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Gearing trans or transfer case help

EarlybroncoHI

New Member
Joined
Feb 3, 2018
Messages
49
Loc.
Honokaa, Hawaii
I’m 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. It’s like having a race car with a bronco body. The gearing in the rear end is 3.50. So here’s my issue.. it’s great on the highway. It’s fast it has good pick up and doesn’t rev high at high speeds, But it sucks in low gear, when I go off reading in 4 low it’s to trusty uphill and doesn’t 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 33” tires.. and it doesn’t burn out very well even in the mud. Seams like gearing is to high. But I don’t know much about gearing. Thought of putting 4:10’s

Thanks for any help
 

BanditBronco

Sr. Member
Joined
Jul 2, 2008
Messages
689
The only info you left out that we are going to need, is what transmission it has in it?
 

Local Boy

Full Member
Joined
May 23, 2016
Messages
191
Loc.
Mililani, Hawaii
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:

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,833
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.
 

joshd1971bronco

Full Member
Joined
May 19, 2009
Messages
335
Loc.
Oklahoma City, OK
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
 

BanditBronco

Sr. Member
Joined
Jul 2, 2008
Messages
689
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
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,833
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.
 

bigmuddy

Contributor
Bronco Guru
Joined
Dec 28, 2004
Messages
7,001
Loc.
Marthasville Missouri
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..
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,345
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
 

jckkys

Bronco Guru
Joined
Mar 15, 2012
Messages
5,196
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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