DR3A wiper motor, sweep angle query

[thefarmer]

i'm losing the plot...

I have a DR3a wiper motor, with a 120 degree gear....however, when you take apart the motor and look at the gear, the pivot on it has been moved further out from centre. This is achieving a suitable sweep for the wipers. (see photo below...pivot is almost on the edge of gear)
I decided to then try a 'normal' 130 degree, and the sweep is way to small....useless in fact. A 'normal' 120 is about the same.

So...what actually effects the change in sweep? The position of the pivot? The size of gear? The length of the connecting rod/link?

The main reason for asking is that my 'altered' 120 is pretty much shagged...and therefore needs replacing. However, nothing which is supposedly 'normal' is actually any good...which then leads me to also query as to why this gear was altered.... as every other mini out there doesn't seem to have issues with 'normal' gears.

Any ideas, please let me know.

Cheers,
Ben

'altered'

IMAG0352.jpg

'normal'

IMAG0353.jpg

[dklawson]

I have no answer except to suggest that maybe a previous owner changed the wheelboxes for something non-standard due to availability. That may have dictated the customized wiper gear.

I think it is a brilliant fix by someone who was patient and creative.

[ianh1968]

Exactly as Doug says...

What will change the sweep is:

1) How far out the "big-end" stub is from the centre-line of the
driven gear in the motor.

2) The number of teeth on the wheel boxes

The number of teeth on the large gear will only affect the speed
of operation as it only transforms the drive from the worm gear
through 90 degrees to the main gear.

The length of the conrod will not change things either, just as it
won't in an engine either. In an engine, a longer rod will just put
the piston further away from the crank centre-line and nothing else.

Early type wheel boxes had 22 teeth and 6 sided nuts.
(53/64 0.828125" A/F or about 21mm (Measured, not official))

Late type wheel boxes have 32 teeth and 8 sided nuts.
(3/4" A/F or 19mm)

I have not checked the threads of the nuts, but the late type
are reputed to be metric...

Have a look at your nuts....


If you have 8 siders on there, you have a mixture of Early and
Late components in your setup which may confuse matters.

After much very helpful information posted by "InimiaD" I was
able to produce a summary of the main differences in rack
assemblies which is at the bottom of this thread:
viewtopic.php?f=3&t=8846

Ian

[thefarmer]

Thanks Ian...
I'll check the wheelboxes...as I find it odd that there was a need to manually move the stub out any further from the centre., why not just change the gear(unless something else was throwing it out)?

I'm going to be renewing the whole rack, wheelboxes etc anyway, so I'll have a good starting point.

Thx
Ben

[ianh1968]

... Just had a re-check on the MkI type wheel box nuts...

A 13/16" spanner goes on and this would seem far more
likely than the previously mentioned 53/64" size.

Ian