Model B gearbox for a Model A?

[roenidoc]

I am keen on an overdrive, but it is expensive and hard to get in Germany. Now I would have the chance to buy a synchronized 4-speed gearbox from the Model B.
Will this gearbox fit into the Model A without any problems? Do any of you have experience with it? Would it give me the desired advantages of an overdrive: better progress uphill (closing the gap between 2nd and 3rd gear) and protection of the engine when cruising on the highway?
Thanks for your opinion!

[alexiskai]

Here's a discussion on the HAMB of some things to know about this mod. It does not give you an overdrive. It requires at least as much work as installing an overdrive.
https://www.jalopyjournal.com/forum/...daptor.616719/

[Joe K]

My experience (another's car) is that the Model B box saves you from having to double clutch between 2nd and 3rd. I still double clutched in 1st to 2nd. Some might not have to depending on the transmission oil used? (I guess this was 600W)

I can't tell you WHAT 600W oil this was. There have been a lot of modern oils sold as 600W but were not.

There is no difference in the speeds/shifting times/feel of the car.

Joe K

[Charlie Stephens]

I am confused. The standard Model B box was 3 speed synchronized upshifting first to second, and second to third. Downshifting was synchronized third to second. The 4 speed box was totally totally unsynchronized and used primarily in large trucks.

Charlie Stephens

[Joe K]

Originally Posted by Charlie Stephens

I am confused. The standard Model B box was 3 speed synchronized upshifting first to second, and second to third. Downshifting was synchronized third to second. The 4 speed box was totally totally unsynchronized and used primarily in large trucks.

Charlie Stephens

I suspect you're describing the B box "as advertised" and likely as new. As I said there have been changes in the oil, some of which may have increased the tendency to "clash."

I've seen this myself in the Model A which even while double clutching CAN clash - but usually doesn't. The oil makes a difference in the ease - and one of the reasons why I run straight "Lubricity additive" rather than 600W in my gearbox (it's been a while and probably better alternatives since then but my feeling was that the additive was more "consistent" in its stickiness and lubricity than 600W)

The "lubricity additive" as a lubricant has been discussed - we don't need to re-hash. Many opinions differ by their very nature and we can leave those to their foundational threads.

The Model B box doesn't have true "synchronizers" as would be found in modern transmission - rather the gear helix/geometry was made to make mesh occur while minimizing the clash. One imagines the oil one used MIGHT make a difference here too.

The 4 speed box was basically a "re-hash" of the Borg-Warner 4 speed. While I don't claim a direct familiarity, I imagine it was similar internally to the Model A with straight cut gears. Green Book might tell more.

Joe K

[roenidoc]

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Originally Posted by alexiskai

Here's a discussion on the HAMB of some things to know about this mod. It does not give you an overdrive. It requires at least as much work as installing an overdrive.
https://www.jalopyjournal.com/forum/...daptor.616719/

That is a helpful statement and a worthwhile link. Thank you!

[Bob C]

Here is a picture of the 1932 trans and synchronizer.

[Jim Brierley]

Originally Posted by Charlie Stephens

I am confused. The standard Model B box was 3 speed synchronized upshifting first to second, and second to third. Downshifting was synchronized third to second. The 4 speed box was totally totally unsynchronized and used primarily in large trucks.

Charlie Stephens

Charlie is correct, totally. Even putting the passenger 'B' trans is a lot of work, but rewarding because of better gear ratios and synchronized 2nd and 3rd gears. The best and easiest thing to do is put a V8 trans behind your A, using an adapter kit from Cling's.

[Joe K]

Originally Posted by Bob C

Here is a picture of the 1932 trans and synchronizer.

Bronze fingers inside that sync? It shows as "assembly."

The owner of the Model A/Model B swap didn't say - but the tranny he swapped may have had some miles on it too - which might result in my observation?

My mind goes back to a 1990 Chevrolet 5 speed C1500 truck which at 48K miles started to require "double clutching." According to my brother the Chevrolet nut draining the oil might reveal pieces of "synchronizer" - which it did.

According to the Chevy Garage that particular model year had no less than FIVE different sources for manual transmission. Mine was Borg-Warner but he shakes his head and says "BW has 'forgotten' a lot on how to make a good tranny."

I traded the truck to get away from an issue. And a manufacturer.

Prolly should have stuck to an automatic.

Joe K

[Chris Haynes]

You will be better off using a V8 trans and the Clings adapter kit. http://clingsaftermarket.com/addtocart.asp?prod=3000

[PC/SR]

The V8 installation with Clings adapter is quick and easy, no different than swapping an A trans in and out.

[jack backer]

32 early synchro, 1939 and up later synchro, later synchro is way superior. There are many ratios available, including Lincoln zephyr ratios that will fit in a 32 case.. way better to get a late top loader 3 speed (used in pickups till ‘48) which is a better design.. and a late dual detent shift tower with a swan neck shift lever ..

[rotorwrench]

The folks that manufacture the Mitchell overdrive also manufacture a gear set for the model A that is synchronized between 2nd & high. They have been selling this as a complete transmission using the model A case. The box uses spur cut gears but has ratio choices for low & 2nd gears. It makes it more like the B gearbox without the hassle of all the changes to use one.

The B transmission has the old style spur cut gears with the B Synchro sleeve & hub. They work OK but not as well as the 91A transmission of 1939.