Wiper Parking

Converting my LHD 1963 E Type to RHD was straightforward except for the windscreen wiper operation. Due to lack of time I initially cheated by fitting RHD wiper arms and disconnecting the single wire from the limit switch, which meant that I could manually switch the motor off when the blades reached the bottom of the screen. After receiving conflicting advice about the right way to do it I finally took the time to figure out how the whole thing works and once I’d done that the conversion was simple.
So in case it will help others in the same position here is how I did mine.

Although this is about converting LHD-RHD the opposite applies

First remove the wiper arms….

You really don’t want to ram them into the scuttle accidentally – and you will need to fit RHD arms anyway as they are cranked differently.

Next convert the Limit Switch….

Drop the central instrument panel and remove the central air duct. On the OTS you may find it easier to partially remove the mirror rod and bottom bracket to make access easier.

The limit switch is now visible.  Its job is to ‘open’ only when the mechanism is at the very end of its travel with the wipers parked.

If you switch on the wiper it’s obvious how it works – there is a springy brass ‘finger’ wiping against the quadrant-shaped brass plate fixed to the wiper rack. 

There is a long slot in the finger part of the mechanism and it is held at one end of that slot by a screw.  Simply slacken that screw and move the finger to the other end of its slot.

Positioned for LHD

 

 

Positioned for RHD

 

My limit switch then worked correctly without any more tinkering, but there is a knurled knob on the bulkhead to adjust the opening position if necessary. The ‘finger’ must run off the edge of the brass plate when the wipers are in the parked position otherwise they will never stop, but don’t make the mistake I did and expect it to run off during normal operation. Screwing the balljoint on the end of the control rod (visible above) in/out also affects the opening position.

Finally convert the motor to turn the other way….

Unfortunately, because of the design, I couldn’t figure out any way to change the motor rotation via the external connectors so you will have to remove the motor to swap over the wires where they are soldered to the brushes.

The workshop manual covers removal / replacement and the only problem I had was with the bracket that holds the connector block to the bulkhead. It was a real pain to replace – perhaps that’s why it is so often missing?

When wired correctly, a RHD motor will be turning the spindle anti-clockwise (viewed from the spindle side) under normal running.

And that’s it.


If interested in WHY this works though, read on:

If you take the control rod /arm off the wiper motor you will find that it actually has an eccentric cam (i.e. the hole for the spindle is offset from the centre of rotation) built-in, with ‘stops’ that give it 2 possible positions.

When the motor turns clockwise the cam is forced against its’ stop in one direction, when it turns anti-clockwise it is forced against the other stop.  Because it is eccentric, the effect is that the rod has a shorter overall length when the motor turns one way than the other.

The reason becomes clear when you realise that switching the wipers to OFF actually puts the motor into REVERSE. It is not until the limit switch gets to the end of its travel that the motor stops.

So this is the way it all works:

Wiper Blades are normally parked tight against the windscreen rubber surround so as to be out of the way.

Switch the wiper ON (slow or fast) and the motor turns one way, forcing the cam to adopt a position which leaves the control rod at its ‘short’ length.

When the blades complete a sweep and come back down to the bottom of the screen this ‘short’ length means they stop well before the surround (to avoid hitting it) and continue the next sweep. The ‘finger’ of the limit switch never leaves the brass surface.

Now move the wiper switch to OFF and the blades will actually reverse their direction of sweep, back up to the vertical position. The cam is thrown to its other stop, effectively lengthening the rod.

The extra length means that when the blades sweep towards the bottom of the screen this time they keep going until they touch the rubber surround. At this point the ‘finger’ runs off the edge of the brass plate and the motor stops.

It is an ingenious bit of engineering so I wonder why Jaguar didn’t bother explaining it in the Workshop Manual?

Please note: All technical information on this site is given in good faith, and may vary from one vehicle to another. Please seek professional advice if you are unsure of whether it applies to, or is suitable for, your vehicle or not.

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