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Old 09-09-2017, 07:23 PM   #1
50fordcoupeman
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Default 1950 Ford rear end

My avatar car has a 4.11 rear end, a '77 302 and 3 sp manual. At 55mph I am at 3000 rpm's so it is not really a freeway car. Sometimes I just plain need to use the freeway.
Question is what could I expect if I were to change the rear end to a 3.73? Any other comments are certainly welcome as to gear ratios.
Thanks in advance!!
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Old 09-09-2017, 07:50 PM   #2
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Default Re: 1950 Ford rear end

I don't know the ratio is, but you might want to check out 51-56 automatic rears. I am not sure the 52-56 rears are a direct fit, ,maybe some one here can comment on this.
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Old 09-10-2017, 02:19 AM   #3
JeffB2
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Default Re: 1950 Ford rear end

If you had an AOD behind your 302 with the 4:11's at 70 MPH you would be around 2250 RPM with it's .67 Overdrive. If you want to stay stick shift a T-5 swap would be a good idea. A 1952-54 Ford with a Ford-O-Matic rear end is a bolt in for your '50 the ratio was 3:31, the 3:73's won't gain you enough to be worthwhile. A 70's Maverick rear will fit many had a 3:00 ratio you will need a NEAPCO 2-0291 rear conversion U-joint.
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Old 09-10-2017, 10:52 AM   #4
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Default Re: 1950 Ford rear end

You may consider the top loader 3 speed + o/d trans. I believe Merc. 3'rd members thru 54 are a direct fit. 55-56 Ford should fit but you may need to swap spider gears or axles as they may be 28 spline. 3.55 gear ratio is a good middle of the road. With a 28" tall tire at 65 would put you close to 2750 rpm.
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Old 09-30-2017, 10:51 PM   #5
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Default Re: 1950 Ford rear end

A big "thank you" to Sid for reviving my avatar's rear end. New friend and hero!!!!
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Old 10-14-2017, 12:46 AM   #6
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Default Re: 1950 Ford rear end

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Just dawned on me that I never posted the results of the rear end fix that Sid did on my avatar. We all seem to like to know the results of questions that are posted. He ended up putting a rear end of a '55 Ford under the '50. The gears I believe are 3.22s. My rpm's at 60mph dropped from 3300 to 2400. Much more driveable on the highway. I like it!! Thank you Sid!!!
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Old 10-15-2017, 06:53 AM   #7
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Default Re: 1950 Ford rear end

If you are running 3000 rpm, the 3.73 will drop it to 2722 rpm. 3.55 will drop it to 2591, a better road gear but still turning about 3300 at 70 mph. 3.00 will turn 2788 at 70 mph. This option would require a rear end swap to a later model 8" as 3.30 is the highest ratio you are likely to find in the early rear end. Maybe the OD transmission is the way to go if you are planning road trips.

Math is simple on this. Divide the new gear ratio by the current one and multiply the current rpm times the dividend. 3.73/4.11=.9075 .9075 X 3000=2722 rpm at 55 mph using your numbers.

70 mph divided by 55 mph gives the multiplier for increase in rpm as speed increases. In this case, 3000rpm X the factor of 1.2727=3818 rpm at 70 mph with the 4.11 gear.

Try it for yourself and verify my numbers; we tend to fat finger numbers as we get older.

As to the question of the '56 and earlier rear ends with A/T, the ratio was 3.30 at least in '55 and '56 with the Y block except in '56 with the 312 engine there was a 3.22 (close) ratio but these are rare now a days. To the question of direct fit, yes but there were 2 spline choices coarse and fine (don't remember the count). If changing the differential, make sure you get the axles too if the splines are different.

Last edited by Motorhead6; 10-15-2017 at 07:02 AM.
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Old 10-19-2017, 12:28 AM   #8
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Default Re: 1950 Ford rear end

Thanks Motor for the info. I am very satisfied with job Sid did on it. Still has good low end performance and now has good highway performance too.
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Old 10-19-2017, 09:30 AM   #9
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Default Re: 1950 Ford rear end

Years ago, my 54 Vicky rear axle took on water through the vent. I found a 56 auto trans center section and bought it. It would not fit all the way in, the ring gear touched the bulge in the housing. I heated the bulge red hot and hammered the snot out of it, then it fit just right. I had axle bearings only a year old, so I didnt want to change axles. After removing the center shaft in the diff, the spider gears rotated enough to remove them and put the 54 spiders in the 56 housing. I removed a 3.54 and replaced it with a 3.30, and after some prime, and flat black paint, some 85-90 lube, all was well in Miss Vickies rear. I also used a vent from a Ranger, it uses a hose to vent the axle up at frame hight.
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Old 10-24-2017, 05:25 AM   #10
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Default Re: 1950 Ford rear end

