I have a 1953 Chrysler with the 331 extended bellhousing block and the M6 "Fluid Drive" transmission. I'd like to get the RPMs down a bit on the freeway now that I've got the car all balanced out, and its REALLY fun to travel in and runs great on cheap piss gas. I've read through some forums here, and though there are some O/D options, they are mostly VERY expensive, and require a LOT of modification (cut off bellhousing of trans and bolt front pump to adapter, custom cross member needed, park brakes to be reconfigured to back wheels...) and I'd like to keep it simple. Also, Gear Vendors is very expensive, the external/remote overdrive adds additional gear/bearings and losses to the system, but is probably easier and maybe even cheaper than the trans swap. One thing about the M6, you can select a "low" range and the transmission will start in 1st and shift into 2nd. For me, this 1st gear is WAY to short. The car LUNGES off the line, but then it's topped out too soon and it's time for a let off the gas, count to 20, shift. Or shift into "high" range. In this case, "low" range would only be used in VERY extreme situations, or maybe the ratios were picked originally to help the 6 cylinder cars to get moving. Trans ratios are, 3.28, 2.04, 1.61, 1:1. I think I could either swap the rear gear set, or the entire axle, and both drop RPM and gain economy out of 4th (1:1) gear, and have a more useable 1st and 2nd gear. Currently I believe I have the most "highway" ge****t for '53 with 3.36:1 rear ratio. Is anyone aware of longer legs that will fit the '53 rear axle? Or any gear sets for different model axles that fit? If not I might just be doing a whole rear axle ***embly swap.
The rear end swap is likely the least expensive option. If they are available, something like a '66-ish Coronet may be very close, a 10" drum should be fine. The Ford 9" with stock axles keeps the lug pattern the same, if it is the same as the '53 pattern.
You sure it’s 3.36 gears? That’s not really considered deep rear ratio, like say 4.11’s, etc. 3.36 (imo) is a decent compromise between acceleration and highway cruising. You should search on how to figure out the actual ratio, the get busy with a floor jack. What’s the RPMs and speed you are at on the highway?
My initial thoughts were the same as Budget’s, are you sure it’s 3.3? Mark the prop shaft and count wheel vs shaft revolutions. If it turns out to be something else then maybe you can get a 3.3.
Yeah, my 61 Impala has 3.36 gears and it goes down freeway with ease. You had better jack up one rear wheel, put a chalk mark on the rear end housing and a corresponding mark on the driveshaft. also a chalk mark on the tire, now turn the tire 2 revolutions and count how many times the driveshaft goes around. 3.36 would be just a little more than 3 1/4 turns. let us know what you find
My 55 Plymouth with automatic transmission has 350 ish gears and it cruises down the highway fine. I'm thinking you have something steeper.
I would posit this is the main issue, regardless of the rear gear ratio. A granny first gear will be slightly more tolerable with a lower rear ge****t, but if it's already in the "WAY" category, I have my doubts a change in the rear diff alone will make you happy. ****s, but this is what we sign up for.
The change in your transmission gearing is not going to change. If you alter the rear gear to make low "work better" your going to create a worst "lugging" problem after it shifts (which is probably your current problem). If you really have a 3:36 rear gear, what you have is probably as good as it gets without spending a lot of money putting a "real" automatic or manual transmission in the car. What you currently have is very nearly the top performance car, of that year, that was available. A 54 Chrysler New Yorker 2 door sedan with 331 hemi and a single 4 barrel carburetor was the "fastest production car in the world" you could buy at the beginning of the 1954 automobile production. The HP wars were just starting to be cranked up, times changed.
Play with this calculator a bit https://www.advanced-ev.com/Calculators/TireSize/ you can plug in any three factors and get the fourth. Speed, tire diameter, rpm and rear end ratio. It doesn't have provisions for an over drive ratio unless you multiply the over drive ratio by the rear end ratio. 3.36 gears with a 28 inch tall tire at 70 mph would be right at 2822 rpm. For some reason a lot of Mopars had rear axles that were real close on WMS to WMS width over the years so a rear end swap might be fairly simple.
The 65-67 or so C body axle bolts into most Mopars, moves the axle about an inch. Gets rid of the pressed on brake drums. There are adaptors for the long tails for stick ******s. QEC is supposed to be working on one for a C-4.
,,,,supposed to be.... Yup, still in the works but......since I started the project and have made mention of it in various forums there has been surprisingly little interest. The project sits at about 50% and maybe someday I'll get back to it. Anyone need a project?
The cheapest/easiest way to change rear gearing and lower highway RPMs is to install taller rear tires. Tire Size Comparison
Agree with others, 3.3 gear is 'normal' for a freeway car. Are you expecting to zip around like the SUVs at 75+ and cutting through traffic, or are you keeping up just fine at 65-75? Also check your fluid drive level. My 47 would upshift pretty quick when you lifted the throttle. You can always start out in low and shift to high range as fast as you are able, not waiting for it to kick from low 1 to low 2. P-15 D-24 and the Imperial forums have troubleshooting and repair info.
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