Alfa differential gear ratios - Page 3 - Alfa Romeo Bulletin Board & Forums
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post #31 of 51 (permalink) Old 12-08-2013, 11:54 AM
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Quote:
Originally Posted by 60sRacer View Post
I got an LSD rear end from APE in the 70's that was from a 2L, but it's a 4.56 ratio!

Robert
Robert, unless the car was special ordered with another ratio, all 2L Alfas in the U.S. from the 70's had 4.56 diffs. The switch to the 4.10 didn't happen until some time in the 80's.

Erik
'66 GTV racecar, '71 Spider racecar, '74 GTV street car, '71 GTV project
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post #32 of 51 (permalink) Old 12-08-2013, 12:34 PM
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Originally Posted by luca220cv View Post
my friend has a 10/41 not lsd.....why?
I have one too, small rear end from 1971 1750 Gtv

Giulia Super "Biscione" 28th February 1969
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post #33 of 51 (permalink) Old 12-08-2013, 12:44 PM
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2 litre AUTO Lsd

In Australia,the Auto cars= Berlina + Coupe autos had a 14 tooth pinion + a 46 tooth crownwheel witch makes it a 3.2 ratio.These models were 1974-1976 cars.
Installed one in my 2 litre manual car and it is high speed,,low rpm
Its like an extra gear.
Great for long distance crusing + fuel economy.

Just thought I would mention it cause I saw no reference to it in the above posts.

Over the years,I have dismantled many auto diffs for the LSD internals.
Many have said they were a 3.9 ratio,,but when you divide 46 crownwheel teeth by 14 pinion teeth ,you get a 3,2 ratio.
Pull another one apart last week= 46-14.

Customer=also a BB member,purchased a Berlina LSD diff,,believeing it was a 4.3 ratio,which were standard LSDs in all Berlinas that came to Australia.Berlina manuals came standard with a 4.3 LSD Ratio,and Coupes + Spiders with 4.1 LSD ratio.
Pulled it apart and it was a LSD,but from an Auto= 3.2 ratio= 46-14.
So,,add another ratio to the list.= Standard fitment to Australian delivered Auto 2 litres.
There are many Berlinas that have standard 1 wheel screamer diffs,cause maybe I swapped them over the years cause the 4.3 is a great diff for raceing + modified Alfas..
Still enjoying the 3.2 ratio in my GSGT 2 litre.
When you guys are in 4th gear,,im still in 3rd gear.
When you guys are in 5th gear,,im still in 4th gear,,with 1 gear to go.


Robert

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1976 2L Spider
1984 GTV 6 3 litre
1967 GSGT 2 litre
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post #34 of 51 (permalink) Old 12-08-2013, 12:48 PM
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The European 1750 GTVs & Spiders were fitted as standard with a 10/41 open differential. LSD was an option. The 1750 Berlina had a 10/43 open as standard with an optional LSD.

The 1750 USA versions all had 9/41 open differentials with an optional LSD.

Jim

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post #35 of 51 (permalink) Old 12-08-2013, 02:18 PM
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Hi Robert,

For SCCA Solo events, cars in Street Prepared classes are not allowed to change transmission ratio. However, since the 4.11 differential was used in a later Alfa, I can use it under the update / backdate allowance. I changed several years ago but, if I remember correctly, this resulted in 9 MPH more at 6000 RPM compared to the 4.56. This really helped in faster autocrosses.

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Originally Posted by 60sRacer View Post
George,
Do you still use the stock TX ratios? I've collected a set of CR gears for the same reason - useless 1st, too many 2-3 shifts in AX - and wonder what Diff ratio Would go well with them.

Robert


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post #36 of 51 (permalink) Old 12-08-2013, 06:56 PM
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The pdf file posted earlier in this thread listed a 3.73 diff ratio but did not say what model it cam from? Does anyone know?

I actually have a use for a 3.58 or 3.73 ratio posi diff that might otherwise be to long for other applications. If someone has one to sell, please contact me.
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post #37 of 51 (permalink) Old 12-09-2013, 02:35 AM
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Quote:
Originally Posted by luca220cv View Post
my friend has a 10/41 not lsd.....why?
I re-checked and compare different sources, there's some confusion in 1750 data: some report 9/41 for the 1st series and 10/43 for the 2nd, some say it was only for the berlina, spider and GTV had always the 10/41.

