Regearing for 37’s

Running 33s but just lifted and want 37s. Daily driver but no more than 5 miles/day. No speeds above 55. What are the consequences of not regearing right away?? 9” rear and Dana 44 front

No Power

Yep, what kselden said.
But what trans do you have? Auto or Manual? Low first gear, or standard?
And what diff gears now? Stock 3.50's or 4.11's? Or something else?

Being a dog off the line is not in itself detrimental to anything but your happiness. Perhaps not being able to achieve 55 in a timely manner is not a good thing either.
Eventually though it puts a strain on everything in front of the differential.
Certainly added strain on other components in the rear end, just due to their size and weight of course. But the stuff in front of the diff is what takes the heat. Literally, in the case of an automatic trans.

If a manual, then the clutch suffers. If an auto, it will build up more heat and that is never good for an auto.
The driveshaft u-joints take some abuse as you rev the engine (to build more torque) and try to get the heavier tires rolling.

So while it's totally doable, what happens next is up to you and your right foot.
Oh, and how are your brakes? The bigger tires will surely tax the brakes.

Paul

Like Paul said, it'll be hell on your clutch or torque converter...otherwise it'll just be less than fun to drive in the "get up and go" department. On the up side, if you ever had an inkling to run over 100 MPH, you might be geared for it now.

Given that it's a mostly street rig, why not swap out the rear 9" gears only and make it more fun to drive in the interim while you save up to do the D44?

Keep in mind your speedometer will be way off as well.

The side benefit (some would say the main benefit!) of doing only the rear gears at first is that it's less expensive by a ton, and gives you a chance to see if you made a mistake in gearing choices.
If you're happier, but still not perfectly happy with the performance, changing them once again is less of a pain to mind and wallet.

Paul

regear soon as you change out...

Apogee said:

Like Paul said, it'll be hell on your clutch or torque converter...otherwise it'll just be less than fun to drive in the "get up and go" department. On the up side, if you ever had an inkling to run over 100 MPH, you might be geared for it now.

Click to expand...

y eah for sure.. be tough on it

I did the same. then installed 4.88s. originally had a c4. It drove fine but i wish i had done the 4.56s instead. now I have a 4r70w with OD and the 4.88s are perfect.

regear it. its totally worth it.

I did 5.13’s with mine. Running a C4. Still do a bunch of highway miles too.

Mark

I'm doing 4.88's on mine with 37's and a 351W, however I would probably go 5.13's with a 302/5.0. I may wish I'd gone 5.13's as is, but we'll see.

I did 5:13 with a 302 and a c4.....pretty low for a lot of hiway but perfect for heading up the hill...

I'm on 5.13 with 5.0/4r70w/35s. I wish I had a little more get-up-and-go, but I think it may be in the way my transmission shifts. It has a little quirk about hanging in 1st and 2nd longer than it should. Once I reach enough RPM that I think it should be shifting, I lift to keep from blowing everyone around me away. So it just hangs there for a second before shifting. So I don't get to go as hard as I'd like.

So, I am in a similar situation. I have a 73 with the original 302 (rebuilt with only a mild cam and 4bbl intake/carb) and an NP435 with granny low. My 9" rear has 3.54(?) gears on 33" tires. Seems like I am a little sluggish which is fine and I have gotten up to 60 no problem, but it seems to lag from there. Still have more pedal if needed, and I haven't gone on interstate just local highways. This will be a mostly street use truck with some off-roading and trailing. Which way should I go with gearing to get better fuel efficiency and drive ability? I know the 4bbl drinks more, but is the engine working harder with these gears set up? Not looking to hotrod it but I would like to be able to drive on I40/I65, etc around Nashville without being run over. My friend was telling me I should go like 3.25s or lower to be able to drive at highway speeds with no problem. Also, having read some of the replies on this post it seems like I should change the gears in the front Dana44 as well? Does higher gearing equate to higher torque and vice versa?

