OK I got a 52 Plymouth Cranbrook. It has a 3 on the tree and a flathead 6.

The car is geared seriously low! The effective top speed is like 50 mph.

So my question is this, what is the easiest way to get a little more speed out of the car? Changing rear end gears?

Is there an overdrive for it? Is there any later model trans that I can just bolt to the motor?

I have never attempted a rear end change, is it difficult?

 

in those years they had factory O.D. for 3 speed stick trans. they was for better MPG, not speed. they may be hard to find. to in gauge the O.D. you pull a lever. thats all i can remember.

 

Check and see ? It may have one of the early 8 3/4 rears Other wise you can adapt almost any rear end 8 3/4 would probably be the easiest

 

How do I measure that? I have never touched the drivetrain behind the engine. Trans, rear ends, total mystery to me.

 

I find this difficult to believe, "unless....................."

Have you checked tire diameter against what would have been original?

I'm sure these didn't cruise at 70-80 in their day, but in my local area, growing up, we certainly had 65 mph highways.

 

Measure the total width of the rear end and measure the distance between the spring perches

 

Great point....

 

Someone else could have changed it before you go your hands on it as well. Check out what the other's have mentioned. Maybe pull the diff cover (if not a 8 3/4) and divide the amount of ring gear teeth by the amount of pinion teeth. This will tell you what your axle ratio is.

 

Seems really strange to me. I had a 1953 Plymouth Cranbrook, flathead 6, 3 on the tree stock set up and it would easily hit 65 - 70 mph. It didn't have a lot left powerwise at that speed but would certainly cruise right along.

 

Yeah it turned out it was a combination of facts. I changed out the front shocks, which were useless, and the carb was seriously lean. Changed the shocks, gave the car a tune-up, took it for a test and got it up to 70.