Isostatic Feedback

[Duk]

Because I haven't driven my 75 for so long, I'd like to get some feedback from you guys who have the isostatic equipped transaxles.
After seeing the photos that Clayton105 posted on AlfaBB http://www.alfabb.com/bb/forums/milano-75-1987-1989/197633-shift-rod-bolt-stuck.html and it had be wondering about modifying the isostatic mechanism to make changes to its geometry and so the front to rear and left to right throws.

So who wants to give their thoughts on the amount of throw in the 2 directions?

And before anyone asks why I'm not just modifying the gearlever itself, there should be some real benefits to working the isostatic mechanism, part of which will include some overhauling and making the mechanism more durable. The other advantage is that you can change how much forward/backward movement independently of the left too right movement.

Incidentally, I was tempted to follow in MD's footsteps and go for a shifter set up similar too what he has created in 3 of his Alfa (not all set ups were the same, though), but ultimately I figured it a bit too dramatic for a road car. Plus there is still heaps to do in plenty of other areas.

[MD]

Hey Duskter. Forget this crap. Move into the 21st century and start working on how we are going to convert the tranny into a SEQUENCIAL shifter and you wont need to worry about the gate at all (except to keep the dog in 

[Duk]

I'll leave the mechanical wizardry of sequential conversions to you mate  .

Or once the V8 car of the future season starts, just do a bit of 'slight of hand' at one of the the banana bender rounds and pocket yourself an Albins TA and shoe horn that big b@stard under the back seat of your GTV  .

[MD]

Hahaa you slack arse. ...and you call yourself a machinist too..

Er...ok then a couple of tips.
Don't go too nuts just lengthening the selector below the fulcrum as it will foul the transmission. (Incidentally, Alfa has already made this part longer than say a typical Alfetta. The entire parts list is "reviewed" and upgraded).

To correctly lengthen the lower section, you have to RAISE the fulcrum mount assy in the cabin. Then lengthen the rod by the amount you have raised the mount. This way, the selector below the fulcrum can move freely as before without fouling the shaft.

At the same time, the tunnel needs stiffening. I know of some modifications made by welding in a tunnel cut out from a wreck and double layering this part of the selector mount. The darn original section is too flimsy to form a solid mount feel like a Stick-in-the-box selector which is what is required. As it is, it feels more like a wooden spoon stirring a Caesar Salad..but I digress.

BTW Don't fall for the trap of replacing roll pins with bolts. What is required in these applications is a high interference fit (machinists know all about interference fit  ) ) and not a compression fit from a bolt. No bolt is ever going to be inserted into the same opening as a good quality high tensile roll pin.

With this basic modification, the best you are going to achieve is a shorter throw but the gate will remain the same. To redesign everything, er.. how many spare hours did you say you had again..?

As for sequential, I have decided to take a short cut and go chain drive by installing one from a Kawasaki two wheeler.

[AikenDrum105]

As for sequential, I have decided to take a short cut and go chain drive by installing one from a Kawasaki two wheeler.

Only a short step further to this .....   Heh heh heh..   (Honda S600)

[MD]

I want one..

[Sheldon McIntosh]

Cool story about an S600...  http://blog.hemmings.com/index.php/2012/04/23/cars-ive-loved-and-hated-michael-lamms-unauthorized-auto-biography-chapter-11-honda-s600/

I also want one.  9500rpm in 1964!

[AikenDrum105]

Heh heh -   only car he liked less than the S600 ->   http://blog.hemmings.com/index.php/2012/05/14/cars-ive-loved-and-hated-michael-lamms-unauthorized-auto-biography-chapter-14-alfa-romeo-montreal/

[Paul Gulliver]

only car he liked less than the S600 an Alfa Romeo  Montreal 

I hope Gary Pearce is away today or not in the room.

[LukeC]

I have just introduced myself in the apppropriate place this morning.

Nice to see a link to my post re: iso from the Alfa BB here...

BTW Don't fall for the trap of replacing roll pins with bolts. What is required in these applications is a high interference fit (machinists know all about interference fit  ) and not a compression fit from a bolt. No bolt is ever going to be inserted into the same opening as a good quality high tensile roll pin.

I have had a roll pin drop out on me, and the vehicle had only 80,000 km on it. Some of these vehicles now have the fit between the ID ond OD where the roll pins pretty loose now. Placing a high tensile bolt there with a nylock nut is very reliable, and with a split in the female part ensures that the male parts are clamped firmly. I have increased the side to side throw, and is the lever is adjustable for lateral placement. Works a treat!

BTW: I am a qualified Fitter and Machinist, Motor Mechanic and Mechanical Engineer.

[MD]

Luke C

I have had a roll pin drop out on me, and the vehicle had only 80,000 km on it.

How on earth could you reach that immediate conclusion?
Was the pin original?
Was it replaced by a non metric almost close fit by someone during a service that you are not aware of?
So why wasn't the connection redrilled with a new roll pin of a larger size?

The fact of the matter is that no bolt can make as intimate a close fit to the internal sides of the coupling as a roll pin does. They are expressly designed for such purposes. Generally a bolt thread is of a smaller diameter than the shoulder and so there is a potential slop right there. If you use a socket head bolt, this may avoid that issue but nevertheless, the fit will be so tight that you will not be able to push the bolt through the opening because its diameter cannot be compressed like a roll pin.

I am not saying a bolt will not work because it will. It is simply the inferior choice.

[Duk]

A fitted bolt would do a better job than a roll pin, but the holes would have to be reamed to size and then a bolt machined down to the correct size to give a transition fit.

Another alternative is to find a bolt that has no thread inside the rod, only on the outside (best of luck) and put Loktite Bearing Retaining compound on the shank. This will fill up any remaining gap between the hole(s) and the bolt. Pain in the arse to disassemble, but the fit would be 100%

[scott.venables]

A fitted bolt would do a better job than a roll pin, but the holes would have to be reamed to size and then a bolt machined down to the correct size to give a transition fit.

Another alternative is to find a bolt that has no thread inside the rod, only on the outside (best of luck) and put Loktite Bearing Retaining compound on the shank. This will fill up any remaining gap between the hole(s) and the bolt. Pain in the arse to disassemble, but the fit would be 100%

Or you could just fit a roll pin. Minimal slop and they shouldn't fall out.  Not disputing what happened to Luke, but it seems to be the exception to the rule.  The ultimate solution to the problem is to ream the hole with an appropriate tapered reamer and fit a tapered pin.  Problem solved.  Zero slop and won't fall out.

Scott

[LukeC]

The 75 that this happened on was one I owned back in 1995: too long ago for me to remember the full details.

Both the GTV and the 75 had some wear in the mating parts (male and female) where the two roll pins are: Of course you can reclaim these parts with effort and expense.... The best way I felt without access these days to all the equipment required to elimate the movement was in this way.

I have done this on several cars before when twirling spanners full time and never had any issues. To me it is a simple, inexpensive and reliable solution if there is play between these parts.

[Duk]

Hey Duskter. Forget this crap. Move into the 21st century and start working on how we are going to convert the tranny into a SEQUENCIAL shifter and you wont need to worry about the gate at all (except to keep the dog in 

For you reading pleasure, Emmmm Deeee: http://www.alfabb.com/bb/forums/transmissions/203872-transaxle-project.html
It will be interesting to see how far this progresses.