Technical Apply rebuild kit first and reverse gear

[Jay74]

Hi Classic Fiat 500 community,

There are many part shops that offer such a rebuild kit, containing a main shaft, the first and the reverse gear for around €200.
These are indeed the gears that I have issues with (both make noise and shoot out of gear).

I am looking for the level of complexity to do this rebuild, before I start working on it.
I managed to get the gearbox out, and see the damaged cogs, but am a little scared to continue.

Is it just a matter of taking the tail end off, replace the main shaft, replace the two gears and put the whole thing back up? (cleaning a bit, new gasket, new oil)
Of is it more delicate, requires fine tuning and calibration?

In other words, can it be done with only little experience?

Thanks for any other suggestions that I need to think of!

 

[Toshi 975]

The thing to avoid is disturbing the diff setting or if you have dismantled it I must be assembled exactly as it was or be reset.

 

[Jay74]

Thanks! I did not plan on touching that end of the box, and actually hope that I don't need to be there. Hence the question if I can do it 'from the tail'.

 

[Goldnrust]

Without knowing your level of experience it’s really hard to say over the internet whether it will be ok or not.

It is a relatively involved task, just getting the gearbox out is something that may daunt an inexperienced mechanic.

But, crucially, I would say that the 500 is very easy to work on, due to the small physical dimensions and comparative simplicity of the design. If you have a suitable work area, take your time and make notes and take pictures to help you along the way, there’s no reason anyone with basic mechanical experience couldn’t take the gearbox out and rebuild it.

It is not hard to remove the differential without upsetting the bearing settings, you just need to know to be careful not to turn the adjusters as you disassemble. Marking their position before you extract the diff is a good idea

 

[Jay74]

Yes, I am inexperienced, but getting handier with each replacement. Already did fuel pump and carburettor (both quite easy), and managed to get the gearbox down (a bit more complex indeed).
Next step is the rebuild kit, but trying to get an idea of complexity before I move on.

 

[Goldnrust]

Yes, I am inexperienced, but getting handier with each replacement.

With that attitude, you’ll be fine. Best way to learn is to get stuck in and have a go.

I would consider myself ‘experienced’ now, but far from an expert, very much a hobbyist not a professional. I figure if there’s not a point half way through a bigger job where you don’t worry that you’ve ‘bitten off more than you can chew’ then you’re not doing it right! Haha.

 

[Jay74]

That's a line I should hang on the wall - so right.
I feel I'm just before the point of no return now. Only took out the gearbox and could put it back in 'easily'. This was just bolts and nuts.
By messing around with something I have no clue of (gear settings and stuff), I may do harm. But you're right - when I first opened the engine bay I had no clue at all of what I was looking at.

 

[Goldnrust]

If the gearbox is out, the hard part is done!

The only real 'setting' in the 500 gearbox is the preload on the differential bearings, which also is used to adjust the mesh between the pinion and differential crown wheel. The bearing races are held in position by a thick metal ring which thread into the bearing housing and turning these rings is what makes the adjustment.

When you remove the rubber boots from the axles, you will find a thin metal lock washer, with tabs that locate in the teeth of the adjustment ring. Remove this, and then mark (paint pen / nail varnish) the position of the adjustment ring to the bearing housing. As long as you don't try to move the adjustment ring there's no reason it should come out of adjustment. When you remove the 4 bolts that hold the bearing housing to the gearbox case, then you can carefully slide/pry the bearing housing out from the case, and then remove the bolts holding the bell housing on and separate the front half of the gearbox.

Have you got a Haines manual or similar, that can guide you through the process of how to remove the gear set?

Hopefully these couple of pictures makes it more clear how the bearing housings come out.

 

[Toshi 975]

I went in at the deep end having never tackled the Fiat gearbox before. I got fed up with tripping over the seven 126 gearboxes I had here. I knew some had problems so with the Haynes manual to guide me I stripped them all down at the same time then initially rebuilt three good gearboxes then with a few new bits another one later.