Technical Rear Axle Questions

[Italino]

I needed to redo the brakes on m 500F, necessitating new backing plates to match the new drums, which are much more husky than the original rusted ones. I noticed that the stub axles differ. On the left side, the stub was drilled near the tip, and bolted into the flexible joint using a bowl shaped, 4-flanged washer that is keyed into opposing grooves in the teeth of the stub, and held into the flexible joint by a castle nut with a cotter pin through the hole. It had very little torque applied when last tightened. Is that correct? The torque spec of .36 ft/lbs seems like almost nothing. 1/3 of a ft/lb?

On the right side, the stub was not drilled for pinning; there is a key groove in the end of the axle that looks like it wants a wedge shaped key, but none was present. A conical stover nut that was tightened quite dramatically to hold the axle stub into the flexible joint. Should that be .36 ft/lbs, as well?

Thanks!

 

[fiat500]

I needed to redo the brakes on m 500F, necessitating new backing plates to match the new drums, which are much more husky than the original rusted ones. I noticed that the stub axles differ. On the left side, the stub was drilled near the tip, and bolted into the flexible joint using a bowl shaped, 4-flanged washer that is keyed into opposing grooves in the teeth of the stub, and held into the flexible joint by a castle nut with a cotter pin through the hole. It had very little torque applied when last tightened. Is that correct? The torque spec of .36 ft/lbs seems like almost nothing. 1/3 of a ft/lb?

On the right side, the stub was not drilled for pinning; there is a key groove in the end of the axle that looks like it wants a wedge shaped key, but none was present. A conical stover nut that was tightened quite dramatically to hold the axle stub into the flexible joint. Should that be .36 ft/lbs, as well?

Thanks!

You would be best to get hold of a workshop manual. In principle, tightening the hub bearings is simple, but for me it is hard to explain.
Put simply, rather than a torque setting, the nut needs tightening until it achieves a specified turning resistance of the hub. Initially, that can mean very tight. If it is ever loosened, and on retightening you can't achieve that specification, there is a special spacer that needs to be replaced.
I think that a later design did use a different method to secure the nut.

 

[the hobbler]

You would be best to get hold of a workshop manual. In principle, tightening the hub bearings is simple, but for me it is hard to explain.
Put simply, rather than a torque setting, the nut needs tightening until it achieves a specified turning resistance of the hub. Initially, that can mean very tight. If it is ever loosened, and on retightening you can't achieve that specification, there is a special spacer that needs to be replaced.
I think that a later design did use a different method to secure the nut.

At sometime in your car's life the right hand stub axle has been replaced with the more modern version. The older 500s used a castellated nut and split pin but the newer cars (and 126s) use a nut that has a 'soft' outer edge that is deformed into the slot in the stub axle to 'lock it'. The rear hub bearings are tightened (with a new deformable spacer between the bearings) to a 'rotational torque' of:-- 1lb at 4.3 inches (500 grams at 11cm). The proceedure is not easy to describe, but if you would like to contact me direct ( [email protected] ) I will try and describe how to do it.

 

[Goldnrust]

Just to add for clarity, the torque figure mentioned, either the .36f/lb or the 1lb at 4.3" (which are the same figure quoted in different ways) is how much force is needed to rotate the stub axle itself when you have tightened the nut enough to preload the bearings. It is not hot tight the nut needs to be.

As mentioned above you will need a new crushable spacer, and the nut will need to be tightened with considerable force (likely over 100f/lbs) to crush the spacer. As you tighten the nut down and compress the spacer then you keep testing the torque needed to turn the hub, when it reaches .36f/lb then you have tightened the nut enough.

 

[the hobbler]

Just to add for clarity, the torque figure mentioned, either the .36f/lb or the 1lb at 4.3" (which are the same figure quoted in different ways) is how much force is needed to rotate the stub axle itself when you have tightened the nut enough to preload the bearings. It is not hot tight the nut needs to be.

As mentioned above you will need a new crushable spacer, and the nut will need to be tightened with considerable force (likely over 100f/lbs) to crush the spacer. As you tighten the nut down and compress the spacer then you keep testing the torque needed to turn the hub, when it reaches .36f/lb then you have tightened the nut enough.

Just for interest, I have been assured by a "very experienced Abarth specialist" in the UK that if you are just replacing the rubber/alloy drive coupling you do NOT need toreplace the crushable spacer. There are 2 typesof crushable spacers on the market---a 'goldish'coloured version which is just about impossible to crush, and a 'silvery' coloured spacer which CAN be crushed,and looks very like the origina lFiat part--it is lighter in both looks and weight than the 'goldie' coloured spacer.

 

[Italino]

Just to add for clarity, the torque figure mentioned, either the .36f/lb or the 1lb at 4.3" (which are the same figure quoted in different ways) is how much force is needed to rotate the stub axle itself when you have tightened the nut enough to preload the bearings. It is not hot tight the nut needs to be.

As mentioned above you will need a new crushable spacer, and the nut will need to be tightened with considerable force (likely over 100f/lbs) to crush the spacer. As you tighten the nut down and compress the spacer then you keep testing the torque needed to turn the hub, when it reaches .36f/lb then you have tightened the nut enough.

Thanks!

 

[Italino]

Thanks!

Thank you! That axle does hav a deformed nut on it. Was that done with a punch?

 

[Toshi 975]

It’s what they call a staked nut where you lock the nut in position by punching the nut fringe into a key way in the shaft.

 

[Italino]

It’s what they call a staked nut where you lock the nut in position by punching the nut fringe into a key way in the shaft.

Thanks! Now I understand the reason for the keyway. Does it need replacing if you remove it?

 

[the hobbler]

Thanks! Now I understand the reason for the keyway. Does it need replacing if you remove it?

Yes. when you remove the nut, the 'deformed' part will break away, so you do need to replace the nut with a new one. I made myself a 'deforming' tool out of an old, large chisel, with the end rounded off---if you leave it as a chisel, you run the risk of splitting the 'deformation' lip.