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Rear diff identification


74tiiGolf

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I searched 5 or 6 different terms to find how to identify a diff by the stampings but couldn't find a thing. Any help would be appreciated. Thanks!

Any of this make sense:

33.11-1207 719.0 GGG-40 WH 7 0 3108

Matthew

Chastity: the most unnatural of sexual perversions.

74 tii, 99 BMW R1100R, 99 E320, 01 S4 Avant

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simply divide I think

last four numbers

3108

divide 31 by 08 = 3.875

Whatcha got there is one'a them 3.90:1 rear end jobbies

test it out too... for every 3.9 complete revolutions of the pinion shaft (input side) you will get one on an output shaft

Make it different... or just do it differently

Bill in Petaluma, CA

1969 1600 supercharged m20 in progress

1970 2002 RIP -- crashed then quartered

1971 2002 M20/02 RIP -- nothing but pieces now

1972 2002 gone, but not missed POS

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Sorry, Bill,

the 3.91 has more than 8 teeth on the pinion!

And the math works out much more closely than that.

How many, I wouldn't try to remember, however.

Turn the input and watch the output- that's the only surefire way.

I load different ratios into 3.91 diffs, so the stampings

really can be wrong...

However, you're looking for 2 numbers stamped on the vertical flat of

the diff, close to the nose.

Kinda random, by themselves, like 11 and 41...

fwiw,

t

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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I do know that there is a string of numbers, four-long either in the front or at the end of the line that division of the numbers yeilds the ratio... I did however give the way to check the math by checking the number of Input revolutions:output

Not to offend, and not offended.

I didn't know that the second number is the number of teeth on the pinion gear, good to know. Also I didn't know that those numbers were elsewhere on the case-- this too, good to know

Make it different... or just do it differently

Bill in Petaluma, CA

1969 1600 supercharged m20 in progress

1970 2002 RIP -- crashed then quartered

1971 2002 M20/02 RIP -- nothing but pieces now

1972 2002 gone, but not missed POS

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There should be some stamped numbers high up on the drivers side of the diff about 1/2" big but very fine stamping - thats is stamped NOT cast(under the crud). Numbers like (11 40) (10 41) - these are the ratio 40÷11=3.64 - which means its a 3.64 diff. You can open the back and count the teeth for the same result (number of teeth on the crown wheel, divided by number of teeth on the input shaft). Have fun with it, Beaner7102

1971 - 2002 RHD VIN 1653940. Agave (stock with Pertronix & 32/36 Weber) - "Cactus"

1972 - 1602 RHD VIN 1554408. Fjord (with 2L motor, 5spd & LSD - Weber 40/40 to come) - "Bluey"

1984 - E30 318i VIN WBAAK320208722176 - stock daily driver

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There should be some stamped numbers high up on the drivers side of the diff about 1/2" big but very fine stamping - thats is stamped NOT cast(under the crud).

Note: the stamped numbers are on the passenger on left hand drive cars!

The stampings are not very deep and are often obscured by crud and rust.

BMWCCA #2762
72 2002/71 2002ti, 67 2000CS, 2x 72 3.0CS
86 635, 2x 05 330Ci ZHP, 
'11 Corvette Grand Sport

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