Jump to content
  • When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

What differential is this?


Dug Nichols

Recommended Posts

All right, stamp says 11 and 40 on top, and below this is a 1 over 7. So if I'm interpreting the coding correctly this means I have a 3.64 ratio built in January '77. Right?

 

I'm neither excited nor displeased to know this isn't a 3.91. I've got that in my '76 with a 5 speed and it's great, but this car has a 4 speed which I don't have any immediate plans to replace so the 3.64 will be nicer on the highway.

 

 

IMG_3472.jpg

  • Like 1

--

'73 Sahara numbers matching 

'74 Mintgrun sunroof car w/ oem Golde deflector, euro bumpers, 5spd, owned since 2002

 

Link to comment
Share on other sites

49 minutes ago, otto said:

All right, stamp says 11 and 40 on top, and below this is a 1 over 7. So if I'm interpreting the coding correctly this means I have a 3.64 ratio built in January '77. Right?

 

I'm neither excited nor displeased to know this isn't a 3.91. I've got that in my '76 with a 5 speed and it's great, but this car has a 4 speed which I don't have any immediate plans to replace so the 3.64 will be nicer on the highway.

 

 

IMG_3472.jpg

But what this does mean, is you have a set of half shafts and inboard stub flanges that will work if you swap to an LSD without needing redrilling for larger diameter bolts

Edited by Guest_anonymous
  • Like 1
Link to comment
Share on other sites

17 hours ago, otto said:

All right, stamp says 11 and 40 on top, and below this is a 1 over 7. So if I'm interpreting the coding correctly this means I have a 3.64 ratio built in January '77. Right?

 

I'm neither excited nor displeased to know this isn't a 3.91. I've got that in my '76 with a 5 speed and it's great, but this car has a 4 speed which I don't have any immediate plans to replace so the 3.64 will be nicer on the highway.

 

 

IMG_3472.jpg

 

That’s right: it’s a 3.64 manufactured in January 1977!

 

And, yes, I agree: with a four-speed, the 3.64 is certainly a better highway ratio. The original 3.90 from my ‘76, for instance, is currently resting up while a 3.64 LSD serves a tour of duty in the (four-speed) car. ?

 

By the by, the 3.90 and 3.91 diffs represent different gear sets. The 3.90 is largely an oddity of the U.S. 1976 2002 market, intended to recover some acceleration lost over the years to emissions controls, and has a 39/10 ring/pinion combination. I’ve not yet seen a factory LSD example of this ratio. The 3.91, on the other hand, is an e21 differential, a common mate to an overdrive five-speed, and has a 43/11 ring/pinion combination. LSD versions of the 3.91 are relatively common.

 

Regards,

 

Steve

 

Edited by Conserv
  • Like 1

1976 2002 Polaris, 2742541 (original owner)

1973 2002tii Inka, 2762757 (not-the-original owner)

Link to comment
Share on other sites

8 hours ago, Conserv said:

The 3.91, on the other hand, is an e21 differential, a common mate to an overdrive five-speed, and has a 43/11 ring/pinion combination.

 

My thought is the 11 tooth pinion offers more tooth contact with the ring gear than the 10 tooth pinion in the 3:90 diff and maybe a stronger set up as far a tooth loading is concerned.

  • Like 1

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

Link to comment
Share on other sites

2 hours ago, jimk said:

 

My thought is the 11 tooth pinion offers more tooth contact with the ring gear than the 10 tooth pinion in the 3:90 diff and maybe a stronger set up as far a tooth loading is concerned.

 

Thank you, Jim. I never got past “the two gear sets are different”! ?

 

Best regards,

 

Steve

 

1976 2002 Polaris, 2742541 (original owner)

1973 2002tii Inka, 2762757 (not-the-original owner)

Link to comment
Share on other sites

The tooth contact patch is going to be roughly the same regardless of the number of teeth. Remember that the ring and pinion are numbered and matched to each other for a smooth mesh. Usually the last 4 digits of the ring gear # is scribed on the pinion, either on the gear end or the bearing mount area. 

 

A pinion gear with fewer teeth will by definition be stronger because each tooth is larger. Hence, 39/10 would be stronger than 43/11.  Check out the Metric mechanic torque ratings on diffs and see how they decline as the ratio rises. Hence a 4.27 ratio in any diff has less torque capacity than a lower gear such as a 2.93. 

  • Like 1

73 2002 Tii Sold

71 2002 Ti Vintage racecar

84 BMW 325 E-Prod racecar Sold

Link to comment
Share on other sites

20 hours ago, RussTii said:

Check out the Metric mechanic torque ratings on diffs and see how they decline as the ratio rises. Hence a 4.27 ratio in any diff has less torque capacity than a lower gear such as a 2.93.

Not convinced that it's the pinion/ring gear that determines those torque limits and that one can't surmise from those tables that the pinions are or are not stronger for either end of the table ratios.

As I read the tables, it's the input torque limit and the input torque is multiplied to the output side by the speed reduction ratio.  There may be other elements of the diff that set the limits, like the spider gears that seem to break.

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • BMW Neue Klasse - a birth of a Sports Sedan

    BMW Neue Klasse - a birth of a Sports Sedan

    Unveiling of the Neue Klasse Unveiled in 1961, BMW 1500 sedan was a revolutionary concept at the outset of the '60s. No tail fins or chrome fountains. Instead, what you got was understated and elegant, in a modern sense, exciting to drive as nearly any sports car, and yet still comfortable for four.   The elegant little sedan was an instant sensation. In the 1500, BMW not only found the long-term solution to its dire business straits but, more importantly, created an entirely new
    History of the BMW 2002 and the 02 Series

    History of the BMW 2002 and the 02 Series

    In 1966, BMW was practically unknown in the US unless you were a touring motorcycle enthusiast or had seen an Isetta given away on a quiz show.  BMW’s sales in the US that year were just 1253 cars.  Then BMW 1600-2 came to America’s shores, tripling US sales to 4564 the following year, boosted by favorable articles in the Buff Books. Car and Driver called it “the best $2500 sedan anywhere.”  Road & Track’s road test was equally enthusiastic.  Then, BMW took a cue from American manufacturers,
    The BMW 2002 Production Run

    The BMW 2002 Production Run

    BMW 02 series are like the original Volkswagen Beetles in one way (besides both being German classic cars)—throughout their long production, they all essentially look alike—at least to the uninitiated:  small, boxy, rear-wheel drive, two-door sedan.  Aficionados know better.   Not only were there three other body styles—none, unfortunately, exported to the US—but there were some significant visual and mechanical changes over their eleven-year production run.   I’ve extracted t
  • Upcoming Events

  • Supporting Vendors

×
×
  • Create New...