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 (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!
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.
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
The 75 gearboxes have better synchros in them.
'Isotatic'???, Colin.
Quote from: Duk on March 07, 2016, 06:24:54 PM
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.
Quote from: sportiva on March 07, 2016, 09:14:17 PM
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.
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 (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 (http://www.alfaclubvic.org.au/forum/index.php?topic=7387.0)
Quote from: Darryl on July 17, 2011, 09:49:10 PM
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.
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.
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.
The synchro so are all the same
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..... :-\
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.
Quote from: Paul Newby on March 08, 2016, 04:51:44 PM
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.
(http://www.alfabb.com/bb/forums/attachment.php?attachmentid=187623&stc=1&d=1285236074)
(http://www.alfabb.com/bb/forums/attachment.php?attachmentid=187624&stc=1&d=1285236079)
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.
(http://img.photobucket.com/albums/v521/Vindicator64/Cars/Alfa%20Romeo%20GTV6/diagram.jpg)
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 ;D) 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/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 (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:
Thanks for this reply. It answers all my questions.
Separating 3rd and 4th sounds very challenging. Is it worth the effort?
Someone else will have to chime in. t depends on your application.
I have niether done it myself or driven one. Vin Sharp at pace will be more than glad to talk to you about it.
The gear ratios in my group s race car are
1. 2.875
2. 1.72
3. 1.25
4. 1.04
5. .88
Good for 206 kph.
PTP, I started out with a standard Twin Spark box. With the 4.1 final drive and the 0.79 fifth gear I would only get into fifth gear after the start finish line at Phillip Island! It was pretty much useless.
My box has 1st and 2nd ratio from the Twin Spark box, 3rd and 4th from an early Alfetta box I had lying around and 5th gear is actually the Twin Spark 4th gear, which Vin machined on. The 4.3 diff came out an early South African Alfetta 1.6 but I'm pretty sure that 1.8 Giuliettas and I think late 2.0 GTVs had the 4.3 diff as standard. Now 5th gear is a lot more usable.
This is probably the ultimate affordable solution. I understand you can source Colotti straight cut close ratio gearsets from Italy but they are mega expensive.
Yeah, mine has 4.3s, which mean around 6000-6500rpm in 5th at the end of the straight at PI (I think, I was busy looking through the apex, not at the tacho), which is pretty good. A slightly shorter 5th with the rest the same ratios would be ok, but taller first and second, and shorter 5th would be best. But worth $6K plus? Doubt it.
Quote from: John A Pucak on March 13, 2016, 09:52:20 PM
The gear ratios in my group s race car are
1. 2.875
2. 1.72
3. 1.25
4. 1.04
5. .88
Good for 206 kph.
I can find the origins of 1-3, but are 4 & 5 custom gears?
are all isostatic ratios the same or did this change as well
Gear set
3rd late series Alfetta
4th early series Alfetta
5th .88 Billett
That's a cool idea. Would be better still if it was also welded.
Quote from: PTP on April 07, 2016, 11:30:47 AM
That's a cool idea. Would be better still if it was also welded.
You'd want to seriously know what you're doing to weld heat treated/heat treatable alloy steel and expect it to continue doing a job like this.
Assuming that the welding process didn't cause distortion in the part, which it would, a welded area has to be considered as a
cast area. So any forging process that has gone into the parent metal is ultimately undone. Shot peening after welding would be a good idea, but can't replicate the effects of proper forging.
To be honest, the 3rd to 4th gear ratio spread isn't really the issue with these cars. It's the 1st and 2nd ratios, and for racing probably the 5th gear too.
Quote from: PTP on April 07, 2016, 04:10:47 PM
To be honest, the 3rd to 4th gear ratio spread isn't really the issue with these cars. It's the 1st and 2nd ratios, and for racing probably the 5th gear too.
Hi Here in Sweden we race some with the 116 gearbox..
The problem we got is that the 5th gear is to long..
so I do use to take the
3 gear from the early Alfetta 1:35 and the
4th gear from Bacci Romano 1:15
the stock 4th in 5th 0:94 or the Alfetta 4th 1:02
Weldin is not any problem ..
/ Hans