9 inch rear
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From: Tulia, Texas
9 inch rear
i have an 86 bronco with a worn out 8.8 so im about to replace it with a 9 inch out of an 81 f150...my bronco has a 3.08 ratio and the 9 inch has a 3.00....is that too big of a difference with it being 4x4? i know the 9 inch went from 3.00 to 3.25 to 3.50 unless i changed the front end ratio which i do not want to mess with or could i get after market gears closer to that 3.08 for the 9 inch 3rd member?
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This will be a 2.6666666% difference. If you search for "axle ratio mismatch" or similar, you will find a general rule of a 2% difference being acceptable off road. And you will find people running much greater mismatches without any problem.
Ford installed a 3.50 in the rear, 3.54 in the front on some vehicles for example. 4.10 vs. 4.11 is common. Both are less than your difference, but not by much.
In your case, as long as you are on SOFT or slippery surfaces, you will be ok. The faster you go, the more noticable it will be as the mph difference will grow with speed. Your combination will tend to push in corners, as the rear tires will be spinning faster than the front. I doubt it will be a problem unless you are running fast on really slippery stuff.
So, no hard surfaces and you should be ok.
Ford installed a 3.50 in the rear, 3.54 in the front on some vehicles for example. 4.10 vs. 4.11 is common. Both are less than your difference, but not by much.
In your case, as long as you are on SOFT or slippery surfaces, you will be ok. The faster you go, the more noticable it will be as the mph difference will grow with speed. Your combination will tend to push in corners, as the rear tires will be spinning faster than the front. I doubt it will be a problem unless you are running fast on really slippery stuff.
So, no hard surfaces and you should be ok.
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well it sounds like it will get me by for now and i can always change the front end later down the road... what do you think would be a better over all gear ratio for my bronco running 33 inch tires with a 300 6 cyl and a granny 4 spd...3.00 or 3.50's? thankyou for responding..if it wasnt for this site and each and every one of you thats been there when i had tough questions i dont know what i would have done
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33's and 3.50s will work.
At 65 mph you will be running 2316 rpms--maybe a bit high. That's about 28 mph per 1000 rpms if you want to figure more speeds etc.
With 3.00s you will be at 1985 rpms at 65 with 33 mph per 1000 rpms.
Then there are 3.25s: 2151 at 65, 30 mph per 1000 rpms.
With the low first gear, you will be able to pull fairly easily in first even with 3.0s
You could run the 3.08s (or whatever you have close to that) in the front with the 3.25s, but only in the really slippery stuff or at really low speeds--in theory, based on what others have done, ymmv, you might have to adjust tire pressure to even things out--.
At 65 mph you will be running 2316 rpms--maybe a bit high. That's about 28 mph per 1000 rpms if you want to figure more speeds etc.
With 3.00s you will be at 1985 rpms at 65 with 33 mph per 1000 rpms.
Then there are 3.25s: 2151 at 65, 30 mph per 1000 rpms.
With the low first gear, you will be able to pull fairly easily in first even with 3.0s
You could run the 3.08s (or whatever you have close to that) in the front with the 3.25s, but only in the really slippery stuff or at really low speeds--in theory, based on what others have done, ymmv, you might have to adjust tire pressure to even things out--.
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From: Tulia, Texas
i dont know how youre doing that figuring but im glad you can...that helped me make a decision...this will just be a cruiser not a rock crawler so the 3.00's will be the best option, from what i hear the 300 6cyl works better under lower rpms and i bet it would be torquey enough to handle 33's at 70 or 75 mph and not be straining..what do you think?
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About 2300 rpms for 75 mph with 3.0s.
You will have large rpm drops between gears, but you knew that.
Do you know which 4 speed you have? BWT18 or NP435? NP has an aluminum top cover. Ratios vary slightly.
You could drop from 3100 rpm back to 1800 rpm on a 3-4 shift for example.
Not much you can do about that with the granny 4 speeds, but the six will pull pretty good at 1800 rpms on the flat. On a hill.....
You will have large rpm drops between gears, but you knew that.
Do you know which 4 speed you have? BWT18 or NP435? NP has an aluminum top cover. Ratios vary slightly.
You could drop from 3100 rpm back to 1800 rpm on a 3-4 shift for example.
Not much you can do about that with the granny 4 speeds, but the six will pull pretty good at 1800 rpms on the flat. On a hill.....
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From: Tulia, Texas
ok correction i origionally said the front end was geared at a 3.08...pulled the tag off and its a 3.07 dont know if that will make much of a difference running 3.00's in the rear as compared to the 3.08's
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