Technical Gearboxes and drive shaft and clutches and.. compatibility?

[Steve366]

Hi People, I have about 5 or 6 gearboxes and see a wide range of different splines, driveshaft sizes, bell-housings. Our current setup had been these massive fat driveshafts on what might appear to be an older gearbox and bell-housing(chunky rather than finer splines on the clutch and input shaft, 2 bolt starter mount). Is there a compatabilty guide anywhere or does it matter as long as you have the right matching .. splines for example? Thanks

 

[the hobbler]

Hi People, I have about 5 or 6 gearboxes and see a wide range of different splines, driveshaft sizes, bell-housings. Our current setup had been these massive fat driveshafts on what might appear to be an older gearbox and bell-housing(chunky rather than finer splines on the clutch and input shaft, 2 bolt starter mount). Is there a compatabilty guide anywhere or does it matter as long as you have the right matching .. splines for example? Thanks

The early 500s used a 2-bolt mounting for the starter---this was a weak point and there is a bracket on the market which helps support the starter. Later 500s went to a 3-bolt mounting--stronger and not so susceptible to breaking off! TECHNICALLY, when you needed to replace the bell-housing, Fiat said that you needed to replace the gearbox housing as well---I wonder how many people did? When the 126 came out, the location of the starter changed (to the side of the bell-housing). Early 500s used thin drive-shafts (16mm I think) and on the very early 500s, only a 3-bolt coupling. This soon changed to a 4-bolt coupling. Eventually, (definately 500Fs and later) they went over to 25mm (sometimes called 24mm) drive-shafts. I am not sure whether you can fit the 25mm shafts into early gearboxes). All the 126 models used the 25mm drive-shafts. When fitting a 126 gearbox into a 500, the drive-shafts have to be changed (to 500 shafts)---the 126 shafts are too long---not a difficult job. The bell housing from the 500 has also to be transfered over to the 126 gearbox and the specific 126 starter, dust-shield and "3rd-bolt" obtained. Early 500s did have chunkier spigot-shaft (aka, first-motion shaft) splines. I am not sure of the exact timing of them going over to the finer-spline spigot shafts. I would be only too happy if some of the more 'historical minded' Forum members would advise us of the actual dates/models for these change-over of specification

 

[Bigvtwin996]

problem using 25mm drive shafts on early cars is the rear wishbones are narrower where the outer coupling goes and they won't fit...
People open up the wishbones (with a big hammer) to get them in or change to later FLR wishbones (so it can be a big job)
Internals from Later F on wards boxes will not fit early pre 65 cases...
I am always interested in purchasing any 2 bolt gearboxes and starters and 15mm shafts as they do tend to let go with some style when you increase the hp above 16-18.
Clutches etc cannot be used from later cars on early cars nor can flywheels....
as the owners ofNewer 500s like to point out from the F onwards Fiat got things a lot better...

 

[Steve366]

problem using 25mm drive shafts on early cars is the rear wishbones are narrower where the outer coupling goes and they won't fit...
People open up the wishbones (with a big hammer) to get them in or change to later FLR wishbones (so it can be a big job)
Internals from Later F on wards boxes will not fit early pre 65 cases...
I am always interested in purchasing any 2 bolt gearboxes and starters and 15mm shafts as they do tend to let go with some style when you increase the hp above 16-18.
Clutches etc cannot be used from later cars on early cars nor can flywheels....
as the owners ofNewer 500s like to point out from the F onwards Fiat got things a lot better...

OK thanks for that. Spoilt my plans somewhat but better to know ahead of time.
What about cutting and joining the two different input shaft types? Older spline to clutch side and newer to the gearbox. The support/bearing surface in the middle is appears the same size. Is there something else that would cause issues?

 

[Bigvtwin996]

I doubt cutting a clutch shaft welding it and tring to balance it etc would be very cost effective...
we did a sheared shaft on a cenent mixed....
put everything in a lathe to boire a center pin hole to ensure everything was lined up....
even welded it in the lathe, and it was still a tiny fraction out...
I can't remember all the issues.... but I am sure Sean (Dexter the 1962 Fiat 500) covered it all when he spent ages trying to do something with a later box in his D
It may also be to do with flywheels...

 

[Steve366]

problem using 25mm drive shafts on early cars is the rear wishbones are narrower where the outer coupling goes and they won't fit...
People open up the wishbones (with a big hammer) to get them in or change to later FLR wishbones (so it can be a big job)
Internals from Later F on wards boxes will not fit early pre 65 cases...
I am always interested in purchasing any 2 bolt gearboxes and starters and 15mm shafts as they do tend to let go with some style when you increase the hp above 16-18.
Clutches etc cannot be used from later cars on early cars nor can flywheels....
as the owners ofNewer 500s like to point out from the F onwards Fiat got things a lot better...

Well so we did this anyway, bored the big shaft, press(hammer) fitted the very interference shafts, used a hot/cold method, welded and annealed. So far so good. Done about 30-40km with no evidence of issues. I do actually have a lot of spares (like 3 x 2 bolt bell-housings) but they are in NZ.. feel free to arrange a trip out