Different Tranny or Gears

Desert Rider · Post by **Desert Rider** » Tue May 29, 2012 3:42 pm

I don't get on this forum very often, so forgive me if I say something stupid..That said, here's the deal. I have a 76 bronco, with 3.50 gears, 3 speed manual transmission on the column, a Wild Horses 3.5" lift, and 33" BFGs. With the 3.50 gears, my rig has a little trouble taking off from a dead start, and I am considering switching to lower gears. Keep in mind that I do 95% on the street, and 5% offroad/hunting. I called all the big bronco parts guys (WH, Tom's, Jeff's, B Hut, Jeff's, BC Bronco, Driven, etc.) to get their opinion. Most said, to help fix my problem and save my tranny, go to 4.10s. Some said 3.92s would also work better for the street. Driven said don't bother with swithing gears; instead, consider swapping out transmissions first, to say a NV3550 4-speed. He further said that swithing gears first is like "buying a saddle before you buy the horse". What are your thoughts?

Post by **Entourage** » Tue May 29, 2012 3:59 pm

I have the same setup - C4, 33's and 3.50 gears, and the combo is slow off the line. Personally, I would keep the automatic and change the gearing. I love my automatic.

Post by **ZOSO** » Tue May 29, 2012 4:31 pm

The 3550 swap would be ideal if you drive a lot of highway. If it was me and money wasn't an object I'd go with the 4.10s and 3550. That combo would give you plenty of low end and with the overdrive it will allow a nice cruiser down the highway.

Post by **akaFrankCastle** » Tue May 29, 2012 8:01 pm

Desert Rider wrote:I don't get on this forum very often, so forgive me if I say something stupid..That said, here's the deal. I have a 76 bronco, with 3.50 gears, 3 speed manual transmission on the column, a Wild Horses 3.5" lift, and 33" BFGs. With the 3.50 gears, my rig has a little trouble taking off from a dead start, and I am considering switching to lower gears. Keep in mind that I do 95% on the street, and 5% offroad/hunting. I called all the big bronco parts guys (WH, Tom's, Jeff's, B Hut, Jeff's, BC Bronco, Driven, etc.) to get their opinion. Most said, to help fix my problem and save my tranny, go to 4.10s. Some said 3.92s would also work better for the street. Driven said don't bother with swithing gears; instead, consider swapping out transmissions first, to say a NV3550 4-speed. He further said that swithing gears first is like "buying a saddle before you buy the horse". What are your thoughts?

4:10s are just going to make you mad if you use your Bronco for a regular commuter. Sure, you can make it off the light with a quickness, but when you hit the interstate you are going to hate the high RPMs at anything over 65mph. And your Bronco will become very thirsty.

That being said, I would vote for a new transmission. While the NV3550 might look great on paper, your wallet might not like it as much. ClassicBroncos.com tech section listed the average cost of the swap at around 3000.00 with all the parts included. Check out this write up: http://classicbroncos.com/tech/nv-3550-install

Another alternative might be the NP435, if you are on a budget. Total cost for the conversion would be about 1/3 of the NV3550, and that is a liberal estimate. Most salvage yards have them a plenty and for usually less than 150.00. Throw a rebuild kit and an adapter on there and you are well under the NV3550 price tag. However, those savings come with an added requirement to modify the body (read: chopping up that tunnel cover to fit that massive top cover and shifter through). Draw back being you are working with a granny low to get you off the line.

I am in total agreement with Zoso though. If you have the money and want to do it right, I would drop in the NV3550 and 4:10s which would result in very comparable numbers between the NP435 and the NV3550, until you factor in the 5th/overdrive gear.

Post by **airbur** » Tue May 29, 2012 10:00 pm

I have your same setup but with 35s and 4.10s. I'm very happy with it and I've been up to 80 on the freeway with no issues.

If you swap out to any of the other manuals, it's going to drive much more like a truck....maybe you don't mind but I didn't want that. Also, you'll have to make a big hole in your floor up by the firewall for the shifter...I didn't want that either.

Have fun either way!

Post by **akaFrankCastle** » Tue May 29, 2012 11:22 pm

75mph speed limit on I-25:
Me: 4.10's with 33" tires and stock 3 speed = 3100-ish RPM
4:10's with 35" tires and stock 3 speed = 2900-ish RPM
Desert: 3:50's with 33" tires and stock 3 speed = 2600-ish RPM

None are really that great and I have it the worst when it comes to fuel economy at that speed. Additionally, I personally do not like running over 2000 RPM for extended periods of time. Maybe I'm just getting old or I don't like wasting gas. Plus, the more people I force to pass me on the interstate, the more people I am giving the privilege of checking out a fine example of FoMoCo craftsmanship.

