Optional Gear Ratio for 3 speed or Overdrive Transmission

[Loren]

There's an old joke told by Rodney Dangerfield about dinner at his house.

"You don't brush your teeth after dinner, you count them!"

Well, I am going through an Overdrive transmission and I decide to try the only optional gear set for the 1940-54 transmission.

At the same time I am building a 1939 Ford V8 transmission and a Studebaker R10 Overdrive ( very old school, mounted in the middle of the torque tube ) to replace the hated T5 in my Model A. My Dad said he had a set of Lincoln Zephyr gears and I thought I try them at the same time. Well a Lincoln Zephyr gear set is 3 gears and if you want a NOS set they are astronomical in price! ( there's a set like I thought I had for $2,895 on eBay ) Turns out what I had was two of the correct gears and a cluster for a 1955-56 Ford with a 272 V8. When I looked at a gear chart from Van Pelt Sales and counted the teeth nothing made sense. Hence the Rodney Dangerfield joke. It took a phone call to Mac Van Pelt to identify what I had.

Back to the Plymouth:

At the time my cars were built ( 1949 & 52 ) the speed limit was 55 mph and the closest thing to a freeway in Los Angeles was the Arroyo Seco Parkway ( aka Pasadena Freeway ).

Which is kind of laughable as a "Freeway". Anyway that's why the old cars had 3.90 rear ends and 3 speed transmissions. When Chrysler went to column shift ( largely so a 5 passenger car could suddenly become a 6 passenger car ) They tried the one year only second gear ratio and thought better of it for 1941. Turns out that 1940 second gear ratio was highly regarded with the "Boy Racers", it making the mopar gear box more close ratio. Not only were there lots of factory gears sold as replacement parts, the after market made them too. There's plenty of them for sale on eBay for less than $300! That seemed to me like a cheap experiment.

So here we go counting teeth again.

The 1940 Cluster Gear ( aka Transmission Countershaft Gear ) is part number 853-885 and has the tooth count of 32-25-19-14

Whereas the 1941-54 tooth count is 32-23-19-14. Second gear is the only different ratio and thus you only have to change two gears.

The 1940 second gear is part number 692-687 and it's tooth count is 23.

The 1941-54 second gear tooth count is 25.

Enter the Overdrive:

The Plymouth R10-G1 Overdrive will shift into 2nd Overdrive plus the top gear overdrive making it actually a 5 speed.

When new, the cars were delivered with 4.30 rear end gears giving them lively acceleration....to 55 mph.

Now days as the song says "I can't drive 55!"

My 49 came with a 3.73 rear end and with Overdrive that car is really happy at 55 mph and 70 sounds like 55 used to.

When I installed the Overdrive I swapped the speedo gear from my old transmission which has 17 teeth and the speedo is close ( p/n 652-848 ). With a tire size change and I would change to a 16 tooth speedo gear P/N 652-846 which is also useful with a 3.54 rear end ratio ( there being no other smaller tooth count speedo gears ).

One fly in the ointment:

Between the loose needles used in the cluster gear and the thrust washers it's a challenge to assemble the countershaft. Chrysler had a solution for the dealer mechanics, the Miller Special Tools C-578. It is a short rod slightly smaller in diameter than the countershaft and only as long as the cluster gear with the thrust washers. You assemble the cluster gear with grease ( to hold the needles and washers ) with the tool inside. After all the other parts are installed you invert the case and the cluster falls into place. Then you push the counter shaft in and the tool keeps everything aligned until the counter shaft is in place. The same method is used by locksmiths changing the pin combinations.

Only one problem, try and find one! SO...I am going to make some from plastic rod stock which will work even better than the metal one did.

 

If you enjoy using your brain and working little issues out, the old car hobby is the best! Have fun!

[Sniper]

13 minutes ago, Loren said:

. Chrysler had a solution for the dealer mechanics, the Miller Special Tools C-578. It is a short rod slightly smaller in diameter than the countershaft and only as long as the cluster gear with the thrust washers. You assemble the cluster gear with grease ( to hold the needles and washers ) with the tool inside.

 

Same deal for the A833, which a broomstick is the perfect diameter.  Not sure what diameter you need though,, going to be close the counter shaft diameter.  

