Technical 1968 Fiat 500 gear box leak

[Daniel68]

Hey guys

My fiats gear box is leaking just wanted to see if anyone knows why it’s leaking from that spot, also would this be a reason for it crunching even when double clutching? Thanks

 

[the hobbler]

Hey guys

My fiats gear box is leaking just wanted to see if anyone knows why it’s leaking from that spot, also would this be a reason for it crunching even when double clutching? Thanks View attachment 423949View attachment 423950View attachment 423951

If I remember correctly, the 500 gearbox has no seal on the gear-change shaft, inside the rear-housing of the gearbox, and relies on the closeness of the shaft in the housing to prevent leakage. Looking at your pictures, it would seem that the rear housing has worn has worn to a point that it is no longer sealing. Rectifying this is a gearbox 'out' job, but once the box is out, removing the rear casing is not a difficult job. It might be possible for an engineering shop to put a bush in the housing. If the leak has been ongoing for some time, it might be that the gearbox IS low on oil, contributing to some 'crunchy' gear changes. The filler point on the gearbox is on the side of the box (your driver's side), just before the 'gearbox body/bellhousing' joint. It is a 13mm square, which is sometimes VERY tight. The easiest way to remove this filler/level plug is to us a short 1/2in drive extension THE WRONG WAY ROUND over the 'square' and then a suitable socket over the 'male' square of the drive. It can be a real 'faff' trying to fill the box through this plug, so I use a funnel attached to a piece of clear plastic tubing (so you watch the oil go into the gearbox) that will go INTO the filler hole. Make the plastic tubing long enough that you can fill the gearbox through the engine bay. As well as the 'filler' orifice, this is also the level orifice---when the oil starts coming back out of the hole, that is the correct level. The 500 gearbox uses a SAE 90 oil---as the gearbox wont be 'dry' a litre will be more than enough.
I will also admit that it is some years since I had a 500 box apart, as against a 126 box which DOES use seals on the gear-change shaft, so if the more "500 gearbox experts" wish to correct me, feel free---only too happy to have my memory refreshed!

 

[Daniel68]

Thank you I’ll have a look and see what I can do and get the mechanics opinion on it, low oil sounds like it might be the case for the crunching which can be fixed by rectifying the leak I appreciate the advice

 

[fiat500]

I think there's a narrow "O"-ring, sometimes two of them, in a groove(s) of the selector rod; there might as well not be!

 

[the hobbler]

I think there's a narrow "O"-ring, sometimes two of them, in a groove(s) of the selector rod; there might as well not be!

Since reading Peter's comment, I have dug out and looked at my (Factory) "Catalogo Parti di Ricambi", and although the workshop MANUAL does not show a selector-rod seal on the gearbox 'plans' (or the pictures of the selector rod), the 'parts' catalogue DOES show a seal--part number 4120686. The selector rod (or 'lever' in the catalogue), part number970810 shows a groove for the 'O' ring to sit in. Sadly, it does not give the 'O' ring's dimensions, but I am sure that an 'O'ring to match would not be too difficult to find.

 

[Daniel68]

If I remember correctly, the 500 gearbox has no seal on the gear-change shaft, inside the rear-housing of the gearbox, and relies on the closeness of the shaft in the housing to prevent leakage. Looking at your pictures, it would seem that the rear housing has worn has worn to a point that it is no longer sealing. Rectifying this is a gearbox 'out' job, but once the box is out, removing the rear casing is not a difficult job. It might be possible for an engineering shop to put a bush in the housing. If the leak has been ongoing for some time, it might be that the gearbox IS low on oil, contributing to some 'crunchy' gear changes. The filler point on the gearbox is on the side of the box (your driver's side), just before the 'gearbox body/bellhousing' joint. It is a 13mm square, which is sometimes VERY tight. The easiest way to remove this filler/level plug is to us a short 1/2in drive extension THE WRONG WAY ROUND over the 'square' and then a suitable socket over the 'male' square of the drive. It can be a real 'faff' trying to fill the box through this plug, so I use a funnel attached to a piece of clear plastic tubing (so you watch the oil go into the gearbox) that will go INTO the filler hole. Make the plastic tubing long enough that you can fill the gearbox through the engine bay. As well as the 'filler' orifice, this is also the level orifice---when the oil starts coming back out of the hole, that is the correct level. The 500 gearbox uses a SAE 90 oil---as the gearbox wont be 'dry' a litre will be more than enough.
I will also admit that it is some years since I had a 500 box apart, as against a 126 box which DOES use seals on the gear-change shaft, so if the more "500 gearbox experts" wish to correct me, feel free---only too happy to have my memory refreshed!

I took the fiat for a drive today the car drives fine no crunching for the first 10-15 minutes but then once warmed up and driving very difficult to get into gear pretty much crunches no matter what even in reverses not sure why it would be different from going cold to hot

 

[the hobbler]

I took the fiat for a drive today the car drives fine no crunching for the first 10-15 minutes but then once warmed up and driving very difficult to get into gear pretty much crunches no matter what even in reverses not sure why it would be different from going cold to hot

Could simply be that as the (possibly) small amount of oil left in the gearbox is heating up, getting thinner and not having as much lubrication effect in the gearbox. I would DEFININATELY check the gearbox oil level and top-up as required.

 

[Daniel68]

Could simply be that as the (possibly) small amount of oil left in the gearbox is heating up, getting thinner and not having as much lubrication effect in the gearbox. I would DEFININATELY check the gearbox oil level and top-up as required.

Took it to the mechanic today, all sorted, clutch cable was loose causing it to not engage properly and then it needed a top up of oil

 

[Toshi 975]

Took it to the mechanic today, all sorted, clutch cable was loose causing it to not engage properly and then it needed a top up of oil

That makes sense. You should have a special adjuster nut on the clutch cable backed up by a locknut. Items 7 in the picture. Without the locknut the cable will simply work loose again so worth checking if it starts to happen again.