Technical Possible clutch/transmission issue on a 1970 Fiat 500F

[MotoLojo]

Greetings all! This weekend, I was out for a drive in my 1970 Fiat 500F when all of a sudden, I heard a rotating "clunking" noise start below the car just behind and below the shifter. I was at a stop light, and when I took off, it got in gear and the noise became louder, and then "clunked" out of gear. It will no longer go into gear. (Engine runs fine). Managed to get it to the side of the road and got a free tow back to my garage. Before I pull the engine, any thoughts or similar experiences out there? My feeling that it is clutch/pressure plate related, but not really sure. Hence...where do I start? Thanks in advance for your advice and counsel!

 

[Toshi 975]

Is it possible that one of the drive shaft couplings has given up. When that happens you loose all drive giving the impression that the car is not in gear. To test you need to start the car, engage a gear then have somebody look under the back to see if a drive shaft is turning free.

 

[MotoLojo]

Thank you @Toshi 975 I will take a look this week after I get it up on stands. Appreciate the response! Next I'll have to figure out how to replace them.

 

[the hobbler]

Thank you @Toshi 975 I will take a look this week after I get it up on stands. Appreciate the response! Next I'll have to figure out how to replace them.

The drive-shaft couplings can be replaced without having to take either the engine or the gearbox out. I have suffered this problem whilst trying to pull away from a set of trafffic lights, and I was the front car in the queue! In my case it wasn't the actual coupling that had broken, but the sliding part of the coupling on the drive-shaft. The cheaper 'sliders' are not properly heat-treated (if at all!) in the area of the splines, so the splines rip out of the 'slider'. Strangely, the splines on the drive-shaft are not usually affected. When inspecting a 'slider', the area of the splines should have a bluish colour, which indicates that they HAVE been heat treated.
Put the car upon stands and as Toshi has suggested, put the car into gear and engage the clutch---if a 'slider' has lost it's splines, you will see (and hear) it. Replaciong the 'sliders' (change BOTH) is simply a matter of undoing 4 x 8mm bolts (13mm head and spanner), lifting the drive-shaft away from the alloy/rubber coupling, removing the little end-stop' circlip on the end of the drive-shaft and removing the 'slider'. When fitting the new 'slider', make sure that the splines on the drive-shaft are well lubricated (but NOT with 'Copper-slip'!). All the best---keep us informed of progress please.

 

[MotoLojo]

The drive-shaft couplings can be replaced without having to take either the engine or the gearbox out. I have suffered this problem whilst trying to pull away from a set of trafffic lights, and I was the front car in the queue! In my case it wasn't the actual coupling that had broken, but the sliding part of the coupling on the drive-shaft. The cheaper 'sliders' are not properly heat-treated (if at all!) in the area of the splines, so the splines rip out of the 'slider'. Strangely, the splines on the drive-shaft are not usually affected. When inspecting a 'slider', the area of the splines should have a bluish colour, which indicates that they HAVE been heat treated.
Put the car upon stands and as Toshi has suggested, put the car into gear and engage the clutch---if a 'slider' has lost it's splines, you will see (and hear) it. Replaciong the 'sliders' (change BOTH) is simply a matter of undoing 4 x 8mm bolts (13mm head and spanner), lifting the drive-shaft away from the alloy/rubber coupling, removing the little end-stop' circlip on the end of the drive-shaft and removing the 'slider'. When fitting the new 'slider', make sure that the splines on the drive-shaft are well lubricated (but NOT with 'Copper-slip'!). All the best---keep us informed of progress please.

Thank you @thehobbler! Is this the slider you mean?

 

[the hobbler]

NO

Thank you @thehobbler! Is this the slider you mean?View attachment 449696

!

Thank you @thehobbler! Is this the slider you mean?View attachment 449696

NO!---if you have taken that end apart be very careful---that is the bearing carrier for the diff. The part that I am talking about is at the other (OUTER) end of the drive shaft and is attached to the alloy/rubber coupling that is on the stub-axle.

 

[MotoLojo]

Got it. Thank you!

 

[MotoLojo]

@the hobbler I think I’ve identified the problem…

 

[MotoLojo]

So just two more questions...does anyone know the mm Size of the nut over the slider? I removed the cotter pin, but the nut is larger than I have sockets for. Also, the bolts had sheared off as the coupler failed, and I think I may be missing two pieces that attach to the drive shaft. Please see the attached. Thanks in advance as any help would be greatly appreciated!

