Need help with gears: 302/NP435/D20/37's

[mp]

I am torn on gearing selection between 4.88 and 5.13's. This Bronco will see some highway to and from work and around town, but won't be a cross country cruiser. Not a daily driver, but not a dedicated trail rig.

What gears would best fit? Thanks!

 

[Skiddy]

What tires will you be running? Duh I didn't read the whole thing. I think 4.88 would probably work out best for you.

 

[malcolmzilla]

For 35's and my C4 I am debating between 4.10's (too tall for trail) and 4.56's (too deep for highway)... Given that I plan to drive mine on highway a fair bit, @ 55-62 mph cruise, 4.10's or 4.30's seem the best compromise for economy, given that a deeper low range is in the future.

I am going to drive the Bronco with the 3.50's and 35's 1st to find the 302 sweet spot then pick gears after that... I had 3.54's and 33's in a FS Cherokee with a TH400 and a 360 and that wasn't all that bad... My Exploder I have the 4.0 and 3.73's / 33's and lock out OD and it works not bad, a bit lacking on steep hills but cruising @ 62 turns about 2500 and returns decent power and economy, but the transmission has a lock up convertor than can unlock. The C4 will slip a bit, 1-2%, your 435 better not! I assume the old 302 has comparable torque and the bronco weight and aerodynamics about the same as the lifted Exploder.

Here is a calculator by a fellow Bronco owner:
https://home.comcast.net/~jcmiley/maingears.html

The RPM's seem low with this calculator, but most tires actually measure smaller than labelled OD, and static loaded radius is often even shorter. Keep that in mind running your #'s.

 

[trailpsycho]

I would also say the 4.88s. At 3000 rpm your only going to be rolling about 68mph. So, if you have any desire to travel highways, I wouldnt go any lower.

 

[daddyg]

Although I am going to be running about the same setup I am going with 5:13s but I am mainly building a trail rig. If I was doing alot of hwy driving I would go with 4:88s

 

[SaddleUp]

4.88's will be a close match to the stock gearing with the stock tires. Based on the description though I would say the 5.13's will better fit what you are looking for. They will give great response around town pulling away from stop signs etc. and will run out well up to about 50 MPH. Above 50 expect them to be wound up a bit though. The day I bought mine though I ran it down the freeway about 180 miles with 4.56 gears and tires that measured out to about 31 1/2" tall which is even a little worse than the combo your looking at I think so it will still be able to run on the freeway. I wouldn't want to do it all the time though. (I had it at about 3300 RPMs most of the way)

 

[Broncobowsher]

At 3000 RPM, the difference in speed at 3000 RPM is 65 vs. 68 MPH. Now weight in how much freeway driving you want to do. Don't forget to correct for the huge drag penility from shoving a huge brick through the air with a little 302. For grins 5.38 gears at 3000 RPM is good for about 62 MPH.

 

[DebosDave'72]

I think it is rare for anyone to say they want less gears.... That being said, if you aren't commuting it, and can get by a little slower when you do, the 5.13s might be better suited, you won't regret it offroad...

DD