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Offline Poison Pinto

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FAQ: Rear End Ratios
« on: June 28, 2004, 08:17:00 PM »
One frequently asked question is how to tell what the gear ratio of the rear end is. This is especially true if looking at a rear end that is out of a car or if you know that the rear end in a car is not the original unit. Provided the rear end itself has not been modified, the following information should help you determine the gear ratio of your rear end.

The rear end case should have a small metal tag. On the 6.75" differential, this is on a bolt that holds the back cover on.

The tag has several codes on the top and bottom edges.

The easiest method is to look at the numbers on the bottom edge. This is useful if you're looking at a non-Pinto rear end (such as an 8" rear end out of a different Ford model).

Example:

3     40     #   #     ####

This indicates a conventional 3.40:1 ratio.

Limited-Slip/Traction-Lok differentials will have an "L" between the numbers.

Example:
3 L 40     #   #   ####

The original 6.75" rear ends put in 4 cyl and some 6 cyl Pintos have codes along the top edge that should comply with the following:

1975-76
C2-WGF-H or -K ..... 3.40:1
C2-WGF-U, -R2, or -AA ..... 3.18:1
C2-WGF-N or -R ..... 3.55:1

1977-78
C2-WGF-KI, -UJ, or -AA ..... 3.18:1
C2-WGF-AJ ..... 2.73:1

1979
C2-WGF-AM ..... 2.73:1
C2-WGF-AN ..... 3.08:1
C2-WGG-C ..... 2.73:1
C2-WGG-D or -E ..... 3.08:1

The "C2" in the code denotes a conventional rear end.

Sources: Haynes Auto Repair Manual for 1975-1980 Ford Pinto & Mercury Bobcat; www.mustangii. org/decoder/axle.
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Offline PintoBro

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Re: FAQ: Rear End Ratios
« Reply #1 on: September 04, 2004, 02:31:22 AM »
If the tag is missing, or you suspect that the rearend has been modified, another way to tell the gear ratio is by jacking the rear of the car up, and put it on jack stands. Then mark one of the tires and the driveshaft. Slowly rotate the tire one full revolution, while counting the revolutions of the driveshaft. If you get 3 full turns of the driveshaft to one full turn of the tire, you have a 3.00:1. If you get a little over 4 full turns of driveshaft to one full turn of the tire, then you probably have a 4.11:1 ratio. This method is not exact, but it will get you in the ball park.
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Re: FAQ: Rear End Ratios
« Reply #2 on: September 04, 2004, 10:53:20 AM »
If you do that, you must make sure both tires turn exactly the same amount, or your reading will be off.  If the rear doesn't have limited slip, one wheel can lag behind the other when you are turning the driveshaft.
What I have done when that is a problem is lock one wheel so it can't turn, then count the turns of the driveshaft to make the other wheel turn two revolutions.  Sounds weird, but it works.
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Offline steveo

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Re: FAQ: Rear End Ratios
« Reply #3 on: February 17, 2005, 06:57:06 PM »
HI
I have a rear end with tag numbers that read  WGF-AL-7J6

It came with but not in the pinto i just bought, and i haven't been able to find a code that matches it.  Does anybody know what this code is for or what it might be out of?  it looks like a 6.75"

thanks

Offline billnall

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Re: FAQ: Rear End Ratios
« Reply #4 on: February 17, 2005, 07:01:03 PM »
What is the 2nd line of numbers on the tag?
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Re: FAQ: Rear End Ratios
« Reply #5 on: February 18, 2005, 12:54:29 AM »
It looks like  18 6 7 224C    it's a little hard to read, but i'm pretty sure that's right

Offline billnall

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Re: FAQ: Rear End Ratios
« Reply #6 on: February 18, 2005, 05:11:36 PM »
WGF-AL
3.18 6.7
1978 PINTO 3.18 RATIO 6.75 RING GEAR 23 SPLINE AXLES
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Re: FAQ: Rear End Ratios
« Reply #7 on: August 29, 2005, 08:56:24 AM »
I just "SCORED" a rear from a 78 cobra II, as well as the front and rear sway bars and assorted parts. The rear has a tag:

wdy oaan 7jd
40 8 244c

I am assuming that it has 3.40 gears (I know it is an 8 inch), am I correct? I did check the rotation and it seems to be about that for sure (spining both hubs at the same time).

