1977-1979 Ford and Mercury

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rear-end gears

Printed From: The Ford Torino Page
Category: Model Specific Forum
Forum Name: 1977-1979 Ford and Mercury
Forum Description: Technical discussion for 1977-1979 Ford and Mercury
URL: https://forum.grantorinosport.org/forum_posts.asp?TID=21259
Printed Date: 26-March-2026 at 10:26AM
Software Version: Web Wiz Forums 12.06 - https://www.webwizforums.com

Topic: rear-end gears

Posted By: fordpower
Subject: rear-end gears
Date Posted: 14-May-2024 at 12:42AM

Ok looking for new set up for 8in I want 3.55 or 3.75 online people are posting 4.56 and higher ring and pinion. One person said 4.56 is a 3.50 rear end I am confused.

Replies:

Posted By: derth
Date Posted: 14-May-2024 at 4:04AM

Without knowing anything about the 8 inch, I will mention that final gear ratio is a matter of tire size, transmission gearing and rear gearing. Depending on goals, you could start by finding your desired rpm at cruise speed and then working from there. Depending on transmission, a 4.56 may give you a 3.5 final gearing? Sorry if this is not helpful, but it was confusing for me first time I dealt with it.

Well, of course, now that I'm thinking about it, all the transmissions that came in these cars are 1:1 in 3rd, so everything I just said is useless unless you've got something with overdrive.

Posted By: fordpower
Date Posted: 14-May-2024 at 5:39AM

thanks

Posted By: 72FordGTS
Date Posted: 15-May-2024 at 6:02AM

Are you sure your car has an 8" rear, and not a 9"? What gears are you running now? A lot of those late 70s cars had really steep gears, like 2.50:1. What size rear tires do you have? What type of driving do you do with your car? Is your engine stock or modified? What are you hoping to achieve with new gears?

Ford 8" rear have slightly different rations than Ford 9" rears. You could upgrade to 3:00:1, 3,40:1, 3.55:1 or 3.80:1. I probably wouldn't go much lower gears than that for a street driver.

https://www.summitracing.com/search/part-type/ring-and-pinion-gears?N=differential-case-design-type%3Aford-8-in" rel="nofollow - https://www.summitracing.com/search/part-type/ring-and-pinion-gears?N=differential-case-design-type%3Aford-8-in

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Vince

1972 Ford GTS Sportsroof - Survivor, One Family car

GTS.org Admin

Posted By: fordpower
Date Posted: 15-May-2024 at 12:39PM

It is for my pinto going with AOD it has 2.75 there about.Someone had a 4.56 ring and pinion locker clams that is a 3.55. Just a thought I have a 3.25 non locker but people want 4-500 to put new bearings and set it up I have the bearings.

Posted By: 72 RS 351
Date Posted: 16-May-2024 at 2:49PM

The 3.25:1 range is not a bad ratio for an AOD car, the OD is .70:1, typical for all over drive trannies. A 3.5 or 3.75ish is also very good depending on the vehicle weight and power level.

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Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000 rpm 351 stroker
73 Ranchero GT 351C-4V &4R70W for sale later.
92 Lincoln Mark VII SE GTC, OBDII 347/4R70W

Posted By: 72FordGTS
Date Posted: 17-May-2024 at 8:42AM

With a little Pinto, assuming it's still a 4 cylinder, be careful not to over gear it. With the .67 OD, a 3.25 gear will give you a 2.18:1 overall ratio. A 3.80 gear seat gives you a 2.54 overall ratio with an AOD.

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Vince

1972 Ford GTS Sportsroof - Survivor, One Family car

GTS.org Admin

Posted By: 72 RS 351
Date Posted: 17-May-2024 at 11:21AM

Well given an AOD, it'd likely be a V8 I hope, but a V6 at the least. I know how tight the engine bay is, my best friend's nephew had a Cleveland in one in the mid 80's. I hate to think how tight it is for headers, the trans, plus the exhaust. Good luck of course.

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Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000 rpm 351 stroker
73 Ranchero GT 351C-4V &4R70W for sale later.
92 Lincoln Mark VII SE GTC, OBDII 347/4R70W

Posted By: fordpower
Date Posted: 18-May-2024 at 2:12AM

It's a 302 bought it yrs ago for 1000 because who knows wife would not ride in it to loud and 6in hood scoop . took it apart found right oil pan and got old. my question was people saying 4.56 ring and pinion is a 355 ratio.

Posted By: Rockatansky
Date Posted: 18-May-2024 at 6:36AM

what they're saying, based on their own specific combo factoring in tire size i imagine?

is that with OD they can run a 4.56 gear and it equates to the 3.55 gear w/o OD

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72 GT Ute

Posted By: fordpower
Date Posted: 18-May-2024 at 12:26PM

thanks.