ford 8 and 9 inch with a 4.20 gear ratio - Hot Rod Forum : Hotrodders Bulletin Board
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Old 12-31-2008, 09:54 AM
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ford 8 and 9 inch with a 4.20 gear ratio

I have several 9" rears that i got yesterday and the ring and pinion on 3 of them that I got yesterday, along with 1 9 inch

1 was just a C7AWE third member that I found layin in a scrap pile, 1 from a 79 Bronco (def. trac loc) and on with one other truck rear I found in a pile.. Nothing outta the ordinary, but they all say they are 42 10 on the ring gear. I'd never heard of a 4.20 so I counted the teeth to be sure and they are 42 ring and 10 pinion. One of them had a 3 leaf clover shape but they are all stamped with withb the ford oval so I think they are stock gears.


Also the 8" i found has the extra webbing and it say's 42/10, and counts 42/103 times over with marking a paint marker so I am certain the count is right. This is an entire rear drum to drumIt has leaf spring pade on it and thats measures 51 7/8" wide flange to flange with all the brake hard ware off. the numbers I have so far are C7OWA case casting and the ring gear #'s.
It is 4 lug and has 28 spline axles. I first thought it was from an older mustang but I'm not sure cus I am not really a big frod guy.... You guys got any ideas????

What about the 4.20 (42/10 gears)?? ever seen these before??? What about the clover leaf?? All are SUPER THICK gears. Also just to clear up any doubt, It is def not a 47/19 (2.47) I have on of those to from a t-bird, so I know what they look like, and as I said I have counted the teeth on all rings and pinions and they are def 42/10. I've seen a 4.10 and a 4.30, but not a 4 20!! Until now.

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Old 12-31-2008, 10:15 PM
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I've always assumed Ford 9-inchers to have 4.10 or 4.30, never 4.20.

Sorry to derail your thread a bit, but is that 2.47 T-Bird ratio on a 9-inch? I thought you couldn't get taller than the 2.75 in my Torino? A 2.47 ratio would get my cruising speed sweet spot up from 48-57 to 54-65, which would seriously help me running 70mph around central TX...
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Old 01-01-2009, 10:06 AM
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Quote:
Originally Posted by occupant
I've always assumed Ford 9-inchers to have 4.10 or 4.30, never 4.20.

Sorry to derail your thread a bit, but is that 2.47 T-Bird ratio on a 9-inch? I thought you couldn't get taller than the 2.75 in my Torino? A 2.47 ratio would get my cruising speed sweet spot up from 48-57 to 54-65, which would seriously help me running 70mph around central TX...
76-77 Ford passenger cars with 460s +C6 trans had 2.50 rear 9 inchers with 28 splines. Even in the trailer towing packages. I had one new and put in a pickup 300, and only went down from 12.6 to 12.1 mpg in identical conditions, but towed better with the 20% more gear.
I think there was a 247 in Granada.
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Old 01-01-2009, 11:11 AM
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most of the ford 9 inch rear diffs I found have the 2.75 gear ratio in them.

I do not recall a 4.20 gear.
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Old 01-01-2009, 12:15 PM
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No comments on anything other than...4210 is likely the engineering number stamped on the gear...not the teeth count. The middle code in the part #'s is 4209.... There was no 4.20 gear the 2.47 was probably a 9 3/8" 2.50, they will fit a 9" housing.
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Old 01-01-2009, 12:22 PM
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Quote:
Originally Posted by woodz428
No comments on anything other than...4210 is likely the engineering number stamped on the gear...not the teeth count. The middle code in the part #'s is 4209.... There was no 4.20 gear the 2.47 was probably a 9 3/8" 2.50, they will fit a 9" housing.
About 7 years ago I pulled a 78 Vesailles 9 inch and drive shaft out of a running and driving car, and replaced it with an 80 Monarch 8 inch and drive shaft. Direct bolt out.
The Monarch had the seats and console and fancy trim just like a Versailles, but not the fake top. Sold the Versailles and made money and kept the rear end!

One was a 2.47 and one was a 2.50. But I can't remember which was which.

And ya, I thought the 4210 was an engineering code, but he said he counted the teeth.
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Old 01-01-2009, 12:28 PM
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Also he mentioned SUPER THICK GEARS.

Not anything special about being made stronger.

