Alfa differential gear ratios

Little Italian · #1 (**permalink**) 08-01-2012, 11:54 AM

Can someone please advise me when the rear end gear ratios were changed
from 4.56 to 4.10 in the Series Three / Series Four Spiders.

Also, the 1750 Spiders had a 4.10 ratio as an option in 1971 I am told. Can someone verify this?

What years were the automatic Spiders produced? Did thay have a 3.73
(11:41) or a 3.58 (12:43) ratio?

**papajam** · #2 (**permalink**) 08-01-2012, 03:55 PM

USA version Spiders.
69-79 - 4.56, 41/9. LSD from 1972, optional in 69 & 71. No 4.10 option.
80-94 - 4.10, 41/10. Manual gearbox.
91-94 - 3.58, 43/12. Automatic gearbox

60sRacer · #3 (**permalink**) 08-02-2012, 09:42 AM

Jim,
There was a 4.3 diff, I think in the Euro Sedans. Do you have any data - years, models, LSD, etc??

Thanks - Robert

Alfajay · #4 (**permalink**) 08-02-2012, 09:59 AM

Quote:

Originally Posted by Little Italian

Also, the 1750 Spiders had a 4.10 ratio as an option in 1971 I am told. Can someone verify this?

**papajam** · #5 (**permalink**) 08-02-2012, 10:01 AM

Without having any parts books at hand to study, I'll assume the following for Euro version cars;

68-72 1750 GTV & Spider - 4.10 open, LSD optional
68-72 1750 Berlina - 4.30 open, LSD optional
71 on 2000 GTV & Spider - 4.10 LSD
71 on 2000 Berlina - 4.30 LSD

Alfajay · #6 (**permalink**) 08-02-2012, 10:29 AM

Quote:

Originally Posted by papajam

Without having any parts books at hand to study, I'll assume the following for Euro version cars;

**papajam** · #7 (**permalink**) 08-02-2012, 12:34 PM

Yes. The USA & Euro market cars had different standard diff ratios.

Little Italian · #8 (**permalink**) 10-02-2012, 09:14 PM

I'm going to try to make a Series of videos of the Complete Differential Set-Up procedure using the Factory Tools and the Factory publications. Give me a little time and I'll post it all. It's a long drawn-out procedure that takes me about twelve hours to do completely, with new bearings and all. At the end, I'll mark the gear set with machinist bluing to show you the gear mesh that is produced with a proper set-up.
I've done a few "set-ups" perfect in the past several years. I'd say with proper maintenance, a Alfa Rear-End Differential Assembly could last a lifetime or longer. Improper maintenance can destroy a good differential in a heartbeat. I know one guy who exploded the Aluminum casting of the differential trying to drive the car a few hundred feet to the Shell station without gear lube. (Wasn't Me!)

I hope this concludes to be very informative for everyone.

Lets' take a look at the Pinion Backlash first.

ALFA DIFF 01 - YouTube
This video shows how the Ring Gear is locked-up using the Oil Plug Locking tool.

ALFA DIFF 02 - YouTube
With the Ring Gear locked, a Dial Indicator is used to measure the amount of Gear Backlash existing between the Pinion Gear and the Ring Gear. The Alfa Manual allows .15 to .25 millimeters of Backlash for the 105 / 115 differentials.

This check is made at four places on the ring gear by unlocking the gear, rotating the weighted tool one revolution , relocking, and then re-indicating the tool - four times. If you have it between .15 and .25 millimeters at all four locations, the pinion backlash is correct.

I'LL GET BACK TO THESE VIDEOS WHEN THE WEATHER GETS A BIT BETTER. I BET IT WILL TAKE 15 TO 20 VIDEOS.

eedneco · #9 (**permalink**) 10-03-2012, 12:35 AM

Subscribed !

Caroni · #10 (**permalink**) 10-03-2012, 01:10 AM

Suscribe me as well.

60sRacer · #11 (**permalink**) 10-03-2012, 07:51 AM

Wow! Thanks a lot!

Robert

**alfaparticle** · #12 (**permalink**) 10-03-2012, 08:36 AM

I parted out a 1970 Euro spec Spider that had been imported from Canada. I am almost certain that it had a 4.3 axle.

Little Italian · #13 (**permalink**) 10-03-2012, 10:50 AM

I've been working on this wall chart drawing for a while and don't consider it complete. I'll post it here now for you guys following this post but I will eventually complete it so we can have a chart for the garage. Please send me your comments or corrections if you see things that you know are incorrect.

( I probably could send a copy to Papajam and let him fill it out one night, but then I wouldn't have anything to do for the next six months. )

You can see that ALFA (ZF in Germany) made a lot of different ratios - nine different ratios for the
105 / 115. I understand some of the ring gears had 10 hole flanges and some had 8 hole flanges. This refered to the tapped mounted holes that were used to mount the rings to the carrier. I've only seen 8-hole models. It could very well be that the 750/101 series cars had the 10-hole carriers and gears.

I'd love to have one of each just for toys.

3/2013 I UPDATED THE CHART WITH A GEAR SET I FORGOT. ALSO ADDED THE ALFA PART NUMBER. ALL THE GEAR SETS WERE LISTED IN THE 1982 DEALER PRICE LIST BOOK EXCEPT THE LIGHT WEIGHT ONES.

Alfajay · #14 (**permalink**) 10-03-2012, 11:26 AM

I find it interesting that all differentials in Little Italian's chart have a prime number of teeth on the ring gear (e.g., 41 or 43 teeth). I guess this minimizes the number of times that the same pair of ring and pinion teeth come in contact with each-other. That way, a burr or other irregularity on a tooth will take longer to wear out the mating gear.

For example, a 45:10 ring and pinion would produce a 4.50 ratio - quite close to the 4.56 ratio that a 43:9 yeilds. However with a 45:10, the same teeth are in contact every other rotation of the ring. With the 43:9 the same teeth are in contact every ninth rotation of the ring. So it should take an irregularity 4-1/2 times as long to cause the same amount of wear in the 43:9 as on the 45:10.

Little Italian · #15 (**permalink**) 03-24-2013, 12:03 PM

I had the rear end ratios in my chart labeled backwards. Sometimes my brain just don't want to work - very hard. Our friend ConeDriver - George Schweikle came over and straightened me out. His brain works better.

I also added the Alfa Part Numbers for the different ratios but did know the Automatic Ratio Part Number. Just for fun.....