89 pinions?

[p03t13]

Hi there, Name's Dustin

First off let me appologise and let y'all know up front I am by no means a mechanic, in any way shape or form.

That having been said I've always liked Broncos and now ive got an 89 with an auto trans.

She's nowhere near cherry but drives like a champ (with the occasional new part anyway)

Heres my issue:

I love the 32x11.50R15 Tires ive got on it.

It seems like the green beast just hasnt got the power to keep up with them at speed.

If I'm driving 65mph my speedo reads 59mph and if i climb a hill she boggs out unless I floor it till it downshifts.

I was talking to a buddy of mine at work and telling him i wanted to buy a trans with more power on the

high gears so that doesn't keep happening. He told me all i really needed was bigger pinion gears.

Now like i said i'm no mechanic, and i dont want to ruin my winter vehicle trying to do this myself. So my plan

is to search around and see if anyone knows the gear size/ratio w/e i need to up the power at highway speed

(just enough to keep from bogging out on hills and stuff. Buy the parts and have a real mechanic install it and

recallibrate the speedo at the same time.

I intend THIS Bronco to be my winter vehichle / funvee. but I mainly only do highway driving. I would love to take a

cross country tip with her (3000ish miles round trip) but if i have to fight the gears on every uphill that would just **** it.

Also incase its relevant its the 5.0 v8 model Eddie Bauer edition (1989)

Any thoughts, ideas, tips, or instructions would be very much appreciated.

Thanks in advance,

Dustin

 

[nelbur]

Your friend is generally correct, that a change in the gear ratio in both differentials will be needed to correct for much larger diameter tires, but in your case, the 32s are not really all that large.    I have 31s on my '86 302 and have pleanty of power but I do have a replaced engine.    I would guess you have reduced power from your engine, that is exacerbated by the larger tires.   I think I would concentrate on the engine power before I paid the big money to change the differentials.   The speedometer can be corrected to match your tires.   In my case a plastic gear on the speedometer cable has to be changed.   Yours may be the same, but the later Broncos did away with the speedometer cable, and I am not aware of their method of correcting the speedometer.

 

[Bully Bob]

Hi Dustin, welcome..!

"He told me all i really needed was bigger pinion gears"

That would be Ring & pinion sets..., front & rear. This doesn't come cheap.

Does this rig have overdrive..?

Least expensive would be stock tires.

You likely have 350 gear ratios in the differentials. Going to 411 would likely  do the trick.

(maybe 456's..., i.e. don't know where you are..?)

I believe M5 has a chart that lists RPM's, gear rarios, & power curves.

You'll likely have to do a little math then run it by a driveline shop in your area to see if they agree.

They won't charge you anything for advice.

PS  what Nelbur says.., a run-out eng. would def. slow you down.

       See rogmits post "no power on hills"  just below yours.

 

[miesk5]

yo Dustin,

Here you go!

Gear Ratio Guide for Larger Tires Source: by Jeff's Bronco Graveyard via Seabronc at SuperMotors.net

compare to:

Gear Ratio Guide for Larger Tires; Scroll Down or Click, Another RPM/Gear Ratio/Tire chart if site reverts to main page; MIESK5 NOTE, Rough Country® removed this same chart from their site in FEB 2011 & company rep said it isn't there anymore. Source: by Rough Country® via https://web.archive.org/web/20111117131542/http://www.broncocity.com/resources.htm

Scroll Down to the Chart

Take time to read all Notes.
---------------

Then compare to Jer's info that he compiled from (probably) above & other sources;
Updated 11/11/03
Here are some really good equations for determining what gear ratio you may want to concider.
Remember that this is reference only and is based on equations from simple math.
Your tire size may be listed as 33/35/37, etc. but the actual measurement of the tire could differ once it is mounted on your rim.
Also this write is assuming you have an E4OD, or similar auto tranny.
These are figures that I came up with, to do your own just do:
Circumference of tire divided by the gear ratio you want.
Then compare you answer to the stock forward measurement of 25.5"s and then you will know if it fall over or under.

************************************************** **
Stock 29" tire (235/75R15), with 3.55 gears, 90.7" is circumference of tire, thus for every turn of the drive shaft, you go forward 25.5" or so.

33" tire, 3.55 gears = 103.7" circ, forward 29.2", about 15% more than stock
33" tire, 4.10 gears = forward 25.3" basically same as stock
33" tire, 4.56 gears = forward 22.7", about 11% less than stock

35"s with 4.10s = 26.8, 5% over stock roughly.
35" tire, 4.56 gears, 110.0" circ, forward 24.1", about 5% less

37" tire, 4.56 gears, 116.2" circ, forward 25.5", identical to stock (within error)
37" tire, 4.88 gears, forward 23.8", about 9% less than stock.