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Originally Posted by Ole Don View Post
Years ago, my 54 Vicky rear axle took on water through the vent. I found a 56 auto trans center section and bought it. It would not fit all the way in, the ring gear touched the bulge in the housing. I heated the bulge red hot and hammered the snot out of it, then it fit just right. I had axle bearings only a year old, so I didnt want to change axles. After removing the center shaft in the diff, the spider gears rotated enough to remove them and put the 54 spiders in the 56 housing. I removed a 3.54 and replaced it with a 3.30, and after some prime, and flat black paint, some 85-90 lube, all was well in Miss Vickies rear. I also used a vent from a Ranger, it uses a hose to vent the axle up at frame hight.
That's interesting; I have a 3:30 in a '51 rear axle housing and no interference problem at all. Never know what Ford may have done back then. Or perhaps your housing could have been damaged somewhere along the way; we'll never know.
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Old 10-24-2017, 12:51 PM   #11
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Default Re: 1950 Ford rear end

Sid here on the Barn said that the ring gear rubbed on my original '50 gear case too. He put in the entire axle housing to make the '55 Ford rear end work.
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Old 10-24-2017, 01:40 PM   #12
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Default Re: 1950 Ford rear end

Quote:
Originally Posted by 50fordcoupeman View Post
My avatar car has a 4.11 rear end, a '77 302 and 3 sp manual. At 55mph I am at 3000 rpm's so it is not really a freeway car. Sometimes I just plain need to use the freeway.
Question is what could I expect if I were to change the rear end to a 3.73? Any other comments are certainly welcome as to gear ratios.
Thanks in advance!!
Actually that rear gear set is a B5A 4209C, it was to be used with an over drive. I have such a rear set and it's worthless. I found a 1951 gear set out of a automatic and it is B5A 4209 B and is 3.89. A little better but not much. My latest find is a B5A 4209 A in a 3.30 ratio. The pinion is .5 inches larger in diameter and it took some case trimming and grinding but it's in there. At 2200 rpm I'm at 60 MPH. If you could find an overdrive transmission in your area, That would solve your problem. Last time I drove thru Alamagordo, the 50 ford I bought my rear end out of was still there and it had a overdrive. It's called 54 Auto Parts. The other option is a T-5, that solves lots of problems.
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Old 10-24-2017, 01:57 PM   #13
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Default Re: 1950 Ford rear end

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Originally Posted by Motorhead6 View Post
That's interesting; I have a 3:30 in a '51 rear axle housing and no interference problem at all. Never know what Ford may have done back then. Or perhaps your housing could have been damaged somewhere along the way; we'll never know.
I have a 50 third member and a 51 automatic third member, they have the same casting numbers. To get the 3.30 gears in my case it took 12 hours of grinding 15 re-assemblies. It now fits perfect and was worth it.
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Old 10-24-2017, 02:07 PM   #14
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Smile Re: 1950 Ford rear end

Quote:
Originally Posted by 50fordcoupeman View Post
Sid here on the Barn said that the ring gear rubbed on my original '50 gear case too. He put in the entire axle housing to make the '55 Ford rear end work.
Sid is the man. I wish I was near him.
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Old 08-30-2020, 07:48 PM   #15
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Default Re: 1950 Ford rear end

Is a 1955 Ford Thunderbird Automatic Rear End the same as the full size 1955 Ford Automatic Rear End ???
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Old 08-30-2020, 08:24 PM   #16
paul2748
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Default Re: 1950 Ford rear end

No - rear ends are of a different configuration unless the car rear is a wagon. I think fit wise the whole Bird rear will fit the sedan without any mods, but there could be a u-joint difference.


When asking a new question, it's always better to start a new thread rather than using an old one.


Quote:
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Is a 1955 Ford Thunderbird Automatic Rear End the same as the full size 1955 Ford Automatic Rear End ???
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Old 08-30-2020, 09:36 PM   #17
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Default Re: 1950 Ford rear end

Having pulled a wagon rear end (Dana) and put it in a bird years ago I know the spring mounts are taller on the bird, lowering the car. I used 2" blocks to bring the bird back to stock height. You'll be going the other way I'd guess.
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