Help- Gearing/Transmission advice

[texbroncos]

I recently bought a bronco. It has a standard 4 speed but 1st gear is a granny gear that is geared very low. On the highway I can run 65mph but it feels pretty stretched out. I was wondering if anyone has put different gear ratios in the differentials? Thoughts on if this would be a good idea?
I appreciate the help, thank you.

 

[bigmuddy]

So this is a NP435 tranny?

What size tires are you running currently?

If they are 33" or 35" tires then I would suggest a 4.10 or 4.30 gear set/

 

[WILDHORSES]

An AX15 or NV3550 5 speed tranny swap would give you an overdrive gear and a usable first gear. Just another option.

Jim

 

[Apogee]

Post up your engine, gear ratio and tire size and we should be able to be more specific. Given the description of the transmission, the most obvious assumption would be the NP435, but it could just as easily be a T-18.

There are some good gearing calculators that provide RPM and/or speed for various combinations for just such analysis. I have used the GrimmJeeper calculator in the past and like how it structures the data for all of the various gears.

 

[spap]

Tex just to let you know the 4 speed was never standard only 3 speeds on the tree manual and c4 auto

 

[Broncobowsher]

First off we need to know what you have. A 4-speed is a start. But we need more.
Tire size, what is on the sidewall is fine. Don't need exact rolling radius.
Gear ratio. There is a link in the bronco tech articles on the left side of this page.
As noted, what 4-speed? Probably a swapped in NP435, that was real common and has a really low first gear. It is still a 1:1 top gear. The only 4-speed with an overdrive is the oddball toploader and that doesn't have a really low first.
What engine do you have?

Couple things to consider. Bronco cooling systems are a little undersized stock. So a fixed fan was used. Moves a lot of air needed to cool. That makes a lot of noise on the highway.
If you are used to modern cars/trucks you are probably accustomed to engines turning a fairly low RPM, 2000 RPM-ish. Old school carburated engines tend to run faster at highway speeds. 2500-3000 RPM is what is common. That makes them noisy.
Broncos are boxes. Wind drag is much higher in a Bronco as well. This takes more HP to push that wind. Which leaves less HP in reserve. Feels like you have little power left, because you do.
And even engine tune. Timing real retarded, loss of power.
Carburator linkage, is the throttle actually opening enough?
List goes on and on.

 

[Johnnyb]

My two cents on this, after running for more than a decade with a NP435, 3.50 gears, and 31-in tires: I could cruise on the highway at 75 turning about 3,200 RPM with no problems but I always wish I had 4.10 gears.
Better yet, I wish I had 410 gears and an overdrive!

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[texbroncos]

Thank you for the replies. It has the NP435. Bought the Bronco with a 2.5inch lift running 30in tires. The Bronco is uncut with a rebuilt 302. I would like to run 33's or 32's if the 33's do not fit. I'm ok with the lift right now but eventually would like to get a bigger lift. Very new to Broncos, but not at all to classic cars and trucks. I thought about swapping transmissions to the NV3550, but just figured re-gearing would be the faster and cheaper fix. I am daily driving this Bronco, and really only taking it on the highway on weekends. Figured I would do the transmission swap 10ish years from now when I am older and have the extra money to take it apart and paint it as well. Again, thanks for the input. I'll be looking into all options shared.

 

[DirtDonk]

It has a standard 4 speed...

Tex just to let you know the 4 speed was never standard only 3 speeds on the tree manual and c4 auto

I almost said that myself!
That was until I regrouped mentally and realized that texbroncos was (possibly) just using the term "standard" as the traditional reference to a manual trans.

So in fact the Bronco does have a "standard transmission". It's just not a stock original one.
Or I could be wrong...;D

Paul

 

[Timmy390]

On the highway I can run 65mph but it feels pretty stretched out.

You need to explain this. In what way is it 'stretched out"? RPM's or just no more power?

Everyone will suggest what they run...I'm no different.

I was going to do a NV3550 swap but after doing lots of research I decided to run the M5ODR2 because I'm 99% street and the M5 shifts so more sporty.

You might take some time and consider it. I've not made the swap yet but got a M5ODR2 sitting waiting to go in.....

Tim

 

[texbroncos]

I was using the term standard to refer to a manual transmission

 

[texbroncos]

Yeah, feels like it has no more power. The RPM's are high but I understand that is normal. I'll try changing the gear ratios, and see where that gets me.

I appreciate everyone letting me know what they're running- gives me more ideas of what to research.

Thanks,
Hailey

 

[Timmy390]

Going to lower gears will impact the granny low making it unusable on the street. It will also increase the RPM's

What are you considering high RPM? My stock 3 speed with 4.11's turns 2800ish at 65mph. Sounds high? Not at all.....right in the power band of my cam.