[DJ194950]

If I remember right a 1" or was it a 3/4" wood dowel works just fine!

 

I rebuilt 2 R-10's some years back with the wood dowel doing just fine.

 

Nothing fancy or expensive here.

 

DJ

[Sniper]

10 minutes ago, DJ194950 said:

If I remember right a 1" or was it a 3/4" wood dowel works just fine!

 

Both are on the shelf at my local hardware store.

[Booger]

Very impressive break down...

And yes the 49 3.73 with an R10 skips right along at 70 mph

(Wish I could find a R10)

[JohnS48plm]

I used a wood dowel, it's still in my toolbox.

[FarmerJon]

3 hours ago, Loren said:

There's an old joke told by Rodney Dangerfield about dinner at his house.

"You don't brush your teeth after dinner, you count them!"

Well, I am going through an Overdrive transmission and I decide to try the only optional gear set for the 1940-54 transmission.

At the same time I am building a 1939 Ford V8 transmission and a Studebaker R10 Overdrive ( very old school, mounted in the middle of the torque tube ) to replace the hated T5 in my Model A. My Dad said he had a set of Lincoln Zephyr gears and I thought I try them at the same time. Well a Lincoln Zephyr gear set is 3 gears and if you want a NOS set they are astronomical in price! ( there's a set like I thought I had for $2,895 on eBay ) Turns out what I had was two of the correct gears and a cluster for a 1955-56 Ford with a 272 V8. When I looked at a gear chart from Van Pelt Sales and counted the teeth nothing made sense. Hence the Rodney Dangerfield joke. It took a phone call to Mac Van Pelt to identify what I had.

Back to the Plymouth:

At the time my cars were built ( 1949 & 52 ) the speed limit was 55 mph and the closest thing to a freeway in Los Angeles was the Arroyo Seco Parkway ( aka Pasadena Freeway ).

Which is kind of laughable as a "Freeway". Anyway that's why the old cars had 3.90 rear ends and 3 speed transmissions. When Chrysler went to column shift ( largely so a 5 passenger car could suddenly become a 6 passenger car ) They tried the one year only second gear ratio and thought better of it for 1941. Turns out that 1940 second gear ratio was highly regarded with the "Boy Racers", it making the mopar gear box more close ratio. Not only were there lots of factory gears sold as replacement parts, the after market made them too. There's plenty of them for sale on eBay for less than $300! That seemed to me like a cheap experiment.

So here we go counting teeth again.

The 1940 Cluster Gear ( aka Transmission Countershaft Gear ) is part number 853-885 and has the tooth count of 32-25-19-14

Whereas the 1941-54 tooth count is 32-23-19-14. Second gear is the only different ratio and thus you only have to change two gears.

The 1940 second gear is part number 692-687 and it's tooth count is 23.

The 1941-54 second gear tooth count is 25.

Enter the Overdrive:

The Plymouth R10-G1 Overdrive will shift into 2nd Overdrive plus the top gear overdrive making it actually a 5 speed.

When new, the cars were delivered with 4.30 rear end gears giving them lively acceleration....to 55 mph.

Now days as the song says "I can't drive 55!"

My 49 came with a 3.73 rear end and with Overdrive that car is really happy at 55 mph and 70 sounds like 55 used to.

When I installed the Overdrive I swapped the speedo gear from my old transmission which has 17 teeth and the speedo is close ( p/n 652-848 ). With a tire size change and I would change to a 16 tooth speedo gear P/N 652-846 which is also useful with a 3.54 rear end ratio ( there being no other smaller tooth count speedo gears ).

One fly in the ointment:

Between the loose needles used in the cluster gear and the thrust washers it's a challenge to assemble the countershaft. Chrysler had a solution for the dealer mechanics, the Miller Special Tools C-578. It is a short rod slightly smaller in diameter than the countershaft and only as long as the cluster gear with the thrust washers. You assemble the cluster gear with grease ( to hold the needles and washers ) with the tool inside. After all the other parts are installed you invert the case and the cluster falls into place. Then you push the counter shaft in and the tool keeps everything aligned until the counter shaft is in place. The same method is used by locksmiths changing the pin combinations.

Only one problem, try and find one! SO...I am going to make some from plastic rod stock which will work even better than the metal one did.

