VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc 235 700R4 Transmission

I have a 57 Chevy pickup, mostly stock except for lowering springs. 235 engine, three on the tree. My uncle gave me a 700R4 auto transmission from a project he was building that he decided to go in a different direction. My question is: can I pair them? Is there an adapter to allow for the two to work? Or am I looking at a new engine setup?
My truck is gorgeous, but it's not very drivable in terms of highway driving. Reluctantly I've decided to update some things and forgo the stock set up. An overdrive option, perhaps power brakes and power steering. Looking for advice.
Thanks,

Welcome to VCCA Chat. Hopefully we can offer some help. Many of us focus on keeping our vehicle close to original but some of us do modify vehicles.

I am not familiar with a C400 transmission. I wonder if you are referring to a Turbohydramatic 400 which is a fairly heavy duty 3 speed automatic transmission. Some people call it aTH400. It is the automatic transmission that Chevy paired with big block V8’s. They were also used in early 70’s Corvette’s that had small block V8’s.

Those transmissions are direct drive in top gear which the same ratio as your manual three speed when it is in top gear. That means that the engine speed at 60 mph will be the same with either transmission unless you change tire diameter or rear axle ratio.

I do not know if you can bolt a TH400 to a 235.

If there really is a C400 transmission I am interested in learning more about it.

I'm not a mechanic so now I'm embarrassed. It's 700R4. I don't know where I got the other? I love my truck, but at a top speed of 60, it's a little limited in drivability. On the highway, most people smile and give you a thumbs up, but the ones in a hurry aren't so happy

There are adapters to mate the late model overdrive automatic transmissions to your 235 engine. I have the name of the company somewhere. A google search would probably find it also.
I have a 3 speed manual transmission with overdrive that might bolt to your existing bell housing. I do not know about the availability of all the controls and switches to make it work and appear authentic. If those items could be found, you could have authenticity and drivability. A complete rear axle setup from a pickup, from 1970 or earlier, which was originally equipped with an automatic transmission, would give you faster gears and retain the 6 bolt pattern for your wheels.
I like my vehicles to be as original as possible, but I have no problem with stealth modifications which enhance drivability and safety.
Where are you in Missouri? Call me, if you like at, 573 864 6539

Mike

Thanks! I'm in Lee's Summit (Kansas City area). I'm not looking for heavy modifications, just a little more convenience in driving around town. I'd share a pic, but I'm new to the forum and can't figure out how to do it! LOL

Ok, that makes a lot more sense. With the 0.7 4th gear I can understand why it is of interest to you.

I do not know if the transmission will bolt to your 235. I do know that the conversion will require that you install a flex plate to replace your flywheel. The flex plate bolts to the torque converter.

I also know that the shifting in a 700R4 is controlled by a TV (throttle valve) cable. You would need to add some linkage to your accelerator and carburetor to operate that cable. Plus you will need to either modify the current column shift mechanism or adapt some type of floor shifter to the transmission.

You also need to consider whether the 235 in your truck can handle that high a final drive ratio. A lot depends upon the current rear axle ratio.

Consider this example. If the engine is turning at 2800 rpm when driving at 60 mph today, the engine speed will drop to 1960 rpm at 60. The engine might not produce enough torque to run well under those conditions.

One other point to consider is whether the rest of the truck is capable of the operating at higher speeds safely. Remember that in 1957 vehicles were not designed to run all day at 75 - 80 mph. Are the brakes, steering, and suspension up to the task?

Those are excellent points. And as a novice mechanic (meaning I can do a tuneup and change brakes and not much else) I have no idea. I know I have drum brakes and for today's driving probably needs disc. But as a school teacher I have limited funds. This truck has been a lot of fun to restore, but I've done it over a period of about 15 years as I could afford it.

Rusty,
I'm kind of getting the impression that you would recommend a new engine/transmission combo with some updates on brakes. Do you think that's best? And how in the world does everyone afford to do this?! LOL. Do you guys install new crate engines? Or find used ones from a salvage yard?

Garrison,
PLEASE call me before you start planning major, unnecessary, and expensive modifications to your truck. I have no axe to grind, just some solid info that directly applies to your situation. If you know someone at Jim Carter truck parts, (Jim, himself, maybe) call there and anyone will vouch for me.

Mike Russell
Columbia, MO
573 864 6539

Thanks, Mike! I will. I actually occasionally make it to Columbia to the Indian dealership -plus you guys have a White Castle!
Dan

Hi Garrison,

I know that you would enjoy meeting and talking with Mike. He and I share a lot of similar ideas about these classic vehicles.

By no means am I suggesting that you need to make any major updates. My comments were intended to help you make the best decisions for you and your vehicle. A 1957 vehicle is very safe at reasonable highway speeds. I simply wanted you to not think that just because you changed the final drive ratio you would have an 80 mph all day long vehicle.

Mike would also be a good person to offer additional inputs about how your 235 would handle that steep top gear. I cannot remember where the torque peak is for that engine.

If you can operate above the torque peak the engine responds nicely if your load increases. Here is a made-up example. Assume that engine has a torque peak at 2400 rpm and that it runs at 2600 rpm at 60 mph. If you start up a slight incline the engine speed will start to drop but torque increases so you will be able to hold that 60 mph. On the other hand if the engine runs at 2200 rpm at 60 mph, your speed will drop quickly when you encounter an incline.

You can actually test this with your current drivetrain in your ”˜57. Drive at speeds both above and below the torque peak and feel how it responds.