Thanks for any replies.
Mike

33s, no overdrive, 4.11s all day long. Yes, more RPM. But you have a LOT of drag. 3ss and pushing a barn door. The 3.50 gears (3.54 for the front) were the freeway gears with 29" tires. 3.25 gears would be even worse. Yes, turning less RPM, but the load at that RPM will be pushing you into the power enrichment circuits of the carb. Get the RPM up, get some load off the engine, start actually making manifold vacuum. That will let the vacuum advance work as it should and pick the economy up. Way more fun to drive around town. 4.11s are not excessive, remember that they were the optional ratio with the stock 29" tires even back when the national speed limit was 70.

What 'bowsher said.

EODMike said:

I have a 73 with the original 302 (rebuilt with only a mild cam and 4bbl intake/carb) and an NP435 with granny low.

Click to expand...

EODMike said:

Seems like I am a little sluggish which is fine and I have gotten up to 60 no problem, but it seems to lag from there. Still have more pedal if needed, and I haven't gone on interstate just local highways.

Click to expand...

How well is it tuned? This setup should pull pretty strong at higher rpm still. Should not be running out of steam. You're probably dealing with wind resistance and too LOW of an engine speed.
For sure it's going to be sluggish with 33" tires if you have the 3.50 gears. Do you use First/Low gear to start, or Second?

EODMike said:

My 9" rear has 3.54(?) gears on 33" tires.

Click to expand...

3.54 for the front Dana, 3.50 for the rear Ford. Just a slight variance in the designs, but close enough to work together.
But do you know this for a fact? Did you verify it? As was said, even 4.11 was the rear gear option right from the factory. Lots of them got that option too.
The sluggish off the line should indicate the 3.50's but you still need to check.

EODMike said:

This will be a mostly street use truck with some off-roading and trailing. Which way should I go with gearing to get better fuel efficiency and drive ability?

Click to expand...

No way for us to know. Every engine combo is different and yours may appreciate higher rpm where it's developing more power to push against the wind. As soon as you reach 60mph or so with a Bronco, your mileage is almost always going nowhere but down no matter what gearing you have.

EODMike said:

I know the 4bbl drinks more, but is the engine working harder with these gears set up?
Not looking to hotrod it but I would like to be able to drive on I40/I65, etc around Nashville without being run over.

Click to expand...

A 4bbl carb does not automatically use more gas. Only your right foot does that.
Of course, the whole vehicle combination sets the baseline, but your foot into the secondaries or a poorly tuned carb, or a mismatched cam to the other stuff will just make things worse. But it's not automatically the carb causing the trouble.
But that leads to a question. Which carb exactly are you running? What model and what size? An over-carbureted engine might idle fine and run ok at lower throttle openings, but lose some of that oomph when you open it up.

EODMike said:

My friend was telling me I should go like 3.25s or lower to be able to drive at highway speeds with no problem.

Click to expand...

Never, ever in a Bronco with 33" tires. Your friend is probably used to cars with smaller tires and better aerodynamics. You'll be hating life for sure I would say, but there's nothing that says you can't try it if you think it has merit. Just do the rear only and be ready to change it in the other direction instead though.

The problem is you're not running out of rpm. You're almost lugging the engine right now in fact. AT 60mph you're barely turning 2200 rpm. In stock form your engine was looking at closer to 2800-3000 rpm at the 60-65 range.
Yours is just dogging out, so you likely need to go lower with the gearing (the higher the number, the lower the gearing) to something at least to 4.11 instead.
Yes, you'll be revving the engine more, but it'll have more power to push the wind.

Why not try it right now in fact? What happens when you try to hit 70mph now? By my calculations that's barely 2600 rpm with your assumed gearing and tire size. Hardly breathing hard for a slightly warmed over engine.
What rpm do you think you're running now? Do you have a tach? That 2200 rpm is barely above idle practically!
But you can't go by any modern car that runs 1500 rpm at 70 all day long and loves it. You have a different beast.

What exact cam are you running? For all we know at this point, your mileage might actually go up with lower gearing!

