puzzled by all the
ECUs in my car
Join Date: May 2009
Location: United Kingdom
County: Greater London
sud/33 rear axle
First post to Alfa Owner, so I should probably know better than to step into a firefight like this one. However...
I spent a weekend once with two complete axle assemblies, took each one apart, measured everything, weighed al the parts, put them together to make the lightest I could with standard parts. Then the lightest I could by modifying parts. Unfortunately my workshop is all packed up in storage and in New Zealand, while I am in London UK, so I can't post any pics.
You are comparing different things here. The dimensions of the taper of the stub axle are the same between the Sud and the 33, so you can put a Sud disc on a 33 stub axle, or a 33 drum on a Sud stub axle.
In a Sud, though, the stub axle is a piece of the whole trapezoid arrangement that takes the four suspension links. So Sprint337's pic on the left is the bare axle without the trapezoid and stub axle unit.
In a 33, the stub axle has a much smaller base that bolts to the axle. The axle itself is a single unit with the trapezoid end pieces. Sprint337's right pic shows this - a 33 rear axle, with the stub axles missing, but the trapezoids in place.
So when you discuss which 'hubs' are interchangeable with which 'hubs' it depends what you include in your definition of hubs. If hub is the stub axle, bearing, plus disc or drums, they aren't interchangeable. But if you mean the disc or drum is interchangeable on different stub axles, then they are.
As to why you might want to do it... The standard complete Sud rear axle and the standard 33 rear axle are the same weight, at about 30kg +/- 500g. By complete, I mean with full brakes, everything except wheels. Doesn't seem like it should be so, because drums are heavy and discs aren't, but I've weighed them. Mixing and matching standard parts, you can use the 33 axle, and stub axles, Sud discs and callipers, and you save a grand total of 2 or 4 kg -- I don't remember which. Feels like not a lot of saving for the work required. You save more with aftermarket alloy callipers etc; but ultimately those Sud discs are a big heavy lump of cast iron. What I finally did was take the 33 drums and machine the drum off them to make a small cast iron hub. You then use alloy hats and aftermarket discs, and you can get the total weight of your rear axle assembly down near 20kg.
The original poster wanted to know what callipers to use if going outboard on the front and wanting to keep the Sud rear axle with discs, and needing a rear handbrake. One easy way of doing this is with Alfetta rear callipers. You need to machine up some crush tubes/spacers, as the flanges for bolting the Alfetta callipers in place are much narrower that the flanges for bolting the Sud rear callipers in place, but the spacing is the same. Bleeding them is also difficult, as it puts the bleed nipple in the wrong place -- the solution there is to drill and tap a new bleed hole at the new top of the Alfetta calliper. Then you all need a brake bias adjust, as the piston size on the Alfetta calliper is much bigger than the rear Sud, so you spend a bunch of time locking up the rear and going off the track backwards.
Okay, having written that down it doesn't sound like an easy solution at all, but it is mostly inexpensive.