Regearing and doing 37s right

[kodiakisland]

I couldn't start the Bronco in second gear though, it was too tall. Bronco crawler gear is like the old SM420 1st gear, so you start in first not second with Bronco.

It's no exaggeration to say switching to 35s with stock gearing transformed the driving experience. My family likes driving it better as well. I miss 6th gear usefulness, but I use 1st gear much more than 6th, so the benefit of losing that short first gear outways 6th for me.

I think forum member Dusty who started with a stock base manual found similar experience with first gear, and it's a reason he's ok with the 5.13 and 37s.

As long as it works for you and you're happy with it. I drive in a lot of steep stuff and prefer lower than higher. Stock gearing with 35s was not ideal for me at all.

Besides, 37s today might mean 38s tomorrow and then who knows where you end up.

Sponsored

 

[Oldhippie]

I do not recommend having different gear ratios front and rear but when I first got my ‘47 CJ2a I was in a hurry to go on a rubicon trip and threw in a front end I had laying around…found out when I put it in 4wd at the trail head it was 4.88 instead of 5.38 like the rear…ran the whole trail in 4wd squealing rubber without breaking…skinny tires at 50psi and stock 4cyl helped…party on!

 

[5GENIDN]

I couldn't start the Bronco in second gear though, it was too tall. Bronco crawler gear is like the old SM420 1st gear, so you start in first not second with Bronco.

It's no exaggeration to say switching to 35s with stock gearing transformed the driving experience. My family likes driving it better as well. I miss 6th gear usefulness, but I use 1st gear much more than 6th, so the benefit of losing that short first gear outways 6th for me.

I think forum member Dusty who started with a stock base manual found similar experience with first gear, and it's a reason he's ok with the 5.13 and 37s.

That SM420 had a 7.1:1 first gear.... NOTHING was more granny than that! What is the Bronco 1st? about a 6:1??? a little less gear than that isn't it?

 

[Bmadda]

About 30 years ago I read in one of the old 4x4 rags, in the reader's rides section, someone had an old Ford truck with mismatched gears...to compensate for the mismatched tires. Tractor tires, something like 60" in back and 50" in front.

They used to build 4x4 tractors that way. Tire size F to R had to be exactly what they came from the factory with, and they were weird sizes that are obsolete now. There's a guy local to me who restores old tractors, and he comes around looking for oddball takeoffs (which being an automotive shop I NEVER have)

 

[lakesinai]

I know the topic of 37s has really been beaten to death but I have some specific questions I could not find the answers to. Essentially, I want to make sure I'm doing things necessary or if anything is unnecessary.

I have a 22, 2 door black diamond with MT. Non Sas, so 4:46 gearing.

I would like to go to 37s but also want it to still be capable. I understand the rack and the m190 are considered weak points with 37s, correct?

Plan:
Ford severe duty steering upgrade kit
M210 front with 5.13 gearing
Eibach 2.0 coilovers + UCA

Questions:
What do I need to do to match the rear to 5.13 gearing?

The 5.13 rear gear and pinion from Ford says it fits rear axle with factory rear locker but also that non sas MT have a welded ring gear and requires a differential replacement. Since the BD has the rear locker, does it still have the welded ring gear, having a MT? Would I need to replace the entire rear axle?

Additional Question:
I know that I can get the m210 front with 4:46 gearing, which would negate having to do anything with the rear. But my understanding is that going to 37s with 446 AND MT may be a bit sluggish. Would you definitely recommend going to 5.13 gearing? I do plan to do the ford perform tune as well.

Is there anything else I need to consider?

Just observing, with all the added weight of the 37's, wouldn't you want at least a 2.5" shock diameter? The 2" Eibachs seem a bit light for that application.

 

[MrCooper]

Just observing, with all the added weight of the 37's, wouldn't you want at least a 2.5" shock diameter? The 2" Eibachs seem a bit light for that application.

Anything you'd recommend?

 

[tdhyden79]

Thank you for this feedback and insight! You gave me some additional things to think about.

I do plan to do everything at once, unless I decide to hold off on the m210 just to see how 446 gearing rides.

I would say I'm more "content" than happy with the current performance of 446 with stock 32s. This is a second/fun vehicle and outside of summer, will mostly be driven on weekends. I would like it to be very capable and *less" likely to break things when off roading. But it will still probably be more on pavement/around town than offroading or any serious off roading. Gas mileage is not a huge concern.

Would you say, then, that 5.13 is a good medium for mixed use? If 5.38 is great for offroading but 4.88 is better around town.

I have a MT BAD SAS on 37's so it has 4.70's. Gearing feels right for street use. If I'm on a steep incline I just start in crowl gear and shift into 1st once I get rolling, it basically takes the clutch feathering out of the equation. I have done a few mild off road trails and found that I had plenty of low gear in crawl to slowly creep up obstacles without having to slip the clutch much. I will say... I have little to no use of 6th gear with 4.70's. I'm going to do the Dana 5.38 swap next year so I can really take advantage of the creepy crawly gear and hopefully gain the use of 6th gear. All that being said... 5.13's will be more than sufficient to keep the rig pleasantly drivable on road, and more than capable off road.

