1931 CHEVROLET DOCTORS COUPE - insert 4 speed gearbox

[stein-olav]

1931 CHEVROLET DOCTORS COUPE -    i19,3 KW (26 HK)

is it possible insert 4 speed gearbox?

 

 

[CarlLaFong]

Anything is possible. How much time and money do you have? What is the reason that you want a four speed?

 

[stein-olav]

miss higher speed

[Larry Schramm]

It is best to enjoy the car as it was built. If you overdrive it faster & harder than it was designed & built in the day, generally other stuff starts to break.  If you drive it as built with common sense you will enjoy a ride with pleasure that after being sorted out will be dependable. 

 

I have a 1913 Buick that you can tell when driving it likes 32-36 miles/ hour. It will run faster, but I can sense that the car is complaining and I do not want to break it.  So I just drive it in the sweet spot of the car/ vehicle.  My '15 trucks sweet spot is about 28-32 MPH.

[JV Puleo]

6 hours ago, stein-olav said:

miss higher speed

 

You will almost certainly find the the top gear - whether its a 3-speed or a 4-speed will be 1:1 - i.e. direct drive so a 4-speed box won't go any faster than a 3-speed. With high torque, relatively low speed engines all you'll get are closer gear rations or, perhaps, a "stump puller" 1st gear. There were 4-speed boxes quite early on and a tiny handful had overdrive 4th speeds but none would be suitable for fitting to a '31 Chevy even if you could find one - which would be a trick.

 

 

[stein-olav]

15 hours ago, JV Puleo said:

 

Du vil nesten helt sikkert finne det øverste giret-enten det er en 3-trinns eller en 4-trinns vil være 1: 1-dvs. direkte kjøring, slik at en 4-trinns boks ikke går raskere enn en 3-trinns. Med høyt dreiemoment og motorer med relativt lav hastighet får du bare nærmere girrasjoner eller kanskje et "stubptrekker" 1. gir. Det var fire -trinns bokser ganske tidlig og en liten håndfull hadde overdrive fjerde hastigheter, men ingen ville være egnet for montering på en '31 Chevy selv om du kunne finne en - noe som ville være et triks.

 

 

thanks

[Mark Gregush]

Might be easier to fit a Laycock or similar overdrive in the drive line. Not an uncommon conversion.

[stein-olav]

1 minute ago, Mark Gregush said:

Kan være lettere å montere en Laycock eller lignende overdrive i drivlinjen. Ikke en uvanlig konvertering.

Do you have a link to part
or image
where to buy

[Mark Gregush]

No sorry, I do not have a source. Google Volvo overdrive. One might find them at wrecking yards. There are other brands of inline overdrives. I just redid a rear end for a Model T Ford, the customer supplied a Laycock unit. But thinking on it, is this an open or closed drive shaft? If it is open, this would not work.

Instead of the 4 speed, go with something like a 5 speed (4 with overdrive). Google "Model A Ford 5 speed". While this would not help mount it, you could find information on its use.

[stakeside]

On 9/14/2021 at 1:23 PM, stein-olav said:

miss higher speed

You should consider braking distance at those high speeds. Not such how those mechanical brakes will react.