The Stovebolt Site Forums The Shop Area Driveline 1955 1st series / 1946 Pumpkin 3rd member swap

I think I had read somewhere that the “enclosed drive” center chunk / pumpkin / 3rd member will interchange with a 1955 1st series “open drive” pumpkin…..allowing to change my 1946 to open drive and a modern transmission…..while still using the original axle housing, axles and brakes.

I have searched other archives but can’t find any info.

Does anyone know if this is correct?

I’m thinking this would save a lot of work if I could just change the pumpkin out, (wouldn’t have to change spring perches, wouldn’t have to redo my brakes, wouldn’t have to drop the springs, etc. Obviously, I’d have to have the drive shaft altered to fit and connect to the transmission I chose to go with…..but this seems like an easier swap in my mind.

I have an opportunity to purchase an entire 1955 1st series differential unit. It’s not here, so I can’t visually compare.

The spring perches are different I believe your truck if like my 54 will have the bushings we’re as the newer 55 has the solid no bushing .I think it makes a difference but others will chime in

Thanks Kevinski, that’s why I was asking about changing out JUST the center pumpkin between the two differentials. That way I’d retain my existing rear end housing, perches, springs, brakes, etc.

It should work just fine. I used a 57 1/2-ton pumpkin in 40 housing.

I believe you'll have to add something like traction bars used on drag cars to stabelize the housing relative to the frame. As I recall my 48 half ton had a pivot point at each spring with a rubber bushing. Absent the torque tube the housing can wind up on acceleration. I had a 53 car with a Pontiac rear end bolted solid to the springs and a '53 331 Cad engine. Under hard acceleration the housing wound up far enough to break the u-joint yoke. I added traction bars, sometimes called radius arms, and that cured the problem. The springs weren't strong enough to hold the torque by themselves. The situation is worse with the torque tube housing because of the pivots.

As said above, the torque tube axle housing has to rotate where it attaches to the rear springs as the rear wheels move up and down. You will have to find a way to "capture" the axle to the springs when you convert to an open driveshaft. It's been done before.

The easiest way to avoid the issue with the rubber mounts of the torque tube is to weld on solid spring perches available from most vendors. You will likely need to cut off the rubber-mounted perches to make room for the new perches.

DL, the swap will work. I did a 55 in to my 54 GMC. Keep the axles straight to which is right and which is left. Mine were different lengths. For the pivots. Set the Angle. I had a machinist make a set of perches to weld on the back side, changed out the U-Bolt plate, and added a U-Bolt.

Pictures sure would help.

I put a 55-59 truck center section in my 50 truck housing. We cut off the pivoting perches and welded on solid perches. My friend has done the same thing with a 39 truck housing installed in his 30 Chevy coupe to convert to open drive. 3.90 gears and T5's in both.

I’ll get those up later this week

A 3.90 gear set with a T-5 with .72 overdrive with stock height 28" tires is about as dialed in as it could get for a 216, 235, 261 Stovebolt.
There is an old adage, "There is no such thing as free lunch". Not true at all with the advent of putting a T-5 behind a Stovebolt.
I sure would like to know who the first person was who did it.