Technical Gearbox best option?

[Pouch]

Rebuilding 1965 fiat 500.
650. Engine now rebuilt, it came with original? 500 gearbox.
Options:
Service gearbox seals etc & refit
Change to 650 syncro box,

What are the best options for a good syncro 126 box, if i buy 2nd hand I’ll have no idea what I have.
Any reputable options

Cheers

 

[Toshi 975]

Some owners prefer the original gearbox for the authentic driving experience and once mastered you pretty much forget you are driving with a non syncro box. The 126 box will have a higher final gear ratio.

 

[Pouch]

Some owners prefer the original gearbox for the authentic driving experience and once mastered you pretty much forget you are driving with a non syncro box. The 126 box will have a higher final gear ratio.

Higher final ratio equates to faster acceleration but lower top speed, is that right?

 

[Bleeding Knuckles]

Hi Pouch, In reality it's the other way around. With a standard 500 box you would have a 5.125 final ratio (8/41 gears) which would in theory give you some 47.2 mph @ 4k rpm (with a 145 profile tyre) With a standard 126 syncro box you get a 4.875 final ratio (8/39 gears) which would in theory give you some 49.6 mph @ 4k rpm (145 profile tyre) with a Fiat 126 BIS diff you would get a 4.333 final ratio (9/39 gears) and get some 55.8 mph - in theory!!!
All dependant on the selected tyre (my programme only gives 145 as the nearest) fitted. Do note that your little engine will be screaming away to achieve any rapidity. My modified engine and gearbox (9/39) will give approx 60 mph @ 4k rpm. There are other (expensive) options like 5 speed and 6 speed boxes it all depends on the depth of your pocket!!!!
Ian.

 

[Pouch]

Hi Pouch, In reality it's the other way around. With a standard 500 box you would have a 5.125 final ratio (8/41 gears) which would in theory give you some 47.2 mph @ 4k rpm (with a 145 profile tyre) With a standard 126 syncro box you get a 4.875 final ratio (8/39 gears) which would in theory give you some 49.6 mph @ 4k rpm (145 profile tyre) with a Fiat 126 BIS diff you would get a 4.333 final ratio (9/39 gears) and get some 55.8 mph - in theory!!!
All dependant on the selected tyre (my programme only gives 145 as the nearest) fitted. Do note that your little engine will be screaming away to achieve any rapidity. My modified engine and gearbox (9/39) will give approx 60 mph @ 4k rpm. There are other (expensive) options like 5 speed and 6 speed boxes it all depends on the depth of your pocket!!!!
Ian.

I remeber hitting 100kph without any problem with the car before restoration. I guess I need to have a look and see what I have in my gearbox. I assumed it was a 500gbox with 650 belhousing, but it could have been changed.
Maybe I service current box & install and then look at options when all is up and running.
Otherwise I could end up down a rabbit hole

 

[the hobbler]

I remeber hitting 100kph without any problem with the car before restoration. I guess I need to have a look and see what I have in my gearbox. I assumed it was a 500gbox with 650 belhousing, but it could have been changed.
Maybe I service current box & install and then look at options when all is up and running.
Otherwise I could end up down a rabbit hole

The original 'dog-box' Fiat 500 gearbox is the stronger gearbox---the only reason that I have a '126'gearbox in my car (with a well enhanced 126 652cc engine) is that it came with it! If I had a choice, I would choose to have a 500 'box with a 126 bell-housing fitted to it. Once you have mastered "double-de-clutching" (which you only really need to do on down-changes) it becomes 2nd nature. My first 2 'proper' cars were 500s and I got so used to 'd-d c' gear changing that I find myself 'just doing it' on my every-day car---a diesel Skoda Fabia. My standard 126 gearbox with '165 x 55 x 13' tyres (with a rolling circumference of 160.76mm) gives me 85mph at 6,000rpm ( and yes, that has been achieved on a couple of occassions!)----14.1666666667 miles per hour per 1,000rpm

 

[Pouch]

The original 'dog-box' Fiat 500 gearbox is the stronger gearbox---the only reason that I have a '126'gearbox in my car (with a well enhanced 126 652cc engine) is that it came with it! If I had a choice, I would choose to have a 500 'box with a 126 bell-housing fitted to it. Once you have mastered "double-de-clutching" (which you only really need to do on down-changes) it becomes 2nd nature. My first 2 'proper' cars were 500s and I got so used to 'd-d c' gear changing that I find myself 'just doing it' on my every-day car---a diesel Skoda Fabia. My standard 126 gearbox with '165 x 55 x 13' tyres (with a rolling circumference of 160.76mm) gives me 85mph at 6,000rpm ( and yes, that has been achieved on a couple of occassions!)----14.1666666667 miles per hour per 1,000rpm

Happy with double de clutch gear changes, I have an older Alfa Sprint.
500 gearbox it is then.
Thanks for the info

 

[lazylobster]

I have the sync gearbox. Reason? I drive my car, a lot. So could not be bothered with double clutch action. Works fine, never had an issue with.

