The Stovebolt Site Forums The Shop Area Driveline Is it worth swapping from 3.70 to 3.55?

My 1954 235 specs says it has a 3.70 rear and Patricks 3.55 would be a lot cheaper than a T5 swap, but can you really "cruise at 65 without engine strain"? Anybody have experience with this combo? Thanks.

The difference between a 3:70 and a 3:55 is not worth the effort. You could get the same effect by going to one size bigger tire.

Thanks. I'm going to go with the tallest tire I can find in a radial and hopefully I can do 65 without strain. If not, back to the shop.

Mt54,

Which 1954 truck specs says 3.70 rear?

Most likely that is a miss-type of 3.90 standard 1/2 ton rear in 1954 trucks (there was no optional rear in 1954)?

I agree with Don, I wouldn't change from a 3.70, but I did change from a 3.90 to the 3.55 (31.5" diameter radials). I can cruise all day at 65, stopping every 150-180 miles for gas.

I think he may be working on a car, they had a 3:70 gear in them.

That is what I thought, Don

Being a truck discussion board, I assumed truck, but I did ask the question about the rear.

Will Patrick's 3.55 R&P set work in a car rear-end?

Will the 3.70 car R&P work on a 47-54 truck rear end (with the right carrier)?

No, car differential gears are smaller than 1/2 ton pickup, so are the axles. John

Patrick has the 3.55 gears for both car and truck, although they say the one for the car is 'currently not available'

Bill

The 50-54 Powerglide equipped cars came with a 3:55 rear end.

Interesting point, Bill...I'm glad I'm reading! I had no idea the gear sizes were different from truck to car.

Yesterday, when I spoke with Patrick about purchasing a set of 3.55's, he said they were on order. Then he asked me what I drive. I told him "Fleetline." He then took my address to send me a catalog. So he clearly knows what I need (when the new shipment comes in), but I'll make it a point to specify so that I get the right instructions when I do order.

Sorry missed the conversation. I see I had looked at car ratios. Now it looks like I might have to do a Patricks swap. Thanks to all!

tclederman - What tires are you running at 31.5? Where does that put your rpm at 65 mph?
Thanks.

3.55 rear
31.5 tire diameter
1.00 top gear
65 mph

2461 rpm

Cooper SRM II, LT 215/85R16 Radial on 4.5" wide 16" original wheel

light truck blackwall radial tire

it has a high/narrow profile and looks "normal"

I hear the sweet spot is a little lower rpm. Are you running a stock motor and 4 speed?

My wheels are pretty rusty so I need to source new ones. Did you put tubes in?

I agree about the sweet-spot rpm. I run at 60-65 mph for better gas mileage (261 with 2-barrel Holley AA-1 carb used on 302/270 GMC engines).

4-speed/3-speed - why does it matter? Both are 1:1 in high gear.

Yes, I have have tubes. My Cooper dealer put them in. I'll not use tubes on the '54 I am restoring - it had primo original wheels. I have been driving with the radial/tubes for 9+ years.

One more thing, I'm putting in A/C. Am I asking too much from the 235 even with the 3.55 and tall tires to pull 60-65 mph?

60-65 with the 3.55 gears isn't a problem and as drafty as these things are you shouldn't need A/C at speed, just open the vents and enjoy the breeze personally I think it's asking too much of a 235 to run A/C if you use it regular and want the 235 to live long

Bill

I live in SoCal and wanted the option to run A/C. Thanks for the info.

I was wondering about 3 versus 4 speed myself, but not regarding high gear. I was wondering about how first gear with a 3 speed performs on steep slopes. I have some steep boat ramps and carry way too much equipment in my boat, and am worried about pulling up the ramp with 3.55 gears and 31.5 inch tires. I currently have 3.73 rearend (1970ish)and stock rims with radial tires (outside diameter unknown), and I don't have a lot of power out of the hole on steep grades. I have a 52 235 Blue Flame, BTW. Would I be better off with a 4 speed or a T-5 if I went to 3.55 gears?

The 3-speed 1st with the 3.55 is a little too high for starts on a steep slope (especially if you have a load). It is OK, otherwise.

I start in 2nd with my SM-420 4-speed, unless I want to burn rubber or unless I have a load on a hill.

I went to 3:55 on my 41 1/2 ton. The good thing is they are tapered gears and it eliminated the wining the old gears had. I may have picked up 5 mph. I don't have a tach but can feel the comfortable speed which is about 60 mph. Thinking about a "Gear Vendor" overdrive.
Anyone have any experience wit this?

The T-5 is a good choice but they are not very good for heavy vehicles or used as a tow vehicle. How heavy is your boat?

Its a 14 foot aluminum jon boat, about as heavy as I can safely stop with stock brakes.