What gear ratio?
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Freshman User
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What gear ratio?
I have my 63 F100 9" on the way and I'm going to start checking ebay for a 3rd member, I was hoping I could get some advice on what gear ratio to go with. I have 225/75R15 tires, a turbo 400 trans, and a 425 buick engine that made 340HP and 465 of torque when new. I do alot of highway driving but I also want to be able to haul *** around town and maybe do a burnout or three 
Last edited by 48f1nailhead; Nov 17, 2006 at 04:54 PM.
Postmaster
Joined: Jun 2004
Posts: 4,190
Likes: 2
From: Riverside, So Cal
Since the emphasis will be freeway driving, I would recommend a 3.0:1 rear end ratio for best cruising. You'll be doing around 2500 rpm at 70 mph with 26" tall tires.
With the torque your engine puts out, and the narrow tires, burnouts will be no problem. In fact, I would also recommend a limited slip. That way, you'l be burning both rear tires!!!
3.25:1 is a popular ratio also. It will give you a little more grunt off the line and eat more gas on the freeway (2850 rpm @ 70 mph).
I run a warmed up 351C, FMX auto and 3.50 posi 9" rear in my 56 (3200 rpm @ 70mph), but I also run 12" wide rear meats (P295/50R15), which I can spin very easily. I just moved my gas tank to the rear to get it to hook up better.
With all that torque, you may have the problem of NO GRIP, especially if you aren't running a posi, and may find that you'd like some P275/60R15's on the rear, if your rims are at least 8" wide. But that's about as big a tire as you'll be able to squeeze under stock fenders.
You'll have to drive your truck to know how it all shakes out, but I really think you'll be happiest with the 3.0.
With the torque your engine puts out, and the narrow tires, burnouts will be no problem. In fact, I would also recommend a limited slip. That way, you'l be burning both rear tires!!!
3.25:1 is a popular ratio also. It will give you a little more grunt off the line and eat more gas on the freeway (2850 rpm @ 70 mph).
I run a warmed up 351C, FMX auto and 3.50 posi 9" rear in my 56 (3200 rpm @ 70mph), but I also run 12" wide rear meats (P295/50R15), which I can spin very easily. I just moved my gas tank to the rear to get it to hook up better.
With all that torque, you may have the problem of NO GRIP, especially if you aren't running a posi, and may find that you'd like some P275/60R15's on the rear, if your rims are at least 8" wide. But that's about as big a tire as you'll be able to squeeze under stock fenders.
You'll have to drive your truck to know how it all shakes out, but I really think you'll be happiest with the 3.0.
Postmaster
Joined: Jun 2004
Posts: 4,190
Likes: 2
From: Riverside, So Cal
The second one doesn't even list a ratio (that I can see). It doesn't even say if it is a posi. Pass. OR, email the seller with questions before you consider it.
The first one looks very good. I would buy that baby! (item 2300550519999) It's a 3.0 posi with 28 splines. Stock axles go right in and that setup will hang with 500+ hp.
I would also use a snipe program with a high limit of $450. My new Currie posi cost me $450 (thru a buddy who worked for them).
Just know what your buying and from whom. You should be OK.
But......what do I know? I don't even use eBay.
The first one looks very good. I would buy that baby! (item 2300550519999) It's a 3.0 posi with 28 splines. Stock axles go right in and that setup will hang with 500+ hp.
I would also use a snipe program with a high limit of $450. My new Currie posi cost me $450 (thru a buddy who worked for them).
Just know what your buying and from whom. You should be OK.
But......what do I know? I don't even use eBay.
Last edited by Randy Jack; Nov 17, 2006 at 07:50 PM.
Post Fiend
Joined: Sep 2004
Posts: 5,231
Likes: 1
From: Near Fresno, California
Careful - lots of people think they have a limited slip when they don't. It is easy to spot the difference when you know it - the bolt size on the ring gear is different, as is the casting around the bolts. Bolts for the limited slip carrier have a 3/4" head while the bolts on the open rear end are 5/8" head -
I bought one on eBay that was advertised as limited slip when it wasn't, so it does happen. eBay resolved the problem but I was out the shipping both ways. The seller still thinks I cheated him.
It does not help that the picture is just a drawing out of a book, not the actual item.
For more information:
http://www.kevinstang.com/Ninecase.htm
I bought one on eBay that was advertised as limited slip when it wasn't, so it does happen. eBay resolved the problem but I was out the shipping both ways. The seller still thinks I cheated him.
It does not help that the picture is just a drawing out of a book, not the actual item.
For more information:
http://www.kevinstang.com/Ninecase.htm
Last edited by WillyB; Nov 17, 2006 at 10:32 PM.
Postmaster
Joined: Apr 2004
Posts: 3,005
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From: Santa Clarita
I just went through this same thing. My 9 inch had 3.00 gears in it. The truck actually rode nice both on the street and highway. I wanted that extra kick so I bought a 3.50 ring and pinion gear on ebay and had my rearend guy install the gears for $125. I put the 3rd member in and the truck sure comes off the line much better and is great around town. When I get on the freeway now, I'm keeping at around 55 to 60 because now I'm taching a little more than I would like. About 2500 -2750 versus the 2100 I had with the 3.00's, and I'm running 28inch tall tires. With the engine and drivetrain you mentioned, I'd go with lower gears like 4.11's so you can break traction and do burnout if that's what you want. (I'm being a joker here, remember this is a Ford website). I think 3.25 are a nice ratio for overall use. The lower gears sure are fun around town.
Cargo Master
Joined: Apr 2005
Posts: 3,337
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From: Harpswell Maine
I have not driven Willard yet (since taking him apart) however I went the AOD route with 3.73 gears. Should be the best of both worlds, 3.73 off the line and 2.61 down the highway. Years ago I had a 38 Ford woodie (pic in my gallery) with the stock 3.78 rear and a Columbia overdrive (38% overdrive) behind the stock flathead. It was a great combination.
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Freshman User
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I just did the calcs and my tires come out to be 28 inches tall, does that mean I shoud go a little lower, maybe to 3.25 or 3.50?
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Postmaster
Joined: Apr 2004
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From: Santa Clarita
The lower you go in gears, 3.25, 3.50, 3.73's. , the higher your RPMS will be at higher speeds, making your gas mileage and wear on the engine more at highway driving. 28 inch is not going to make that big of a deal. There a few websites that have tools you can use to actually find out what your RPM will be with size of tires/ gears/ etc.
Check this site out under calculation tools. Have fun.
http://www.cvsr.net/php/links.php
Check this site out under calculation tools. Have fun.
http://www.cvsr.net/php/links.php