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Old 08-23-2019, 11:24 AM   #1 (permalink)
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71 Bronco with 38 tires - new gears

I have a 71 Bronco with 38" tires, 4.9L/300 and an NP435, and I need to change the gears to make it highway-friendly, but still keep it offroad capable. As it is right, it way too low, it's set up for crawling and it doesn't pass 40 mph. I don't know what's in it. I was thinking about putting 456s.

I changed the tires to 38x13 (the ones in the pics 39x18.5)

Any thoughts? Thank you.

Does anyone know a good and honest off-road mechanic in the Catskills area?













Last edited by Thunderchief; 08-23-2019 at 11:31 PM.
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Old 08-23-2019, 11:48 AM   #2 (permalink)
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It doesn't pass 40mph? Whats happening at 40 that makes you think it wont go any faster?
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Old 08-23-2019, 11:55 AM   #3 (permalink)
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It doesn't pass 40mph? Whats happening at 40 that makes you think it wont go any faster?
It's on top of the 4th gear with revs are out of the roof and engine screaming. It was set up for hardcore crawling.
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Old 08-23-2019, 11:56 AM   #4 (permalink)
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Sounds perfect to me as is!

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Old 08-23-2019, 12:06 PM   #5 (permalink)
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drop the diff gears and add a doubler. Best of both worlds.
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Old 08-23-2019, 12:23 PM   #6 (permalink)
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drop the diff gears and add a doubler. Best of both worlds.
with a 6.69 first gear in the np435 he probably doesnt need a doubler
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Old 08-23-2019, 12:32 PM   #7 (permalink)
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C6
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Old 08-23-2019, 12:36 PM   #8 (permalink)
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It's on top of the 4th gear with revs are out of the roof and engine screaming. It was set up for hardcore crawling.
Take the transfer case out of low range

With 5.38s, youd be 2k rpm at 40mph.
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Old 08-23-2019, 12:48 PM   #9 (permalink)
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Take the transfer case out of low range

With 5.38s, youd be 2k rpm at 40mph.
But "hardcore rockcrawler"
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Old 08-23-2019, 01:08 PM   #10 (permalink)
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Take the transfer case out of low range

With 5.38s, youd be 2k rpm at 40mph.
Yep Yep
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Old 08-23-2019, 01:12 PM   #11 (permalink)
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Sounds perfect to me as is!
My f250 is on 40s but i am getting ready to bob the back end to make it shorte! I bet we meet in the middle.
WTF is this Guy asks about his gears in his Bronco and you start posting pictures of your truck talking about bobbing it.



Anyway, your Bronco sounds like it has a great combo as is for off-road. Why is it you need to drive on the highway again? 4:88 is a good ratio for the mix.
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Old 08-23-2019, 01:18 PM   #12 (permalink)
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Take the transfer case out of low range

With 5.38s, youd be 2k rpm at 40mph.

maybe he has d60/70s with 7.17 gears

probably not though
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Old 08-23-2019, 02:38 PM   #13 (permalink)
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Quote:
Originally Posted by Black Sheep View Post
Take the transfer case out of low range

With 5.38s, youd be 2k rpm at 40mph.
This.
Also, are you sure it's a 4.9?
That is not a commonly (like ever) swapped motor into an EB.
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Old 08-23-2019, 04:37 PM   #14 (permalink)
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Quote:
Originally Posted by Thunderchief View Post
It's on top of the 4th gear with revs are out of the roof and engine screaming. It was set up for hardcore crawling.
Take the transfer case out of low range

With 5.38s, youd be 2k rpm at 40mph.
Lol
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Old 08-23-2019, 10:18 PM   #15 (permalink)
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This.
Also, are you sure it's a 4.9?
That is not a commonly (like ever) swapped motor into an EB.

Hi, I know. But the previous owner put a 4.9L/300 long block and moved the radiator to the back.
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Old 08-23-2019, 10:20 PM   #16 (permalink)
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Lol
Ideally, I would like to be able to run at ~60mph without stressing the engine and still be able to have a good offroad setup.
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Old 08-23-2019, 10:23 PM   #17 (permalink)
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maybe he has d60/70s with 7.17 gears

probably not though
It sure feels like it, if not even more. I have no idea what's in there. This is my first offroad vehicle. 1st gear screams to change at 7mph.
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Old 08-23-2019, 10:24 PM   #18 (permalink)
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C6

Eventually, I do want to put a small block an auto.
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Old 08-23-2019, 10:27 PM   #19 (permalink)
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What gears do you have now?

What RPM do you want to run at 60?

With an np 435 you only use 2nd thru 4th in normal driving.

Have you tried an rpm calculator?
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Old 08-23-2019, 10:27 PM   #20 (permalink)
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But "hardcore rockcrawler"

That's what I was told, ahahahahah. I don't know, this is my first offroad vehicle.

Does anyone know a good and honest off-road mechanic in the Catskills area? I'm in Kingston/Woodstock area.

Last edited by Thunderchief; 08-23-2019 at 10:28 PM.
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Old 08-23-2019, 10:30 PM   #21 (permalink)
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It sure feels like it, if not even more. I have no idea what's in there. This is my first offroad vehicle. 1st gear screams to change at 7mph.
Figure it out. If need be, jack up the rear end and count driveshaft revolutions while rotating the tire.
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Old 08-23-2019, 10:39 PM   #22 (permalink)
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What gears do you have now?

What RPM do you want to run at 60?

With an np 435 you only use 2nd thru 4th in normal driving.

Have you tried an rpm calculator?
I would like to be able to drive it somewhat normal in the highway if needed, but it will mostly be a Mountain vehicle.

I was told that the low gears are so granny and I should consider putting 411s or 456s to easy up a bit a be able to drive in town easier. 456s or 488s, or 538s?

No odometer just ears a feel.

Last edited by Thunderchief; 08-23-2019 at 11:18 PM.
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Old 08-23-2019, 10:46 PM   #23 (permalink)
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Tried shifting the tcase out of low to hi yet?

What axles does this hardcore crawler have?
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Old 08-23-2019, 10:46 PM   #24 (permalink)
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Lol
With the 4.9/300 I would to be at 2500 @ 60mph
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Old 08-23-2019, 10:48 PM   #25 (permalink)
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with a 6.69 first gear in the np435 he probably doesnt need a doubler
I read that they make an overdrive kit for the NPs. Have you ever heard of it? it's worth it?
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