Rear End Gear Ratio

[Corkwheats]

Hi Guys,

Is there a way to tell what my rear end ratio is on my 1971 Ranger XLT w/360?

Is there some web site that tells whether it's a 3.0, or a 3.5, or whatever?

This isn't something I plan to tackle anytime soon. But, I'd really like to know.

My mechanic buddy said that for pulling it would be nice to have a 3.70 in it.

If I discover it has a 3.5, that'll be good enough. But, if it has a 3.0, I may want to bump it up.

I wouldn't wanna go too high, as I don't want the thing screaming at me, and guzzling fuel when I'm going 60 MPH down the highway.

Any input would be appreciated.

Thanks,
Bob

[Corkwheats]

Well, I may have answered my own question - http://www.fordification.com/tech/rearends_ford01.htm

I knew that somewhere amongst my bookmarks, I had seen a chart like this.

Now, all I need to do is crawl underneath the truck, and see what the numbers are.

But, according to this chart, my truck at least will be a 3.70, so I'm good to go!

Bob

[Red Mercury]

I am not sure that chart is complete. I have a 1970 F100 with a 360/3speed that has a 3.00 ratio. It is all original and never had the ratio changed.

The tag on the rear axle may not be on your truck anymore--they are often long gone. If the truck has the original gears in it you can get the axle code off of the vehicle identification plate on the door and then cross reference the code to determine the ratio. Now, it's a 42 year old truck and the ratio may have been changed. Get us that code and either myself or someone else on here can tell you what ratio the truck originally had.

You might want to try this (Maybe someone else on here can comment on this method too). Jack up one wheel on the truck, and put the transmission in neutral. Mark the driveshaft and count how many revolutions of the driveshaft it takes to turn the wheel two full turns. I think two turns will need to be counted because the differential is involved. So if you have a 3.70 ratio then the driveshaft should turn 3.7 times for every 2 turns of the wheel. I am just thinking this through in my head so not sure if it is a good method--hopefully somebody else can jump in and help out.

[ultraranger]

As suggested, start by looking on the tag on the door under the Axle heading. If the first two digits are numbers, then that immediately tells you the rear end has an open (single track) differential. If the first two digits are a letter and a number, it tells you the differential is a Traction-Lok.

My guess is the truck likely has a 3.25:1 rear gear ratio. The most common code for this is "17."

The next step would be to look at the tag on the rear end to see if the ratio matches the code on the door tag --if the tag is still attached to one of the (10) studs that holds the 3rd member to the rear end housing.

[Corkwheats]

Hi Guys,

I checked the right side door - the axle # is 08. According to the page on decoding your Vin #, that means I have a:
3.50 - 3300# Ford. I'm cool with the 3.5. That'll work for me. What does the 3300 mean? Thanks!

Bob

[Red Mercury]

Axle weight rating = 3300 lbs.

[Donnie]

On a 40 year old truck, I myself would not put a lot of faith in the tag info, unless you know the complete history of the truck.
It could have been changed many years ago & accumulated enough grime to look original.......Why not do the wheel test? It's easy & the results are positive.............donnie

[ultraranger]

...or, though more involved --but is dead accurate and there's no guessing what the ratio is; that is, pull the 3rd member out, count the number of ring gear teeth, count the number of driving pinion teeth, divide the number of ring gear teeth by the number of driving pinion gear teeth and you will have a dead-accurate knowledge of specifically what your ratio is.

--taking the 3rd member out will also give you the opportunity to clean out the housing and thoroughly inspect the condition of the 3rd member/gears. --would be a good time to replace old axle bearings and housing seals, if those things have not been changed in a good while.

[Corkwheats]

Thanks for all the input, guys.

One other thing.....now that I know I have a 3.5 gear ratio, how can I tell if it's posi-traction, or not?

And, if it's not.....is there a way to change it over to posi-traction?

I'm asking because I plan to do a lot of pulling with this truck, and figure posi-traction would be better.