 

[fiat500]

So just two more questions...does anyone know the mm Size of the nut over the slider? I removed the cotter pin, but the nut is larger than I have sockets for. Also, the bolts had sheared off as the coupler failed, and I think I may be missing two pieces that attach to the drive shaft. Please see the attached. Thanks in advance as any help would be greatly appreciated!

I have a massive, 32mm socket that I think I bought many moons ago for this job. If anyours roughly measures that, I would go for it. I think there are two types of nut..later ones may be different. You ned confirmation from @the hobbler or @Toshi 975 ....they will know for certain.

 

[Toshi 975]

I have a massive, 32mm socket that I think I bought many moons ago for this job. If anyours roughly measures that, I would go for it. I think there are two types of nut..later ones may be different. You ned confirmation from @the hobbler or @Toshi 975 ....they will know for certain.

Well remembered Peter, also fits the big crankshaft nut so quite useful

 

[MotoLojo]

Thank you @fiat500 and @Toshi 975. It's off to the hardware store to see if they have one. Appreciate everyone's guidance!

 

[the hobbler]

I have a massive, 32mm socket that I think I bought many moons ago for this job. If anyours roughly measures that, I would go for it. I think there are two types of nut..later ones may be different. You ned confirmation from @the hobbler or @Toshi 975 ....they will know for certain.

There is NO big nut on the 'slider'---just 4 x 13mm (head and spanner size) bolts. The big nut holds the alloy/rubber coupling onto the stub axle. If the coupling is OK. leave it alone, because replacing it a bit of a faff---that big nut has to be done up to a specific (rotional) torque so that the hub bearings ar e 'pre-loaded'. Clean away all that surplus grease and then inspect the coupling. I think that you will find that the nut size (for the COUPLING) is the same, irrespective of retention/locking system (split-pin or edge deformation). I have just checked in y 'parts dept' and the nut that holds the alloy/rubber coupling onto the stub axle requires a 30mm socket (1-3/16in---1.1811in)---you might find it easier to obtain the 'imperial' size on your side of "the big pond". Take the part that slides up and down ON THE DRIVESHAFT (the slider), and inspect the internal splines---these are what normally strip off and give you the symptoms that you are suffering.

 

[MotoLojo]

There is NO big nut on the 'slider'---just 4 x 13mm (head and spanner size) bolts. The big nut holds the alloy/rubber coupling onto the stub axle. If the coupling is OK. leave it alone, because replacing it a bit of a faff---that big nut has to be done up to a specific (rotional) torque so that the hub bearings ar e 'pre-loaded'. Clean away all that surplus grease and then inspect the coupling. I think that you will find that the nut size (for the COUPLING) is the same, irrespective of retention/locking system (split-pin or edge deformation). I have just checked in y 'parts dept' and the nut that holds the alloy/rubber coupling onto the stub axle requires a 30mm socket (1-3/16in---1.1811in)---you might find it easier to obtain the 'imperial' size on your side of "the big pond". Take the part that slides up and down ON THE DRIVESHAFT (the slider), and inspect the internal splines---these are what normally strip off and give you the symptoms that you are suffering.

You are correct...my bad. The big nut is on the aluminum coupling, and it is destroyed. The holes for the 4x bolts are pretty much ruined, so I'll be replacing the drive shaft coupling joints, bolts, and rear hub nut in question. Additionally, both drive shaft springs and dust covers. As you had suggested, doing both sides to avoid this repeating itself anytime soon. The splines on the shaft (at least on the left side all appear to be in reasonably good shape, which is good! Thanks again for your advice!

 

[fiat500]

There is NO big nut on the 'slider'---just 4 x 13mm (head and spanner size) bolts. The big nut holds the alloy/rubber coupling onto the stub axle. If the coupling is OK. leave it alone, because replacing it a bit of a faff---that big nut has to be done up to a specific (rotional) torque so that the hub bearings ar e 'pre-loaded'. Clean away all that surplus grease and then inspect the coupling. I think that you will find that the nut size (for the COUPLING) is the same, irrespective of retention/locking system (split-pin or edge deformation). I have just checked in y 'parts dept' and the nut that holds the alloy/rubber coupling onto the stub axle requires a 30mm socket (1-3/16in---1.1811in)---you might find it easier to obtain the 'imperial' size on your side of "the big pond". Take the part that slides up and down ON THE DRIVESHAFT (the slider), and inspect the internal splines---these are what normally strip off and give you the symptoms that you are suffering.