 

[lakesinai]

Anything you'd recommend?

There are many here more qualified than me to answer that question. I start with what Ford did on their Raptor with 37" tires. Raptor take-offs would be a start, but the Bronco Raptor chassis & frame is significantly modified to take the Longer-traveling Fox Raptor shocks, so you would have to go aftermarket. Here's an article on how Ford designed the Raptor suspension
https://www.motortrend.com/news/2022-ford-bronco-raptor-chassis-suspension-upgrades/

 

[JerryG]

Thanks. So, to be clear, you think the 5.13 gear and pinion would be sufficient in the rear and not require a full replacement?

Yeah. I don't expect it to perform like a sports car. I'm pretty happy with the stock performance on 32s. I figure FP tune and 5.13 gearing would make up for the extra weight of 37s. My expectation is that with those two upgrades, it would perform AT LEAST similar to stock with 32s?

Not in the least. Stock 32s can stop safely on factory brakes.

 

[KermitBronco]

I'm not the smartest, but I listen to smart people. 4.88 is the recommended ratio for 37" and, I'm glad I took that advice because when I later upgraded to Dana 60 on the rear, they make that gearing. Otherwise, they jump from 4.88 to 5.29 on the rear. Agree with other posters that the Ford Performance Tune really helps with 37". Although I'm super happy with 37" Trail Grapplers, I'd think long and hard about whether you truly want/need them because it opens a true Pandora's Box including we recently shredded our wiring harness off-roading, etc. The Bronco was engineered for 35". It will run 37" but you need to be prepared to upgrade a bunch of things if you're wheeling hard.

 

[Mike leggiero]

I would do lift and 37 first then maybe gears . I run 35 on my base with a 7 speed i also have a bd with a auto on 35. We run the trails here in ky . 37 would be nice on my 4 door but that my wifes daily . My 2 door base does just fine with a 2 in lift and 35s if your doing it.mainly for looks then just lift it and put on 37. If you are going to wheel it go with a good set of true 35s and have fun. Just dont be that guy with all the gear and no idea. I been off roading for over 30 yr. The blue one you will see on broncbuster trail ride at windrock. The green one you will see on trail hunter usa.

 

[HarmCityHammer]

I think the Sasquatch 4.70 gears are a very good choice for 37”s. 5.13, imo is overkill. Maybe if you were doing 38”+ with heavy ass 20” wheels or bigger. 4.70’s work great on my Sasquatch with 37”s.

 

[Charles Miller]

I’ll echo the same as I have a ‘23 WT , 2.7 with 4.7’s and heavy 37” Mickey T Baja Boss AT’s (but 8lbs lighter wheels) and sitting at 108lbs per corner. One thing to think about is MPGs vs you real world usage on and off road as gears will further impact. Once I made my Forscan adjustments, and after driving a while to let the comp readjust, my MPGs regulated at 15.1-15.5 avg. I always planned on 37’s and that I needed the 4.7s from the start.

It still performs amazing offroad , as well as on road, with plenty of power and pep. I haven’t had any issues going over or through obstacles where lower gearing was needed. It has plenty of passing power and no prob hitting 100+ mph. That’s not even getting into Sport mode.

It is a slightly different comparison though since you have an MT… I’d just wheel it, do your lift/wheels/tires, wheel some more and then upgrade where you feel lacking. Also you may not need the JKS depending on your lift/wheel/tire combo. I don’t have it, running 2.5” lift with +0mm offset 17x9 wheels and only get a light rub with steering fully locked and suspension stuffed. At some point I’m just going to do a slight notching of the crash bar mounts to clear, but it’s not bad enough to cause concern.

May I ask what mm size you put into Forscan?

 

[BigMeatsBronco]

I'm not the smartest, but I listen to smart people. 4.88 is the recommended ratio for 37" and, I'm glad I took that advice because when I later upgraded to Dana 60 on the rear, they make that gearing. Otherwise, they jump from 4.88 to 5.29 on the rear. Agree with other posters that the Ford Performance Tune really helps with 37". Although I'm super happy with 37" Trail Grapplers, I'd think long and hard about whether you truly want/need them because it opens a true Pandora's Box including we recently shredded our wiring harness off-roading, etc. The Bronco was engineered for 35". It will run 37" but you need to be prepared to upgrade a bunch of things if you're wheeling hard.

The Dana 60 rear has every ratio imaginable available, 5.13 and 5.38 as well as plenty of others.

 

[KermitBronco]

The Dana 60 rear has every ratio imaginable available, 5.13 and 5.38 as well as plenty of others.

Not sure where you're getting that info from.
Dana still shows that it jumps from 4.88 to 5.38 for Bronco E-locker. I'm not saying that they haven't expanded and now offer a 5.13 but that didn't exist when I installed and it still doesn't show on The Dana website. 4.88 or 5.38 are the choices.

Sponsored