Thanks,
Bob

[ultraranger]

Unless your truck is a Chevrolet, it will never be a Posi (Positraction). The reason is 'posi' or Positraction is a GM trade marked name for their differential that directs power to both axles.

In the case of a Ford, and being that yours is a '71, IF you were lucky enough to have a locking differential in a 9-inch rear end, it would be a Traction-Lok. Through 1968, the Ford locking differential would have been known as the Ford Limited-Slip. Beginning in 1969, Ford redesigned the locking differential to the much better Traction-Lok differential.

If the axle code on your door reads '08' then that indicates you have a single track 3.50:1 ratio (no Traction-Lok differential). One way to check for a locking differential would be to lift both wheels off the ground and rotate one of the tires/wheels. If the opposite wheel/tire turns in the same direction, then it definitely has a locking differential. If the wheels turn in opposite directions, then it's an open (single track) differential. However, I have seen Traction-Lok differentials that had so much wear on the differential clutches that the wheels turned in opposite directions, like they had a single track differential.

Open (single track) differentials will have ring gear bolt heads that are fully exposed (when the 3rd member is out of the rear end housing). They would require a 3/4" socket to break them loose and in fact, you would be able to get a 3/4" end wrench on the bolt heads.

In the case of a Ford Limited-Slip or Traction-Lok differential, they have ring gear bolt heads that are shrouded (partially covered) by the differential case so the bolt heads are not fully exposed like the single track differential ring gear bolt heads. The ring gear bolt heads on a Limited-Slip/Traction-Lok requires a 5/8" socket to beak them loose/tighten and you cannot get a 5/8" end wrench on them.

Example of single track (open) and Traction-Lok differential below. Open differential on left. Traction-Lok on right.




If your door tag code of '08' is correct (single track 3.50:1 ratio) the only way to make it a Traction-Lok would be to install a Traction-Lok differential. --about $400 dollars for the differential plus installation.

http://www.summitracing.com/parts/fms-m ... /overview/

[Corkwheats]

Wow. Somebody sure knows their stuff!

Very informative post - thank you very much!

I bookmarked that site on Summit. That would be a "future upgrade" at some point.

Do I know for sure that my 1971 Ranger XLT is a 28 Spline (and not 31)?

If you wanted to have a truck made for pulling - is this the route you'd go (purchasing Traction Lok) or would it be better to find a different rear axle that already had it?

$400 + Installation is pretty pricey. If I could locate a rear axle that was already set up this way, that may be better.....I dunno.

Anyway, thanks a ton. I feel much better educated about this now. This is why I come here!

Bob

[ultraranger]

Wow. Somebody sure knows their stuff!

Very informative post - thank you very much!

I bookmarked that site on Summit. That would be a "future upgrade" at some point.

Do I know for sure that my 1971 Ranger XLT is a 28 Spline (and not 31)?

If you wanted to have a truck made for pulling - is this the route you'd go (purchasing Traction Lok) or would it be better to find a different rear axle that already had it?

$400 + Installation is pretty pricey. If I could locate a rear axle that was already set up this way, that may be better.....I dunno.

Anyway, thanks a ton. I feel much better educated about this now. This is why I come here!

Bob

The Ford 9-inch rear end first came out in passenger cars & trucks in 1957. The last Ford 9-inch rear to be installed in a passenger car was 1980. The last Ford 9-inch rear end to be installed in a truck was at the end of 1985, which concluded all (factory) production of the Ford 9-inch rear. This means the supply of Ford-produced 9-inch rear ends, from the wrecking yards, has been drying up for 28 years now. It's not impossible to find a 9-inch with a Traction-Lok from the wrecking yard, but they are few and far between anymore. If you're lucky enough to find one, it will likely be the 31-spline version instead of the 28. In either case if you do find either, there's a good chance they have a lot of wear on the clutches & steels inside. That would mean having to rebuild the differential which means you're really no better off than to just buy a completely new Traction-Lok differential assembly to start with.

