Tranny Swap

[weasel]

I have a 49 B1 with a three speed in the floor shift. I found a 4 speed floor shift that I would like to change out.

I don't have the three speed out so I can't expect the shafts etc.

 

The four speed has a date on the top of 1-21-48, the Id number is C-39871 on the top plate. The number on the  main case is C88661. Does anyone know if this swap will work? Are the input and out put shafts the same Etc.

Thanks Dave

[Reg Evans]

Why do you want to do the swap ?  The 4 speed is essentially a 3 speed with a granny low. If it's a 1948 model it's a non synchro crash box too.

[pflaming]

Question:  if a 3:?? Low ratio differential was swapped in, would not that to some degree make the high gear an "over drive " highway gear? I don't know how low the ratios go.

[Merle Coggins]

Unless it is specifically an overdrive transmission the "high gear", as you put it, is direct drive. 1:1 ratio. 

Merle

[Dave72dt]

9 minutes ago, pflaming said:

Question:  if a 3:?? Low ratio differential was swapped in, would not that to some degree make the high gear an "over drive " highway gear? I don't know how low the ratios go.

It could give you a similar effect as an overdrive, meaning lower engine rpm for the same actual road speed.  It also means you have less torque available to maintain that speed which also means you'll need to downshift sooner when going up a steep grade.  Same rpms means higher road speed. Same road speed equals lower engine rpm.

[Don Coatney]

Just for clarification of terminology. In all standard transmissions high gear is a 1/1 ratio. In other words  the driveshaft turns one revolution for every revolution the crank shafts turns. In an under drive transmission the driveshaft turns something less than one  for every turn the crankshaft turns. There are normally several under drive ratios in a standard transmission but top gear is always a 1/1 ratio. In an overdrive transmission the drive shaft turns something greater than 1/1. In a 33% overdrive transmission the driveshaft turns 1.33 revolutions every time the crankshaft makes one revolution. The ratio of the differential has nothing to do with the relationship of the engine crankshaft to driveshaft ratio.

 

So if you want a vehicle to run 70 MPH while turning 2200 RPM,s you must consider the horsepower/torque curve of the engine, the various ratios of the transmission when it is in both under drive, 1/1 top gear, and overdrive along with the ratio of the differential, and the tire diameter.

To make a statement that a change in differential gearing and or change in tire size will make a standard transmission an over drive is just plain not true.

[weasel]

My three speed is flying out of gear.

Third gear

[Jeff Balazs]

The 4 speed tranny has slightly higher ratios for 2nd and 3rd gear as compared to 1st and 2nd gear in the 3 speed tranny. This translates into a slightly higher top speed for a given RPM in each of these two gears. As long as the 4 speed you have is not one that was mated to a fluid drive set up it should fit up to the bell housing just fine. The only thing I can't say is if the drive shaft length will require modification. Likely not an issue but you need to verify this.

Jeff

[P15-D24]

5 minutes ago, Jeff Balazs said:

The only thing I can't say is if the drive shaft length will require modification. Likely not an issue but you need to verify this.

 

And probably the ujoints.

[Dodgeb4ya]

I'd take the much heavier duty 4 speed always over the small 3 speed. The 4 speeds don't really ever have any shifting issues and last forever.

The spur gear non syncro 4 speed transmissions have a great sounding normal whine in 2nd and 3rd gears too.

[MBF]

I'm 99% sure that the bolt pattern on any 3 speed differs from that of the 4 speed and requires a bellhousing change.  Not sure if a 3 spd b/h can be tapped to accept the bolt pattern of a 4 speed.

 

[POPTOP]

does anyone know if the tranny pops out of 3rd  be repaired

[BigDaddyO]

18 minutes ago, POPTOP said:

does anyone know if the tranny pops out of 3rd  be repaired

At the risk of getting voted down, I would first off recommend checking your transmission fluid level.

[Dodgeb4ya]

15 hours ago, MBFowler said:

I'm 99% sure that the bolt pattern on any 3 speed differs from that of the 4 speed and requires a bellhousing change.  Not sure if a 3 spd b/h can be tapped to accept the bolt pattern of a 4 speed.

 

 

1 hour ago, POPTOP said:

does anyone know if the tranny pops out of 3rd  be repaired

Is it a syncro trans? Any transmission can be fixed.

[Dodgeb4ya]

This new format sure is confusing me. I try to just quote POPTOP and also end up with MBFowlers post too.

Tried three ways to change it. Cannot.

[Desotodav]

5 hours ago, POPTOP said:

does anyone know if the tranny pops out of 3rd  be repaired

Could just be a linkage adjustment... if you have a column shift?

[weasel]

It is a floor shifter.

What could cause it to pop out of gear? the 3 speed?

Has correct fluid level.

[William Davey]

Weasel - I had my trans rebuilt by Northwest Transmission in Winchester Ohio. They advertise in Hemmings.  They work almost exclusively on old stuff and claim to have 14 tons of parts on hand. I'm not associated in any way, I just had a good experience with them.