Change my rear end gear in my 66 U14 to what ?

[UNCbronco]

I have a question and would like to hear your opinion: Who all have changed their 1966 - 4.11 rear end gear to something else to run a little faster and lower the PRM`s on your 170 engine ? What did you go with ? And what`s estimated cost this should be ? Thanks

 

[thegreatjustino]

No one does this. The reason the 170 came with 4.11 gears is because the gearing made up for the lack of power.

I have a bone stock 1968 with a 170. Considering the piss poor performance both from an acceleration and top speed standpoint, I can't possibly imagine how awful it would be to use a lower gear set.

 

[bmbm]

I have a question and would like to hear your opinion: Who all have changed their 1966 - 4.11 rear end gear to something else to run a little faster and lower the PRM`s on your 170 engine ? What did you go with ? And what`s estimated cost this should be ? Thanks

I know what you are talking about I drove my 66 with a tired 170 for close to 10 years. I finally put a good used 200 in that helped acceleration a bit but still just grinding along at 50 on the highway. I changed from a 235 15 tire to 30" tires not much taller and did not help much. I basically avoided lengthy highway trips which limits use of your Bronco. With 4:11 gears the fix is a nv3550 5 sp od or similar trans but they probably won't attach to the 170/200. If your goal is to maintain a mostly stock Bronco not much you can do although people occasionally hop up the 170 see info over on fordsix.com.
I went with the 250 six and the nv3550 and it transformed my Bronco, I would drive it anywhere now. Good acceleration and low rpms at 65-70. Much more civilized.

 

[gnpenning]

A cheap easy way to test is throw a set of taller tires on. If you don't put it in 4wd you only need to do the back.

This should help you understand what changing the gears would give you.

 

[jamesroney]

No one does this. The reason the 170 came with 4.11 gears is because the gearing made up for the lack of power.

I have a bone stock 1968 with a 170. Considering the piss poor performance both from an acceleration and top speed standpoint, I can't possibly imagine how awful it would be to use a lower gear set.

"lower gear set" = "Higher" gear set.

3.50 is higher than 4.11.
4.56 is lower than 4.11.

and of course you are 100% correct about performance. It would go from barely adequate to non-existent.

 

[Chiclassics]

I would try to answer your original question. I would say 3.5s it would be around $2k these days (parts +labor). But once you change rear to 3.5 then your front diff gears would be off from rear and you wont be able to use 4wd, so that will cost you addl 2k to change front if you want to retain 4wd .


What is your current tire size? both diameter and width. Whats you suspension - stock or lifted

 

[UNCbronco]

I would try to answer your original question. I would say 3.5s it would be around $2k these days (parts +labor). But once you change rear to 3.5 then your front diff gears would be off from rear and you wont be able to use 4wd, so that will cost you addl 2k to change front if you want to retain 4wd .


What is your current tire size? both diameter and width. Whats you suspension - stock or lifted

Tire size is 235/75-15 on stock rims, stock suspension for this 66 U14 with 170 engine. Thanks

 

[DirtDonk]

One way to do this with minimal stress to the wallet, might be to keep your eyes open constantly for someone selling a used third member for the rear end.
Preferably in a gear ratio at, or close to what you are thinking of.
That way you can do a fairly easy quick swap without any additional expense, just to see if you’d like the gearing.
If you do, then you can rebuild your existing one with the proper gear ratio, and then do the front as well.
If you don’t, at least you’ll find out without having too large of an expense.
I would imagine a workable used one could be had for a couple of hundred dollars?

Just make sure it’s a 9 inch, with a 28 spline differential, and hopefully the appropriate 1310 you joint yoke.
But the yoke can be changed relatively easily as well, if needed.

 

[DirtDonk]

Oh, and by the way. Do you know for sure that it’s 4.11 ratio currently? I’m pretty sure 4.56 was an option with the six cylinder.
Heck, either one of those would be pretty desirable to most Bronco owners. Could probably find somebody willing to swap you a 3.50 for your 4.11 I would think.

 

[Chiclassics]

Tire size is 235/75-15 on stock rims, stock suspension for this 66 U14 with 170 engine. Thanks

Thats close to stock size. (28-29in)

As others stated that gear ratio is highly desirable. These straight inline motors were designed for high low end torque operation. Are you hitting more than 3k RPM at 65mph?how much more.

If you want to get better highway performance start looking into getting 200CID engine with 31 tires. Probably you can get under 1k used 200engine. and then you can still keep 4.11s and only need to change tires. I wouldn't change those gears if I were you. and totall get another regular car for highway drives..

You always have option to get 302...1k-5k depending on condition.

 

[nvrstuk]

The reason so many people that I know that have bought Broncos with 170's in them and tried to drive them around town for fun on weekends/whatever all sold them within a year or two... they aren't fun to drive at any speed over 45mph because of like what you're experiencing. High rpms, engine noise, no power stock with those gears & tires and less than no power when gears or tires are changed to try to lower 45+ rpms. I mean not enough power to even use 3rd gear on a very slight incline. Just not a good combo for anything but Utility - which they were sold for really. Not in anyway badmouthing your '66 as they were built for Utility, not really for cruising. Think of those Scouts with the 152ci, 4 bangers in them- even worse!

Engine swap is the best remedy then an OD with taller tires and you have a comfortable weekend driver.

