Looking at purchasing a Ford 9" Currie rear -end assembly. The tec where I'm going to buy at said 3.70 ratio would be a good cruiser. Everything I found said 60-70 mph you be at 3000 rpm's. My 55 is stock 2sp power glide but with a 327 /4barrel. The research I found said they were 3.55 for V8 & power glide back in 55. Wouldn't a 350 ratio be better cruiser?
It's possible the tech is trying to balance the first gear of the glide and is why he suggest's 3:70"s. But yes, 3:50's would be better RPM wise on the highway.
I'd recommend a 3.5 or 3.55 as a compromise for all-around use with that engine and trans. Or 3.70 for mostly around-town or 3.0 for mostly highway driving. I had a stock 3.55:1 behind a Muncie M-22 & mild 355 SBC in my '55.
Stock Tri 5's had a 3.36 rear with the powerglide. Stick trans were 3.55 or 3.70 and overdrive were 4.11. A couple of years later they had 3.08 for the powerglide. There is enough torque multiplication in the PG to run the higher gears. Kind of a dog around town, but better hwy cruiser. I'm wondering why you feel the need to put in a 9". With the PG you're not going to break the stock rearend.
Wife's 55 ran for many years as our main car with a PG and stout 327-had 3:55's Was and excellent cruiser at all speeds but 327 liked the R's too.
A 3.50 gear is still pretty low for behind an automatic. That'll only gain you a bit less than a 200 RPM drop at freeway speeds over the 3.70. A 3.25 will save you closer to 400 RPM and still give good around town performance. But if it were me personally, I'd run a 3 flat... but most of my driving is at speeds of 50 MPH or more.
If this chart copies, it is for a 27" tall tire Using Transmission Gear Ratio: 1 gives these RPM data: Engine Speed (RPM) MPH 3.08 Gear MPH 3.36 Gear MPH 3.70 Gear 8000 RPM 208.64 MPH 191.25 MPH 173.68 MPH 7500 RPM 195.60 MPH 179.30 MPH 162.82 MPH 7000 RPM 182.56 MPH 167.34 MPH 151.97 MPH 6500 RPM 169.52 MPH 155.39 MPH 141.11 MPH 6000 RPM 156.48 MPH 143.44 MPH 130.26 MPH 5500 RPM 143.44 MPH 131.48 MPH 119.40 MPH 5000 RPM 130.40 MPH 119.53 MPH 108.55 MPH 4500 RPM 117.36 MPH 107.58 MPH 97.69 MPH 4000 RPM 104.32 MPH 95.63 MPH 86.84 MPH 3500 RPM 91.28 MPH 83.67 MPH 75.98 MPH 3000 RPM 78.24 MPH 71.72 MPH 65.13 MPH 2500 RPM 65.20 MPH 59.77 MPH 54.27 MPH 2000 RPM 52.16 MPH 47.81 MPH 43.42 MPH 1500 RPM 39.12 MPH 35.86 MPH 32.56 MPH 1000 RPM 26.08 MPH 23.91 MPH 21.71 MPH
I had a 57 BelAir in 1971, had a three speed in it when I bought it, had 3.08's and as far as I know they were original and hadn't been touched, when I blew up the spider gears and went to put the replacement third member (4.11's) in it I broke the head off of the slide hammer axle puller they were in there so long. I do know that gear swap and subsequent four speed change was like adding nitrous to it.
@DDDenny, First year for the 3.08 was 1959 with a 348 PG only. 1960 it was available with a 283PG also. I bought my first '57 in 1965, a red & white 4dr wagon. Blew up the PG, got a 3sp, blew that up & got BW 4sp. The spider gears in the 3.36 didn't last long, got a 4.11 posi, then 4.56 and the most fun was the 5.13. By that time I built a 270HP. Lots of fun from stoplight to stoplight. Floor it, shift 1,2,3 then slam on the brakes for the red light at the end of the block. Do it again.
