Well I may have screwed up but I have a 350 SB, 400 turbo trans, and a 4:11 to 1 gear in the rear(31 spline) The engine is revving too high at Hwy speeds and I want to put a better hwy gear in. Well I bought a used 9 " 31 spline with no tags and when I got it home and dropped the punkin out and counted the teeth it is a 2:48 to 1. It looks like a good clean gear set but do you think it will work with my set up ? or is it too tall ? thanks
For anyone to make an educated reply you would need to include more info. Your camshaft and torque converter would be two very important factors.
Typically you will want a 3.08 [tall side for cruising] to a 3.73 gear. More gear if you have a cam ,higher stall converter ect. I honestly have never heard of a 2.48 gear ,I guess they made them ?.
A 2.48 is a pretty tall gear, but as others have noted, tire size, engine build level, and the torque convertor used will make a considerable difference. Car weight definitely enters into it also; in a light car it may give satisfactory performance, not so much in a heavy car. Generally speaking, with an automatic trans you want your cruise RPM to be higher than the convertor stall speed to keep trans temps down.
I have never seen an original 2.48 gear in a 9in Ford (doesn't mean it isn't, I just have never seen one.) Can you do a recount on the RG&P? Also, post a pic of the thickness of the ring gear. You can get a good idea of the ratio by the thickness of the ring gear. A 2.48 would be really thin. -Abone.
You need great big gobs of low end torque or super low weight to be happy with that gear. The converter and cam need to match too.
Hope this helps? Never heard of a 248 though? I like 3.55-3.90 ratios as said before weight tire size cam & converter makes a huge difference My 406sbc 350th 4.11 M/T 30x9 slick cruised well at 2700 rpm @60mph but had a tight nitrous converter in my chevelle that was 3800 lbs! "Heavy chevy" lol Sent from my SM-G930P using The H.A.M.B. mobile app
Sell the 2.48's to Bonneviile guy, replace the trans with a 200R4, keep the 4.11's, and be a very happy Hot Rodder. The other option is a GearVender OD right on to your 400 TH. You will be very happy that way too.
I had an F100 that came with 2:47 gears. It never reved high enough to lock up the converter. And it was rally slow in the hills. So 2:47s were no good there. I also had a small, light stick shift car with 468 cubic inches that was only used for motoring in a highly saline environment at high rates of speed. On that cat 2:47s were fine. What are you going to do?
Hold your horses. What sort of car? I your car would look great with tall rear rubber, such as an open tired 32 (cool!), then simply getting some cool looking tall meaty tires should take care of it. That move might make you happy you have 4.11s to accomodate them, and save you a ton of effort locating and changing gears to fit the short short tires. Try some tall fat cool tires if it works with the car style. They will certainly bring those excessive revs down without a lot of work. If you have to use more "normal" tires, you should look for something in the mid 3's if you still want a little pep without the annoying highway screaming engine. or possibly low 3's if you prefer quiet comfort. If you're spending money, I recommend a 700r4 or 4l80 for the overdrive that will make your 4.11 gears JUST PERFECT. They will also have a low first gear that will make your car JUMP away from stoplights and stop signs. Best of both worlds. The money you save on a gear swap could go a long ways in paying for the trans that will make you REALLY like your car . WHY BE ORDINARY ?
I had 2.47 gears in my 55 chevy for a little while, it cruised nice at 75. The engine had plenty of torque (blown 454) and the switch pitch converter let me run it in low stall (about 1500 rpm stall speed) easily so it didn't overheat the trans. I think they made 2.47 and 2.50 gears for the 9" in the 1970s. Yup, it's a good idea to turn the parts in a rear end, to see about what the ratio is, before you buy. Depending on the engine specs, you may be happy with the gears you bought, or you might not. I've put a lot of happy miles on 2.75 gears.
The 2.47 gears came from a later 70's Lincoln. I have some I was going to put in my '54 Ford panel as a poor mans overdrive. But it does have a 390 FE with has tons of torque. Depending on the motor and what vehicles it's in you could run it. I have a '41 Ford p/u with a 3.08, 215/75R15 tires and stock SBC that works great on the freeway and around town (I wouldn't mind a 2.73 if they made one), the panel I mentioned has a 3.00 in it now. The Stude Lark has a 2.79, 225/60r15 with the stock 259 and is great around town.
Agreed! The 4.11 is perfect gear with the 700r4. Even with a short tire the overdrive will put it in the sweet spot rpm range. Any taller gear will lug the engine down in overdrive and actually suck more fuel. Sent from my iPhone using The H.A.M.B. mobile app
I was thinking highest I had ever ran across in OEM, was 2.78 . But that doesn’t mean it never happened . I have had many to set up , again never seen a 2.48 . That will take a bunch of torque to get motivated and top end is what we say “ whiskey runner “ speed . I have a 3.00 in my 32 at this time , I have tried 3.70, 3.50 , 3.25 in 2800 lb car 3.00 seems best for me . I have no OD in my trans . If you have OD most are near .70 , so a 3.70 would be a great gear set for OD running trans . Look around for I couple used already set up gear sets try them to see what is best . Easier than removing setting up gears numerous times . 2.48 / 31 spline that is a rare bird indeed ! Sent from my iPhone using H.A.M.B.
If you have a stock cam in the 350 it might work OK providing the rear tires are not real large and the car is not real heavy
I have the rear end out and counted the pinion teeth (19 ) and the ring gear has 47 teeth = 2.47 or 2.48 right ? 31 spline axles the guy I bought it from said it was in a 79 Rancharo but .... my rear tires are about 26 " tall
If you put a 700R4 trans in ,and kept the 4.11's it would cruise 70mph at 2600RPM , and get up and go in the lower 3 gears. You would need a 2.87 ratio rear to do the same with the T400
47 / 19 = 2.4736842105263157894736842105263 and that rounds to 2.47, so yeah, it's a 2.47 ratio gear set.
I don't know why we spend so much time expressing opinions on rear gear ratios with almost no information about the vehicle. I have an OT shop truck that weighs 5000+ lbs. I have run 2.42 rear gears in it. Not great when the light turns green, but certainly livable. But, since you don't know the rest of the story, you can't tell if it would work for you. I tried flipping the change gears winding up with 7.01. MISERABLE!!!!!!
I would probably recount it, yes Ford had a 2.48 but I never saw one in 31 spline. And yes that gear is only good for a salt car or a low revving big block car. I am putting a 3.55:1 in my sedan, it is a good tradeoff gear. Fair on the interstate and good around town. If that is any help to you. My personal preference is a 3.26:1 [which is also a stock Ford gear], for a street gear. But the 3.55 is already set up and ready to roll.LOL
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