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What Rear Gear should I run?

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JW79 View Drop Down
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    Posted: 30-July-2022 at 7:12AM
Hey, I own a 1973 Ford Gran Torino Sport Fastback. It came with a 400 but I want to put a 460 in it and put a C6 Transmission in it. What Rear Gear would be good for and everyday driver?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AUS GTS Quote  Post ReplyReply Direct Link To This Post Posted: 30-July-2022 at 12:19PM
I'm gonna say 3.25... fine on the highway & can still induce some "fun" if needed.
Al
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 30-July-2022 at 12:48PM
 yeah 3.25 should be a good all around gear
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 30-July-2022 at 3:12PM
Yeah, as the engine size and torque go up at the low end, a taller R&P works better than they would for a smaller engine etc. My 73 with 351C-4V has 3.70:1 gears and the C6. It's fine for around town, but at higher speeds for long at all, it needs less gear.

I would vote for the 3.25:1 also for a 460 engine.
Don
73 Ranchero Sport "72 front end", floor shift/console, planning EFI 7000rpm 351-4V &4R70W
73 Ranchero GT 351C-4V 3.70 gears for sale later.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Eliteman76 Quote  Post ReplyReply Direct Link To This Post Posted: 31-July-2022 at 9:02AM
Without getting side tracked...
I tend to agree with 3.25's but also what rear tire size are you running? 
A 275/60R15 will spin slower than a 295/50r15 for example.

I'm running 3.70's with my tremec 5 speed and a 295/45R18 and I almost wish I would had just done 3.50 gearing.
Andrew: Long time Torino guy and GTS.ORG admin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote handsofstone Quote  Post ReplyReply Direct Link To This Post Posted: 31-July-2022 at 3:17PM
I put 3.25 set in a trac-lok. Nice on back roads but highways leave a lot on the table. Another two speeds would be nice for sure but I pretty much stay close to home base so I can live with it for now.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Inkara1 Quote  Post ReplyReply Direct Link To This Post Posted: 31-July-2022 at 4:51PM
On the topic of rear gears... I believe I have a 3.00 rear end. Since I was planning to use the wagon as a tow vehicle in the future, should I switch it to 3.50? It's a 351C that a prior owner changed to 4-barrel and swapped the C4 for a C6. Or should I switch to something different than 3.50?
1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote handsofstone Quote  Post ReplyReply Direct Link To This Post Posted: 31-July-2022 at 6:22PM
It would depend on what you are towing and how far I suppose. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 78FordLtd2 Quote  Post ReplyReply Direct Link To This Post Posted: 31-July-2022 at 6:28PM
If youre planning to drop the 460 in as planned, either the 3.00 or 3.25 will be fine. Growing up, we had a 75 Montego wagon with a 400 and we did quite a bit of towing with it and had no trouble crossing mountain ranges and i believe it had a 3.00 gear in it. Your 460 will have enough low end grunt in it to tow just about anything anyway. You might get a little better mileage with a 3.25 but it wont be much. She's going to be thirsty no matter what. I believe big block Ford wagons were all equipped with a 3.00 gear from the factory and were considered (at the time) to be a "performance" gear ratio.

If it were up to me, I'd choose the 3.25 with a Traction Lock. It would give you the best of both worlds in terms of mileage and performance. I'd also beef up the cooling system as well. A 3 or 4 row core rad would be a great upgrade, along with a cooler foe the trans.

Damn! Thats going to be an awesome wagon!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Inkara1 Quote  Post ReplyReply Direct Link To This Post Posted: 31-July-2022 at 8:34PM
I should clarify that it's the other guy with the fastback that's putting in a 460. I currently have no plans to swap out the 351C in my wagon.

I put in a 3-row Champion aluminum radiator and a rather large trans cooler already.

The idea is to tow the 1962 Fairlane because I'm getting too old to sweat that much with no a/c. Then once I get to the show I can enter both cars because the Fairlane Club covers both. Some of the shows are ~6 hours away and I'd be crossing the Tehachapi pass each time.
1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 01-August-2022 at 5:43AM
Originally posted by Inkara1 Inkara1 wrote:

I should clarify that it's the other guy with the fastback that's putting in a 460. I currently have no plans to swap out the 351C in my wagon.

I put in a 3-row Champion aluminum radiator and a rather large trans cooler already.

The idea is to tow the 1962 Fairlane because I'm getting too old to sweat that much with no a/c. Then once I get to the show I can enter both cars because the Fairlane Club covers both. Some of the shows are ~6 hours away and I'd be crossing the Tehachapi pass each time.


I like that goal, but the wagon will have trouble with the towing, and AC running for a long trip with hills. The rpm's will be high on the highway for most any trans and gearing, you'll have to keep the speeds down almost the whole trip. A bigger engine would let you run taller rear gears, but the 351 will need I'd bet at least 3.50 or 3.70 gears.

