Anyone install three speed with overdrive behind a slant six

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SMCARNUT

SMCARNUT

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I have a 71 Dodge Demon that has a slant six 225 with a three speed on the floor transmission. I have converted the car to BBP front disc brakes and changed out the 7 1/4 to an 8 3/4 3.55 posi with 10 x 2.5 BBP rear brakes. My question is now I want to convert to a 4 speed but have found a cast iron 3 speed with overdrive transmission. What else do I need? Can I use a regular 4 speed shifter? Hopefully someone has already done this conversion and can help with a parts list.

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The F body cars offered a 3 speed + overdrive behind a slant. They were fairly common in Aspen/Volare cars.
 
Plenty have done it. It's not a "three speed with over drive". It's a Mopar A833 four speed over drive. It has the A833 designation. That's four speed, over drive or not.

Four speed automatics are not called "three speed with over drive". They are called "four speed automatic" because that's what they are.

But yes, with the right gear ratio, it can be a good swap. I would go somewhere between a 3.73-4.10. That will take advantage of the over drive and also make the gear jumps better to over come. The final drive ratio for the over drive transmission with a 4.10 for example is 2.99. So don't be afraid of using a lower gear ratio. Thay are a better match for the over drive transmission, IMO.
 
IDK why some guys call them that... "3 speed + overdrive" IS a 4 speed trans.....
 
All right are you talking about the 4 speed modified to have an OD gear, or are you taking about an acutal 3 speed with an OD unit? How many shift levers does the gearbox have?

This is a Mopar 4 speed overdrive Notice the 3 shift levers and notice the front lever POINTS DOWN. This was originally a 4 speed design, and Chrysler re-worked what had been 3rd gear into an OD gear. Then they pointed the 3-4 shift lever DOWN which reverses it's action. So when you shift the OD box, shifter 1-2-3-4, the box itself goes 1-2-the old 4-the old 3--which is the OD gear

dsc08299-jpg.jpg


Below is a generic photo (probably GM) of a 3 speed overdrive gearbox. NOTE that it only has 2 shift levers, R-1 and 2-3. The round electrical unit shifts the OD in/ out

36047424f8b27e0bd1452bfddcb90680c703d9f-jpg.jpg
 
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67Dart273 said:
All right are you talking about the 4 speed modified to have an OD gear, or are you taking about an acutal 3 speed with an OD unit? How many shift levers does the gearbox have?
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RIGHT! Herein lies the confusion.
 
Nothing wrong with a 3-speed, no 4th needed.

Mine is very fun to drive and yet it averages 21.5 MPG with the 3.23 gear.

Original 3-speed cars are awesome. :)
 
Chrysler mated the 3+1 to the slant six, and so should you. Not a bad combo in the least.
 
Its a A833 4 speed overdrive has three levers excuse my ignorance years ago we called them three speed with over drives. If anyone knows all the particulars I would appreciate there responses. I will need a shifter which one works the best stock a body four speed? Can I use the stock three speed bell housing. Just trying to come up with a parts list. Thanks in advance first slant six car that I have not converted to V8. I want to stay with the slant six just do not want to waste time looking for the wrong parts.
 
SMCARNUT said:
Its a A833 4 speed overdrive has three levers excuse my ignorance years ago we called them three speed with over drives. If anyone knows all the particulars I would appreciate there responses. I will need a shifter which one works the best stock a body four speed? Can I use the stock three speed bell housing. Just trying to come up with a parts list. Thanks in advance first slant six car that I have not converted to V8. I want to stay with the slant six just do not want to waste time looking for the wrong parts.
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There's a machined pad on the passenger's side of the main case. It will have PP833XXXXX or some such. If you can post all those characters, one of the boys will decode it.
 
SMCARNUT said:
Its a A833 4 speed overdrive has three levers excuse my ignorance years ago we called them three speed with over drives. If anyone knows all the particulars I would appreciate there responses. I will need a shifter which one works the best stock a body four speed? Can I use the stock three speed bell housing. Just trying to come up with a parts list. Thanks in advance first slant six car that I have not converted to V8. I want to stay with the slant six just do not want to waste time looking for the wrong parts.
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Then remember, it will need GEARS. And I don't mean a sucky 3.55. Final drive ratio with a 3.55 gear will be 2.59. That will SUCK dead elephant balls on the highway, because on the slightest little incline or hill, you'll be reaching for the shift lever to go back to third. If it was mine, I'd consider a 3.91 the absolute least and would probably go straight to the 4.30. 4.30 final drive with an over drive is only 3.05. The over drive makes a big difference. Where people fail is putting a pussified gear in. Doing that, especially with a slant 6 makes it a PITA to drive, because you have to wind the gears out to keep the engine in its toque curve. Does that make sense?
 
