Technical Swapping rear gears

Welcome back to amateur hour! Looking to make my '49 Chevy 3100 a little more highway friendly. Right now it's all we can do to get to 50 mph and she's screamin' when we do. I opened up the rear to make sure exactly what I've got back there an it's definitely 4.11 ...

My question: We've got a set of 3.55's from a '69 Firebird. Can they be swapped in for the 4.11's in my existing original rear end? Thanks in advance for any info y'all might be able to offer...

 

No. The physical parts from the torque tube rear and the later open drive will not interchange.

 

I don't know if pass car and truck rears are the same but a car with auto trans [54' back?] will have higher gears, don't remember what the ratio is but may be too much in opposite direction and the truck will be a real dog....

 

car and truck rears are different. No interchangeability between them.

 

There are also brand new gearsets available from the various classic Chevy vendors.

 

Define screaming. What does your tach say?

A 4.11:1 gear should be pretty highway friendly with a tall tire like the truck came with. That would be comfortably cruising in the 55-60 mph range. But most of the time the fellas like a taller gear, I totally understand that.

Do you have the whole rear from the fire bird? They swap in pretty easy.

 

Don't have a tach. Truck tops out at 50 mph or a hair over, and when there it sounds like my drivetrain could be in 100 pieces in the middle of the highway at any given moment.

15 inch wheels with 75r15 tires all the way around.

We do have the whole Firebird rear, but then we'll also need a drive shaft (to replace the torque tube) and tranny. The original plan was to do all three, but the more I look into it, the more it looks like my budget isn't big enough. I'd have to pay labor as well, since this is not a job I could do by myself. Might be able to do a gear kit and have a couple of 5 lug axles made (to match up with the disc kit we already have in front). Need to do a little more searching.

Thanks all for the info! Much appreciated...

 

With the stock size 600 x 16 tires it should be turning about 2550RPM's at 50 MPH with a 4:11 gear

BTW in case you don't have this info, here is a lot of the factory spec information on your truck
https://www.gmheritagecenter.com/do...its/Chevrolet-Trucks/1949-Chevrolet-Truck.pdf