Gear Ration Spreadsheet

[LukeC]

I have made a spreadsheet to model gear ratios. This site will not accept .xls files so I have posted over on the US Alfa BB.

Here is the link:

http://www.alfabb.com/bb/forums/gearbox-transaxle-differential-propshaft/360697-gearbox-ratio-spreadsheet.html#post5800145

I made it for transaxles, but will work with all cars.

Enjoy!

[PTP]

Old post, I know, but:

I haven't pulled apart a 116 or TS transaxle to check, but as we all know the TS boxes are more expensive.

If I'm reading this table right, the Aus 75s have the same ratios as the earlier 116 boxes. Is that correct???

If so, why all the fuss about 75 boxes? Is it just for the LSD? Or in fact are the 75 1st, 2nd & 3rd ratios taller in the Aus boxes, and the table is a bit confusing for easily confused folk like me?

Thanks in advance for clarification.

[carlo rossi]

i thought the post july 83 series 2 alfettas had different ratios with the isometric (not sure what they called it )changer
and maybe i'm  completely wrong but I thought all 75s had Lsd

[Duk]

The 75 gearboxes have better synchros in them.

[colcol]

'Isotatic', Colin.

[PTP]

The 75 gearboxes have better synchros in them.

Yep, Duk, that's the confusing table.

Regarding synchros, I'm not worried about them as I'm investigating dog modifications.

That's really why I am asking: I want to know what gearbox I can find for cheap, but with the best ratios. I have a TS box already, so I can steal the LSD and 4.3s that are fitted to it, but I don't want to possibly destroy my only gearset.

twin spark 75's and 3lt have LSD's the 2.5 had an open diff all of them had taller 1st 2nd and 3rd the ratios are different........

So if I was to find a 2.5l or 3L trans, that would be the same first 3 ratios as TS? 

Thanks for your help, all.

[PTP]

I should also clarify: I have a GPS speedo similar to this (http://www.speedhut.com/gauge/GR338-GPS-01/1/GPS-Speedometer-Gauge-120mph), so I am unconcerned about the speedo drive.

Update: I might have found my answer here: http://www.alfaclubvic.org.au/forum/index.php?topic=7387.0

You do realise it was only the 3L and the TS 75s that were LSD? 2.5 V6 is open.
If you can be a bit more precise on what you have (what transaxle, what car and in particular tailshaft and what the dedion/half shafts are from) you will be able to get some specific advice re swapping. But in brief, the major external variations in alfa transaxles can be summarised as follows (basically working front to rear):

Clutch input / tailshaft flange - one size for Alfetta 2L and 75 TS, another for V6

Input shaft on gearbox - same but sleeve on which throwout bearing slides 2 different diameters (V6 vs 2L)

Clutch push vs pull type (and corrsponding location of slave cylinder etc)

Selector shaft - short version with pin for isostatic shifter on 75s, longer version splined for alfetta type selector

Speedo drive - mechanical gear drive vs magentic pulse electronic - internally different - not a simple swap

Output shaft flanges - all same PCD, but V6 has M10 thread, all 4 cylinders M8

The above is almost right - there were some differences in early Alfettas / GTs (pre about 1978) - I think the output flanges on those were M10...

There is quite a lot of mixing and matching possible (but not everything...).

Also, regarding my clutch question, the quote above says the input shaft is the same diameter, which appears to be supported by a bit of Googling on the Exedy website - it appears that the V6 and 4 cyl clutches use the same shaft (22mm diameter, 19 spline - what a stupid spec ...). So same clutch plate.

If anyone has any information that contradicts this information, please post.

[Paul Newby]

A lot of the ratios in that spreadsheet are wrong.

As far as I can recall only GTV6 and 90s (but not Supers) had that ridiculous short 3.5 first gear.

All Alfettas and 'Nuovo' Giuliettas had the same gearbox ratios as 105s with the 3.3 first gear as depicted by the early Nuova Giuliettas in the spreadsheet. I think somewhere along the line third gear ratio may have been altered but no by much.

The Vin Sharp Twin Spark gearbox in my Alfetta GT racer has an assortment of ratios:
2.875, 1.72, 1.345, 1.026 and 0.946 with a 4.3 diff.

A couple of things I've noticed with this box is that you can change from second back to first on the move and the crown wheel and pinion are stronger than in the open gearboxes.

