Posted By: reidy 1958 261 with 4 speed auto - Mon Aug 17 2020 09:53 AM
Hello all

As the title suggests I have a few questions about installing a 4 speed auto behind a 1958 261. This will be going in a 1941 Chev pickup. I did a search but did not find a relevant post. Maybe I put the wrong perimeters into the search engine.

Firstly to answer the why question that may come up. I am building this as a long term keeper and my knees aren't getting any younger. The rest of me is not far behind either frown. I also want the option that both my grown up daughters can drive this, and they only drive autos. Where I live there is becoming more stop start traffic and I cannot see this getting any better in the next 10 plus years. Lets just say I am trying to future proof this build.

Therefore are all 261 blocks the same bolt spacing or will the later ones allow a 4 speed to bolt up with no adapter plate.
I am leaning towards a TH700 as they are more common in Australia. If there is a strong reason for a difference transmission I can go looking. My Diff ratio will 3.72 and my tire diameter will be about 30 inches if that alters the recomendations. I will also be using a manual speedo.

From what I have read I will need to go to center mount engine mounts.

I am keen to hear any advice, pitfalls and tips that you can pass on. Especially those ones that you wish you knew as it would have halved the cost of the project.
Also if there is an option of drilling the block I would like to hear it. Freight costs for things like adapter plates from the states are going through the roof.


Posted By: 3B Re: 1958 261 with 4 speed auto - Mon Aug 17 2020 03:04 PM
Hy reidy, I'll give you the bad news first, the only automatic transmissions that will bolt up to the 1958 Chevrolet 261 WITHOUT AN ADAPTER are the Powerglide and the Dual Range Four Speed Hydramatic. All other transmissions be they three speed or four speed will require an adapter between the engine and transmission. I obviously have no idea what kind of facilities you have, or your ability to have an adapter fabricated for you in Australia to save the shipping costs, or if that option would ultimately end up being cheaper? I think you have some more investigating to do before you proceed, good luck!
Posted By: Hotrod Lincoln Re: 1958 261 with 4 speed auto - Mon Aug 17 2020 03:26 PM
Buffalo Engineering makes the best adapter plate to mate the TH700 trans to the stovebolt engines. They also sell a modified flex plate (flywheel) that allows the original equipment starter to be retained. Yes, you will need to alter the motor mounts to the mid-engine position and a single mount at the rear of the transmission. The Turbo 700 is extremely sensitive to throttle pressure (TV) cable adjustment, and it requires some sophisticated geometry at the throttle linkage bell crank to make not only the total movement of the cable but also the rate of travel correct. There are a few websites with detailed information on that subject, but someone else will need to link to a reference to them. When the TH-700 was new, it got such bad publicity that GM changed the name- - - -not the transmission on later models. The "4L-60" (without the "E" suffix) is the same transmission, just with a few upgrades!
Posted By: Fox Re: 1958 261 with 4 speed auto - Tue Aug 18 2020 05:55 AM
I’d get those girls into that truck and teach ‘em how to drive a manual. My sisters did when we were young on the farm. The sooner we learned to drive “Old Green”, the sooner we didn’t have to load square bales of hay!

“Dad? What’s there burning smell?”

“That’s the clutch bud...”
Posted By: reidy Re: 1958 261 with 4 speed auto - Tue Aug 18 2020 07:59 AM
Thanks for the info so far. I will check out Buffalo engineering. What is the opinion of the TH700 VS the TH200?

Fox, the truck in question is a 3 ton that I am putting on a 1/2 ton chassis. From a young age I drove this truck in every decreasing circles, carefully lining up small square bales of hay into the early hours of the morning as Dad had the opinion that hay bailed at night was better. Something to do with the dew and moisture content.

Both my girls learnt to ride motorcycles and have/had the ability to drive a manual. Both are in big cities and only drive autos now. They both have their Masters degrees in their chosen fields so I think the days of me to get them to drive a manual again are long gone.

Posted By: rfs56trk Re: 1958 261 with 4 speed auto - Tue Aug 18 2020 03:28 PM
The 2004R is sort of a baby brother to the 700R4. It was used in cars with 4 and 6 cylinder engines with presumably less HP.
However, they were used in the Buick Grand National which set records at the strip. The 2004R is shorter and generally can be a direct replacement for a Powerglide or TH350. They can built for performance cars - IE: California Performance Transmissions (Art Carr) specializes in these units.
Posted By: EdPruss Re: 1958 261 with 4 speed auto - Tue Aug 18 2020 05:13 PM
Reidy, your dad was right, high moisture(dew) keeps the leaves from breaking off the bale.

Posted By: Hotrod Lincoln Re: 1958 261 with 4 speed auto - Tue Aug 18 2020 11:52 PM
Somebody would have to run really fast to try to give me a 2004R, and I've got two titanium splints and 15 screws between my left knee and my ankle, thanks to a blown rear tire on a Honda Gold Wing 1200 six years ago. Take all the bad features of a 200 Metric transmission, add a really flaky variable-displacement pump and another planetary unit to get 4th. gear OD, and you've got a real mechanic's nightmare on your hands known as a 2004R. It's not even heavy enough to make a good boat anchor!
Posted By: Tony292 Re: 1958 261 with 4 speed auto - Wed Aug 19 2020 12:05 AM
No doubt the 200R4 is weak from the factory but The grand national racing guys Have been building them for serious power for decades now.
Posted By: 87GN Re: 1958 261 with 4 speed auto - Thu Aug 20 2020 10:39 AM
Thank you Tony 292
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