If you had a Gear Vendors overdrive unit, then you could push the gears a little lower(say 3.90 or 4.11), and use the OD for anything but big inclines. Lower gears help you to get up to speed, but they raise the rpm's at high speeds in 3rd gear.
Don
73 Ranchero Sport "72 front end", floor shift/console, planning EFI 7000rpm 351-4V &4R70W
73 Ranchero GT 351C-4V 3.70 gears for sale later.
92 Lincoln Mark VII SE, OBDII 347/4R70W
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 78FordLtd2 Quote  Post ReplyReply Direct Link To This Post Posted: 01-August-2022 at 10:53AM
What is a Torino factory rated for towing? 5500 or 6000 lbs?? Id find out what the GVWR is and go from there. A 62 Fairlane on a flack deck car trailer may exceed the towing capacity of the car. The Fairlane would weigh in minimally 3000 lbs and the flat deck trailer will likely come in about the same. I'd probably look at using a tow bar instead...to shed some weight.

Your 351 might be adequate at best, even with a 3.70 gear, but my question would be with the abilty to stop with a fully loaded flat deck trailer.

I like the idea though! 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 01-August-2022 at 12:25PM
You have to use a car trailer and not a heavy flat bed type. I towed a 1998 Explorer 170 miles from NC over a big mountain climb of about five miles, with my stock 98 Explorer. Those 2nd gen Explorers weigh about 4500lbs, and the car trailer I borrowed was a nice one with good brakes. The total weight was more than the tow rating of the truck, but not by much and I was careful for that one need.

The actual weight of the towing vehicle is part of the tow rating, heavier vehicles are rated higher than light weight cars etc. The transmission is a major factor for towing, small engine models are much weaker than huge transmissions in bigger trucks etc. So the gearing is just a minor factor compared to some others, you can only do so much with a given vehicle.
Don
73 Ranchero Sport "72 front end", floor shift/console, planning EFI 7000rpm 351-4V &4R70W
73 Ranchero GT 351C-4V 3.70 gears for sale later.
92 Lincoln Mark VII SE, OBDII 347/4R70W
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Inkara1 Quote  Post ReplyReply Direct Link To This Post Posted: 01-August-2022 at 2:20PM
So from what I can find online, the curb weight of a Fairlane Sports Coupe with 260 V8 (what I have) is about 3,220 pounds, and the U-Haul flatbed is 2,210. I've seen 6,500 pounds quoted on this site as the capacity with the top towing package, so I'd be about 1,000 under that. I might look for either a rental trailer that's lighter than that or a used one to purchase. I fully intend to figure out how to wire in a trailer brake controller, and U-Haul has a Class 3 hitch available for the same year Ranchero (I believe Ranchero and wagon use the same frame). That one is rated for 5,000, so I'd probably want to find a lighter trailer (the U-Haul one is overbuilt so it's strong enough to tow an SUV). As for the tow package, my understanding is it required a 400 or larger V8, upgraded radiator, upgraded transmission cooling, and upgraded rear springs, and probably a shorter rear end than 3.00. I'm short on cubic inches, but a prior owner put on a 4V intake and a C6 transmission, so I'm at least ahead of stock in that regard. I've upgraded cooling with a large trans cooler, 3-row aluminum radiator, and clutch fan. Last concern would be the gear ratio (hence my post here) and rear springs. Towing speed limit in California is 55, and I have no intention to exceed that given my setup, so since I'd usually have overdrive off when towing, I think I'm OK with a C6 and its reputation for strength. Maybe I should find a way to install a transmission fluid temperature gauge as well.

So that's the plan. I'd probably not consider it with towing another Gran Torino, but 62-65 Fairlanes are pretty light compared to what people expect of 1960s cars.
1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 78FordLtd2 Quote  Post ReplyReply Direct Link To This Post Posted: 01-August-2022 at 5:30PM
Sounds like you're figuring it all out there and getting a good plan together.

Yeah, 55 mph is about as fast as i want to tow. I keep it between 50 and 55 when towing my travel trailer and let the world race by. My 2005 GMC Safari tows my trailer great excpet on the hills where it feels like someone just threw an anchor out the window.

Wiring up a brake controller is pretty easy. Ive done a few. The hardest part is working under the dash in awkward positions. Should be no trouble.

The weight of the trailer is going to be the key. I just asked a friend of mine how much his car trailer weighs and its in the neighborhood of 4500 lbs but his is built to accommodate a winch, welding equipment and his tools...and thats without a car on it. He uses an F450 dually with a Powerstroke.

As mentioned before, your 351 might be a bit short on cubes, but with the 4V and the 3.70 gears, it might be okay. Youll just have to see where she'll be happiest in the torque curve when climbing those grades fully loaded. Install a tach and drive by the rpm and forget about the speed. As long as you can maintain 40ish mph going uphill, youll be doing pretty good.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote handsofstone Quote  Post ReplyReply Direct Link To This Post Posted: 02-August-2022 at 5:33AM
The problem with renting from u-haul is they will do the hookup on approved vehicle. They may balk at your wagon even though it is within the towing capabilities of the vehicle.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 02-August-2022 at 1:34PM
There were two factory tow packages, Class II at 3500 lbs which included heavy duty suspension, extra cooling package, wiring harness, and required a 351-2V or larger engine, automatic, power steering and power brakes.  The Class III 6000 lbs package included all of above plus the HD battery, alternator, and frame (except station wagon - I'd assume because all wagons had a HD frame).  It required a 400-2V engine or larger and 3.25:1 gears.   Keep in mind for 1972 wagons there were only two axle ratios, 3.00:1 or 3.25:1.