[Duk]

Sortiva are you absolutely sure that the later TA's didn't have better syncros?
My nearly 200,000km 75 has much better syncros (there actual ability to speed up and slow down the gearbo for gear changes) than my old, but similar km 1980 Giulietta had.

And the Alfa transaxle cars don't have a torque tube.

[rowan_bris]

The synchro so are all the same

[LukeC]

Actually, there was a "red" (as opposed to yellow) synchro available for use on second gear. I am not sure whether this was fitted from the factory, or it was an improved item that was developed later on. It had a coarser finish for greater bite and was more expensive.

I installed them on cars when I worked in an authorized Alfa service centre before I left the trade in '97.

And the later TAs had an improved first gear synchro mechanism to improve the neutral to first shift. I pulled apart a non-iso box recently that had this mechanism.

As a matter of interest, very early 105 series cars have a similar synchro that works on the same principle. If you use the later one in this type of box, it will not engage smoothly..... 

[GTVeloce]

Speedo issues can easily be rectified with the Dakota Digital box maintaining the original speedo head unit. Also enables correction of factory inaccuracies and for wheel size changes.

If the synchros are the same then surely something else must have changed as I went through three Alfetta boxes before I installed a TS box which has since seen many kays with no degradation. I later bought a 75 TS and it felt just as good. Both can select 1st gear while on the move albeit if with much speed it requires a racing change. The old Alfetta boxes had no chance of first unless you were very still.

[PTP]

The Vin Sharp Twin Spark gearbox in my Alfetta GT racer has an assortment of ratios:
2.875, 1.72, 1.345, 1.026 and 0.946 with a 4.3 diff.

Any idea which box(es) Vin uses for these ratios? I guess he has a bunch of boxes lying around so he can pick and choose. What I don't get (ignorance showing here) is that, depending on the gearbox design, one of the shafts (main or output) has gears that rotate independently until engaged via dogs, while the other shaft has fixed gears.

The diagrams below would suggest that the Alfa transaxles have fixed gears on the input shafts, and 'floating' gears on the output shaft.





Thus, it would seem that the gears on the input shaft are fixed, but I have now read several times that you can mix and match.

Am I to assume that the output shaft has some fixed gears, but others can be swapped? If I'm comparing the spreadsheet to the Vin Sharp race box, it would seem that there are pairs there - 1st and 2nd appear to come from one box, 3rd and 4th from another, and 5th from another (actually a 4th ratio). Therefore, are either 1st and 2nd, or 3rd and 4th permanently fixed to the output shaft, while the others can be swapped?

The diagram below would suggest it's actually 2nd & 3rd fixed (1st, 4th and 5th not fixed). I'm confused, because the spreadsheet doesn't list any factory sets with 1.72 2nd and 1.345 3rd. Hmm.

[LukeC]

Part 1 on the parts diagram (the input/main shaft) is manufactured in 2 parts: the shaft with gears 1 and 2, and gears 3 and 4... 3 and 4 are pressed on to the main shaft. For normal use, this is a permanent fit... I have tried to get them apart and gave up with my (only) 20 tonne press. However, they can come apart...

If you get them apart then you can swap the 3-4 from one shaft to another. This is the first and easiest way to create a CR box. Using the early Giulietta 3-4 gears in a T-S box tightens up the Ratios to 1-4. Using the Giulietta 5th gives you the ratios at the bottom of the chart. This requires machining.

If you want to go further with your box, this required machining gears (i.e. machining teeth off gears, parting the 3-4 set apart etc). It's all possible and more if you have the skills and equipment.... 

There are a few good (and entertaining ) threads over on the US Alfa BB on this subject.

http://www.alfabb.com/bb/forums/alfetta-gtv6-1972-1986/157315-close-ratio-transaxle.html

http://www.alfabb.com/bb/forums/gearbox-transaxle-differential-propshaft/178651-build-cheap-close-ratio-gearbox.html

BTW: I have compared Alfetta GTV and early Giulietta gear sets, and they do match the above chart. I recently sold the Giulietta short gear set with a T-S gearbox.

This spreadsheet  compares the T-S, Modified, and Alfetta trannies:

[PTP]

Thanks for this reply. It answers all my questions.

Separating 3rd and 4th sounds very challenging. Is it worth the effort?