Now, the NV3550 with 3.50's and 33" tires = 1950 RPM

And 4.10's and 33's = 2286 RPM

Winner on the highway: NV3550. And why? Because 5 speeds beats the crap out of three.

Off the line ratios:
NV3550/4.10/33= 16.44:1
NV3550/3.50/33= 14.04:1
Stock 3 speed/4.10/33/35= 12.26:1
Stock 3 speed/3.50/33= 10.46:1

Yup. NV3550 wins again. Especially when the 4.10s are added.

Adding the 4.10s without the NV does give Desert a little bit of a boost off the line now, but at the cost of some RPMs on the highway.

Viperwolf1 · Post by **Viperwolf1** » Tue May 29, 2012 11:24 pm

The manual 5 speed and 4 speed auto transmissions are double-edged swords. Sure, they have deeper first gears for better accelleration off the line but they also have steep overdrive gears which will require axle gearing in the 4.88 range in order to make that gear useful (unless you like 28" tires). That makes the overdrive swap a lot more expensive than it initially seems. It will never pay for itself in fuel savings either. In my opinion, the best benefit to them is the lower non-overdrive gearing which combined with lower axle gearing gives you a lot more capability off road and at low speed. Kinda sounds like what you're looking for. If the expense is too great for your tastes just put some mildly lower axle gears in and call it good.

Post by **Rox Crusher** » Wed May 30, 2012 5:47 am

Viperwolf1 wrote:The manual 5 speed and 4 speed auto transmissions are double-edged swords. Sure, they have deeper first gears for better accelleration off the line but they also have steep overdrive gears which will require axle gearing in the 4.88 range in order to make that gear useful (unless you like 28" tires). That makes the overdrive swap a lot more expensive than it initially seems. It will never pay for itself in fuel savings either. In my opinion, the best benefit to them is the lower non-overdrive gearing which combined with lower axle gearing gives you a lot more capability off road and at low speed. Kinda sounds like what you're looking for. If the expense is too great for your tastes just put some mildly lower axle gears in and call it good.

Having just used my Bronco with the new 4R70W (4 speed auto mentioned by Viper) for the first time................

I already love the added benefits of the lower first gear while wheelin'.

The overdrive is relatively useless with my current axle gearing, which are 3.50s. This combo has the motor running at 1200 to 1900 rpm while doing 60 - 65 in 4th gear.

As Viper says, these swaps have the added expense of needing to re-gear. I plan to go with 5.13 and ARB lockers.

Then I will have a really great crawl ratio in 1st and 2nd and a usable 4th on the hi way (not for fuel efficiency per SE, but more for comfortable cruising)

Post by **Jesus_man** » Wed May 30, 2012 8:53 am

There are gear calculators out there. You want your final highway/rpms etc to be as close to stock as you can. Decide what size tires you will likely have for a long time and work your way backwards. Play with the ratios of different tranny's and axle gears to see what it takes to get there. But keep in mind that with larger tires comes more rolling resistance and more power required to turn them, so might want to go with slightly deeper gearing than stock to compensate.

The cheapest is probably axle gears.

I've never done the research for a bronco, but there are also under and over-drive units you bolt in front of your tranny. Not sure there is one for your application, but it may be worth checking into. You'll want it to be able to shift on the fly.

Post by **Justin** » Wed May 30, 2012 9:38 pm

x2 on the 3550 and 4.10s, if you've got the money. That said, if I were in your shoes I'd probably stick with the 3 speed (I like the column shifters) and lower gears, maybe with limited slip as long as the diffs have to be set up anyway. 3.92 would probably be great for a rig that is almost street-only, with 4.10s being better if you're going to do some wheeling. I've got the NP435 Frank mentioned in my truck and I love it, but it isn't a super friendly transmission. I like it because they're simple and bomb-proof and my Bronco is more trail oriented than yours. Not so great for a street truck because first gear isn't synchronized, which means you get to learn to double clutch if you want to use it on a regular basis. It would give you a first gear that is almost twice as low as stock and allow you to keep your 3.5s for freeway use.

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