Lots of factors to consider with gear change or trans swap. That's why it's taken me so long to do either. My 4.11'a will be borderline too high for the M5ODR2 in 5th but I think I can live with it.

33's and 2.5SL with 1 inch BL fit fine. I run them.......

Tim

 

[Boss Hugg]

Yeah, feels like it has no more power. The RPM's are high but I understand that is normal. I'll try changing the gear ratios, and see where that gets me.

I appreciate everyone letting me know what they're running- gives me more ideas of what to research.

Thanks,
Hailey

I assume when you talk about changing diff gears, you'd be going to a lower gear (higher number). That's only going to hurt the situation you describe because it'll take more RPM to make the speed at which you run out of power. When you change diff gear ratios, you need to add an overdrive transmission to bring the RPMs back down to something more modern and sensible. There are several OD transmissions that will bolt to the SBF (Small Block Ford, ie 289, 302, 351W) so do some more searching here on CB on overdrive transmissions to pick the best one for yourself.

Also, I'm assuming your in Texas by your "handle." There are lots of us folks in TX willing to help if you need a hand. And I see by your post count that you're new to the forum. Doesn't hurt to tell us a little about yourself so we'll know how in-depth to get while helping you. (like the spelled out SBF above?) There is a lot to learn in this forum. Grab that search button up there and use it up!

 

[Boss Hugg]

So in fact the Bronco does have a "standard transmission". It's just not a stock original one.

I think we can all agree the NP435 was standard in SOMETHING... right?? LOL.

 

[texbroncos]

I plan to change to a lower number (higher gear). We do this on my dads 69 camaro (drag racing 1/4 and 1/8th mile) to get the RPM's to "run longer" (Sorry I think I am better at explaining things in person and not through text Lol) so I was thinking this would help on my Bronco as well. Don't worry, I do understand Bronco does NOT = Racecar Haha. But I figure its a similar concept for gearing.

I am out of Houston, but in school at Texas A&M so that's my biggest commute in the Bronco so far- I plan on going to the next LEBC event but have a few small things I want to do to the Bronco first. Disc brakes conversion (it has p/b), powder coat my wheels, and mess with this differential.

I just want to drive it, so pulling the transmission sounds like something I want to avoid for the time being. But I for sure see the perks of getting a tranny with overdrive. If I end up going that route, I'll for sure search through the forum and try to find what transmission works best for me. Then come summertime, do a swap.

 

[DirtDonk]

I think we can all agree the NP435 was standard in SOMETHING... right?? LOL.

Right. And stock in Ford trucks to boot!

I plan to change to a lower number (higher gear).

You might verify two things.
First, which gear ratio is in the rear end right now. For V8 equipped Broncos that was either 3.50 or the optional 4.11, but could be anything after all these years.
I don't know anyone who has ever gone below 3.50 in a Bronco.

And second, find out why you're tapped out on the freeway.
Are you running out of rpm, or are you running out of power. Could the cam be going flat? Could the carburetor be under-sized, or having other issues? Could the choke plate be partially closed even when fully opened up, thereby limiting the ability of the engine to pull harder when you open up the throttle?
Could it just need a full tune-up even?
Lots of things to consider.

If it's already got a lower gear, such as having been changed to a 5.13 to suit 37" tires that the previous owner had installed and removed, then you may just be well beyond the engine's happy place on the highway.
Without a tach it's extremely hard even for the experienced driver to determine what rpm the engine is running. Especially if the exhaust has been altered.
But figuring out the engine speed vs vehicle speed is a simple matter of measuring a tire exactly and finding out what gear ratio is in the differential. This will avoid the need for a tachometer right away at least.

Don't worry, I do understand Bronco does NOT = Racecar Haha. But I figure its a similar concept for gearing.

Hah! Yep, I'm sure you had a few of us worrying for a minute there.
Definitely the same concepts in putting the rpm where you want/need it.

Good luck.

Paul

 

[texbroncos]

Awesome, I appreciate the advice and will check everything suggested! Thanks guys for the help. Will post updates of what I find/ the road I take. And I'm sure I'll be back with more questions...
Hailey

 

[Seventee]

If you are currently running 30" tires and want to swap to 33's, change tire size first before you change gear ratios. The taller tires will help alleviate what you perceive to be too low of gears.

 

[Johnnyb]

With the new NP435 and 350 gears you should have plenty of room to go 70 plus on the freeway with 30-in tires.

I would look at your ignition system and then possibly valves if it seems like it's tapped out on the freeway. I once had that experience when all my valve springs had given up the ghost and high RPMs just weren't viable anymore. Ignition timing points plug wires and or a bad distributor are all equal possibilities.

An aftermarket tachometer is a cheap investment and will tell you how much you're actually turning on the freeway. A 302 should be able to turn 3200 to 3500 all day long, right in its maximum power band.

-JB

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