Old Hot Rod Article about converting a std 4 speed to OD

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DionR

DionR

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I know it's come up several times before, but when I ran across an interesting article in one of the old Hot Rod magazines I snagged at the swap meet this summer, thought I would share some info.

In the January 1976 issue of Hot Rod, Dick Landy does an overdrive conversion on an older A833 box, and they show what parts need to be swapped. Looks like there are 6 pieces that are different.

ODSwap.jpg


ODSwap1.jpg


ODSwap2.jpg


Makes me wonder. If the input shaft is the same between a 3.09:1 first gear box and an OD box, then the nose of the output shaft isn't any different. So I would guess, the synchro splines are the only other difference. If so, you could perhaps keep the standard 4 speed 3rd-4th gear synchro, and then be able to keep the original output shaft. Then all you would need for the conversion is the 2nd and 3rd gears, the cluster and the input shaft (if it wasn't already a 3.09:1 first gear).

Probably not a big deal, but thought I would share in case someone was interested.
 
Years ago, I wanted to put a 3.x:1 4 speed for the lower gear in my FJ-40 Landcruiser, for the lower gear, but Advance Adapters didn't make the proper shaft. At that time I clearly had it in my head that the OD boxes and the 3.09 boxes used the same main and input shaft. I've been wrong before, but that was in my head back then.
 
67Dart273 said:
I clearly had it in my head that the OD boxes and the 3.09 boxes used the same main and input shaft. I've been wrong before, but that was in my head back then.
Click to expand...

I always heard that the output shafts were different, but I always thought it had to do with the nose of the shaft where it went into the input shaft and rode on the roller bearings there. Now I think it is only related to the 3rd-OD synchro and (I think) if they are kept together, the OD parts can be swapped without swapping the output shaft. FAIL - see below post.

I'm sure someone has some experience with this, I am just guessing from what I read in the article.
 
I don't know much, but i do know the a-833 O.D. Trans has a bigger input shaft bearing retainer, i do not know if the internals are compatible. Just if you change to a O.D trans. you need the larger diameter bell housing, or you need to have the main pinion opening bored larger. (I used to know the specs, but I can't remember)........Also the O.D trans has a weaker case. I do know that this post is not relevant to the O.P
 
ironracer1 said:
I don't know much, but i do know the a-833 O.D. Trans has a bigger input shaft bearing retainer, i do not know if the internals are compatible. Just if you change to a O.D trans. you need the larger diameter bell housing, or you need to have the main pinion opening bored larger. (I used to know the specs, but I can't remember)........
Click to expand...

That's one nice thing about this info, if you swap the parts you can use the earlier bellhousing. Just make sure you swap the bearing to match the bearing retainer, and it is all good.

ironracer1 said:
Also the O.D trans has a weaker case.
Click to expand...

It's not that the case is necessarily weaker, it's that it uses a floating countershaft which can pound the bore out and create issues. The cases are the same, just machined differently.

BTW, I'm not advocating for doing this or anything. I just thought I would share some info I tripped over.
 
Based on the below picture, I am going to guess that the synchro splines aren't the only thing smaller on the OD output shaft. Looks like the area where 3rd gear rides is smaller as well, which means you will need to swap the shaft to put the OD parts in an earlier case.

Darn.

od-mainshafts-hubs.jpg
 
LOL, read about 1/4 of this before I realized it was 10 years old
 
67Dart273 said:
LOL, read about 1/4 of this before I realized it was 10 years old
Click to expand...

Yeah, wouldn't have brought it back from the dead if I could have edited the original post. Or if Photobucket hadn't turned everything into a steaming pile.

When I saw that they were images from my Photobucket account I figured I would at least update it just in case.
 
DionR said:
Makes me wonder. If the input shaft is the same between a 3.09:1 first gear box and an OD box,
Click to expand...
There are 4 fine-spline A833 ratios, and AFAIK there is only one gear that interchanges between any of them, namely the low gear in the 2.66 box and the low gear in IIRC the 2.47 low box.
ZERO of the other gears, AFAIcan remember, are interchangeable.
I have the tooth counts kicking around.
I'll see if I can find them.
Hang on.....
Nope, they're packed away.
BTW
there are TWO, A833 od ratios, namely
the common .73 od, which has a 20 tooth od gear, and another that
I found; the .71od, which has a flimsy 18 tooth od gear.
As far as I recall, NONE of the gears interchange.
That .71 is worth 60rpm at 65mph..... over the .73
I have been told that the .71 comes out of a chevy truck......... but mine came out of a friends F-body, and has a 1x23 spline input. but with the smaller 904-sized output shaft splines. The seller said it came out of a slantycar.