Boy I want the whole car, still has the engine/tranny, but the car is soooooo rough.

I plan to transplant the meatball into the 68 rear I have in the pinto (it currently has 2.79's), It should fit... right???

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Re: FAQ: Rear End Ratios
« Reply #8 on: August 29, 2005, 09:15:42 AM »
Pretty sure the rear axel tag would say WFK... if it were a Posi.
Besides the L that would be in the 3l.40 which is sometimes crushed by the retaing bolt.
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Offline ernie

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Re: FAQ: Rear End Ratios
« Reply #9 on: September 22, 2005, 06:27:12 AM »
I have a 1980 with a tag that says WFG  AN  3.08 that i am selling.  I noticed others saying tag is WGF?  are there 2?

Offline billnall

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Re: FAQ: Rear End Ratios
« Reply #10 on: September 22, 2005, 04:41:08 PM »
1980 Ford Pinto rear end tags decoded from Ford Parts Catalog.
WDY-AS=2.79 - 8"
WDY-AT=3.00 - 8"
WGF-AM=2.73 - 6 3/4"
WGF-AN=3.08 - 6 3/4"
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Re: FAQ: Rear End Ratios
« Reply #11 on: September 22, 2005, 05:42:03 PM »
FORD CAR REAR AXLE DOOR CODES for locking/limited slip
If it is a number from 1-9 it is not locking/limited slip.

YEARS 1980 Pinto
locking/limited slip
Z=3L08

YEARS 73-79
locking/limited slip
C=2L47
H=2L73
J=2L50
P=3L40
W=3L45
X=3L55

YEARS 69-71
W=4L30
Y=4L11

YEARS 69-79
K=2L75
L=2L79
O=3L00
R=3L25
S=3L50
V=3L91
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Re: FAQ: Rear End Ratios
« Reply #12 on: July 16, 2006, 04:39:45 PM »
Are those door post sticker codes in the previous post?

I have a '79 wagon that says AX=Y on that sticker. I'm 99% sure that it isn't posi.
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Offline americanpintobean

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Re: FAQ: Rear End Ratios
« Reply #13 on: September 01, 2011, 06:21:23 PM »
I would like a posi 3.55,  6.75 rear end/axle for a pinto.  Can someone help me out?  Please help

Offline americanpintobean

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Re: FAQ: Rear End Ratios
« Reply #14 on: September 04, 2012, 12:48:57 PM »
I have a rear end tag that says WGF-K, which means it should be a 3.40:1, but the numbers underneath are 3 18 xx xxxx

Offline Wittsend

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Re: FAQ: Rear End Ratios
« Reply #15 on: November 03, 2012, 10:18:27 PM »
From my experience these cars would benefit from having a 3.25 as an overall best ratio.  Sadly (in the 8" type) you have 3.00 and then jump to 3.40. And I have found the 3.40 very hard to find. They all seem to be either 3.00 or 3.55. I did the turbo swap so an 8" is essential. Otherwise the 3.16 / 6-3/4" seems a logical choice. Ford actually did use a 3.25 for a very short time.  This from the guy who was pillaging all the 8" rears and I fortunately happened beat him to the one I got.
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Re: FAQ: Rear End Ratios
« Reply #16 on: November 03, 2012, 10:23:43 PM »
i have one 3.25 ratio or my 8 inch rear end. not selling
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Offline oldkayaker

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Re: FAQ: Rear End Ratios
« Reply #17 on: November 04, 2012, 03:24:33 AM »
For the Ford 8", the ratios 3.25 and 3.40 are still available new.  Maybe scarce in the junk yards.  The second link does not function as is, it needs to be copied and pasted to work.
 
