Gearbox internals discussionfrom Alfa Digest

[chris.richard]

gearbox/diff discussion (http://www.digest.net/alfa/FAQ/164/forum2/DCForumID2/4149.html)

[rutthenut]

Hmm, doesn't really state much that hasn't been covered here.

However, the following post did at least provide some actual figures:

For UK models there is no point in changing gearbox internals - because they are all identical, except for some early V6's which had a slightly higher first gear.
The ratios for early TS and ALL later models are:- 3.75, 2.23, 1.52, 1.16 and 0.914.
Early V6 ratios are:- 3.5, 2.23, 1.52, 1.13 and 0.93.

What is different is the final drive ratio:-
early V6-2.94, early TS-3.42, later V6-3.35, later TS-3.56 and cloverleaf-3.41.

To change gearing either change the tyre profile or the differential or both.

The commonly-recommended solution for the Stratos replicas is to fit a 2-litre (TS) diff in a 12V V6 transmission. But that does increase revs at 'cruising' speed, which isn't ideal if you are doing long road journies in your Strat.

I think that the 24V V6 had a different ratio (later 164 in list above) as it was fitted with 16" wheels, whereas the earlier 12V variants ran on 15" wheels.

[CorseChris]

Now I'm confused....I've got a 3.11 CWP set in the garage. Wonder where that came from....

[rutthenut]

Lancia Thema, Fiat Chroma perhaps?
Or some other Alfa (155, 156)?

Or even perhaps from a Beta transmission, but I think the gearshaft is different on those (or some other incompatibility)

[CorseChris]

I think I checked my 164 data disc and 3.11 was listed as a standard ratio...and I was told on good authority that it came from a 164...but this new data had me wondering...

I've also got a 24V 'box with a broken CW or P so might have a dig at that and see what's what. Might be able to make up a decent spare.

..also got an 8V Thema turbo box to play with as well.

[David May]

The 1998 Alfa Spider 3L 12V had a 3.111:1 FD.

[chris.richard]

Here's some more from the digest:-

The gearbox used on all 164s is the Fiat C.503. I don't know if it is used on Iveco trucks, but I do know that it is used on Fiat Croma and a number of Lancias. The Lancias include not only sister model Thema, but also the Delta, the Dedra, and their successors (although not with the smallest of engines such as the 1.3 l). It was also used on the Fiat Coupe, the Alfa 155, and the FWD Coupe/GTV. If you get a C.503 from a Lancia, you can look for one with Viscodrive, the viscous coupling limited slip differential which in my opinion makes the car more fun to drive.
The easiest way to determine which cars share this transmission is to get a Fiat Auto Parts CD or DVD, locate the differential carrier or another shared part, and use the shared parts search function to find other models that share that part. Then look up the various ring gear/pinion teeth combination for that model to find the final drive. But note that the same parts have different numbers whether sold for use on an Alfa or on a Fiat/Lancia (so Fiat can charge more for the Alfa part).

The C.503 was continually upgraded, notable with a synchronized reverse around 1992. The latter type is recognizable by its reverse lockout where the driver has to lift a ring to engage reverse (e.g. on the US 94-95 models). Those who believe that 2 liter cars have a better tranny may be comparing a latter version with an older one.

The 6 speed transmission from the 156/166 is also used on other Fiat Auto products and is called the C.530. The C.530 was initially made in a 5 speed version which was fitted to late Lancia Kappas and, if I have understood correctly, to larger displacement versions of the 156. Other boxes have also been used on the 156. I think it was the C.510. I am not sure if the C.510 was ever used with the V6, which would probably be necessary to find a fitting bellhousing.

Another option is to get the Getrag 6-speed box from the Q4. It should fit right in but may need different halfshafts. The PTO (power take off) for the rear wheel drive is easily removed and the output hole welded by someone who can weld aluminum.