The majority of F-100s through 1972 had 28-spline axles. There were some (I believe '70-'72) that had 31-spline axles but they weren't very common. I am not certain of this but I think the only pre-'73 models to have 31-spline axles were the trucks that had the 9-3/8" 3rd members. In 1973 (through 1985), the majority of pickups with a 9-inch rear had 31-spline axles.

The Ford Traction-Lok differential first came out in 1969. It replaced the Ford Limited-Slip differential and is a much better design over the older Limited-Slip. However, 1969 is the worst year Traction-Lok diff to have, due to (4) large holes in the driver's side half of the differential casting. Heavy torque loads tend to break the '69 differential casting between these holes. This problem was addressed by Ford with the '70 model ('70-'85) Traction-Lok differential. The diff casting was made solid in this area.


Photos of weaker 1969 Traction-Lok differential with the (4) large holes in the driver's side half of the casting;






'70-'85 Traction-Lok differential on left. (broken) '69 Traction-Lok differential on right. This is what happens to the '69 Traction-Lok differential when too much load/torque is applied to it.




If a truck came from the factory with a towing package, the 9-inch rear end would have been equipped with an N-case 9-inch 3rd member. This is the strongest 3rd member offered in the 9-inch rear ends. N-cases came out around the mid-'60s. N-cases up through 1969 did not have the large "N" cast on the face of the 3rd member. 1970-1985 N-cases will have the large"N" designation cast on them. You would not have to have this case to do towing but I'm just presenting it so you know that it exists. It has a high degree of nodular iron content (thus the N-case name) that allows the case to flex rather than shatter like the much older '57- early '60s gray iron cases.





Any of the single vertical-ribbed (C7AW casting) 9-inch 3rd member cases would stand up just fine to most any towing you would do. The 9-inch cases to stay away from are the early gray iron cases with the; WAA. WAB or WAR casting inside them. They have two vertical ribs on the face like an N-case, but there are thing to look for to tell it from an ealier N-case that didn't have an "N" cast on it.

...if you think finding a wrecking yard Traction-Lok is difficult, it's many times harder to find an N-case at the bone yard. I took several years before I found the two N-cases I have, and this was back in the mid-to-late '90s.

Here are some links from my website that gives some details on the Ford 9-inch and the differences in components (my site is geared more towards early Mustangs & related Ford cars, but any Ford 9-inch 3rd member will fit any Ford 9-inch rear end housing (car or truck), so long as the differential spline count matches the spline count of the axles).

1. http://www.ultrastang.com/info1.php

2. http://www.ultrastang.com/info2.php

3. http://www.ultrastang.com/info6.php

[sargentrs]

I went with the Richmond Powertrax No Slip. Fits in existing 9" single speed carriers and installation is simple. At $500 it was my most cost effective solution to having limited slip. Got good reviews in the Mustang mags.

[Corkwheats]

Well Guys,

They say even a blind squirrel finds an acorn now and again......

Since I got home early, and it was a beautiful Spring Day, I finally got a chance to tinker with the Truck for just a few minutes.

Guess what I found???

I was looking for my tag on the rear end, and got a very pleasant surprise.....when I looked, I saw a nice big Letter "N" on the rear end!!!

I'm so psyched! I bought this truck for pulling, and now have the good rear end for that purpose.

One other question: I don't know how to decipher the numbers I found on the tag.

They are: 1AA, and 301A. Can anyone direct me to where I can find this out?

Thanks, guys.

Bob

[Corkwheats]

Okay.....Squirrel was blinder than first thought......I wiped 'er down, and found the other numbers:

WDM - W

When I looked it up, it said "N.L." for this rear end. I'm guessing that means non-locking.

So, then, the only thing I'd need to do is get a Traction Lok, and install it, then, eh?

Thanks, Guys.

Bob