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Discussion Starter · #1 ·
Currently I have a 4bt ve pump with a hx30w, and an ax15 and 4.11s and 33" tires on my early bronco, dana 30 and 20 and ford 9".

Right now I have the itch to change to 3.5 gears on the axles since this is basically a daily driver and rarely sees low gears unless I'm dragging trees to be cut up. I do get it up to 70 for cruising but that's about it.

Does anyone have that setup and like it? I feel like I'm changing gears too quickly just driving around town, but it is a lot better than my toploader OD used to be.
 

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Unless you plan on pulling stumps or doing a lot of off road crawling you'd use a 3.54 front axle ratio that was standard for the Dana 30 and you'd use a 3.55 in the 9". Have to be careful because some companies only have a 3.50 for the 9" but you want the 3.55 to properly match the front.
 

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I have often wandered this , 3.55 rear , 3.54 front . Is there really that much difference ?
2% difference is what I have always been told was the max that is acceptable for "normal" driving, dedicated racers and off roaders run more for specific tasks but 2% or less and you will be good.
 

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1978 F800 CrewCab Marmon Herrington
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OEM would be a 3.50 in the rear and 3.54 in the front. There are millions of that combo running around out there for the last 50+ years. I wouldn't worry about it.
 

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My 72 BRONCO Is what your asking about. Now Mine barely runs 55mph. & I have 3:54 & 3:55s.. I have a stock 4BT * NP435 trans. .. I use mine mainly of the farm. SO I hardly ever get over 15 mph. But I do go to town for fuel & about 55 is all I drive now . I can't believe mine would ever run 70mph.
I might have white knuckles IF I DID..
I DO USE 1ST gear all the time to take off. I did want 4:11's but I've decided I'll Just stay with my 3:55's.
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......................... & YES If you only drive in town . THEN I'D say fine a used 3:55 & swap it into the rear axle & Give it a try .
Rear axle swap only takes an hour or 2 ... Nothing like the front swap.
& If I were you & needing to put a 3:55 in the front. Then I'd find a DANA 44 & put in new Ball Joints & do the front Chevy Disk Brake Swap .. & Get the entire ball & Chain In one swap.
 

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If you don't know what your need for the front Disk swap Chevy Style I can do a write up for you . Just ask.
I'm an old parts man from 1967 until 1995 & worked 10 year at Jeep & Dodge Pickups for another 10 & At a FREIGHTLINER STEALERSHIP For the last 12 years . Now retired thank GOD.
bUT i BELIEVE i CAN REMEMBER MOST OF THE DISK SWAP . AS I'VE DONE 2 OF THEM . .
 

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If it helps I have a 66 bronco 4bt P7100 hx30w
Nv4500 dana 20 ford 9. Went from the stock 4.11s to 3.89s on 35s and wish I would’ve gone taller still, the low is great but highway cruising is not where I really wanted it. I’m seriously considering 3.50s or even taller.


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I'M GOING TO SAY .. gIVE THE 3.55'S A SHOT 1ST.
I HAD AN old 4x4 1980 Bronco that Had something like 3.23 in It I guess it was nice on the Highway.
but It sucked everywhere else it was . I put 3:55 in it .& Drug a small trailer into New Mexico 3 time hunting & 4x4 wheeling while hunting & The 3:55's got me 16 mpg on that old 300 cid .& one year we put 454 mile on it in 4x4 ... Now those miles did not get but about 4 mpg .
But back out o the Hwy I got 16.
But It worked fine in the mountains . With 30x10:50R15S.
.
 

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Discussion Starter · #11 ·
75 is the fastest I’ve driven since the restoration, but that was on old unbalanced 36x14.50 tires and quite brief. Really only pushed that to see how it pulled, it would have kept going.

I do have discs front and back and likely will stay with the dana 30. I like the gear spacing on the ax15, just wish it was rated for more torque so I could tow the 24’ mastercraft. Sounds like the 3.5 ratio will be about right for daily driving. If I need more gears, I’ll take the dog house for getting an atlas tc.
 

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The Dana 30 will probably be OK as long as you don't abuse it. It has a Gross Axle Weight Rating of 2770 lbs. Now if you got into some serious off roading that 7" ring gear may not like the torque put out by the 4bt. Guys have broken Dana 44 axles. The AX15 may be a weaker link. it has a torque rating of 300 lb ft which about a bone stock 4bt. Actually, a 130 HP 4bt has 325 lb ft which would be pushing it to the limits. The Ford/Mazda M5OD-R2 is rated at 330 lb ft and has been used by several swappers. Has great gear ratios for a 4bt. So much depends on how you drive it.
 

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Discussion Starter · #13 ·
I’m going relatively easy on it, I do push the skinny pedal but I’m not dropping the clutch. Not sure what torque I’m getting with the hx30, haven’t messed with the wastegate either. I’m about 1500 miles into the build, and from what I understand with the bronco not being that heavy, it should be fine.
 

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If you have a basic 4bt with the HX30W and adjust the waste gate on the turbo, \ fuel, and timing on the injection pump you'd be in the neighborhood of 150-200 HP. That's a wide range but it depends on those last 2 adjustments. That would put the torque output to somewhere in the 350-450 lb ft range.
 

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Actually most of the general consensus over on the classic web sight Is the week link in Our Bronco is the main shaft in the Dana 20... & With 3500 members .. Everyone believes in swapping to the Dana 44. Most of the Dana 30's are left in pure stock rides . Or for the Guy who just can't afford the swap .
...........Is the AX15 AN Overdrive trans . SOME of the guys use them . But I guess I've not read their post close enough to know the ax15.
 

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My Power Wagon has HX30 , NV4500 and NP205 with Dana60 both ends , 3.54 and 3.55 . It’s great , easily run 70 MPH if needed . I normally drive the 55-65 MPH speed . My tires are 265/75-16 and it’s around 18-1900 rpm . I dare say the old Wagon is much heavier than your Bronco will be also .
 

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Dave do you know what the W2500 weight is . I believe our little Broncos are about 5K .
.. I ALSO HAVE 2 OF THE D2500's one is Diesel & the other is a 318.
 

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Discussion Starter · #18 ·
I think the early Broncos are 3400 or so without the top. Add a few hundred for the engine difference.
 

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The old Power Wagon is 6900 lb with me sitting in it . It has huge bumpers and a front hydraulic winch . My avatar(?) has the image of it . The old tank will do an Avg . MPG of 24 .
 

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Holly Smokes 24 mpg that's great.
....Kills me as I have a 2000 24V Auto .2 wd & MINE Gets 14 most of the time.
I don't know what my 1989 12V get's .. Auto Trans is out. .
 
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