http://www.summitracing.com/search/department/drivetrain/section/differential-rear-end-components/part-type/ring-and-pinion-gears/axle-model/ford-8-in?keyword=ford%208%22%20gear
 
http://www.yukongear.com/PartsList.aspx?SearchMode=Cat&CatID=35&CatName=Ring & Pinion Sets&MakeID=2&MakeName=Ford&ModelID=275&ModelName=Mustang&Side=Rear&DriveType=RWD&DiffID=160&DiffName=Ford 8"
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Re: FAQ: Rear End Ratios
« Reply #18 on: December 07, 2017, 09:03:26 PM »
There's one near me for sale that has Code 1867 207A, it's that any good? My rear end on my 4 speed 72 sounds like it's howling . The r-end for sale near me
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Offline dick1172762

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Re: FAQ: Rear End Ratios
« Reply #19 on: December 08, 2017, 12:44:52 PM »
Over the years I've tried just about every gear ratio that you buy from 3:00 to 4:69. On one of my 80's Pinto I had a 4:11 gear in it and around town(Denver) it was great. The ratio of 3:55 looks like the best because it is good from a dead stop and will be just right for city driving. Too low? No because how much of your driving is going to be on the interstate? Around town it'll be just right. Try it / you'll like it!
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Re: FAQ: Rear End Ratios
« Reply #20 on: December 08, 2017, 12:54:28 PM »
Is the one you're saying is the good one to have, the one I'm asking about ?

Thanks for input  8)
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Re: FAQ: Rear End Ratios
« Reply #21 on: December 08, 2017, 01:02:41 PM »
I have no idea about what ratio is in the one pictured. If it has been changed along the way it could be any ratio. Taking it apart is the only way to know for sure.
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Re: FAQ: Rear End Ratios
« Reply #22 on: December 08, 2017, 01:23:53 PM »
Do know that your tire size is as much a "gear ratio" as the gears themselves. Here is a calculator link that can be very helpful http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php

I quickly ran a few tests at the Federal 65 MPH speed limit. Here are the results:

3.00 gears, 24" tire (likely a 13")        = 2,730 RPM

3.40 gears, 27" tire (likely 15" or 16") = 2,750 RPM

So, as you can see there is only a 20 RPM difference at 65 MPH between 3.00 and 3.40 gears because the tire size became the great equalizer. And just to prove the point:

3.00 gears, 24" tire (likely a 13") = 2,730 RPM

3.40 gears, 24" tire (likely a 13") = 3,094 RPM

Not altering the tire size made a 364 RPM difference. That is significant. Thus, know your goal.

  I have a 2.3 Turbo in my car with a very low 3.97 first gear (T-5) and a 3.40 rear gear. With the 175-70-13" tires I find it too low.  Previously I had the same set up with 3.00 rear gears and the 215-60-`14" tire.  I actually liked that for acceleration as it gave longer "pull" time between gear shifts with the turbo. HOWEVER, for everyday driving it was awful. The car was always in the wrong gear for normal everyday speeds. As an example 45MPH was too wound out in third gear but too bogged in fourth gear. Therefore the 3.40 gears were better in that regard because it put the engine in a 'sweet spot' for the speeds posted even though it came as a trade-off for the low (too low for my liking) first gear.

My opinions are a bit altered because of the Turbo motor but I'd think about 3.25 is a good overall ratio with 13" tires. And because I'm accounting for more highway driving than scooting around town my numbers are different than Dick's. As to the tag posted I'm thinking you are missing the "3" in a 3.18, 6-3/4" rear.  If you are running 13" tires and do a fair amount of highway driving it should be acceptable.  BTW, what ratio do you have now?  It would be good to know so you have a point of comparison.

Offline Crazy Lacy

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Re: FAQ: Rear End Ratios
« Reply #23 on: December 09, 2017, 07:47:52 PM »
Is the Ratio in the VIN # ?
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Offline Wittsend

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Re: FAQ: Rear End Ratios
« Reply #24 on: December 09, 2017, 09:14:57 PM »
No, the code as far as I know is not in the VIN. You have to look at the tag on the axle..., and as Dick stated it still might not be that ratio - but hopefully is.