You could go to the effort of putting a 5speed in but you'd only use 5th gear downhill because you couldn't pull a 1% grade or even a flat road with a 10mph headwind. Just isn't feasible.

 

[Glass Pony]

I'm sure somebody with 33's and a non overdrive tranny will trade you even-up, their 3.50 ratio chunk for your 4.11 ratio chunk.

 

[okie4570]

Changing out a gear set isn't terribly expensive. Having someone else change one out is though. No way I would have higher gears than 4.11 with a 170 or a 200. You may run lower rpm at highway speeds, but it may take you 30 days and 3 clutch disks to get up to highway speeds with 3.50 gears, lol. And that's on flat ground, any hilly mountain driving no way.

At 65mph with 28" tires, there's about 500 rpm difference between 3.50 and 4.11 gears with a 1:1 third gear. The performance difference when just driving around at lower speeds though, it won't be enjoyable to drive whatsoever with higher gears.

The only way I could see getting around this, and I'm sure it will raise eyebrows, is to swap to 3.50 gears and use 2H when you know you're getting ready to be on the highway and highway speeds............for the trips around town and usual driving at 40/35mph or less, put it in 4L and don’t lock the front hubs. That would give you in-town power at in-town speeds without burning up your clutch and being starved for low speed power.

 

[bmc69]

I swapped a 250 in to a '69, kept the 4.11 gears, and put 33" tires on her. I could keep up with traffic at 65 mph and manage most grades OK..but not more than that. I can't imagine a 170 with 3.50 gears...

 

[nvrstuk]

I swapped a 250 in to a '69, kept the 4.11 gears, and put 33" tires on her. I could keep up with traffic at 65 mph and manage most grades OK..but not more than that. I can't imagine a 170 with 3.50 gears...

... and there is a huge difference between a 170 and a 250! More than a third more cubes... almost the same from a stock 302 to a 408 stroker...

 

[UNCbronco]

Changing out a gear set isn't terribly expensive. Having someone else change one out is though. No way I would have higher gears than 4.11 with a 170 or a 200. You may run lower rpm at highway speeds, but it may take you 30 days and 3 clutch disks to get up to highway speeds with 3.50 gears, lol. And that's on flat ground, any hilly mountain driving no way.

At 65mph with 28" tires, there's about 500 rpm difference between 3.50 and 4.11 gears with a 1:1 third gear. The performance difference when just driving around at lower speeds though, it won't be enjoyable to drive whatsoever with higher gears.

The only way I could see getting around this, and I'm sure it will raise eyebrows, is to swap to 3.50 gears and use 2H when you know you're getting ready to be on the highway and highway speeds............for the trips around town and usual driving at 40/35mph or less, put it in 4L and don’t lock the front hubs. That would give you in-town power at in-town speeds without burning up your clutch and being starved for low speed power.

Yea, after all the reply`s, I`ve decided to keep what I have and just enjoy it. I was just throwing the idea out there to see what everyone would say. Thanks

 

[bmbm]

Yea, after all the reply`s, I`ve decided to keep what I have and just enjoy it. I was just throwing the idea out there to see what everyone would say. Thanks

Yes good idea. As Mr. DirtDonk pointed out you could have 4:56 gears as that was an option as seen here:

1966-brochures-page-12.jpg (629×796)

If so a somewhat expensive change to 4:11 gears will help some.

Also less expensive but with less improvement would be to temporarily mount some 31" tires on the back, if will fit within fenders, and see if that will make enough difference for you. From what I remember about Oklahoma it is pretty flat so steep grades won't be a factor.

 

[okie4570]

Yes good idea. As Mr. DirtDonk pointed out you could have 4:56 gears as that was an option as seen here:

1966-brochures-page-12.jpg (629×796)

If so a somewhat expensive change to 4:11 gears will help some.

Also less expensive but with less improvement would be to temporarily mount some 31" tires on the back, if will fit within fenders, and see if that will make enough difference for you. From what I remember about Oklahoma it is pretty flat so steep grades won't be a factor.

He's got 4.11LS gears and he's in North Carolina.

 

[Chiclassics]

Yea, after all the reply`s, I`ve decided to keep what I have and just enjoy it. I was just throwing the idea out there to see what everyone would say. Thanks

Yep ! Don’t change gears on it. If you decide to sell it yiu get more if you keep it stock than change one thing for performance that is not widely desired like 302. When you decide to change it go all the way 302/coyote. Keep your gears as they will let you run bigger tires like 33s.

I hv a 66 prev owner changed to 3.5 but put 200 inline I run 30s on it. I never had power issues I go 70 easily on fwy and my acceleration is super . I don’t even have tach on it my ear tells me I’m in the sweet spot of 2600-2700. Sometimes people think I have coyote underneath based on my acceleration. What I like about these inline engines is how quiet they are ( once they meet your power requirement) and smaller space they take and lighter too! Like 150 lbs lighter compared to 302. If you have hardtop you could switch to soft top that will help quicker acceleration but not gojng to change rpm’s at cruise. If you like to entertain further tweaks in the given drivetrain setup, you could try getting some cheap 30x9.5 and see how it performs it will reduce 200-250 rpm with 1inch taller . I never tried 30s on stock suspension so not sure of clearance issues.