EODMike said:

Also, having read some of the replies on this post it seems like I should change the gears in the front Dana44 as well?

Click to expand...

It's not just an option. It's a requirement that if you change the rear gears you MUST change the front gears to match. You can't use four-wheel drive otherwise.
You can do just the rear gears first of course, and this lets you make sure you actually like the gear ratio you chose. And it's cheaper to change the 9" usually than the 44, so it's better to have a mistake with a 9" only than both.
If you change to 4.11 and decide you like it, then the typical "matching" 44 gear is something like a 4.09 or 4.10 (hard to remember all of them sometimes) to match.
But like we said, do just the rear first.

Verify what you have for gearing, then measure the exact height of a rear tire from the ground to the center of the hub. Then double that measurement for your "rolling height" and with that info and the gear ratio we can determine your engine speed at any vehicle speed with the calculators at hand.

EODMike said:

Does higher gearing equate to higher torque and vice versa?

Click to expand...

No, but higher numbers do. It's "lower gearing" that increases torque to the wheels. The engine torque output is fixed for any given rpm and throttle opening. The larger tires are fighting you all the way, so lower gearing (higher number) is what brings back the lost power at least by feel.

With passenger cars and smaller tires and better (sometimes) power-to-weight ratios, it's a different beast. Especially the newer stuff where the engines are tuned to within an inch of their lives at almost every rpm and throttle setting.
We strive to get our Broncos there, but we're not always successful!

Just to give an example, my '68 with Explorer motor and auto w/overdrive has 4.56 gears and 30" tall tires and gets 20mpg at 60mph max. Any higher and mileage tanks. Just pushing too much wind for that stock little engine and horrible aero.
But it's full EFI and well tuned and matched parts (factory) and so is able to do things that a modified '73 engine with a carburetor can't do. Yet...

So there's more to think about still. But get us a measurement of the tire and verify your current gearing, and then try going 70mph with your newfound information regarding engine rpm and see what you get.

Paul

I'm 4.56 at the moment with 37"s. NP435 handles it and final drive is great, Torquey 351W helps also. It will roll off a stoplight in 3rd gear. With the AOD i may go with 4.88
if it doesn't like the 4.56

DirtDonk said:

What 'bowsher said.



How well is it tuned? This setup should pull pretty strong at higher rpm still. Should not be running out of steam. You're probably dealing with wind resistance and too LOW of an engine speed.
For sure it's going to be sluggish with 33" tires if you have the 3.50 gears. Do you use First/Low gear to start, or Second?



3.54 for the front Dana, 3.50 for the rear Ford. Just a slight variance in the designs, but close enough to work together.
But do you know this for a fact? Did you verify it? As was said, even 4.11 was the rear gear option right from the factory. Lots of them got that option too.
The sluggish off the line should indicate the 3.50's but you still need to check.



No way for us to know. Every engine combo is different and yours may appreciate higher rpm where it's developing more power to push against the wind. As soon as you reach 60mph or so with a Bronco, your mileage is almost always going nowhere but down no matter what gearing you have.



A 4bbl carb does not automatically use more gas. Only your right foot does that.
Of course, the whole vehicle combination sets the baseline, but your foot into the secondaries or a poorly tuned carb, or a mismatched cam to the other stuff will just make things worse. But it's not automatically the carb causing the trouble.
But that leads to a question. Which carb exactly are you running? What model and what size? An over-carbureted engine might idle fine and run ok at lower throttle openings, but lose some of that oomph when you open it up.



Never, ever in a Bronco with 33" tires. Your friend is probably used to cars with smaller tires and better aerodynamics. You'll be hating life for sure I would say, but there's nothing that says you can't try it if you think it has merit. Just do the rear only and be ready to change it in the other direction instead though.

The problem is you're not running out of rpm. You're almost lugging the engine right now in fact. AT 60mph you're barely turning 2200 rpm. In stock form your engine was looking at closer to 2800-3000 rpm at the 60-65 range.
Yours is just dogging out, so you likely need to go lower with the gearing (the higher the number, the lower the gearing) to something at least to 4.11 instead.
Yes, you'll be revving the engine more, but it'll have more power to push the wind.