 

If you enjoy using your brain and working little issues out, the old car hobby is the best! Have fun!

I am mid-build of a R10 as well. Have you already gotten yours done with the "fast second" 1940 gear set?

My OD was from '55 and had pin type synchros, making the '40 second not a direct drop in. The gear has a different spline size than the gear for pin synchros. You can switch to the earlier strut synchros, but you will also need to swap in the matching input shaft, clutch gear, and shift fork.

Here is the difference in the two ratios vs rpm & speed, based on a 28" tire and 3.9 rear gears.

 

The countershaft is just a few thousandths larger than .750

 

[Booger]

 Who wouldnt love those results? Rough math sez 65mph at 2300 rpm in OD? what Im talkin bout

[kencombs]

Dad always kept a normal cluster shaft, cut to the correct length for common trans.   He ground a short taper on each end to aid in starting it.  In those days is was the 55-64 Chevy and Ford 3spds.   use it to drive out the installed shaft and use the 'real' one to drive out the dummy.   Or, since he did this almost every  day , he could just fill the gear with needles and lots of sticky wheel bearing grease and put it together    I used the cheat shaft.

[KLyons]

Thank you for all of that useful information. Trying to decide whether to stay with the original 1940 gearset in my P9 and keep it 3 speed or rebuild an R10 I have had sitting and swapping the "fast second" gearset into that. I dont plan on driving highways often but it would be nice to have that option !

[FarmerJon]

On 3/10/2024 at 10:03 AM, KLyons said:

Thank you for all of that useful information. Trying to decide whether to stay with the original 1940 gearset in my P9 and keep it 3 speed or rebuild an R10 I have had sitting and swapping the "fast second" gearset into that. I dont plan on driving highways often but it would be nice to have that option !

I am interested in what @Loren has to say, but if you look at the charts I worked up, "Fast second" in an OD doesnt make much sense, because 2nd OD is SO close to straight 3rd. At 3000rpm in 2nd OD, a shift to 3rd is only gives you 5mph and maybe 100 rpm before you are right back to 3000rpm.

Now if your driving style is to treat it as a 4 speed, shifting from 1-2-2od-3od, sure, that will work. But I plan to wire mine up with the standard kickdown and a shifter mounted kickdown switch, so I can shift 1-2-2Od-3-3od, so I like the standard second better. 

 

I think either way, you are better off with an R10, especially if you have one on hand. Dropping to lower numerical rear gears doesn't gain much on the highway, and numbs low speed performance.

I drive my '48 with standard 3speed and 3.9 gears in traffic and on the highway (70 is no problem, other than loud). While I have enough power to generally keep up, I wouldn't want less!

Now if you do not have a OD, the Fast Second makes great sense. I often find that if I upshift to 3rd too soon (below 40) while merging onto the highway, it is a total dog untill RPM come above 2100 or so.

 

Edited March 12 by FarmerJon

[Tired iron]

I recently rebuilt the 3 speed transmission in my International Scout and used the same trick with a extra lay shaft with a slight taper ground at the ends to help get it started when pushing the dummy shaft out. That plus assembly grease plus a string cradle to lift the cluster gear slightly as needed did the trick.

[KLyons]

2 hours ago, FarmerJon said:

I am interested in what Loren has to say, but if you look at the charts I worked up, "Fast second" in an OD doesnt make much sense, because 2nd OD is SO close to straight 3rd. At 3000rpm in 2nd OD, a shift to 3rd is only gives you 5mph and maybe 100 rpm before you are right back to 3000rpm.

Now if your driving style is to treat it as a 4 speed, shifting from 1-2-2od-3od, sure, that will work. But I plan to wire mine up with the standard kickdown and a shifter mounted kickdown switch, so I can shift 1-2-2Od-3-3od, so I like the standard second better. 

 

I think either way, you are better off with an R10, especially if you have one on hand. Dropping to lower numerical rear gears doesn't gain much on the highway, and numbs low speed performance.

I drive my '48 with standard 3speed and 3.9 gears in traffic and on the highway (70 is no problem, other than loud). While I have enough power to generally keep up, I wouldn't want less!

