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Old 05/17/19, 11:47 AM   #1
EarlybroncoHI
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Honokaa, Hawaii
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Gearing trans or transfer case help

Iím looking to get some help or advice on what to possibly do to deal with gearing issues in my 73 bronco.. so the bronco has an an 89 mustang 5.0 HO motor that has been upgraded. Itís like having a race car with a bronco body. The gearing in the rear end is 3.50. So hereís my issue.. itís great on the highway. Itís fast it has good pick up and doesnít rev high at high speeds, But it sucks in low gear, when I go off reading in 4 low itís to trusty uphill and doesnít hold you back going down hill. What would be suggested to fix this issue.. I love having the high end power on the road but would love to have great low end off road gears. Should I change gearing in the axels, should I get a different transfer case or trans?

Oh it has 33Ē tires.. and it doesnít burn out very well even in the mud. Seams like gearing is to high. But I donít know much about gearing. Thought of putting 4:10ís

Thanks for any help
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Old 05/17/19, 11:53 AM   #2
BanditBronco
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Bingo!

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The only info you left out that we are going to need, is what transmission it has in it?

351W, 4R70W, Atlas 2, 3.5 inch lift 1 inch body lift, full cage, suspension seats, discs, 37 12.50's, full widths, nics, nacs
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Old 05/17/19, 12:30 PM   #3
EarlybroncoHI
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Oh shoot! It has a column shift automatic. I think it’s the stock trans, but not sure.
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Old 05/17/19, 12:35 PM   #4
fordguy
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Quote:
Originally Posted by BanditBronco View Post
The only info you left out that we are going to need, is what transmission it has in it?
yes you will need to find out if it is a C4 (original) or an overdrive of some type.
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Old 05/17/19, 12:56 PM   #5
Local Boy
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More throttle...Less talk

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Howzit Brah...

Your 3:50 gear set is killing your low end, but are good for HWY driving as it keeps your RPM's down...

With your set-up, 4:11's will wake that bad boy up! You will definitely feel the difference and have no problem spinning it in loose terrain and mud... But the trade off is that you will see higher RPM's on the HWY... But, with your motor that should not be a problem...it will give you better passing speed when at 50-60 mph... That's good!

I would suggest do a gear change (front/back) and run it .... If/when you break something (U-joints/axles/trans/transfer case) then up-grade to stronger and better stuff...

I've always sought to explode things before I replaced them... Good Times!

Give me a shout if there is anything I can help with...

Aloha

Last edited by Local Boy; 05/17/19 at 01:13 PM..

XCON BR #1 - 408 Stroked Dart block, Forged rotating assembly, Jon Kasse P-38 heads, Jesel valve train, Atlas II, Hughes Built C-4 w/ manual valve body, RCV 31 spline front axles, F-9 Currie 9' 35 spline rear end, BigStuff3 Pro SEFI
"Every time I turn on my Bronco, it returns the favor!"...
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Old 05/17/19, 01:04 PM   #6
Broncobowsher
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Sounds like you have a C4. And I bet that transmission is trying to kill itself trying to push 33" tires with 3.50 gears.

Change to 4.88 gears and put a 4R70W in it. Freeway will be about the same, just a touch lower RPM since the effective gear ratio is 3.42 and the convertor will lock up. But it will scoot off the line REALLY good. The extra gearing will actually give engine braking going down hills. It will be a riot to drive. And it will still go down the highway great.

"She's built like a steakhouse but she handles like a bistro"-Zapp Brannigan
Why do people keep expecting "normal" from me?
Full throttle, it either solves the problem or ends the suspense.
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Old 05/17/19, 01:50 PM   #7
joshd1971bronco
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Oklahoma City, OK
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Not yet mentioned, but you could put an NP435 manual trans in it. Super low granny gear, and three other 'normal' gears to give you the same final drive ratio.
Would be more involved than a gear swap but you could keep the highway friendly 3.50's.
Also depends on your ultimate goals for the truck.

