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Rebuilding a wiper motor


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Correct. Both wires to ground should run slow.

Your post reads like it runs slow when parking but fast all the time when on?

I think this may be the switch not the motor.  Try it out by making direct connections to ground that don't pass through the switch.

Just spotted that this is a Lotus.  Is this the one with a rheostat switch with continuously variable speed?

What is the part-number on the cover-plate,  like 75XXX?

Edited by AlanT
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Alan, thanks for your reply. The part number looks to read 5407 (I will confirm later when in the garage) it doesn’t look to have a rheostat although I’m not entirely sure what I am looking for.

 

i am testing the motor on the bench when encountering the issues without the switch so that can’t be the issue. I’ve tested the cables from the bare ends to the soldered connections inside and all have a low resistance eliminating a broken cable. 
 

I really am stumped with this.

 

thanks, Steven

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Hi Folks,

 every now and then TRiumph do something odd between similar items on the different TR's. You would think there would be consistency along the parts/marques.

Now Lucas are giving a single speed part number to a two speed motor.  

I suppose the inconsistency is consistent on its own right !!!! 

 

Roger

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This motor is different to the usual TR two-speed.

The field coil does not have a resistance overwind.

The field coil does not connect to the grounded side of the armature AT ALL.

These used a unique switch with a built-in rheostat.  This completes the connection of the field-coil to ground and gives continuously variable speed. Also found on Zodiacs.

If you ground both the RED and YELLOW wires you will get maximum field and will run SLOW.

I often make replicas of these for Lotus owners and also fix the switches which are usually ROPEY.   The problem is that a trivial fault with the switch will leave you with no field excitation and burn out the armature.  BE CAREFUL!

You won't get two speeds without the correct switch because there is no way to reduce the field.  I suspect you are trying to run with residual magnetism because the rheostat needs fixing.

 

 

 

sherwood-6.jpg

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On another related topic.  What is the difference between a DR3 ans a DR3A?

Well I've worked on hundred of these and am still not sure.  I think Lucas marked these somewhat inconsistently.  

The earliest ones, DR3, used a one-piece Aluminium cover and a parking switch with a knurled brass adjuster. Usually these are reverse-parkers on Jaguar/Rover.

Later on the type with a steel cover and parker in the round cap came and these are DR3A.

Except that later Jaguars have the plate marked DR3A even though its aluminium.

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7 hours ago, AlanT said:

Oh and before you ask,  yes you can convert a 75501 to be like a usual two-speed and use a switch, if you don't have a rheostat.

And go the other way if you have a rheostat but no motor.

Alan, I don’t have a rheostat switch although the switch may have a built in resistor which would do the same job I presume, albeit a fixed speed rather that constantly variable. 
 

if the switch doesn’t have a built in resistor can I install one inline?

do you happen to have a wiring diagram?  
 

thanks again, Steven

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You can use a 10 Ohm 10W wire wound resistor instead of an overwind on the field coil.  You can put the resistor inside the motor or anywhere that suits.

I've done two-speed conversions with resistor like in the photo.  But an overwind like Lucas used is actually much easier.

But you will need the right kind of switch.   What switch do you actually have?

I think I'd look at the field-coil and see if there is an overwind just in case it's been modified.

 

2speed-mod-4.jpg

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I have a 3 position rocker switch similar to the one in the picture. 
 

it may not be the original switch for the car as it has been modified to look like an elan sprint in other areas so wouldn’t be surprised if the dash had also been changed. 
 

I have attached the best picture I have at the moment.

if the motor had been wound would it not work on both speeds the way I had carried out the bench test?

i have also tested the resistance between each of the wires 

Yellow to green 8.7

yellow to red 10.3

green to red 2.0

do you have a wiring diagram to show the way it should be wired in it’s in altered state?

thanks again for all your help was almost ready to give up!

 

E55E9F8D-874E-4262-9497-0A90533E9BA4.png

BFADA7A4-1610-47BA-A7CA-FF83671226CD.jpeg

FC3BFC00-D485-4A18-9320-3E1C4C388A1D.jpeg

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2 Ohms GREEN to RED is the resistance of the armature and brushes.

8.7 Ohms GREEN to YELLOW is the resistance of 700 turns of field-winding.

Motor is correct original and would need an external 10 Ohms in series with the field at the YELLOW wire end to get FAST running.

Other side of the resistor goes to the RED wire.

Your switch now has to ground the RED wire in BOTH SLOW and FAST positions.  This powers the armature and field.

To run SLOW you would also ground the YELLOW wire. This shorts out the resistor, which increases the field and reduces speed.

I'll sketch this for you if you can't follow.

Does not look as if your switch has enough contacts to do this, but you'll need to check it out.   Usually light switches work because it's like doing just side-lights or side-lights with head-lights.

There are many ways you might use as a last resort, to make this work.  Like a separate FAST/SLOW switch.

The switch from a TR5 might do.

Edited by AlanT
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  • 11 months later...
On 2/19/2014 at 12:39 AM, AlanT said:

A well known register member passed a DR3A wiper motor to me recently.

It's got a 130 degree gear-wheel and came from a TR3A most likely.

 

It ran OK, but took more current than they should do, indicating it was a bit stiff.

It always amazes me how well these have stood up and I've yet to see one that is beyond repair.

 

But there are a couple of common failures and so here I dismantle this and show how to restore and improve these.

 

Hi all,

This thread has been very useful.

A kind friend is overhauling my Lucas DR2 windscreen wiper motor and found that my contact disk has a section missing.  Not clear what or why however, as you can see, it needs to be replaced.

Looks like the disk is made from brass sheet.

Does anyone know where I could buy a replacement contact disk?

Cheers and keep safe, Mick (Sydney)

Correct contact disk.png

My contact disk.jpg

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Hi Mick,

 the void is meant to be there. 

With the wipers running the system gets its earth through the switch.

When you turn it off the contact disc then provides an earth return to allow the motor to keep running until it reaches its park position.

The position of the parked blades will coincide with the void.

 

Roger

 

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Hi Mick -  I guess you mean the bottom picture which looks as though a big section of the disc is missing on the r.h.s? 

I've never seen that part for sale separately but it shouldn't be difficult to make one from thin sheet.  Finding suitable rivets might be difficult but it might be possible to use alternative fixings like small countersunk screws. The important part is making sure they do not earth out where they go though the case.

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