Alaskan_TA said:
Nothing wrong with a 3-speed, no 4th needed.

Mine is very fun to drive and yet it averages 21.5 MPG with the 3.23 gear.

Original 3-speed cars are awesome. :)
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I love my 3 speed! My only worry is, now, I have a slant 6 that's strong enough to break it, by a good margin.
 
Rusty
Thanks for the advise. I really appreciate your help. I am not that familiar with these transmissions. I am getting a really good deal on the A833 four speed overdrive transmission. I will look into all of my options before getting to far into this project. Have a great evening.
 
SMCARNUT said:
I have a 71 Dodge Demon that has a slant six 225 with a three speed on the floor transmission. I have converted the car to BBP front disc brakes and changed out the 7 1/4 to an 8 3/4 3.55 posi with 10 x 2.5 BBP rear brakes. My question is now I want to convert to a 4 speed but have found a cast iron 3 speed with overdrive transmission. What else do I need? Can I use a regular 4 speed shifter? Hopefully someone has already done this conversion and can help with a parts list.

Chrysler Corp. did, and.....
You cannot use the 3 spd bell, the input shaft uses a large brg./retainer & the trans pattern is different. One could machine the retainer reciever bore in the bell oversize, but attn needs to be paid to release-arm fulcrum mounting bolt location, & there are at least 2 diff fulcrums moving the position in relation to the mt bolts. The 3-4 shift lever is mounted "upside down" to change the direction of shifter motion from backward to forward to put 1:1 in "3rd" position, this requires a special 3-4 shift rod, depending on the stock rod You can "make do". Yes You can use a std 4 spd shifter...
There are some 3/4 speed bells with both patterns I believe, but I couldn't tell on what & when they were used, best of luck on the swap...
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Sorry, I wiped the end quote out, You have to expand the quote to read the above...
 
Call Brewers Performance. They have everything you need and excellent advice.
 
SMCARNUT said:
Its a A833 4 speed overdrive has three levers excuse my ignorance years ago we called them three speed with over drives. If anyone knows all the particulars I would appreciate there responses. I will need a shifter which one works the best stock a body four speed? Can I use the stock three speed bell housing. Just trying to come up with a parts list. Thanks in advance first slant six car that I have not converted to V8. I want to stay with the slant six just do not want to waste time looking for the wrong parts.
Click to expand...

Your bell housing should have a dual pattern for 4 speed and 3 speed. The shifter is a standard A body Hurst with the O/D lever pointed down and a special O/D 3/4 rod. You would want an O/D with the small front bearing retainer to fit in an early bellhousing. Check your output shaft spline and get the O/D with matching output splines. I think your drive shaft will work.
 
Don't think I've ever seen a small retainer OD. The frt. Brg was oversized I believe because it was going to be so heavily loaded in OD having to transfer the torque thru' the 3rd gear set & for long periods of time.
 
Killer6 said:
Don't think I've ever seen a small retainer OD. The frt. Brg was oversized I believe because it was going to be so heavily loaded in OD having to transfer the torque thru' the 3rd gear set & for long periods of time.
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They made a few early ones with the 307 bearing. You just swap the front retainer for the standard 4 speed retainer. I have converted a couple O/D to standard main housing to fit in the 66 without mods. Does not seem to be a problem.
 
