Is a automatic trans possible for a 236 straight 6?

[Isaiah92260]

My last question is what should my rear end gear be? I did a couple calculations I found online and I’m considering on doing a 3.07 rear gear.
Why do you guys think? It shows my rpms

[oem4me]

I certainly am not an expert on this, but a 3.07 rear gear AND overdrive trans might lug that 6 cylinder a bit. Maybe do one or the other, but not both. Ask around before going through with this combo.

[Isaiah92260]

I hope I’m not asking too many questions but I also noticed there are different sizes for 3.07. I seen 8.5” 8.25” and 7.5

What’s the right size 3.07 to go into a 3.90 truck rear? I guess if the 3.90 is 8.5” then that’s what I’m looking for?

I’m looking all over the forum and can’t find the size..

[Isaiah92260]

Originally Posted by oem4me

I certainly am not an expert on this, but a 3.07 rear gear AND overdrive trans might lug that 6 cylinder a bit. Maybe do one or the other, but not both. Ask around before going through with this combo.

Ohhh okay I see. If I don’t go with 3.07 then I could always do 3.38. I find a couple for cheap already on eBay but don’t wana buy until I’m sure.
Thanks bud! I am just learning that these motors are low rpm

[cwcarpenter98]

If you currently have a 3.90 gear, there is no reason to change to a 3.07. The 3.90 will still give you off the line torque and with OD, you will be able to run highway speeds all day. You do NOT want to lug the OD transmissions because of how they are built. Needle bearings can get squished, and that is real bad. That is why Borg Warner engineered the governor to keep the OD system from engaging below 28 MPH. I like to keep my trans in 2nd OD under 50 MPH, but when I go much above that, I go 3rd OD. I spent a good bit of time researching how they operate, but I really gained the knowledge of how it all works when I started driving it. These transmissions are great for cruising, but don't try to speed shift into OD. My trans takes a good 2 to 3 seconds to engage OD when I take my foot off the gas.

Sometimes long posts are good to really get the info out there and understood. If you don't understand something, please let me know so I can try to explain it better

[Isaiah92260]

Originally Posted by cwcarpenter98

If you currently have a 3.90 gear, there is no reason to change to a 3.07. The 3.90 will still give you off the line torque and with OD, you will be able to run highway speeds all day. You do NOT want to lug the OD transmissions because of how they are built. Needle bearings can get squished, and that is real bad. That is why Borg Warner engineered the governor to keep the OD system from engaging below 28 MPH. I like to keep my trans in 2nd OD under 50 MPH, but when I go much above that, I go 3rd OD. I spent a good bit of time researching how they operate, but I really gained the knowledge of how it all works when I started driving it. These transmissions are great for cruising, but don't try to speed shift into OD. My trans takes a good 2 to 3 seconds to engage OD when I take my foot off the gas.

Sometimes long posts are good to really get the info out there and understood. If you don't understand something, please let me know so I can try to explain it better

Oh okay, dang it does sound like that is great tranny to invest in that works well with my 235.

Would a 3.07 still work good with a stock 3 speed? I found one for cheap, I never use my truck really for anything besides just cruising around. I went to go pick up some old beach cruisers with my girlfriend last weekend I was getting frustrated not being about to go over 45 without noticing my engine starting to run a little warm and reving loud.

It’s gonna take me some time to save up and pull the trigger on the rebuild 3 speed over drive. But I’m loving to soaking up all this info on it, I really wana get one!

I also found a 3.23 10 bolt for a good price.

Something I’m considering for the to get me by on the temporary

[cwcarpenter98]

I do not have any experience with rear gear swapping, so I am no help there. If it is cheap, and you can make it work, might be a good idea to get you by

[Captainfab]

The only gear ratios available for the Eaton HO32/33 differential were 3.38 and 3.90. If you want any other ratio, a complete differential swap will be needed. Swapping gears in the Eaton is easy if you can find a complete assembled 3rd member. Otherwise some specialized tools are needed to swap the gears into the 3rd member. If you go with an OD trans, I would just leave the 3.90 gears in the differential.

[Railroader]

Another suggestion is to look at the transmission you have now and see if the side plate (gear selection rods) is the same type as the OD your thinking about purchasing. If so, you can swap the plates and most likely enable you to use the shift Linkage to the column you have. That's what I did when I put OD in my 63.

Attached is wiring diagram for the OD setup. If you don't want to fool with kick-down switch, solinoid can be wired to a switch you cut on or off. On on the highway / off in town. If you go the OD route, I'm sure you'll love it. I can confirm that 65 - 70 MPH at 2100 RPM with 390 gear is a reality.

OD Wiring Diagram.pdf

[Isaiah92260]

Originally Posted by Captainfab

The only gear ratios available for the Eaton HO32/33 differential were 3.38 and 3.90. If you want any other ratio, a complete differential swap will be needed. Swapping gears in the Eaton is easy if you can find a complete assembled 3rd member. Otherwise some specialized tools are needed to swap the gears into the 3rd member. If you go with an OD trans, I would just leave the 3.90 gears in the differential.

Thank you I’m going to get a 3.38 then if that’s the only thing that’ll fit and hold on to my 3.90 when I get OD Trans.

What is an3rd member?

[Isaiah92260]

Originally Posted by Railroader

Another suggestion is to look at the transmission you have now and see if the side plate (gear selection rods) is the same type as the OD your thinking about purchasing. If so, you can swap the plates and most likely enable you to use the shift Linkage to the column you have. That's what I did when I put OD in my 63.

Attached is wiring diagram for the OD setup. If you don't want to fool with kick-down switch, solinoid can be wired to a switch you cut on or off. On on the highway / off in town. If you go the OD route, I'm sure you'll love it. I can confirm that 65 - 70 MPH at 2100 RPM with 390 gear is a reality.

Attachment 1895887

Wow I didn’t think about that. That’s good to know, hopefully it won’t be a problem if I do have to swamp them out. Sounds like you had good luck when you did yours. I’m guessing this is probably a later 1st gen is tranny I’m looking at

Thank you for sharing your experience with the OD. I’m glad to hear I could manipulate the wiring to do that! It would probably make it easier to use no?

[Captainfab]

The 3rd member refers to the entire assembly that unbolts and comes out the front side of the housing. This pic is of a Ford 9 inch but it looks much the same.

Originally Posted by Isaiah92260

Thank you I’m going to get a 3.38 then if that’s the only thing that’ll fit and hold on to my 3.90 when I get OD Trans.

What is an3rd member?

[Railroader]

I went the on/off switch route because it was easier. If the switch is on, once you obtain about 30MPH, let up on the gas pedal and the trans will shift into OD. If you stop (red light or traffic) switch still on. Repeat process and trans goes back into OD once you obtain speed and let off gas.

I will add, on the 6 cylinder, you will loose speed when going up an incline. I have never tried to cut the OD switch off at highway speed. Don't want to screw something up. Might be OK but I'm not going to chance it.