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Discussion Starter #1
Hi
This is baffling me !
The wipers work fine - good strong action, Switch works well on slow fast and intermittent.
until it rains....
When it rains all is well for a while and then after an hour or so, the wipers get slower and weaker, and eventually stop.
Give them a waggle and they move a bit but grind to a halt again. As if the motor is still getting power, but not enough.

Next day they are back to full function again. Its happened twice now.

Im guessing that rain water might be getting into either the wiring or the motor - but would have expected that to blow the fuse, which is still OK.....

Does anyone have any ideas where to start looking please?
Has anyone else had this?

thanks

Chris
 

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The first thing to do, after checking fuses, is to check all the electrical connections to the motor and clean those up. Then every connection to the relays (and clean them up). Then make sure the relays themselves are functioning. See this photo from my car (with notes on identifying each relay, then look up the functions of each in the Workshop Manual or Parts Manual):

LRK37110_Wiper_Relays_Sm.jpg
 

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See also the topic, Windscreen Wipers (and there are others, too) on the RROC-Australia forums.
 

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Discussion Starter #4
Many thanks - I will do that at the weekend.
The odd thing is, after cleaning all the contacts, I will have to wait till it rains again to see if its fixed !
:)
 

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Most likely corrosion that has impeded current flow on the terminals causing poor flow of electrons. I would also check the brushes in the wiper motor.
You do not have to wait for rain to test
 

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Discussion Starter #6
Many thanks
just to clarify - the wipers work perfectly when the weather is dry.

So the only true test after any repair, regardless of what the repair is, will be if they work the next time it rains.

I do see the point you both make though, it logically can only be some form of poor contact reducing the power to the motor when wet.

Ill let you know what I find when I find it.

many thanks for the quick assistance to you both.
 

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There is also the possibility there is too much drag between wiper blade and windshield and eventually heating up the motor. If you know it will rain, I would clean the windshield thoroughly and I have found using a basic car wax on the glass, greatly lowers the drag factor.
 

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Discussion Starter #8
Hi Wraithman
Great minds think alike - that's how we got home last weekend. :)
I had a bottle of glass cleaner with me (we were doing a rally so always have some cleaning kit with me) and gave the windscreen a good spraying - it lowered the drag enough to get a few strokes of the wipers every 5 minutes to get us home.
BUT on the next day, when dry and the windscreen and rubber are completely dry (with most drag) they work well.

However your idea of the wiper motor overheating is also a possibility.
I will check the wires and relays this weekend and take it from there.
The car is on "season plates" (common for oldtimers in Germany) so it will be parked up for 6 months after 30th Sept - if I have not got it fixed by then, i have 6 months to do so.

many thanks
Chris
 

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I reviewed section M (I think!), and there is a paragraph indicating the wiper motor dray in lo and hi if you are into diagnostics. The diagram also has the pin descriptions showing lo and hi terminals.

Like Brian mentioned, work your way backward from wiper motor connector, to the relays and beyond ,de-oxit, and leave everything shiny with a dab of dielectric grease.
At this point you covered a suspected connector issue.
BTW, the Lucas relays will easily come apart. You will find the contact points pitted/corroded and may not be aligned as well. Again, it never hurts to check this stuff. Fully diagram the connectors with color code or your own tags and keep the cellphone handy for pics.
 

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I agree with @Wraithman except on the dielectric grease part, because it serves as an insulator. There are definite applications for it, but if you want maximum conductivity, along with the protection against corrosion that it offers, use an electrically conductive grease instead. I use Sanchem No-Ox-Id A-Special, but there are others. Here are a couple of options:

Sanchem NoOxID A-Special

Gardner-Bender Ox-Gard
 

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Discussion Starter #12
Hi
I had an hour last night so had a look at the 3 Relays Guyslp pointed out.

Slightly different on my car as they are all in a line and on sockets, not free wires connected to them - great, makes it easier to change them.
They are all Bosch metal bodied relays that are sealed
2 of them had contacts that were brown and dirty, the other shiny and bright - although the outside casing of all 3 relays are corroded and pitted - probably original.
As I had a spare matching relay, I simply swapped it with dirtiest one and cleaned the other.
The result - the wipers didn't work. .......OK we are getting somewhere as they worked before !
I swapped it back putting the new relay were the other dirty one was and cleaned the other dirty one, and they work OK .............
Looks like one of the relays was fautly.
BUT, maybe its just co-incidence and i still haven't found the "doesn't work when wet" issue.

The outside casing of all 3 relays is corroded and pitted, so I will just buy 3 new ones as they dont cost much (It was 12 euros when I bought from a Bosch service center but see the same ones on line for just 4 Euros) and lets see what happens long term.
Id rather pay a few Euros for new relays than be stuck again in the middle of a old-timer orientation rally with no wipers again.

We have one more Rally to do this season, so i it rains, that will be the true test.

many thanks for all the help - it is greatly appreciated.
Chris
 

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Appears the original Lucas relays were replaced by Bosch relays.
 

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Discussion Starter #14
thats interesting.
Someone must have replaced the whole lot then !

This is my first Rolls, Ive only had it one and half years, and so all I know is what I see.
The complete selection of relays, under the bonnet and in the fuse box are all identical and very old looking Bosch in metal boxes. Except the ones Ive already had to change that is.
(see image of the one Ive just swapped out - looks OK in this pic, but I had to use a pencil to be able to see the number as its fairly badly corroded)
As it is a Bosch is why when i needed the first one (for the head lights), I took it to a Bosch service center for a replacement.
He said they don't make those any more, but a Hella 4RD 007.794-021 is the same.
Maybe at under 5 euros each I should buy a box full and swap them all out before more things stop working.
:)


20200909_135835_resized.jpg
 

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It's quite funny that the Bosch place recommends a Hella replacement.
I bought a whole box of standard relays off ebay to check if mine were OK - most of the ones in mine are just standard switching.

Have you not got your car registered with a "H-Kennzeichen"? I don't bother with the seasonal plates on the H, as the registration is fairly cheap.

Were do you live in Germany? I'm just north of Stuttgart.

Es
 

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Discussion Starter #16
Hi
small world ! Im up near Minden.
Yes I use H plate and 6 month season plate as it half's the road fund and insurance costs, and I wouldn't be using this in the bad weather anyway, especially with a soft top.
It mainly gets used for doing old timer rallys which are almost all between April and October.
yes I was a bit surprised with the Bosch service centre. He just said, "I'll order you an exact replacement you can plug in" - at something like 12 euros I said make it 2, hence having a spare. A day later he gave me Hella. Ive just ordered half a dozen more online at under 5 euros each.
I shall have a check how many more on the car are these simple switching relays, as it might save time to just swap them all out.
 

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Bosch relays became the standard relay, but I can never remember what year that occurred. Then Bosch stopped making them, Tyco bought out Bosch. I can't remember who is the "official successor" of Bosch these days.

But the Bosch type relay has become pretty much the world standard, and many of us have replaced our original Lucas relays with that style as that's become necessary. Hence the reason I created the following for those who don't have plug-in receptacles for the relays:

28713
Bosch&Lucas_SPDT_Terminals_w_Explanations.jpg
 
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Thanks Brian, good info and well documented. Print n' save
 
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