66fs said:
They made a few early ones with the 307 bearing. You just swap the front retainer for the standard 4 speed retainer. I have converted a couple O/D to standard main housing to fit in the 66 without mods. Does not seem to be a problem.
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Lol, page 6 of Jamie Passon's book, "1975-only that used a small 307 bearing and had the large 5.125 inch OD. "
 
SMCARNUT said:
Its a A833 4 speed overdrive has three levers excuse my ignorance years ago we called them three speed with over drives. If anyone knows all the particulars I would appreciate there responses. I will need a shifter which one works the best stock a body four speed? Can I use the stock three speed bell housing. Just trying to come up with a parts list. Thanks in advance first slant six car that I have not converted to V8. I want to stay with the slant six just do not want to waste time looking for the wrong parts.
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You will need an OD bellhousing, the retainer hole size is larger. I have one if you cannot find one.
The standard 4-speed shifter and linkage will work, if you lengthen the 3-4 rod.
If you zoom in on the pic, you can see where I lengthened the shift rod.
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67Dart273 said:
All right are you talking about the 4 speed modified to have an OD gear, or are you taking about an acutal 3 speed with an OD unit? How many shift levers does the gearbox have?

This is a Mopar 4 speed overdrive Notice the 3 shift levers and notice the front lever POINTS DOWN. This was originally a 4 speed design, and Chrysler re-worked what had been 3rd gear into an OD gear. Then they pointed the 3-4 shift lever DOWN which reverses it's action. So when you shift the OD box, shifter 1-2-3-4, the box itself goes 1-2-the old 4-the old 3--which is the OD gear

View attachment 1715793523

Below is a generic photo (probably GM) of a 3 speed overdrive gearbox. NOTE that it only has 2 shift levers, R-1 and 2-3. The round electrical unit shifts the OD in/ out

View attachment 1715793527
Click to expand...

Sorry to hijack this thread, but I've always wondered this...
I've just bought an A833OD, so hopefully I can get some clarification here.

"So when you shift the OD box, shifter 1-2-3-4, the box itself goes 1-2-the old 4-the old 3--which is the OD gear".

-When the shifter goes from 3 to 4, but the box goes 4 to 3, won't the engine "rev up" like it would when you downshift a normal 4 speed tranny into 3rd gear?
-If you turn the 3/4 lever back around and have it pointing up (and then use the correct linkage arm), would the box revert back to shifting 1-2-3-4?

Thank you for any help.
 
jonn6464 said:
Sorry to hijack this thread, but I've always wondered this...
I've just bought an A833OD, so hopefully I can get some clarification here.

"So when you shift the OD box, shifter 1-2-3-4, the box itself goes 1-2-the old 4-the old 3--which is the OD gear".

-When the shifter goes from 3 to 4, but the box goes 4 to 3, won't the engine "rev up" like it would when you downshift a normal 4 speed tranny into 3rd gear?
-If you turn the 3/4 lever back around and have it pointing up (and then use the correct linkage arm), would the box revert back to shifting 1-2-3-4?

Thank you for any help.
Click to expand...

Yes, but with the 3-4 lever up the car would go from 1st to 2nd to O/D then 1:1. So with the 3-4 lever down the O/D is a higher gear, say .73 so it feels like a 4 speed with the gears spread farther apart.

64-70 standard gear ratios: 2.66, 1.91, 1.39, 1

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77 up O/D gear ratios: 3.09, 1.67, .73, 1.00

P1010030.JPG
 
Last edited:
jonn6464 said:
Sorry to hijack this thread, but I've always wondered this...
I've just bought an A833OD, so hopefully I can get some clarification here.

"So when you shift the OD box, shifter 1-2-3-4, the box itself goes 1-2-the old 4-the old 3--which is the OD gear".

-When the shifter goes from 3 to 4, but the box goes 4 to 3, won't the engine "rev up" like it would when you downshift a normal 4 speed tranny into 3rd gear?
-If you turn the 3/4 lever back around and have it pointing up (and then use the correct linkage arm), would the box revert back to shifting 1-2-3-4?

Thank you for any help.
Click to expand...

No what I was trying to explain, is, that Chrysler RE GEARED the "old" 3rd gear to be an overdrive. The "old" 3rd gear is now HIGHER geared tnan the "old" 4th gear which is not a gear at all. 4th gear in all traditional American 4 speeds (and high gear in traditional 3 speeds) is nothing but a shaft coupliing--the input and output shaft are coupled

The point is that you cannot "re gear" the original 4th gear--it is not a gear. So "Ma" re-geared 3rd instead

So with 3rd now re-geared, flipping the lever now causes the 3-4 shift (at the shifter) to actually be 3--the old 4th gear and------4----the old 3rd gear which is now your overdrive

By the way Ford also did this, and GM just "chicken out" and bought Chrysler boxes. LOL
 
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