@PeggySue I’d suggest figuring out what gear you have now, then look at a change in ratio If you are happy with highway rpms, no reason to change ratios. If you’re thinking of a future upgrade with power, etc as well as transmission, I’d suggest doing the tranny first. Think along the lines of a 2004R Then see how it runs/feels and adjust ratio in the rear from there
55's and 56's were 3.55"s with a powerglide, 3.70 with a stick and 4.11"s with overdrive. 57's because of the lower 14" tires were 3.36 for the powerglide cars, stick cars were 3.55 and still 4.11 for Overdrive... with all that said, how did it drive with the factory 3.55's in it? were you happy with it? Personally if it is a cruiser and most of the driving is on the freeway, I would go with the 3.0 gears for the ford rear that you now have....
Having just bought the car a month ago, doesn't have tac, but having run equipment for 35 years can tell it cruises good now with stock rearend 55-60mph,which my research showed 3.55 for V8 /power glide for 1955 , figured 3.50 would be good. Just didn't want the tappets coming out of thevalve covers. Thanks for the responses give me much to consider.
Should work--we drove ours for years with those at 70+ all over as our main car. 327 did just fine. 70000 miles like that.
I can say from personal experience that a 4.10 gear with a 26 inch tire is not a good freeway combination. Good for 0-60 times, bad for extended 60 plus cruising. An SBC can take the rpms, but it will be a lot of engine noise and poor mileage. For the OP, I would suggest 3.36 to 3.00 gear for a nice driver. Sent from dumb operator on a smart phone
Not that it’s a 55 Chev but I went from 3.21 to 2.74 and could not be happier. Speed limits were 55 in the mid fifties when these cars came out. Your only draw back is the 2 speed trans that doesn’t have a gear in the mid 2’s to start out. With that said my 65 Chevelle 283-2 barrel had a 3.08 and was fine for the 15 years we had it. In the 60-70’s.
OP, if wasn't mentioned already, you can verify your current gear ratio, by... 1) putting the rear end on jack stands 2) mark your driveshaft with tape/chalk/etc 3) trans in neutral 4) spin rear tire manually 10 complete revolutions, while counting full & part revolutions of the drive shaft. for example, if you spin the tire 10 times, and the driveshaft makes basically 3.5 revolutions, then you have a 3.55. A 3.70 would be more like 3 & 3/4 revolutions. A 4.11 would be 4+ revolutions. I mention it so you can have a better idea or piece of mind when making your final choice of a rear gear if you think you might want to make adjustments in regards to the rpms generated at highway speeds. I say all that in light of the chance a different gear diff made it into your rear axle after the car left the factory. Best wishes with your choice, Gotta56forme/Scott
Low gears and loud mufflers drive me crazy. They are cool as hell once around the block, but get old real fast. I have a 3.25 in my cruiser, and even that makes the motor run a little fast. I liked the 3.00 ring and pinion better.
I like 2:73 with a Turbo 400 and build around that.. Too bad you don't have a 454, it would love the 3:08.. I heard the 454 is a lot of fun with a Turboglide.
Remember reading that some where before. Just looking at the rear-end housing everything looks stock, I know there's a chance the third member was changed but doesn't appear to be.
I just ordered a Currie 9" rear -end assembly with 3.50 third member. Thanks again for all the input.
My vote is 3.50's you can cruise on highway and at least have some oomph around town where most do there driving. If I can go down highway at 2900-3000 doing 65MPH I'm happy. Also tire dia. can fine tune what you want on highway. Pat
Nice choice. And thinking ahead, the PG might be a difficult item to have rebuilt. So a new tranny might be in order. So why change it out for a 9inch? Are you thinking of some engine upgrades, etc? Or is your rearend making noises, etc?
Pretty good howl to the rear end. The pinion seal is leaking, was low when I bought it . Probably been low and run before. Don't know about up grades time will tell and will be ready if I want to. Did some looking for used but sometimes up here in northern Minnesota your lucky to find bread and milk. LOL
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