Last edited by d.albe72; 12-09-2013 at 02:55 AM.
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post #38 of 51 (permalink) Old 12-09-2013, 02:58 AM
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Quote:
Originally Posted by Little Italian View Post
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?
Here in Itly,2L spiders only have 4.1 diff. About Automatic ratio, 12:43 is reposrted as iV series only in original spare catalog
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post #39 of 51 (permalink) Old 01-13-2014, 04:15 PM
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From the catalogorapido (Short Spare parts) Catalogue
It appears that all the 2000 models had the LSD?
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post #40 of 51 (permalink) Old 03-05-2014, 11:41 AM
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Quote:
Originally Posted by Little Italian View Post
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.....
Very nice document. Thanks!

Suggestion: when posting revisions of documents it is probably best to add a version and date in the document somewhere so that it's obvious to the reader that the correct one is being read, and perhaps also a (v2, v3, ...) suffix to the filename.
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post #41 of 51 (permalink) Old 03-06-2014, 12:51 PM Thread Starter
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Originally Posted by jonessjon View Post
From the catalogorapido (Short Spare parts) Catalogue
It appears that all the 2000 models had the LSD?
jonession:

Can you please email me a .pdf of that document. Never seen it before and your book or whatever this came from are not like the USA versions.

Thanks in advance.

Bud Feigel
Lexington, Kentucky 40503
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post #42 of 51 (permalink) Old 03-06-2014, 04:47 PM
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Catalogorapido (short parts catalogue)

Files are easier to distribute via Dropbox links

Catalogorapido.pdf
Part 1 – sections 1-9 https://db.tt/0D4MV3RC
Part 2 – sections 10-20 https://db.tt/CerYcBbM
Part 3 – sections 21-30 https://db.tt/25Lt2IoQ
Part 4 – sections 31-34 https://db.tt/y0jgz8YS

Jon
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post #43 of 51 (permalink) Old 03-06-2014, 06:26 PM
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What a wonderful set of resources. Thanks.

Robert
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post #44 of 51 (permalink) Old 03-29-2015, 06:33 PM
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Thanks for the video. I had made a drop gauge setup to measure the backlash, but don't have a tool to clamp the ring gear. I'm getting 0.010"-0.012" which is about what it appears to be on the video, but I may be getting some error due to lack of clamping. Keep us posted if you made more videos and thanks.

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post #45 of 51 (permalink) Old 05-30-2016, 04:43 AM
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Quote:
Originally Posted by 60sRacer View Post
There are only two axle assemblies that have been used in the Alfas - the smaller (and earlier) one was in the 1600's and most earlier cars (as far back as the 50's!), and was non-LSD. It used 8 mm bolts for the drive shaft flange.

The larger one appeared with the 2L cars in about 1972 or so as an LSD unit. It had larger axle tubes and larger diameter axle shafts with fewer splines, a different center casting, and larger R&P for the LSD parts. This one also had a larger diameter drive shaft, with special 9 mm hardened shoulder bolts coupling the rear U-joint flange with the Diff input flange. It also carried rear brake calipers that were the same external size as the earlier one but with larger diameter pistons.

However, the attachment of both of the axle assemblies to the car is identical. It's the easiest swap of Alfa parts on the car! The only significant issue is the larger diameter holes in the input flange for the 9 mm shoulder bolts. This can be accommodated by reaming the 8 mm holes in the drive shaft, swapping the later rear yoke of the rear U-joint (which is the same on all axles) that has the larger holes, or swapping in a later drive shaft.

The later drive shaft is also an easy swap, only requiring attention to the center bearing carrier, which changed after the 1600 series 1 cars. The bearing itself is unchanged however. The later drive shaft is larger and stronger, presumably to go with the higher power of the 2L engines. It fastens at the front to the same guibo on all cars. There were at least two different lengths of all the drive shafts - for the Sedan and the GTV/Spider. The earliest cars (Guilettas) had yet a different drive shaft.

Easy Peasy.

Robert
Excellent tech.

Scott

72 GTV; 66 Fairlane GT convt, 428, 4 sp; 68 GTO Convt, owner built 455 and TH400; 71 Javelin road race project, owner built 401, T10
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