See this ten year old thread about tightening/removing the nut, with a debate about the sizing: https://www.fiatforum.com/threads/tightening-rear-hub-bearings.359424/
I had forgotten that I actually bought a second, air-tool quality, 32mm socket, with deep sides and six flats for a more secure grip. @Chrismunn said his was 27mm, so @MotoLojo, you can now take your pick of sizes. . I will reimburse you if the 32 doesn't fit, and I am sure that @the hobbler will do the same if his recommendation fails.
I have two x 32mm sockets, both of them have fitted properly on the nuts on my car.

 

[MotoLojo]

See this ten year old thread about tightening/removing the nut, with a debate about the sizing: https://www.fiatforum.com/threads/tightening-rear-hub-bearings.359424/
I had forgotten that I actually bought a second, air-tool quality, 32mm socket, with deep sides and six flats for a more secure grip. @Chrismunn said his was 27mm, so @MotoLojo, you can now take your pick of sizes. . I will reimburse you if the 32 doesn't fit, and I am sure that @the hobbler will do the same if his recommendation fails.
I have two x 32mm sockets, both of them have fitted properly on the nuts on my car.

View attachment 449790

lol! Thanks! Just bought a 32mm. I did measure the nut with my caliper so your money is safe.. Thanks!

 

[fiat500]

You are correct...my bad. The big nut is on the aluminum coupling, and it is destroyed. The holes for the 4x bolts are pretty much ruined, so I'll be replacing the drive shaft coupling joints, bolts, and rear hub nut in question. Additionally, both drive shaft springs and dust covers. As you had suggested, doing both sides to avoid this repeating itself anytime soon. The splines on the shaft (at least on the left side all appear to be in reasonably good shape, which is good! Thanks again for your advice!

@the hobbler hints at the trauma involved in correctly setting up the preload on the rear hub bearing. I think that the thread to which I have previously referred gives some guidance on that process.
Tom has said more recently that he has been told by a reliable but un-credited source, that as long as the bearings have not been replaced you simply need to retighten the nut.....how tight? I'm not easily convinced about that. I would suggest that when you are as deeply involved in this as you are already it would be worth giving bearing replacement some consideration.

 

[the hobbler]

@the hobbler hints at the trauma involved in correctly setting up the preload on the rear hub bearing. I think that the thread to which I have previously referred gives some guidance on that process.
Tom has said more recently that he has been told by a reliable but un-credited source, that as long as the bearings have not been replaced you simply need to retighten the nut.....how tight? I'm not easily convinced about that. I would suggest that when you are as deeply involved in this as you are already it would be worth giving bearing replacement some consideration.

The source was VERY reliable Peter, I assure you. Even if you don't replace the crushable spacer, you do the nut up to the same rotational torque as if you HAD replaced the spacer. I have been supplied with 2 variations of the spacer over time---one is of a 'gold' colour and is just about UN-crushable; the other, of a lighter build, is a silvery colour, and look just like the parts I used to fit when Fiat supplied them---they are the ones to use,

 

[MotoLojo]

The source was VERY reliable Peter, I assure you. Even if you don't replace the crushable spacer, you do the nut up to the same rotational torque as if you HAD replaced the spacer. I have been supplied with 2 variations of the spacer over time---one is of a 'gold' colour and is just about UN-crushable; the other, of a lighter build, is a silvery colour, and look just like the parts I used to fit when Fiat supplied them---they are the ones to use,

Gentlemen...thank you both for your learned guidance. I'll check the manual for the appropriate torque on that nut. Of course if I can't find it, I'll be back on the forum pestering you both. lol! Thanks again!

 

[fiat500]

The source was VERY reliable Peter, I assure you. Even if you don't replace the crushable spacer, you do the nut up to the same rotational torque as if you HAD replaced the spacer. I have been supplied with 2 variations of the spacer over time---one is of a 'gold' colour and is just about UN-crushable; the other, of a lighter build, is a silvery colour, and look just like the parts I used to fit when Fiat supplied them---they are the ones to use,

I think we have evidence that no source is always completely reliable. Although it's a reasonable explanation; because in circumstances where the spacer has not been overstressed, I wouldn't expect it to need to be replaced. But the ball-ache, in addition to getting the spacer to collapse, is getting that rotational resistance correctly setup, with some confidence and without special equipment. After being dismantled I suspect that it's quite likely that an additional nip up of the nut could be required in order to accommodate wear and bedding of the bearing components; so i's not just a simple matter of putting everything back together and the job's a "good-un".