Isostatic Gear Change- How good is it really?

Started by Fylnn, May 20, 2012, 08:30:37 PM

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Fylnn

I might have the option of fitting a rebuilt 75 Twin Spark gearbox to my GTV6.  So from various posts I can see that I either have to panel beat the floor to take the Isostatic gear linkage or change over the selector in the box to the old one.

So question is, not having experienced the isostatic gear change in a car, how good is it?  Did it suddenly make Alfa transaxles like a rifle bolt or was it but a slight improvement that would not make a huge difference? 

Duk

Quote from: Fylnn on May 20, 2012, 08:30:37 PMSo question is, not having experienced the isostatic gear change in a car, how good is it?  Did it suddenly make Alfa transaxles like a rifle bolt or was it but a slight improvement that would not make a huge difference? 

It is better but its far from being stick in the box good. And with typical crap boots and plastic bits, they don't seam that durable. I think the cable shift mechanism in my MR2 is better.
Check out what MD has done for modifying the shift rod set up (not his in car shifter set up that he shows in his track cars). I would do what he has done before changing to the Isostatic mechanism, especially if you have to bash the floor to make it fit.
I did read a rumor that the Isostatic gear lever had its pivot point set higher up the shaft and that would be better, but you'd have to do side by side comparisons for that. Besides, it can be done to the earlier original gear lever anyway.

Darryl

I'm not a huge fan of the isostatic mechanism. If they aren't worn they are good, but they wear (develop slop), and a worn one is worse than the simpler linkage. imho - ymmv etc...

Fylnn

Sounds I might stick with the standard one then. 

aggie57

To get the best out of them you do need to make sure all the components are in good order. Just like the synchro's in the gearbox... :)

Yes, the gear lever itself is a different length. Can't recall if longer or shorter but as Duk says the effect is a different ratio. You do need to change that as well to get the best out if it.
Alister
14 Alfa's since 1977. 
Currently 1973 GTV 2000, 2020 911 C2S MT, 2021 Mercedes GLE350, 2023 Polestar 2 LRDM
Gone......far too many to list

MD

Flynn,

1 The TS shifter is longer below the ball joint. This shortens the selection throw.
2 You cannot use an Alfetta shifter on a TS box without opening it up and installing the Alfetta selector shaft into it.
3 Using a shifter with a longer lower section may foul the propshaft so the entire shifter housing may need raising to maintain original clearance. Some trial and error needed here.
4 Regrettably even with the above changes, the tunnel area that the shifter base is mounted on flexes so that the changes never   quite feel solid and robust. This can be minimised by stiffening in the area.

5 Finally if you do install the TS box, your speedo will not work as the Veglia GTV6 speedo head requires a different signal than the Jaeger sender provides. With some effort this can be overcome but is a topic in itself.
Transaxle Alfas Haul More Arse.

Current Fleet
Alfetta GTV6 3.0
Alfetta GTV Twin Spark supercharged racer
75 1.8L supercharged racer

Past Fleet
Alfa GT 3.2V6
Alfetta GTV 2.0
Giulia Super 2.0
Berlina 2.0

alfa duk

 Use the iso shift if it is a road car and non iso for track/race. Iso is a smoother shift- if going down this path get the rebuild kit-monkey shift from performatech? i think. The non iso is more direct with less moving parts so less to go wrong but not as nice feel to shift. For those that have iso boxes in gtv6 that want to change to non iso, make sure you locate the correct shift rod first as they are hard to come by.
85 gtv6 dead, cant let go
84 gtv6 24 valve VRA spec
84 gtv6 andalusia
80 gtv group s

Sam

MD, why can't you use an Alfetta shifter on a TS box?

If I remember correctly, the Alfetta shift mechanism and selector shaft have splines while the ISO doesn't, it just slips on to the selector shaft and is held in place with a pin.

