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Rear differential questions |
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anchovieMAN 
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Joined: 19-January-2021 Location: Wisconsin Status: Offline Points: 75 |
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 Topic: Rear differential questionsPosted: 31-January-2025 at 1:25PM |
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Hello I’m thinking about upgrading the differential in my 1973 Torino to a limited slip and there is also a big leak. I have a 4speed I plan on putting in it in the future. So my questions are what gear ratio should I go with and where should I buy from for quality parts?
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Jayden
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pyntre
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Joined: 29-March-2007 Location: United States Status: Offline Points: 275 |
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Posted: 31-January-2025 at 3:01PM |
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Quality / and great service for parts
Quick Performance out of Iowa . New center section and a new set of axles ! Gear ratio depends on many factors . Need a lot more info on what your driving patterns are , and how the car is going to be used .
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anchovieMAN
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Joined: 19-January-2021 Location: Wisconsin Status: Offline Points: 75 |
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Posted: 31-January-2025 at 4:07PM |
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I would like it to do 65-70 mph without the engine exploding. Just a daily driver and not overly worried about being fast
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Jayden
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pyntre
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Joined: 29-March-2007 Location: United States Status: Offline Points: 275 |
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Posted: 31-January-2025 at 4:49PM |
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Lots of RPM calculators that take rearend gear ratio , tire diameter and final trans ratio : ie, is it an overdrive transmission, into the equation . Plug those numbers in and you can dial in what you need !
Simple math , but it’s great when it all works together and you end up with a happy car , and driver !!
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72FordGTS
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GTS.org Admin Joined: 06-September-2005 Location: Ontario, Canada Status: Offline Points: 6780 |
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Posted: 31-January-2025 at 9:11PM |
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With a 4-speed, you'd probably want a 3.25 to 3.50 ratio depending on your tire size. Based on what your saying, maybe a 3.25 would be ideal for your needs. Play around with the RPM calculators. Summit has some complete center sections for 9" diffs, but they aren't cheap.
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Vince
1972 Ford GTS Sportsroof - Survivor, One Family car GTS.org Admin |
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handsofstone
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Joined: 13-April-2018 Location: Northeast Status: Offline Points: 4229 |
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Posted: 02-February-2025 at 4:16PM |
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I went with 3.25 in my car and long cruises at highway speeds had me finding backroads in no time.
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72 RS 351
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Joined: 04-September-2014 Location: Knoxville TN Status: Online Points: 3445 |
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Posted: 03-February-2025 at 2:49AM |
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I didn't mind the 3.25's I put into my first 72 Gran Torino, it was okay for my all around driving. On long trips it would be a bit high rpm for good fuel economy. The OD transmissions are all about .70:1 so highway rpm is 2000 at 70mph, using 3.25 gears. That's what my stock four Mark VII's have been, AOD and 3.27 gears, 26" tall tires. My 302 SUV's run 2000 rpm at 60mph, with 3.73 gears and 29"-30" tires. Anything in those ranges work great on the highway if you can put those together.
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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 |
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72FordGTS
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Posted: 03-February-2025 at 11:27AM |
What was your RPM at highway speeds? Don't forget he has a 4-speed, so there is no slippage like a torque converter. Ford's optional or towing ratio for most engines in 1972 was 3.25. 3.25s were the base gear for Q-codes and 3.50s were optional.
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Vince
1972 Ford GTS Sportsroof - Survivor, One Family car GTS.org Admin |
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handsofstone
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Posted: 06-February-2025 at 2:19AM |
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I had no tach but 60 was the sweet spot. Above that it was in what I would call its power band and throttle response was instant.
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handsofstone wrote: