12 replies to this topic

[Neilson]

Does anyone know what the thread is on the outer CV joint. ie where the castle/hub nut screws on?
It's on a '94 SPI if that makes a difference?

[Ethel]

Computer says 7/8 unf.

There's only one CV so the threads must be the same.

[Neilson]

Does anyone know what the thread is on the outer CV joint. ie where the castle/hub nut screws on?
It's on a '94 SPI if that makes a difference?

Thanks

[Neilson]

Thanks

[MRA]

Actually you will find that most are M22 and have been for some time

[Dan]

True enough but I seem to remember doing a calculation on this a while back and finding that the actual difference between the two was less than the tollerance range so it doesn't really matter (unless you are chasing the thread or something). Metric is after all a Unified Fine threadform, it's just based around Metric cardinal dimensions rather than imperial.

[MRA]

7/8unf is 14 tpi.....which is about 1.8mm per pitch
M22 is either 1.5 or 2.5mm per pitch

It's not close

What did you measure Dan ?

M22 could of course be available in a 2mm pitch but then that isn't the standard

[Dan]

Sorry, missed out some important words.

I meant that judging from the fact that all CV joint nuts fit all CV joints and that as you rightly say Martin the joints now appear to be 22mm in diameter, I don't think they are being made to a standard metric thread. M22 comes in four standard pitches and none of them match the imperial very closely, certainly an imperial nut wouldn't fit them. So I imagine the stubs are being machined to a thread using the old imperial pitch on a 22mm shank. This would have to be a custom tooling obviously but my point is that since the difference in diameter is something around 8 thou, the extra depth of the thread (due to the same pitch being used on a smaller stock and thread depth being based on pitch) into the shaft will be within the tollerance of the original imperial thread and so won't cause any weakening due to a smaller cross section. Essentially, within the scope of the engineering in question, 22mm stock is within tollerance to be classed as 7/8". I'd imagine someone at Rover engineering has found that producing CV joints to 7/8" is extremely expensive in a metric world and has done the calculations to find out if the original nut and so the original thread will be up to the job on a 22mm shaft in order to save money. After all, they did start producing the nut with its original thread inside a 34mm bar for presumably the same reason.

What is odd is that the wheelbearings still seem to fit, nomatter how old the CV joint is.

[MRA]

The CV's are ground finished and metric or imperial is irrelevant at those sizes and tolerances..... apparently Mini CV joints changed over to metric in the late 70's. funny that 1 5/16" hex is cheaper than 34mm hex well it when I buy it anyway.

[Neilson]

I've sorted it now. Mine was definately a 7/8 unf thread. I bought a Die nut and it worked fine.
I measured the OD of the thread and it was 22.05mm. The top limit on M22 thread would be 22.00mm.

Edited by Neilson, 23 January 2010 - 04:55 PM.

[Ethel]

I could understand Rover changing the nut to metric dimensions. It's quite possible that Bodge-fit type service centres could get their mits on Minis for brake servicing etc and wouldn't have a large imperial socket to torque it up without chewing the nut. It would also make sense to keep the thread the same to avoid compatibility issues with older Mins.

[Dan]

I measured the OD of the thread and it was 22.05mm. The top limit on M22 thread would be 22.00mm.

That depends on the tollerance. 7/8" is 22.225mm.

[MRA]

yes 7/8" is 22.225 however as with most threads a certain amount of truncation will occur, therefore 22.05 being about 0.007" undersize would be ok

all threads require a working clearance.