38.5" tire, 4.56 gears, 121.0" circ, forward 26.5", about 4% more than stock
38.5" tire, 4.88 gears, 121.0" circ, forward 24.8", about 3% less than stock.

FYI, for those who are thinking they can run a 35" tire with 3.55 gears...

35" tire, 3.55 gears, 110.0" circ, forward 31", about 22% more than stock. That means that your motor is working (and your clutch or torque converter) quite a bit harder to move your truck. That's why it dogs so bad.

If it falls "under" your motor does not have to work as hard to turn the tires, but it does it at a higher RPM. This means that as you go more "under" you lose top end. If it's "over" you'll have a higher top end, but less grunt.
**************************************************

This is by Chris B; Gear Change Calculator w/Ford Part Numbers, Colors, & Tooth Count http://www3.bc.sympatico.ca/cbradley/speedogearchange.html
To adjust for changing tire size:

Old tire x Old Gear / New Tire = New Gear
OT x OG / NT = NG

(some one told me that 31" tires usually has a 19 tooth gear, and 235/75/15 tires has a 21 tooth gear)
Example:
Old Tire - 29"
Old Gear - 19 tooth
New Tire - 33"
New Gear - ?
235/75/15 = 28.9"

If you change tire size and gears (or just gears), you have to go one step further:
New Gear / Old Ratio x New Ratio = New Gear
NG / OR x NR = NG
17 / 3.55 x 4.56 = 21.8
21 / 33.5" * 28.8" = 18.1
18 / 3.55 * 4.56 = 23.1
Each tooth on the speedo gear adjusts your speedometer reading by approx. 5%. So when you add a tooth, you reduce the speedometer reading by 5%.


See Chris's site to view more Color Codes, here is the 19 tooth as an example;
Ford (truck) Speedometer Gear's
Tooth Count Color Part Number Notes
19 Pink C0DZ-17271-B
 

Gear Color Codes, 80 and up
Source: by JBG via Seabronc



and by Ryan
16 teeth - Wine- C0DZ-17271-A
17 teeth - WHT- C3DZ-17271-C
18 teeth - YEL - C0DD-17271-B
19 teeth - PNK - C0DZ-17271-B
20 teeth - BLK - C1DZ-17271-A
21 teeth - RED - C4OZ-17271-A
aprox $3 each at your local Ford dealer

First you need to search for a couple of numbers:
A) How many teeth are on the drive gear inside your transfer case? (possible options are 6, 7, or 8 teeth)

What is the axle gear ratio?
C) How many tire revolutions per mile? (Look on your tire manufacturers web site)

The formula for finding the correct speedo gear is:
drive gear x axle ratio x tire rev/mile � 1000

My original 1986 Bronco info:
8 drive gear teeth
3.55:1 axle ratio
718rev/mile stock 235/75R15 tires
8 x 3.55 x 718 � 1000 = 20.4
And I found a 20 tooth gear in the transfer case originally.

My Bronco set up to go fast:
Swapped in a 7 tooth drive gear
4.10:1 axle ratio
708rev/mile 285/50R18 Dunlop Sport Tires
7 x 4.1 x 708 � 1000 = 20.3
I was using a 20 tooth gear, it worked great.

My Bronco now with 33in tires:
Still using the 7 tooth drive gear
4.10:1 axle ratio
643rev/mile 33x12.5 Goodyear Wrangler AT tires
7 x 4.1 x 643 � 1000 = 18.5
I am now using a 19 tooth gear, which also works great.
 

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[p03t13]

so as far as replacing the pinions instead of the engine i should go with a combo of:

http://www.ringpinion.com/b2c/ProductDetails.aspx?ProdID=1940&Product=YG_F8.8-411&Brand=Yukon_Gear_Ring_and_Pinion_Sets&ShowAA=True&Year=1989&Model=Bronco&DriveType=Rear%20Diff%20-%204WD&DiffId=276&Source=DiffWizard

for the back

and

http://www.ringpinion.com/b2c/ProductDetails.aspx?ProdID=3291&Product=YG_D44R-411R&Brand=Yukon_Gear_Ring_and_Pinion_Sets&ShowAA=True&Year=1989&Model=Bronco&DriveType=Front%20Diff%20-%204WD&DiffId=129&Source=DiffWizard

for the front?

according to this guide

https://web.archive.org/web/20111117131542/http://www.broncocity.com/resources.htm

it should also be noted that someday, some grand glorious day long from now, i DO plan on buying a brand new engine/trans for this beast but it is currently not an option. for now i just need to get it ready to go from wyoming to texas and back in november

 

[miesk5]

yo Dustin,

 both URLs for the 44 and 8.8 look good!

"...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 driveshafts 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.