If anybody out there wants to build a 3-speed A833, I have several copies that in a former life were overdrives, but those tiny 18 toothers are MIA.... lol.

Ok found them!
here is a summary of the tooth counts, for fine-spline A833s;

25-29-34-35 ---- the 2.47-1.77-134-1.00 often called the "close-ratio" box
30-26-23-17
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24-29-34-35 ---- the 2.66-1.91-1.39-1.00, standard from 69 down
31-27-23-17
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22-27-32-35 ---- the 3.09-1.92-1.40-1.00 , often called the Commando
33-29-25-17
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22-18-30-35 ---- the 3.09-1.67-1.00-.73od, the F-body box
33-37-27-17
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24-20-30-35 ---- the 3.09-1.67-1.00-.714od, mine (79/80 Aspen slanty)
36-42-27-17
 
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I have been kicking this idea around in my head to replace the three speed in my Duster. I would love to be able to run through the first three gears and then drop into OD when I reach highway speeds. Seems like the best of both worlds to me?
 
BrianT said:
I have been kicking this idea around in my head to replace the three speed in my Duster. I would love to be able to run through the first three gears and then drop into OD when I reach highway speeds. Seems like the best of both worlds to me?
Click to expand...

And you don't have to cut or cobble anything up. All the parts are available.
 
BrianT said:
I have been kicking this idea around in my head to replace the three speed in my Duster. I would love to be able to run through the first three gears and then drop into OD when I reach highway speeds. Seems like the best of both worlds to me?
Click to expand...
There are two A230s, one of them has very similar ratios to the first three gears in the A833od; either is a natural to be swapped.
the A230(-1); 2.55-1.48-1.00 / splits of; .58-.68, versus
the A230(-2); 3.08-1.70-1.00 / splits of; .55-.59, versus
the A833od; 3.09-1.67-1.00-.73/splits of; .54-.60-.73 ....for reference,
the Commando is; 3.09-1.92-1.40-1.00, and splits of; .62-.73-.71


A nice street Roadgear for Second, is ~6.50, give or take ~.3
To get there would take;
with the 2.55low/A230, will take at least 4.30s, and 65=3480
with the 3.08Low/A230, will take 3.91s, and .......... 65=3165
with the A833od ............. will take 3.91s, and ........65=2310
with the Commando, will take at least 3.23s, and ....65=2615
All rpms are by the math and, are approximate.
All are with 27" tires.
But now:
Lets say you have the 2.55Low A230, and a 3.73 gear; your Roadgears are;
9.51-5.52-3.73, and 65=3020
Notice;
that 9.51 is a very nice starter gear,
Second is way short of 6.50,
and the cruise rpm is getting right up there into annoying territory.
Let's say you swapped in the A833od
and kept the 3.73s. Your new Roadgears would be
11.52-6.23-3.73-2.72, and 65=2200
Notice;
the super low starter gear of 11.52, and
the 6.23 Second is daymn close to 6.5
the 3.73 Third gear remains the same as the previous combo, and
65=2200 in od is about perfect.
Let's say you installed the Commando, and to get the Second gear up to 6.xx you would need 3.23s. Ok your Roadgears are;
9.98-6.20-4.52-3.23, and 65=2615
Notice;
9.98 is an excellent starter-gear, and
6.20 is a pretty good Second.
4.52 is an excellent third, and
65=2615 is acceptable to most drivers.
Finally
From the ratios list above, and looking at the splits;
the A230(-2) splits are a wide ratio design
the A230(-1) is has a wide 1-2/ short 2-3, nice progression
the A833od is a very wide ratio design, albeit, a nice progression
the Commando is a close ratio design, with a nice dropped starter gear
>> I have driven all of these ratios behind my 367, with numerous rear gears, and if your V8 has a "bit of a cam", then, IMO, the Commando is the hot ticket.
But if a low rpm engine, then any combo will do.
For a stock to slightly hopped up 273/318/340 IMO, the Commando is the natural choice; it's hard to argue with those Commando splits.
The 360 has enough torque to run just about anything, no matter the cam, but I still prefer the Commando, because the starter gear lets me run right down to 2.76s .....if I might be so inclined to. and I once was.....
 
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