Gearing

Dbarnhill

Registered User
Hey guys i'm thinking about putting in some 3:73's on the bird, possibly within the next week or so. Is this the only part I need to do so? Also what is the stock gearing for a 93 AOD and will it be that much of a difference?
 
stock should be 3.31:1

I liked 3.73 gears in my AOD. You are going to want a Yukon installation kit. I would hit up XR7 Dave (David Dalke) for one of those kits. It will come with new carrier bearings, pinion bearings, races, and seals.

The Ford Racing Kit is nice. If you have set up differentials in the past then it is straight forward. If not I suggest you get yourself a dial indicator, and an inch pounds wrench.

Setting the pinion depth is typically the most difficult part. Some folks swear by using the same size shim as teh old pinion gear. I prefer to measure with veneers and use the correct shim. This way you can be certain the pinion depth is spot on and any adjustment you make will be to the carrier if necessary.

My advice is to be certain your pinion depth is correct and set your preload correctly. Then when installing the carrier check the pattern with some grease.

If using new pinion bearings I would recommend about 26 inch pounds of preload and set your gears up with about .006 - .009 of lash.

Also please keep in mind it is a great time to rebuild the traction lok unit. XR7 Dave can get you that rebuild kit too.


Robert
 
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stock should be 3.31:1

Actually, for a 1993, my notes say it's a 3.08 TL.

The 3.31 wasn't introduced until into the 1994 model year, again, according to my notes.

Of course, presuming the original diff, you could just read the axle code in the driver's door and see what it's supposed to have. Second is to check the tag on the diff itself.

RwP
 
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Actually, for a 1993, my notes say it's a 3.08 TL.

The 3.31 wasn't introduced until into the 1994 model year, again, according to my notes.

Of course, presuming the original diff, you could just read the axle code in the driver's door and see what it's supposed to have. Second is to check the tag on the diff itself.

RwP

Thanks Ralph. I always forget where the cutoff is for the 3.08's.
 
I'm pretty sure all AOD equipped SCs came stock with 3.27 gears. Yes, switching to 3.73s will be a noticeable difference and will make the car feel about 500 lbs. lighter. I've got the 3.73s in both my SCs and really like them.

David
 
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Yep, 3.27s in all the cars Ive seen so far with a aod. Man, it doesnt sound like much but the 3L31s would have been great in all the cars. Out of all the differentials i set up I either used the same shim that was behind the pinion, or if it was a empty housing, i would used the average of what i have seen. only once have i had to change shims. Almost everytime it was .025" that worked. I set a rear one time by finding the pinion depth and it was a waste of time since a change in temp would throw everything off a few thousandths. But, that was a aluminum housing too.
 
all 3.8L(including SC) Auto have 3.27, 3.8L Manual has 2.73, and All V8s have 3.08. Unless it was special ordered with different gears
 
Yep, 3.27s in all the cars Ive seen so far with a aod. Man, it doesnt sound like much but the 3L31s would have been great in all the cars. Out of all the differentials i set up I either used the same shim that was behind the pinion, or if it was a empty housing, i would used the average of what i have seen. only once have i had to change shims. Almost everytime it was .025" that worked. I set a rear one time by finding the pinion depth and it was a waste of time since a change in temp would throw everything off a few thousandths. But, that was a aluminum housing too.

you are making the assumption that each pinion gear has identical machining depths??? Re-using the factory shim is a widely used practice but not correct. If you are using an empty carrier then you should always start with a base shim of .030 if using Ford Racing gears. All Ford Racing 8.8 gear sets are setup to be used with a base .030 shim. In fact if you look closely at the Ford Racing pinion gears when new out of the box they are labelled with a number in yellow paint. This indicates how many thousands to add or subtract to the base number of .030. For example if it read -1 then you would use a .029 shim. If it read +1 the you would use a .031 shim and so on.

Again this is a starting point as there could be case variation. I always prefer to have the old pinion gear and shim, so that I can measure total pinion gear thickness including the old shim then measure the thickness of the new pinion gear without a shim. The difference between the two will indicate the exact thickness of shim that is requried for the new pinion gear.

If you can't do this then the only way to be sure is to use a pinion depth tool.

Again I use 26 inch pounds of preload for new bearings and about 19 if using bearings over again.

You can roll the dice and use the old shim over but I have never had a noisy differential.

I prefer my method.
 
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