How is the car now for power?  How is it in the steep hills?  Keep in mind stock 1972 engines were not overly powerful.  So even the upgrades done to your car should make a difference.  Do you have free flowing dual exhaust? Any other engine work?  The C6 with a cooler should be fine, it's pretty tough.

I used to have a Suburban with a 350 that only made about 210 hp and 3.42 gears with 29" tall tires.  It could tow 6500 lbs no problem.  My buddy had a similar setup in his pickup and he regularly towed full-size cars much bigger than a Fairlane without issue.  So, I would think 3.50 gears would be enough if your 351 is a strong runner and you are only towing at 55 mph.  What size tires are you running?  This also has a big effect on the overall ratio.

One thing to consider is the long rear overhang on the wagon.  This can cause the tail wagging the dog effect to some degree. The wheelbase is also much shorter than a pickup too.  A weight distributing hitch setup might help improve stability.  It might also be worth investing in poly bushings for the rear end to help with lateral stability. 
Vince

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 02-August-2022 at 1:46PM
The Gran Torino wagon, 4dr, and Ranchero have a 118" wheelbase, the 2dr has a 114" wheelbase.
Don
73 Ranchero Sport "72 front end", floor shift/console, planning EFI 7000rpm 351-4V &4R70W
73 Ranchero GT 351C-4V 3.70 gears for sale later.
92 Lincoln Mark VII SE, OBDII 347/4R70W
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Inkara1 Quote  Post ReplyReply Direct Link To This Post Posted: 02-August-2022 at 8:15PM
I haven't gotten to drive it up many steep hills yet. Currently have the fan off while I've been working on the a/c, and also need to fix a leak in the gas tank. Need to have it ready by the weekend of September 10 for the Fairlane Club California meet. (Not trying to tow this year. Next year at the earliest.) I'd like to have it going well before then so I can take it on some shakedown runs, at which point I can answer better about steep hills. In the driving I have done with it, it seems to have a bit of a flat spot right off idle then really picks up. The carb was installed as it came out of the box so I probably have some tuning to do regarding the flat spot. Not sure how "free-flowing" the exhaust is but it does have a dual exhaust system with a crossover pipe. Stock manifolds, though, and the pipes have some dents.

I hadn't thought about the upgraded alternator. How much do trailer lights and electric brakes draw?
1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Inkara1 Quote  Post ReplyReply Direct Link To This Post Posted: 02-August-2022 at 8:23PM
Oh, forgot to mention the tires are P225/70R15 all the way around. I tried to get as close to the F70-14 original size but with the 15-inch steelies I had. Cooper's specs say they're 27.4 inches in diameter. 
1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 03-August-2022 at 2:24AM
Originally posted by Inkara1 Inkara1 wrote:

Oh, forgot to mention the tires are P225/70R15 all the way around. I tried to get as close to the F70-14 original size but with the 15-inch steelies I had. Cooper's specs say they're 27.4 inches in diameter. 


That's a decent sized tire. I had those on my first Crown Vic, that size was on all the early CV police cars. I bought dozens of those over the years. I've slowly moved up in sizes, wider but the same diameter as the OEM sizes for my cars.

That size will do fine for most usage including the towing. If you chose to go bigger it would take a wider wheel, such as a 15x8" size with 255/60/15's. That size would be a 1/2" shorter than the 225/70/15's.
Don
73 Ranchero Sport "72 front end", floor shift/console, planning EFI 7000rpm 351-4V &4R70W
73 Ranchero GT 351C-4V 3.70 gears for sale later.
92 Lincoln Mark VII SE, OBDII 347/4R70W
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 04-August-2022 at 9:43PM
Your wagon should have had H78-14 tires originally, which were a bit taller than the 225/70-14s you have now. Since the tire isn't that tall, I think the 3.50 gear would probably be enough.  Trailer brakes draw about 3 amps per brakes.  So you'd be about 6 amps on a single axle and 12 amps on a double. The most heavy duty alternator in 1972 was a 65 amp.  So it wasn't anything too big by todays standards.  It's easy enough to upgrade to a higher amp 1G, or you could convert to a 3G but that is more involved and expensive.

Carb tuning would really make a big difference, especially in fuel economy.  It's not too often a carb is bang on out of the box, even if it runs ok out of the box.  I am doing my carb tuning now with a wideband 02 sensor and it really helps dial the carb in nicely.  If you car is running well, I don't think power will be an issue, unless you are planning huge climbs of going through the mountains.   I'd focus on the chassis and tow setup for stability.  Done right, I think you will have a really sweet tow rig to tow that ol' Fairlane.  It will be quite the sight to see.
Vince

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