dif gear ratio

cvicky

cvicky

Senior Member
my 55 Fairlane revs 2900 rpm at 60mph I have 3spd on the tree with 10 tooth pinion and 33 ring gear is there a newer dif that will fit with Hwy gear like 273 i'm told 55/56 are one of a kind 57 + is bigger
 
Something isn't adding up with the figures you have given. Assuming you have the stock size rear tires and the ratio is 3.30, the RPM at 60 should be about 2428 according to this RPM calculator.
https://spicerparts.com/calculators/engine-rpm-calculator.

The 3.3 ratio would have been in an automatic car, but things get changed over the years.
I don't think there is a numerically lower rear ratio for the '55 rear end. Maybe something aftermarket, I don't know.
 
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Check Ford 8" or 8.8". These were typically found in Rangers and Exploders and came in a variety of ratios. In most of those applications the pumpkin was offset from center so you will need to get the appropriate tube and shaft from a 2nd one to center the diff. Will also need to add spring perches for leaf springs. Some have drum brakes, others are disc, mainly from Exploder. Measure your rear axle flange to flange and go shopping.
 
40cpe said:
Something isn't adding up with the figures you have given. Assuming you have the stock size rear tires and the ratio is 3.30, the RPM at 60 should be about 2428 according to this RPM calculator.
https://spicerparts.com/calculators/engine-rpm-calculator.

The 3.3 ratio would have been in an automatic car, but things get changed over the years.
I don't think there is a numerically lower rear ratio for the '55 rear end. Maybe something aftermarket, I don't know.
Click to expand...

I agree with you. My avatar has a '55 Ford rearend with what I believe to be 3.22 gears. I know that tire size etc can affect rpm's but I am at 2400 rpm's at 60mph.
 
My 100% factory original '55 drivetrain has Y-block, Ford-O-matic and 3.30 rearend ratio. I can't complain about engine RPM's, even at 70mph, but if you went to a lower ratio, say between 2.70-3.00 with a good running Y-block, it still wouldn't dog at start-up from a dead stop.
Many people have switched to the '57 and later 9" rearend that offers lots of different gear ratio selections.
I also have a '55 Ford Courier sedan delivery with a '57 rearend rebuilt with posi 3.25:1 gear ratio and that one has a 223 I-block 6-cyl with Ford-o-matic. No complaints there either. Both cars pretty good highway cruisers and effortless startup from a dead stop.
 
My 55 has the 8 inch rear end with 3:30 to 1 ratio and my RPM's are higher than I would like, but the gears for that rear end are very scarce. i just overhauled mine. Will run it till I can find an 8.8 with a better ratio. Al
 
The F/M was SINGLE RANGE with a 2nd gear start. It had a high stall speed torque convertor. Depending on how it was geared you might have had to use a 1st gear start.

The torque convertor slippage created a lot of heat.

Available ratios OEM FORD CAR -
 

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I don't think you will find an 8" or 8.8" rear axle out of a Ranger or Explorer with anything numerically lower than 3.73:1. Would have to change the ring and pinion anyway.


Sal
 
these engines were made to rev.i cant figure why the first thing people do with these cars is look for another rear end.
 
Probably because at 60 to 65 mph they're wrapped up pretty tight unless you have OD. My Merc has a 4.09 axle and I prefer not to drive it over about 50 to 55 in direct high. Plus they suck gas like there's no tomorrow without OD. When most of these cars were new average speeds were lower and high speeds weren't usually sustained the way they are on modern interstates.
 
they were sustained back in the 60s when i drove them.about 80 most of the time.most 56s i had were std.with 3.70 3.78 rear.the worst thing you can do is put a tach in one.
 
I will say this, I had 3.30 gears way back when in my 55 Ford that had the original Fordomatic and 272. I buried the odometer on two occasions and back then it felt like the engine did not have much more left in it.

With a 292, EZC-G heads, 4 barrel, and now 3.78 gears with the R10 Overdrive, I am over 80 and it seems like I am just cruising with a bunch left in the engine. When I press the accelerator she jumps ahead (and that is not engaging the kickdown). Right now, that is fast as I want to go until I get the front end lined up. :D

LOVE these old Fords!
 

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I run a 3.89 rear in my Ford, at 70 I run about 3300 RPMs. My rear tires are close to 29" tall. I get great acceleration on anything over 55 in 4th gear.
 
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