Why not try it right now in fact? What happens when you try to hit 70mph now? By my calculations that's barely 2600 rpm with your assumed gearing and tire size. Hardly breathing hard for a slightly warmed over engine.
What rpm do you think you're running now? Do you have a tach? That 2200 rpm is barely above idle practically!
But you can't go by any modern car that runs 1500 rpm at 70 all day long and loves it. You have a different beast.

What exact cam are you running? For all we know at this point, your mileage might actually go up with lower gearing!



It's not just an option. It's a requirement that if you change the rear gears you MUST change the front gears to match. You can't use four-wheel drive otherwise.
You can do just the rear gears first of course, and this lets you make sure you actually like the gear ratio you chose. And it's cheaper to change the 9" usually than the 44, so it's better to have a mistake with a 9" only than both.
If you change to 4.11 and decide you like it, then the typical "matching" 44 gear is something like a 4.09 or 4.10 (hard to remember all of them sometimes) to match.
But like we said, do just the rear first.

Verify what you have for gearing, then measure the exact height of a rear tire from the ground to the center of the hub. Then double that measurement for your "rolling height" and with that info and the gear ratio we can determine your engine speed at any vehicle speed with the calculators at hand.



No, but higher numbers do. It's "lower gearing" that increases torque to the wheels. The engine torque output is fixed for any given rpm and throttle opening. The larger tires are fighting you all the way, so lower gearing (higher number) is what brings back the lost power at least by feel.

With passenger cars and smaller tires and better (sometimes) power-to-weight ratios, it's a different beast. Especially the newer stuff where the engines are tuned to within an inch of their lives at almost every rpm and throttle setting.
We strive to get our Broncos there, but we're not always successful!

Just to give an example, my '68 with Explorer motor and auto w/overdrive has 4.56 gears and 30" tall tires and gets 20mpg at 60mph max. Any higher and mileage tanks. Just pushing too much wind for that stock little engine and horrible aero.
But it's full EFI and well tuned and matched parts (factory) and so is able to do things that a modified '73 engine with a carburetor can't do. Yet...

So there's more to think about still. But get us a measurement of the tire and verify your current gearing, and then try going 70mph with your newfound information regarding engine rpm and see what you get.

Paul

Click to expand...

Thanks Paul, that's a lot of information, but I will make notes and do the calculations and trials you suggested. I think it is tuned pretty well, but I am no professional by any means although my friend who has extensive engine history helped me with it and he tuned it pretty well.

I usually start in 2nd due to the low 1st gear. I am running a Holley 600. My cam is a Melling MTF-1 class 1 cam. Should be a really mild cam: .281-.296 cam lift, .450-.474 Valve lift, Lobe CTR 108-116, 280-289 SAE Duration, 204-214 .050 Duration. (hope these numbers help and that I captured all pertinent info). No Tach.

The numbers on the ring gear are Dana 18437 A3D45 46-13. According to Google and sites like Dennysdriveshaft.com and other sites the gears are 3.54. Pretty sure not original as I think my brother had changed the ring and pinion gears at some point due to damage.

Mike

EODMike said:

.. No Tach.

Mike

Click to expand...

A tachometer would really help to find out where you are at. And if you're basing speed off your speedometer, the driven gear in the T-case needs to be changed to account for 33" tires if it hasn't already.

Seventee said:

A tachometer would really help to find out where you are at. And if you're basing speed off your speedometer, the driven gear in the T-case needs to be changed to account for 33" tires if it hasn't already.

Click to expand...

No, it hasn't. It runs about five mph faster than what is showing on the speedo, "verified" using cell phone tracking speed app or whatever. Got up to 70 today no problem and it didn't seem like things were about to come from together so I guess that is good.

I think a tach may be on the horizon, perhaps for Christmas or something.