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8 & 10 cyl Bristol cars Type 407 onwards - restoration, repair, maintenance etc

408 wipers: do they self park?

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Old 21-03-21, 10:13 PM
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Default 408 wipers: do they self park?

I am trying to get mine working. Are they supposed to self park when I switch them off, please?

David
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Old 22-03-21, 09:02 AM
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Yes, they should, given the original motor and switch. The system was dreamt up by a brilliantly contorted mind and relies on a certain amount of slack in the armature that drives the crank which in turn operates the wiper cables. When the armature rotates one way the crank operates the wipers in their normal arc, when rotated in reverse the wipers reverse and due to the deliberate slack in the armature operate in a different arc which then allows the cut off switch in the motor to come into play and stop the motor in the wiper park position.

The switch is a gloriously complicated thing in order to achieve off/park - slow - fast operation as it has to reverse the polarity of the feed to the motor between slow and park/off.

A further point which I think Iím right in saying is that power is fed from the motor to the switch and back again rather than to the switch and then to the motor.

This was all a bit to much for Bristols and you wonít find a Bristol wiring diagram that makes anything clear, but the good news is that these wiper mechanisms were used on other cars and the RR club of Australia have copies of the extremely detailed and well written RR technical manuals on their website. I have a faint recollection that I derived a wiring diagram a few years ago and Iíll endeavour to find it later today.

Note that the switch does NOT cut off power to the motor when it is returned to the park/off position, that is achieved by the cut off switch in the motor itself.

Probably not much help but I trust this may get you on the right track

Roger
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Old 22-03-21, 10:58 AM
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Thank you, Roger. I am beginning to think my problem lies in the switch. More playing around/analysis is needed!

David
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Old 22-03-21, 12:09 PM
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David

Herewith a .pdf of a drawing I put together some years ago showing the diagrammatic wiring and the electrical elements which I hope will be of some help. I recommend that you run off several copies to work out what connects to what and with what polarity in each of the three different switch positions.

Please bear in mind that this is a diagrammatic drawing, I still have the idea somewhere in the back of my mind that the power is taken from the ignition switch to the motor and thence back to the wiper switch.

I have to confess that I am unable to comprehend why yours don't park as that is the default position but my guess is that somebody else has muddled the wiring in an attempt to get something to work in some fashion.

I speak incidentally as an optimist who, in my youth, helped to completely rewire a friends Lotus Elite Mk1 using a large roll of wire that had been "liberated" from the installation dept. Which resulted in the complete car being entirely wired in the same colour - pity the next owner! That's when I first learnt about Lucas's remarkable design for these self parking wipers.

Good luck - Roger
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File Type: pdf Bristol wiper wiring.pdf (60.8 KB, 24 views)
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Old 22-03-21, 12:21 PM
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Thank you so much for that, Roger. I see why you suggest printing several copies! Not the simplest looking system at first glance.

Much appreciated.

David
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Old 22-03-21, 11:21 PM
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There is a wiring diagram for the Lucas 6W wiper motor used by the 408 here - Tom Yang's Ferrari Restoration

And the wiper switch is shared with some Silver Shadows. Though, the Shadows have electrical rather than vacuum washers.
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Old 22-03-21, 11:32 PM
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P.S. if it is not parking, there is a knurled adjuster screw which allows you to move the parking earth to the right place. I found it easier to understand if I took off the case, but there is lots of grease in there.
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