 

[barryfiatman]

My 500 was 1967 I fitted a new 650 engine and gearbox after a terrible journey from B`ham to Plymouth with three of us.
Then the other reason was I used it for commuting, I had to join the A34 at 50mph or get rear-ended.
The engine was tuned to my best ability, the gearbox was a secondhand one from a car that I had driven a lot.
In use my tuned 500 could wheel-spin and 50 mph could be achieved instantly, with a top speed of over 85mph.
the fiddly part was fitting the 500 driveshafts to the 126 gearbox and of coarse the wiring to the starter motor.
in all a worthwhile mod, I hope you enjoy yours as much

 

[the hobbler]

My 500 was 1967 I fitted a new 650 engine and gearbox after a terrible journey from B`ham to Plymouth with three of us.
Then the other reason was I used it for commuting, I had to join the A34 at 50mph or get rear-ended.
The engine was tuned to my best ability, the gearbox was a secondhand one from a car that I had driven a lot.
In use my tuned 500 could wheel-spin and 50 mph could be achieved instantly, with a top speed of over 85mph.
the fiddly part was fitting the 500 driveshafts to the 126 gearbox and of coarse the wiring to the starter motor.
in all a worthwhile mod, I hope you enjoy yours as much

A 500, a Giardiniera AND (unless I am mistaken) a NSU---quite a collection. When I was at Radbourne Racing, our 'parts van' was the van version of the Giardy, with a 652cc Nardi conversion. It made for a fairly rapid little van!

 

[StMarks]

The original 'dog-box' Fiat 500 gearbox is the stronger gearbox---the only reason that I have a '126'gearbox in my car (with a well enhanced 126 652cc engine) is that it came with it! If I had a choice, I would choose to have a 500 'box with a 126 bell-housing fitted to it. Once you have mastered "double-de-clutching" (which you only really need to do on down-changes) it becomes 2nd nature. My first 2 'proper' cars were 500s and I got so used to 'd-d c' gear changing that I find myself 'just doing it' on my every-day car---a diesel Skoda Fabia. My standard 126 gearbox with '165 x 55 x 13' tyres (with a rolling circumference of 160.76mm) gives me 85mph at 6,000rpm ( and yes, that has been achieved on a couple of occassions!)----14.1666666667 miles per hour per 1,000rpm

Hi there Mr Hobbler,
As you appear conversant with these gearbox conversions I wonder if you could please advise on a related situation.:
My sister has purchased a 1970 500.
As part of the renovation & improvements we have started stripping it down, including removing the engine & gearbox (as well as everything else) in preparation for rustproofing, undersealing & respray.
After reading extensively on this forum, we recently also invested in a nicely prepared 650 engine. Now that the two engines are "side by side" I can see that the starter motor location is currently central, but must be re-located to the side on the block casting of the 650 engines.
Must I presume this will necessitate me either sourcing a bell housing for the existing gearbox, or a complete gearbox.?
Will I need to consider anything else please?
Will the three bolt starter motor still be the right size??
Will the starter motor pull cable still reach the new location???
Etc, etc, etc,,,,?????

There may be a well contributed thread that covers the above information, however if there is I have not been able to locate it. Should that be the case, a link would be great (and may save you typing "the same old")..

 

[fiat500]

You will need either a 126 gearbox or just the bellhousing so that you can fit the starter motor, which will be the right one if it has three holes and came with the 650 engine. Either way you're in for a bit of dismantling and rebuilding. If adapting the 500 gearbox, the bellhousing from the 126 will fit. If using the 126 box as is, you wll need to replace the driveshafts with shorter, late 500 shafts.

In my experience you will need a 126 starter cable, and a modified or 126 heater transfer tube. The shield above the exhaust will no longer fit without some bending or chopping, but better to get one from a 126 or Fiat 500R.

There are probably more etceteras, and I'm sure that @the hobbler and @Toshi 975 will arrive here soon.

 

[the hobbler]

You will need either a 126 gearbox or just the bellhousing so that you can fit the starter motor, which will be the right one if it has holes and came with the 650 engine. Either way you're in for a bit of dismantling and rebuilding. If adapting the 500 gearbox, the bellhousing from the 126 will fit. If using the 126 box as is, you wll need to replace the driveshafts with shorter, late 500 shafts.

In my experience you will need a 126 starter cable, and a modified or 126 heater transfer tube. The shield above the exhaist will no longer fit without some bending or chopping, but better to get one from a 126 or Fiat 500R.

There are probably more etceteras, and I'm sure that @the hobbler and @Toshi 975 will arrive here soon.