This is a factor of having to vary the ring gear thickness so that the pininon centerline still lines up because of the pinion diameter. More pinion teeth= larger diameter= thinner ring gear required.
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Old 01-01-2009, 12:44 PM
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Quote:
Originally Posted by eatonde

Also the 8" i found has the extra webbing and it say's 42/10, and counts 42/103 times over with marking a paint marker so I am certain the count is right. This is an entire rear drum to drumIt has leaf spring pade on it and thats measures 51 7/8" wide flange to flange with all the brake hard ware off. the numbers I have so far are C7OWA case casting and the ring gear #'s.
It is 4 lug and has 28 spline axles. I first thought it was from an older mustang but I'm not sure cus I am not really a big frod guy.... You guys got any ideas????

Until now.
8 inch rears:
Extra webbing started in 66.

Rear end width is properly measured as wheel to wheel, since there is some variation in axle stick out.

The 8" 4 lug you describe with extra webbing and 52 housing width/ 57 1/2 wheel to wheel, must be from a Falcon or Maverick six cylinder since it is a 4 bolt.
The housing diameter will be the same diameter as the tube all the way out.
If the tube is tapered to a smaller 2 1/2" diameter at the spring U bolts, then the housing might be from an early 63-65 Falcon or 65-6 Mustang. These were the last to use tapered housings. YES even the V8 cars used tapered housings.

And as for curiosity,
Shelby replaced the factory 9" rears with 58 Ford station wagon rears with the big bearings and big brakes for his original race car creations.

Last edited by ScoTFrenzel; 01-01-2009 at 12:51 PM.
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Old 01-01-2009, 01:40 PM
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tooth count, tapered housing, t Bird 9"

Yes as stated the 42/10 is not an engeneering code, I have now counted them about 4-5 times because I keep doubting myself due to lack of info on the web.... There is 42 teeth on the ring gear and 10 teeth on the pinion... I am 1000% positive of it, my math says 4.20, I just got off the phone with a guy that has been building/selling 9"s and a few others for 30+ years and said that he has seen the 4.20 ratio before but it has been very few times and not in the past 8-10 years do they must be very rare.... How I wound up with 3 of the I have no clue.

Yes the axle tubes do taper to 2.5" as the 65-66 mustangs did, But i thought they were 5 lug so this is confusing me. I have always measured flange to flange, and that's 51 7/8" BARE HOUSING just a guess I'd say wheel to wheel would be around 60" or so.....

The T-BIRD rear is a C7AWE case, the fins do not curve down like a 9 3/8 would. I don't think a 9 3/8 ring gear will fit in that case or on the same C6AW-4205 carrier, so I'm pretty certain it is a 9" NOT A 9 3/8", but I could be wrong. And yes, as with the others I have went through with a paint marker and counted the teeth on the ring and pinion and the ring is def 47 teeth and pinion is def 19, which 47/19=2.473684211(2.47)....

If I new how to send pics on here I would send you photos so you can see all of the above for youself. Could someone explain ho to to this to me?? BTW my dad also went through each of these units and counted the teeth for further accuracy, and he's gettin the same as me, so OBVIOUSLY somewhere throughout history Ford did make a 4.20 gear ratio, they must just be VERY VERY VERY RARE....
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Old 01-01-2009, 01:44 PM
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Tapered Tubes

BTW the tapered tubes section/paragraph was for the 8" only, sorry I forgot to clarify that
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Old 01-01-2009, 01:56 PM
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i remember seeing a 9 inch from a bronco that had a 4.20 gear, i thought it was kinda odd also.
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Old 01-01-2009, 04:15 PM
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To upload Pics, click on the post reply button then scroll down to Manage Attachments button & click, when the small window opens click on one of the Browse buttons & you should find where youre pics are. Find Pic click Open, then upload button. Then Submit Reply. Maybe I said this right.
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Old 01-01-2009, 10:21 PM
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8" rear end with tapered tubes and 4 bolt axles most likely from early 70's maverick. Although my cousin had a 69 mustang with 4bolt wheels and 8" rear end with 200 six and 3 speed on the floor all original. I think at times when there were model change overs or shortages during production runs car makers tended to use what ever they had that would fit to finish the cars and send them out the door.
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Old 01-02-2009, 04:10 AM
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V-6 and V-8 mustang 2's had 4 lug 8" rears in 'em too.
not sure about V-6 pinto/bobcats...
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Old 01-02-2009, 02:42 PM
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I think your tooth count is off. I've never seen a 420 ratio OEM gear. There is a 422 ratio in the aftermarket with Richmond and the tooth count is 38/9. I don't think that ratio would be possible in a Bronco either because Spicer Never made a 420 ratio for the Dana 30 or 44 that would go in the front diff to match.
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