Now if you do not have a OD, the Fast Second makes great sense. I often find that if I upshift to 3rd too soon (below 40) while merging onto the highway, it is a total dog untill RPM come above 2100 or so.

 

     Ahh I see what your saying!

[Sniper]

I love these types of discussions, thanks for starting this one Loren.

[Loren]

On 3/10/2024 at 7:36 AM, FarmerJon said:

I am interested in what @Loren has to say, but if you look at the charts I worked up, "Fast second" in an OD doesnt make much sense, because 2nd OD is SO close to straight 3rd. At 3000rpm in 2nd OD, a shift to 3rd is only gives you 5mph and maybe 100 rpm before you are right back to 3000rpm.

Now if your driving style is to treat it as a 4 speed, shifting from 1-2-2od-3od, sure, that will work. But I plan to wire mine up with the standard kickdown and a shifter mounted kickdown switch, so I can shift 1-2-2Od-3-3od, so I like the standard second better. 

 

I think either way, you are better off with an R10, especially if you have one on hand. Dropping to lower numerical rear gears doesn't gain much on the highway, and numbs low speed performance.

I drive my '48 with standard 3speed and 3.9 gears in traffic and on the highway (70 is no problem, other than loud). While I have enough power to generally keep up, I wouldn't want less!

Now if you do not have a OD, the Fast Second makes great sense. I often find that if I upshift to 3rd too soon (below 40) while merging onto the highway, it is a total dog untill RPM come above 2100 or so.

 

Thank you for the charts!

I have had a couple of vehicles with Overdrives in them. I personally think the flathead Plymouth benefits the most from them. There is a certain charm about a flathead Plymouth and the Overdrive transmission only adds to it.

The governor does exactly what it’s name implies, its in control.

The only gear that is really locked out is reverse. You can’t use Overdrive in first gear because you can’t windup the engine far enough to trigger the governor. Second gear isn’t that easy to trigger either. I’ve done it but its not easy and you’d probably select high gear anyway rather than bother. The governor measures drive shaft speed and not road speed and most of us are not going back to a 4.30 final drive ratio like the factory supplied in Overdrive cars. So in truth you’d likely never use 2nd gear Overdrive.

The drive shaft speed vs road speed will vary with the final drive ratio you have of course, so the governor trigger speed is going to be higher with a 3.73 vs 4.30 final drive ratio.

When you consider the weight of a flathead Plymouth and the fact that its being pushed along with around 100 hp, they do pretty good!

I read a road test of one and it managed a quarter mile in 22 seconds, about the same as a Porsche 924! So they are in good company ( even if there are more flathead Plymouths running around now than Porsche 924s lol )

[Loren]

All ready to re-install.

I bought this one on eBay for $400 delivered. When I changed the Counter Shaft Gear ( aka Cluster gear ) I didn't like the countershaft so I replaced it with a good used one. The reverse lock out switch was open so I replaced that as well. Other than those items it was in very good shape.

If you are going to go through one of these, the service manual and a parts book will help. There's a couple of little secrets you have to know about. Example: the lockout arm must be retracted to take the back housing off and there is this tiny tapered pin you have to drive out with a pin punch to do that. If the transmission is covered in grease you may not find it.

I got all my parts super clean and checked the movement and function at each stage of assembly. I did not however install the governor as the book says to do. When I rolled the transmission over on the bench the pawl slid into place and things wouldn't turn as expected. I took it apart once more and figured out what had happened. Not a bad thing as I am now really good at assembly and disassembly for the experience. lol Of course it happened again and I simply turned it over and the pawl slid back into its rest position.

Since my Suburban has Back Up Lights I wanted to see if I could add the switch with the Overdrive. It does fit and it does work!

The beauty of the B-W R10 G1 Overdrive is all the MoPar replacement parts fit. Most of the wear parts in the Overdrive unit are standard B-W parts common to the other makes that used it. The reverse lock out switch is different however. When you see them on eBay most sellers call them a "Neutral safety switch" because that is what they look like. If p/n 1370-462 ever becomes hard to find at a decent price an adaptor could be made to fit a "real" neutral safety switch. ( another note: there's a short little round part that relays the movement of the reverse shift shaft to the switch. If you remove the switch under the car it will fall out and you could lose it. Best to check it before you install the transmission )