Codes for '81 Chrysler axle

[Trey]

Is there anyway to decode the axle code on the window sticker of my car? The code for my rear axle is D91 on the sticker. I know it's a sure grip but I can't find anything to tell me the ratio from those numbers? The tag on the axle cover is rusty and I can't read it. Thanks for any help.

 

[89.Fifth]

Your only real option is to pull the cover and look for the stamping on the ring gear. Or count teeth. Personally I can't get a reliable number by turning the tire and counting the axle rotations.

 

[XfbodyX]

D91 is a sure grip code, D50-s would be the ratio.

 

[Trey]

Thanks for the tips guys.

 

[BudW]

The only places you will find the differential codes will be on the build sheet (not seen very often on FMJ cars), the window stickers and on new car order sheets.

a build sheet

The differential codes will not be on the fender tag or placed anywhere else on car, that I’m aware of.

Starting in mid or early ‘90’s, Chrysler started to stamp a part number and date code on outside of differentials (trucks, vans and Jeeps) – which made it easier to identify ratios, but the only way to know on most FMJ’s is to pull the inspection cover and look at stampings on ring gear.

Blue arrow is part number, red circle is gear ratio and white line is manufacture date.

Note: it is a very good idea to change the differential fluid every 30k miles, anyway.

Differential codes (sales codes) for FMJ's I’m aware of are:
D51 2.71/2.76 ratio
D52 2.93/2.94 ratio
D53 3.21/3.23 ratio
D55 2.45/2.47 ratio
D56 3.54/3.55 ratio (special order)
D5? 2.21 ratio (D58, I think - can't read my writing).
D81 7¼” differential
D82 8¼” differential
D91 limited slip

BudW

 

[Trey]

Thanks Bud. I've had all the seats out of the car except the front passenger seat and rolled the carpet back as far as I could and didn't find any build sheet. I was hoping to not have to pull the cover but the car has about 50K miles on it and it's probably time for new gear oil anyway. Thanks again.

 

[MiradaMegacab]

How To: Determine the Rear Axle Ratio

 

[BudW]

The factory printed off several build sheets at once before car was built, with one (or several of each sheet) sent to different departments as well as a fender tag. I suspect the fender tag was mostly used for the sheet metal frame – but there is more data on it than what the sheet metal crew used.

The late ‘60’s/early ‘70’s Chryslers had a plethora of build sheets left in cars. I’ve seen some with 12 or more sheets in the cars. The mid ’70’s cars started to taper off, significantly. The late ‘70’s/80’s cars had very few to no build sheets in them. The rumor I heard was the sheets were a potential fire hazard. Chrysler still used the sheets for assembly line purposes even in the '90's, but assemblers would tear out the sheets as car went down the assembly line (which is a shame).

There are two corners of build sheets taped to the dash on my ’77 wagon. One corner was just under the dash pad and above the instrument cluster (used for dash builder?). The other taped corner was on forward most edge of glovebox (viewable before dash was installed into car) so dash could get installed into correct car after dash was built? Both pages were ripped off at the tape – so that appears to support that theory.
No further disassembly performed on my wagon, to check in other places yet.

I’ve personally only seen one complete build sheet in an ‘80’s car (so far).
BudW

 

[BudW]

Just for giggles, I looked up the differential codes on the broadcast/build sheet (above) on a '79 M-body.

It has three codes:
55, 82 and 91. There is a “D” just above the numbers to indicate they should be referred to as D55, D82 and D91.

According to those codes: this car was built with a 8¼” differential with 2.45 ratio with limited slip.

As to why a 2.45 or a 2.47 ratio? The size differential makes the difference on which gear number. In this case, the 2.45 is for 8¼” and 2.47 is for 7¼ differentials – so gear makers/part departments don’t goof up after part is made or delivered
2.45 = 49 tooth ring and 20 tooth pinion gear
2.47 – 47 tooth ring and 19 tooth pinion gear (2.473684… to be more exact)
The speedometer gear usually doesn’t change if you were to change size differentials within the same set.
BudW