As Peter has pointed out, you will either need to change the bell-housing on your '500' box and fit a '126' bell-housing, or fit a '126' gearbox and change the drive-shafts for 25mm (sometimes called 24mm) 500 shafts---the '126' drive-shafts are too long. This is not a difficult job, just a shade tedious (and easier with a 2nd pair of hands). 2nd hand '126' bell-housings are available through 'e-bay'. Whichever option you decide on, you will need to fit a '126' "wire-pull" starter. the 3rd special starter retaining bolt, the starter shield and the starter-brace---all are available. As Peter also pointed out,you may need to go to a'126' starter pull-wire. but I would suggest that you try and see if the original 500'scble will reach before buying the '126' starter pull-wire. Just as a matter of interest, the reason that Fiat moved the starter to the side of the bell-housing was that by moving it away from the top of the engine,they were able to gain 4 inches of extra space in the rear of the '126'.
If the decision was mine to make, I would go the 'bell-housing' route as the 500's gearbox is the stronger box, and learning how to double-de-clutch (which you really only need to do on DOWN changes) is not difficult to master. In "my yoof" I commuted from South London (West Wickham) to the Chelsea area every day in a 500, and found the d-d-c gear changing to be not a chore. As I have mentioned before, I got so used to it that I STILL find my self doing d-d-c down-changes on my 'modern' car---a Diesel Skoda Fabia!
If you would like to contact me direct ( [email protected] ) I will help you with a possible bell-housing supplier, and the other parts that you will need for the starter change. Just as a matter of interest, where did you get your '650'engine from?

 

[MalcolmfromMoffat]

I ended up using a 500R starter cable to fit a 126 gearbox along with the R heater tube. The tube required a bit of heat and hammer to clear the suspension mount, a divot that took a bit of enthusiasm to do. The crappy plastic guide that clips in the tube to locate/guide the cable lasted about two weeks of daily starts before it disintegrated, it’s since been replaced with a brass version which is worth tracking down. The driveshaft swap is pretty easy, there’s a really good pictorial guide that just now I can’t find the link to but again worth tracking down. There are starters on eBay atm which don’t require an exchange item, £200 mind. I think a driveshaft kit is another £100.

 

[Kalijo]

Whilst on the question which gearbox to fit has anyone on the forum fitted a 500F clutch to a 500D? The main benefits are a larger friction plate and a diaphragm spring as apposed to a 6 spring cover. I’m thinking of going down this route and any advice would be much appreciated.

 

[StMarks]

Thank you all for sharing the benefit of your experience.
The car is not mine, but rather my Sister's. I will therefore show her this thread, so that she can decide which way to proceed.
The 500 engine that came with the car seems pretty sound, and I feel a little guilty now because I am the sole reason that she purchased the 650 engine for it, (Everything I had read pointed at that being about the best mod' to make the little car a more viable mode of transport in today's traffic).
I had, somewhat naively, assumed that it was a straightforward question of swapping one lump for another.!

 

[StMarks]

As Peter has pointed out, you will either need to change the bell-housing on your '500' box and fit a '126' bell-housing, or fit a '126' gearbox and change the drive-shafts for 25mm (sometimes called 24mm) 500 shafts---the '126' drive-shafts are too long. This is not a difficult job, just a shade tedious (and easier with a 2nd pair of hands). 2nd hand '126' bell-housings are available through 'e-bay'. Whichever option you decide on, you will need to fit a '126' "wire-pull" starter. the 3rd special starter retaining bolt, the starter shield and the starter-brace---all are available. As Peter also pointed out,you may need to go to a'126' starter pull-wire. but I would suggest that you try and see if the original 500'scble will reach before buying the '126' starter pull-wire. Just as a matter of interest, the reason that Fiat moved the starter to the side of the bell-housing was that by moving it away from the top of the engine,they were able to gain 4 inches of extra space in the rear of the '126'.
If the decision was mine to make, I would go the 'bell-housing' route as the 500's gearbox is the stronger box, and learning how to double-de-clutch (which you really only need to do on DOWN changes) is not difficult to master. In "my yoof" I commuted from South London (West Wickham) to the Chelsea area every day in a 500, and found the d-d-c gear changing to be not a chore. As I have mentioned before, I got so used to it that I STILL find my self doing d-d-c down-changes on my 'modern' car---a Diesel Skoda Fabia!
If you would like to contact me direct ( [email protected] ) I will help you with a possible bell-housing supplier, and the other parts that you will need for the starter change. Just as a matter of interest, where did you get your '650'engine from?

I have been looking at the casings again, and thinking (Always dangerous? ).........

The engine casting appears to have been constructed with the original "hump" at the top that was there to accommodate the starter motor mountings of the original central position.
Has anyone ever considered (or tried & failed even) to cut out the blanked off section, and drilled & tapped the two missing mounts to position the starter where it is located on the 500cc engine block ?

Maybe I'm missing something obvious, but wouldn't that potentially work ?? ( Yes, I realise I'm probably looking like a total muppet even asking.! )

 

[StMarks]

. Just as a matter of interest, where did you get your '650'engine from?

Hi Mr Hobbler, I'm very sorry I've only just spotted that you asked the above in your previous reply. Please excuse my ignorance at not responding by return.

The engine was purchased from a 500 owner in Holmfirth, who had apparently purchased it some time ago with a view to upgrading but had never got around to fitting it.