As far as the tag in the image it was not cleaned sufficiently. The area I circled in red is the ".18", and the dirty area in blue I circled is likely where the "3" is.  As for your own car you will have to crawl under and clean/read the tag (safely secure the car before doing so). I've included a 3.00 tag as an example of the how far the "3" number is close to the bolt hole.


 There is a mean by which one can rotate the tire and count the driveshaft rotations but in an "open" rear end the true count is double the drive shaft rotations and subject to misreading. If for some reason the tag is missing you will need to do that as a way of getting "close."


FWIW if I was choosing a rear ratio and my choices were factory only it would be either the 3.18 or the 3.40. Most likely 3.18 if I was using 13" tires and a fair amount of highway driving and 3.40 if I was using larger tires and perhaps inclined more to city driving.

Offline dick1172762

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Re: FAQ: Rear End Ratios
« Reply #25 on: December 12, 2017, 11:54:15 AM »
Not double. If you rotate the tire one turn and the drive shaft turns 3 turns, you have a 3:00 rear end. If the drive shaft rotates 4 turns you have a 4:00 rear end. Etc, etc. Using this method you will see its very hard to pick out a 2:93 or a 3:18 from a 3:00 gear. If you take the rear end apart, it very simple to check the ratio by dividing the number of teeth on the pinion gear by the number of teeth on the ring gear. (the small number divided by the large number).An example would be 6 teeth on the pinion and 20 teeth on the ring gear would give you 6 divided by 20 and a ratio of 3:00. Easy as pie!
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Re: FAQ: Rear End Ratios
« Reply #26 on: December 12, 2017, 05:20:53 PM »
Dick, you have had too many (race) cars with limited slip rear ends.  When the rear is open the spider gears come into play and the driveshaft rotation is half. The easier solution is to just turn the wheel twice and measure the driveshaft turns.  http://www.mossmotoring.com/the-highs-and-lows-of-differential-gear-ratios/


Or, the relevant part there of:
The easiest way to determine the gear ratio is to jack up the car (safely) and block one rear wheel so it can’t rotate. Most British cars have “open” differentials, where a spider gear causes the wheels to rotate opposite one another. If you block one, the other wheel spins twice as quickly. When driving, this allows the wheel on the inside of a turn to rotate slower than the one on the outside of the turn. With the transmission in neutral, rotate the unblocked wheel two full turns and note how many times the pinion flange of the differential rotates. Marking the wheel and flange with a white marker helps keep track of the rotations. The number of turns is the gear ratio, which is called out as number of turns of the differential pinion to one turn of the axle.



open = two wheel turns


limited slip (etc.) = one wheel turn

Offline dick1172762

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Re: FAQ: Rear End Ratios
« Reply #27 on: December 13, 2017, 09:44:09 AM »
But if you have both wheels off the ground, the spider gears would not come into play or would they?
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Re: FAQ: Rear End Ratios
« Reply #28 on: December 13, 2017, 10:05:29 AM »
But if you have both wheels off the ground, the spider gears would not come into play or would they?

My experience is that:

1. Most cars have an open rear end.
2. Most people prefer to (or, only can) jack up one wheel. And with the open rear end it is necessary.

Hence the one wheel fixed, two wheel rotations method.  Regarding both wheels off the ground in an open rear end situation, yes, that becomes difficult. I've tried doing that in the wrecking yards and as one brake may rub over the other the spider gears come into play and skew the driveshaft rotation count.

 That is why one wheel locked down makes for a consistent result.  That can be difficult to accomplish in the yards. I've tried jamming items in wheel openings, stacking tires until they jam and even turning the brake adjusters (one tight, one loose) to accomplish the task.

As you have stated it is both wheels off the ground and one tire rotation to driveshaft rotation count IF the rear end is limited slip/locker etc.

Offline dick1172762

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Re: FAQ: Rear End Ratios
« Reply #29 on: December 13, 2017, 10:25:41 AM »
As Paul Harvey use to say, "And now you know the rest of the story".
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