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

408 wiper problems

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Old 04-11-22, 03:24 PM
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Default 408 wiper problems

The windscreen wipers on our 408 don't work. Power is getting to the motor but I noticed the motor (Lucas 6 wire I think) was getting warm while I was checking voltages on the wires. This suggests to me that something has seized. If I try to move one of the wiper arms the other moves slightly so it seems that the spindles are probably OK. How should I proceed? Can the motor and gearbox be detached and removed from the wiper mechanism? Unfortunately I don't have a workshop manual that covers any of this.

Hope someone can help. Thanks
Mark
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Old 04-11-22, 03:55 PM
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Never done it and IIRC the motor is in a pretty inaccessible spot up under the wing. I think the motor is a Lucas DR3. It should be removable (if you can reach). There's a video here https://youtu.be/8REday6sH3Y
of how to disconnect it from the drive cable except this is on a Wolseley and is easy to get at. Good luck.

David
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Old 04-11-22, 04:30 PM
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According to the parts book the wiper motor is a later Lucas 75425A but the important first stage and shown in the link David has posted is that if you remove the cover plate you can separate the motor from the drive cable.
This should allow you to check if the cable and the wheel boxes are operating freely. The parts book lists the wheel box as a Lucas 72729A if you use a later but interchangeable motor you need to retain the drive wheel and link bar from the original as this regulates the degree of sweep of the blades.
Geoff.
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Old 04-11-22, 04:37 PM
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Thanks for the info, that gives me a starting point.

Mark
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Old 04-11-22, 05:08 PM
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It's a Lucas 6W on my 408 - same as on some Rolls Royces and Bentleys.

I found this page

Tom Yang's Ferrari Restoration

and in particular the wiring diagram here

http://www.tomyang.net/cars/wiperschematic.jpg

helpful when doing mine.
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Old 04-11-22, 11:21 PM
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Mark,
Sadly the workshop manual for the 408 (up to chassis 7200) has very little information about the windscreen wipers. See attached a photo of the section from the manual. Interesting that it says there is a thermostatic cut-out built into the motor. It reads like it was barely up to the job!

Kevin
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Old 10-11-22, 06:48 PM
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This is essentially a snippet taken from a series of articles I've recently submitted to the BOC Bulletin.

The 408, 409 and 410s (and perhaps a number of the earlier cars - but my knowledge doesnít extend that far) - all used the same wiper motor and switch, which was also sometimes known as the 6 Watt motor. This utilises a separate field coil and a relatively simple 3 pole 3 position rotary switch to achieve the off/park, slow and fast functions through some fairly devious wiring logic.

I attach a diagram, Fig 1, which shows how the voltages are applied through this wiring to achieve the various functions.

It should be noted 1) the motor is reversed to achieve the park/off position. 2) "fast" is achieved (somewhat counterintuitively, but take my word for it) by switching a resistor into the field coil circuit. 3) the diagram shows the rotary switch as seen from the back. 4) power is taken to the motor and thence from the motor to the switch and then back again.

I trust this will help you perceive what voltages should appear at the various connectors at park, slow and fast.

That the motor gets warm and nothing happens suggests that there is an open circuit in either the armature circuits or the field circuits but not both. If the voltages at the various connectors are correct (remember to probe both sides of the connector, also double check that you're actually getting a connection to earth when one is called for) Iíd suggest the most likely point of failure is the brushes.

If you have to take the motor out do take great care to label all the connections to the motor as you do so, the colour coding on the motor wiring used to match, e.g. red/green from the harness connected to red on the motor, but at the motor itself this will all long since have faded into oblivion.

(By the way the 411s used a permanent magnet motor and the wiring and switching logic is completely different, even though the same switch is used)
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Old 11-11-22, 06:28 PM
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Mark,

I might be a little late in posting a reply to your query of November 4th, if you havenít progressed here are my thoughts

I removed the wiper motor on my 410 last year, which wasnít too difficult despite the restricted access, due to its location.
To remove the motor (if my memory serves me correctly), I tackled the job in the following order:-
1. Disconnect Battery
2. Remove both wiper arms.
3. Where the flexible wiper drive cable leaves the wiper motor, there is a knurled nut which attaches a rigid shaped tube to the motor. Slacken off this nut but do not remove it. Slackening it at this stage makes life easier later.
4. The electric wires leaving the motor are braided, sheathed type cabling, which are connected to the carís main wire harness by bullet connectors. Probably the colours on the cotton covered cables will have faded. Tag/mark each wire each side of the bullet connectors independently. Once all wires have been tagged, disconnect them all and donít forget the earth wire.
5. Next stage is to remove the small bolts holding the motor to the frame of the car. Again, slacken off all the bolts. Once all are free/loose, undo the knurled nut.
6. Finally, holding the motor in one hand remove the bolts holding the motor to the car framework.
7. Once the motor is free, withdraw it from the car, together with the drive cable.

Hopefully, I didnít miss any stages out.

Itís not a difficult job but access is very restricted.

Once removed and on the bench, itís a simple job to carry out any repairs.

I personally would not consider trying to remove the wheel housing while the motor is in position on the car.

The wiper motor on my 410, as Geoff noted, is a Lucas 75425A.

Brian
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Old 11-11-22, 08:30 PM
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Thanks for all the additional info. I have managed to do the job and it's all working except for the parking. The problem was the shaft of the large gear was seized in its housing. I found the most difficult part of the job was getting the circlip holding the spring back on. In the end I made a tool that could hold the spring pressure back while I slid the circlip on. Any ideas why the parking doesn't work? Because of the effort involved in the repair I don't really want to take it apart again - I guess I can put up with the problem for now!

I concur with everyone's sentiment that it is a pretty horrible job.

Mark
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Old 12-11-22, 08:09 AM
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Mark,
I suspect your parking problem is an electrical issue. If thatís the case the person best to advise you, in my opinion, is Roger Morrall.
Brian
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