Correct Gear Ratios w/170 for a Happy 50th

[katmandaddy]

We have a (Very) Early Bronco: '66 U13. The only information we have is the stamp on the frame: ☆U13FL735087★.

Over the years we've collected bits and pieces of a few others and have had to put the project on the WAY back burner more than once.

I am going to rebuild it as the 1966 Roadster that it is. But not RESTORE. I do not have the patience, money, or maybe the logeveity for that. AND I'd like to get it on the road for 50th birthday: IT's - I'm well past mine!

I will use another original 1966 170-6.

Which gear ratios should we use?

I'm guessing same front and rear But does either the 3:50 or 4:11 have an advantage?

Our use will be street and 2-lane driving, not freeway; a few logging dirt roads in Michigan's Upper Peninsula: maybe a trip to Silver Lake Sand Dunes (15 minutes from inlaw's farm). I tried a topic search and could not find an answer so Thanks for any guidance and wisdom.

 

[miesk5]

yo  K,

For now here is some info;

1966 Bronco Vin Decoder

U13 U-100 Roadster F

170 cid, 6cyl

L Michigan Truck

Build Month

Aug 732000   - 745999

Ford built our Broncos & other 4x4 trucks & vans with a numerically lower front gear ratio in the front Dana 44 than the rear so that off-road steering is enhanced. A Bronco built with 3.55 rear ratio would have a 3.54 ration in the front Dana 44; or; 3.08 in the 8.8 & 3.07 in the Dana 44; or 4.11 in the 8.8 & 4.10 in the Dana 44, etc.

Following was in my MS WORD Notes and the source, Randy's Ring & Pinion has removed it from their current web site; The gear ratio in the front of a four wheel drive has to be different from the front so the front wheels will pull more. There have been many different ratio combinations used in four-wheel drive vehicles, but not so that the front will pull more. Gear manufactures use different ratios for many different reasons. Some of those reasons are: strength, gear life, noise (or lack of it), geometric constraints, or simply because of the tooling they have available. I have seen Ford use a 3.50 ratio in the rear with a 3.54 in the front, or a 4.11 in the rear with a 4.09 in the front. As long as the front and rear ratios are within 1%, the vehicle works just fine on the road, and can even be as different as 2% for off-road use with no side effects. point difference in ratio is equal to 1%. To find the percentage difference in ratios it is necessary to divide, not subtract. In order to find the difference, divide one ratio by the other and look at the numbers to the right of the decimal point to see how far they vary from 1.00. For example: 3.54 ÷ 3.50 = 1.01, or 1%, not 4% different. And likewise 4.11 ÷ 4.09 = 1.005, or only a 1/2% difference. These differences are about the same as a 1/3" variation in front to rear tire height, which probably happens more often than we realize. A difference in the ratio will damage the transfer case. Any extreme difference in front and rear ratios or front and rear tire height will put undue force on the drive train. However, any difference will put strain on all parts of the drivetrain. The forces generated from the difference have to travel through the axle assemblies and the drive shafts to get to the transfer case. These excessive forces can just as easily break a front u-joint or rear spider gear as well as parts in the transfer case.
Source: by miesk5 at Ford Bronco Zone Forums

Front Axle Dana 30 I believe 4.10 ratio if rear 9" is 4.11

Rear Axle Ford 9" I believe  4.11 was std w/option for  4.57

1966 Bronco Sales Brochure

1966 Ford Bronco Ad

http://lov2xlr8.no/brochures/ford/66brof.html

 

[Bully Bob]

Hi Katman..,

Viewing my signature below.., I have the same rig & similar build date.

As you may know, gearing dictates the tire size you'll need.

This rig came to me with the 456's front-n-rear with BFG 32's (rear posi)

I can't imagine a better combination. (all I had to change was the speedo gear)

I scoot down freeway at 70.., & climb like a big horn sheep. They make me lead

out in the dirt & if I can't (rarely) get up or thru.., they won't try. However,

NO rock slaming/crawling.

411's would work just fine with stock tire size.  I believe the 350's came on the

later EB models.

The I-6 is a torquey, strong  mill.  7 main bearings with great balance.

I sold off all my V/8 rigs & kept this one.

 

[katmandaddy]

Miesk5,

Thanks for the education about the relationship between front and rear ratios. I guess it would not be as relevant when cruising as 4wd won't be engaged. I might go back and count teeth again in the 3-Dana 30s and 3-9" rear axles. I looked at the VIN decoder just after I posted message. As you say Bully Bob it does not even list 3.50 for '66, but shows up in '67. Perhaps mine were replacements during this Bronco's long life - or mistake/experiment/special order at factory?

The 170, being fairly small. I just don't want to burden it with a engineering mistake I could/should have figured out before hand.

So am I right in assuming: all things being equal - smaller gears = a bit more speed and higher gears = a bit more pull.

BTW my Mother worked at the Rotunda and later at Central Office Building for Ford in the 60s. I wish I could go back in time and ask her to archive all the 1966 records!!

 

[Bully Bob]

"So am I right in assuming: all things being equal - smaller gears = a bit more speed and higher gears = a bit more pull."

Close... 

Don't use the word "smaller"

Do it this way.  A "low" gear ratio is higher in number ---  i.e  456's are "lower" than 350's

Soooo.., a "lower" gear ratio = more pull, along with higher RPM's in a given gear.

A  "higher" gear ratio gives less RPM in a given gear.., not necessarily more speed. Especially up a grade.

I can't say as to that chart being real accurate. Some info appears to be left out as well.

I would say, I believe all '66 year models came with 411's front & rear. Except for special orders.

Some of the older Jeffs Bronco Graveyard catalogs have all the EB history thru the years.

And, what changes were made over the 12 year run.

Also, they have a complete vin decoder.