So why can't you drill out the Alfetta's splines so its smooth and slides on the selector shaft like the ISO?
Then all you need to do is drill a hole to line up the one on the shaft (or drill a new one through the selector and the shaft) 


MD

Some good lateral thinking Sam. I believe you are correct but the real question is, why would you want to ?

The complete TS shifter has a number of improvements over the Alfetta unit.

The selector throw is shorter.
The selection gate is better.
The shifter itself is better proportioned so that the shaft doesn't flex as much as.

There are two fundamental design flaws with the transaxle shifter :-

1 The selctor crank is too long. This makes for large gates.
2 To a lesser extent, the lever ratio below the selector fulcrum is too short. This makes for a long throw.

That's why I modify the shit out of them beyond recognition because  I change the actual geometry of how the system works. This of course is not for general consumption and most people just want to tinker around the edges which  does produce improvements but never the quantum improvments that one imagines it will.

In my opinion, Alfa tried to fix these issues in the TS selector and so my response to the question of this topic is that the isostatic selector is about as good a factory an answer as you are going to get without customising anything.
Transaxle Alfas Haul More Arse.

Current Fleet
Alfetta GTV6 3.0
Alfetta GTV Twin Spark supercharged racer
75 1.8L supercharged racer

Past Fleet
Alfa GT 3.2V6
Alfetta GTV 2.0
Giulia Super 2.0
Berlina 2.0

GTVeloce

I managed to link my Alfetta shifter to the TS box via a different method again. I kept the original selector shaft and chopped the end off the TS selector rod and welded it onto the alfetta selector rod. So it has;
Alfetta shifter
Alfetta connection at shifter end
TS connection at linkage end
Iso linkages

To be honest, this isn't a fantastic solution. It works, but I also had to grind away some of the plastic housing of the shifter to allow sufficient movement of the lever. My iso is in good condition and the gear changes are quick and smooth but the lever has a long throw and it was a fair bit of stuffing around to achieve it. I had hoped to increase the length of the shifter below the ball joint or even use a TS shifter but there just isn't room as it starts to impede on the torsion bar cross member unless, as MD said, you would need to extensively modify the design to do so.

What I would like to experiment with (and I believe the Mauceri race car has this employed) is to mount the shifter from top down rather than bottom up - i.e. from inside the cabin. This way you might be able to have the extended throw under the ball joint without impinging on anything.

aggie57

On both early and late Alfetta's I've always cut an inch or so off the gear lever and bent it over closer to the driver.  Plus made sure the little bush on the bottom of the lever is like new.  The OEM part is plastic - best to replace with bronze for longer life and ensure the rubber boot is intact and the joint clean and well greased.

Amazing how much these simple things improve both systems.
Alister
14 Alfa's since 1977. 
Currently 1973 GTV 2000, 2020 911 C2S MT, 2021 Mercedes GLE350, 2023 Polestar 2 LRDM
Gone......far too many to list

Sam


  • On my Red Alfetta I put a TS box and I also used the Iso links. 
  • On my Gold Alfetta I still have the original linkage & Box but with a shorter and slightly bent gear lever (same as per Aggie57)
  • my son's 3ltr 75 has the standard ISO with a cut and shortened gear leaver .


To be quite honest I like the original (non ISO) with a shorter leaver and slight bend towards the back.
It just feels less sloppy that the ISO ones.

On the other hand my son likes the ISO - he thinks its more acurate - so I guess it's down to individual preference.

Now sorry if I railroad the conversation ..... but I have a question that is still along the lines of these discussions
On the gearboxes, there are little metal balls that are under pressure with a spring.
I don't know what they are called but they are used to lock the gears and stop them from jumping out.
On the outside of the Gearbox, there is a bolt that you can turn to increase or reduce the springs compression on the balls.
If you reduce the compression – can I assume this would help to make the shifting less notchy and more smoother?  (I realise there is a limit to how much you can decrease the pressure before the box starts jumping out of gear)
Does anyone know what I 'm talking about here???

Sam

My question about the notchy gear shift really should have been a new post so please ignore it, Ill start a new one