Use oversized tires to lower engine revs?

[egor]

My '38 Special starts to feel like it's over-revving way before I get up to freeway speed, and the car likes to overheat when it's pushed hard.javascript:void(0) I know there will be a sacrifice in riding comfort if I put 7:50-16's on the car, but the added diameter will bring the effective rear end ratio down from 4:44 to about 4:10. It looks like there's clearance in the wheel wells, but before I buy new tires and tubes, I hoped there was a a success story out there. Somebody would make their fortune manufacturing high speed gear sets for pre-war cars!javascript:void(0)

[Guest ZondaC12]

all i know for sure is that its gonna throw your speedometer out of whack! but you could calibrate it, the old "add 5, 10, 15 etc whatever it might be to what the reading is"...

[egor]

Thanks, Zonda.

[Guest imported_JPIndusi]

Try to find a pumpkin from a Century or Roadmaster which may bolt into the Special rear-end housing. I do not know for sure, but I suspect there were other ratios used on the larger series.

I know that the 1940 to 1955 pumpkins will bolt into these rear-end housings, but not sure if other years will fit into a 1938 housing.

Good luck.

Joe, BCA 33493

[egor]

Thanks, Joe.

I'm guessing what part of the differential a pumpkin might be, but I'm not familiar with that term. Could you clarify? Looking for a 40-55 sounds good. 38 Century rear ends are hard to find, and the Roadmaster rear end was almost as low a ratio as the Special (4.19, I think).

Egor

[The Old Guy]

The 40 up unit will not fit your Buick. You need a Century (3.9) or an automatic(3.6) from a 38 I think the 37 Century will also work.

[Guest imported_JPIndusi]

I agree (who wouldn't) with The Old Guy, the 1940 to 1955 pumpkin will not fit your car. He gave some good possiblities and let me say that anything taller than what you have will work wonders. You will think you bought a new car!

The pumpkin refers to all the gears and bearings that fit inside the center of the rear end housing and includes the ring, pinion, side gears, spider gears, bearings etc. If you get one from another car that is in good condition (have an expert check it) the switch-over is possible. You will re-use your drive shaft and torque tube and connect it to the splined pinion shaft. There is usually a roll pin that you need to drive out to release the current drive shaft from the pinion shaft.

Good luck.

Joe, BCA 33493

[egor]

Thanks, Joe and "Old Guy".

This discussion has me thinking about how I changed one of my motorcycles' drive sprocket and radically altered the gear ratio at minimal cost. I'm no mechanic, but it seems to me that doing the same to a car would be possible by putting in a pinion gear with 2 or 3 more teeth. I'm sure getting that machined would be expensive, but a Century or automatic gear set wouldn't come cheap, either. Please forgive my ignorance.

Egor BCA 41415