I'd rather be driving my Bronco

1976 Sport Wagon, NP435/205 combo, 302 carb'd, 3.5" susp lift, 1" body, 4.10's, p/s, p/b
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Old 05/17/19, 01:55 PM   #8
BanditBronco
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with a c4 and 4.11's with 33's I don't think your rpm will be too high for the highway. I used to cruise that exact setup but I had 35's and it ran at about 3k rpm at 70

351W, 4R70W, Atlas 2, 3.5 inch lift 1 inch body lift, full cage, suspension seats, discs, 37 12.50's, full widths, nics, nacs
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Old 05/17/19, 03:05 PM   #9
Broncobowsher
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Adapt and overcome

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4.11s and 33s are a well known happy place in Broncos without overdrive transmissions. As low as you really want to be and still cruise the highway, with a fair bit more RPM but not excessive. As high as you would really want to be in town or on the trail. The C4 is a lot happier as the extra RPM takes load off the convertor so it runs cooler.

"She's built like a steakhouse but she handles like a bistro"-Zapp Brannigan
Why do people keep expecting "normal" from me?
Full throttle, it either solves the problem or ends the suspense.
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Old 05/17/19, 03:06 PM   #10
bigmuddy
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I would like to throw in the odd gear ratio of a 4:30 gear as well. Good on the highway and great offroad, Still gives an option to go to a larger tire at some point. Really the best ratio for the bronco c4, but most don't consider it..

75 EB, 35" tires, EFI 5.0 with Explorer stuff. ARB/ Aussie locker, ZF tranny, 4.56 gears, twin stick, 2.5 BC lift, Cage long arms and dual shock kit,Ghetto fab hydroboost with disc brakes,yada,yada,yada!
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Old 05/18/19, 11:31 AM   #11
EarlybroncoHI
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Thank you all for the suggestions!!! Sounds like you all agree on changing gearing is the first step.
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Old 05/18/19, 04:27 PM   #12
DirtDonk
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It's the quickest and most basic. But the modern preferred equivalent is to take advantage of an overdrive transmission along with even lower gears (like 4.56 or so) and have the best of both worlds.
But obviously that's much more involved, and much more expensive.

I would recommend one thing as an experiment though. It means not using 4wd until you can finish the job, but if you do the rear end only you can get the new gears and decide you really like it before spending the extra money on the front gears.
Obviously you can't put it in 4wd because of the mis-matched gears for a time, but at least it's less hassle if you find you don't actually like the new ratio. Maybe it's too low, maybe it's not enough of a change and not low enough. But you only have to re-change one unit.

Most likely you will love it though, so the choice is yours and can go either way.
I'm guessing your engine sounds like it's revving higher than it really is. That or you're used to modern vehicles with overdrives, or perhaps older passenger cars with big v8's and real "freeway-flyer" gears. Or just don't like revving that high.
Your 302 will spin 2600 all day long (your current setup at 70mph) but how much time do you spend on the freeway at speed in Hawaii these days? I know the roads are way bigger than they were when I lived there (before the original Hawaii 5.0!) but wondering how important the highway rpm is compared to the wheeling rpm?
With the 4.11 and your current trans and tire size, you'll be near the 3100 rpm level at 79mph. Higher than most of us like to listen to, but the engine might actually be pretty happy.

If it comes down to a tradeoff, would you rather keep it biased towards the freeway cruising, or more towards acceleration and wheeling?
And maybe even better overall fuel economy too? That last one is pretty fickle, but sometimes with our rigs the lower gearing and higher rpm take enough load off of the engine that you can get better gas mileage.
Maybe not at 70(!) but maybe average.

Good luck!

Paul

'71 Wagon, 3.5" WH, F150 disc brakes and steering, 4.11 33x11.50 Thornbirds, Kayline soft top, Hanson bumpers. "Built, not bought"

'68 LUBR, 2.5 + 1 WH, 31x10.50, 4.56, Explorer and 4R70w by EFI Guy, WH disc brakes, Hanson front bumper, Warn winch. "Bought, not built"

www.wildhorses4x4.com
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Old 05/19/19, 11:55 AM   #13
fordguy
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Quote:
Originally Posted by EarlybroncoHI View Post
Thank you all for the suggestions!!! Sounds like you all agree on changing gearing is the first step.
change the rear first and see how you like it.
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Old 05/19/19, 04:57 PM   #14
jckkys
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EBs with 302s don't lack HP so the Mustang engine was no help. They do need more low end torque. To fix this the obvious answer is more displacement not a complete redesign of the drive train. In my case a 351W gave me the low end torque I needed. Again the high HP race parts are self defeating. Your current transmission and axles would work well with the 351. I question the need or desire for 33" tires. 30s or 31s work better. Another source of displacement would be a 347 crank. They work well but are more costly than 351s, and they're not as durable.
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