some sort of TV cable and carb linkage hookup as there is nothing stock that cann be used. That chore alone may be more than you want to undertake. TV adjustment on 700r4's is critical to proper operation. I have one in my 57' belair and frankly I liked the previous TH350 better. My advice is to think your objective all the way through first and not allow your thinking to be swayed by free or cheap parts. The rear end change is the way to go IMHO. An AOD would give your 3.91 rear an effective 2.73..way to high for a 235 anyway. Just not practical.

The torque peak on my 55 235 (175 ft-lb) is at about 2100 RPM. With 205R75-15 tires, a 3.90 axle ratio and a 70% overdrive the 60 MPH cruise is 2076 RPM - right about the sweet spot. If you used big tires, like 255R70-15 the 60 mph cruise would be 1895. It might feel a little sluggish climbing from 40-60.

I have the 3sp manual with BW OD tailshaft in my truck, which also is a 70% overdrive like the 700R4. It has 390 rear axle and 205R75-15 tires. It works very well.

BTW, at the risk of starting a religious war, if you're changing the rear to open drive and changing the trans to a modern automatic, you're no longer "restoring" the truck. And I'm fine with that. My advice is, since you've already decided to modify the truck, don't let purism get in the way of building a truck that you'll enjoy owning, driving, and sharing with the public.

Leon

Don't forget it still has 45 MPH brakes unless that is changed too and I'm thinking about his comment of "getting in over my head and $". Sounds like 1953Chevy isn't really ready to undertake all this yet. But he has come to the right place if he decides to go forward. We may have different opinions, just as we all have different expectations but all here will attempt to help.

And that's what I love about the south.

Thanks guys, you gave me much to think about. My first option was to use a saginaw 4speed with the rear end but thought it would be more driver friendly with an automatic. I just want to be able to cruise at 70 mph on the freeway if I need to.

BTW, I just ran across a free axle from a 74 4x4 chevy blazer. It has the 6 lug which I want. Anyone know what gear ratio came with this year and if it will be a good replacement for my torque tube?

The ratio in a 74 Blazer can be anything from 2:73 up to 3;73.
The easiest way to find out, is pull off the cover & look at the ring gear. On the outer edge is the number of teeth stamped for both the ring gear & the pinion gear. Divide the numbers and there's your ratio.