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MG Midget and Sprite Technical - weird wiper fault

When I rebuilt the car I "Blueprinted" the wiper motor, which now works better than factory. Only problem is that now they won't park when switched off, the motor runs so well that it runs over the park cam and then just keeps going. Also this wiper motor is pushing really small blades so I reckon this will only ever occur on a midget. Solution, fit a 2.2 Ohm (5 Watt)resistor in series with the park circuit (contact 5 on the wiper switch), which drops the voltage to approx 8-9 and slows the motor to a speed at which it stops on the park cam. Cheers Rod




R W Bowers


"
When I rebuilt the car I "Blueprinted" the wiper motor, which now works better than factory. Only problem is that now they won't park when switched off"
William Revit

Rod, what did your blueprinting consist of?
Dave O'Neill 2

Na... grounding issue,

I had the same, never.could find the ground problem so I just cut.the park wire and turn it off manually
Prop and the Blackhole Midget

Sorry Prop but it can't be an earthing issue or the motor would run very slowly.



The parking circuit switches lives to function correctly.



Odd fault you have though, never heard of that one.
SR Smith 1

Gday Dave
Blueprinting is probably a bit strong, just a dismantle, clean and regreasing with attention to end float on the motor and gear shafts. Cable and wheelboxes lubed as well. Commutator and brushes were perfect. My motor has a separate earth strap to the body so no problems there.
cheers
Rod
R W Bowers

I refurbished my dashboard a few years ago. When I put everything back, the wipers would not self park and never have since. I checked the connections to the switch etc all to no avail. I'd been keen to hear if you fix yours
Nigel Axtell

Rod

Are you sure you're not missing an earth on the park switch? The switch is a changeover that provides 12v to keep the motor running until it gets to the park position and then switches the park line to earth to stop the motor dead.

Bob
R.A Davis

Hi Bob
Please read the previous posts, my motor is double earthed. If the switch connects the 12 volt park line to earth this would be a dead short. The switch opens when it runs on to the park cam on the main drive gear,which disconnects the 12 volt connection to the motor via the main wiper switch. With sufficient friction from the blades the motor slows and stops "on the cam" - it is "parked". My motor runs so well that it goes past this park position if not slowed by the 2ohm resistor now fitted in the line.
The wipers are now sorted.
Nigell check your connections again or the park switch on the wiper motor may actually be faulty.
cheers
Rod


R W Bowers

Rod

I had read your previous posts and I was aware that you’d got it working, the reason for my post is that I thought you may have got it working by using a work around and not addressing the underlying issue.

My explanation of the operation of the park switch could have been a bit clearer so this time I've included a diagram.

From this you can see that when the switch is turned off, but the wipers are not in the park position, 12v from the green wire is feed via the park switch then via the Brown/Lt Green wire to the on/off switch and then via the Red/Lt Green to the motor. This keeps the motor going until it reaches the park position at which time the park switch moves across (to the position shown in the diagram). This now puts an earth via the park switch, then via the Brown/Lt Green wire to the on/off switch and then via the Red/Lt Green to the motor.

The motor now has an earth on both sides of it, this effectively puts a short across the motor bringing it to a dead stop.

I'm suggesting you’re missing the earth on the park switch, or that there’s an issue with the contact within the switch.

I understand you believe your motor is “now works better than factory” but do you not think Mr Lucas might have taken this possibility into account when he was building them. I understand you’re only running small wipers but this would suggest that running the motor without any wipers fitted it would never self park, this clearly isn't the case.

Finally, I know Midget’s only have single speed wipers and the diagram shows a two speed setup but it was the best diagram I could find at short notice. I does show however how easy it is the upgrade a single speed motor to two speed, all you need is a two speed motor, a two speed switch and an extra wire from the switch to motor.

Bob



R.A Davis

Thanks Bob
I changed the switch. I have the last model 1500 with two speed wipers as standard, my wiring is different, the switch interrupts the 12v feed to the main switch no earthing involved.
Maybe I'm reading the wiring diagrams incorrectly, all I know for sure is that they now park OK.

Thanks for all your input
Cheers
Rod
R W Bowers

Hi all FWIW, this is quite interesting
http://vitessesteve.co.uk/LucasStuff/LucasStuff2

Cheers Rod
R W Bowers

Hi Bob
I owe you an apology, you are absolutely correct as per your excellent diagram, the motor is shorted to earth as you said. In my haste I failed to check this connection on the wiper switch/connector. However that said, all my previous posts (aka confused ramblings) describe the situation correctly, the motor, even shorted to earth, doesn't stop quickly enough to rest the switch "on the cam" i.e. at park. My resistor solution does work. I believe the answer is entirely due to using a heavy duty motor in a light weight application, there isn't enough friction to slow it down to park.
Cheers Rod


R W Bowers

Rod

At the end of the day all that really matters is that it works. The reason for my familiarity with these motors and how they operate is that I've built an intermittent wiper and wash/wipe unit that involved a lot of work with an identical system on my B.

I did the 2 speed conversation on my 1500 Midget bought new in 1977, it was a bit easier getting the parts then as my late father was a vehicle electrician.

Bob
R.A Davis

This thread was discussed between 27/06/2015 and 04/07/2015

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