Windscreen Wiper Motor – Type CWX

In Totally T-Type 2, Issue 20 – October 2013, Ian Linton wrote an article “New life for old wiper motor” that provided details on dismantling and cleaning a T-Type wiper motor.
This article continues the story by describing how to carry out repair or replacement of some of the parts that can fail.

The MG T-Types (TA to TD) all had the Lucas CWX “Screenwiper” (original Lucas part number 732480), referred to in the Lucas “Equipment and Spare Parts ” publication No. CE468 dated 1949. In those days the parts for the CWX wiper included, motor, brush set, armature, as well as blades and linkage attachments. The TF used a completely different Lucas wiper motor designated WT614.

Photo 1 – The familiar view of the Lucas CWX windscreen wiper motor as seen by the passenger!

It is probably true to say that the windscreen wiper motors, mounted on the top rail of the screen, demand very little attention until something goes wrong! It is at this point, normally when it is raining, that it becomes the focus of attention and one is aware of a slight feeling of guilt that it had worked faithfully for many years without even so much as a drop of oil.

Following a summer club drive, during which it rained, my wiper motor came to a complete halt and I needed the help of my passenger, giving the occasional manual twist of the chrome handle, to maintain some forward vision! The approach of the car’s annual safety check prompted me to investigate and get serious about resolving the issue.

I found that one of two (sacrificial) pins on the main drive shaft spindle (P in exploded view – see later comment) had come adrift and possibly damaged the field coil or the armature coil. I replaced the pin in the shaft (with a home made replacement!) and the motor ran without load, (i.e. no wipers attached to the drive shaft.) but came to a stop when asked to drive the wipers.

In the first instance I checked to see about the availability of replacements from the regular T- Type suppliers, or the possibility of a repair from the likes of John Marks of Vintage Restorations in Tunbridge Wells, but John is no longer able to help with the wiper motor repairs.

John Hargreaves will overhaul wiper motors (as reported in October’s Totally T-Type 2) but some repairs can still be carried out by the technically minded owner.

The T-Type suppliers may still “show” the wiper on their parts lists but most now record the item as NLA (No longer available). NTG Services has recently announced a “Wiper Motor Reconditioned Original * Exchange *” and this is a useful service and hassle free if you prepared to pay the price.

For those wanting to look into any problems, the Workshop Manuals offer advice on a number of things to check, but if the fault is a damaged field coil or armature winding, one needs to consider dismantling the assembly for further investigation and repair.

Click to view larger version

Start by removing the motor from the windscreen top rail. This is accomplished by unscrewing the nuts on stud G (see exploded diagram). The rear cover can now be removed as follows. Remove the chrome crank starting handle from the rear of the unit by unscrewing the hidden screw that is set into the crank. Next remove the two screws, one on each side of the rear cover (K), and gently pull the cover away from the front casting. The complete motor assembly is now exposed.

As a point of interest, the front of the cast housing holds the gears and crank, and is separately accessed by removing two screws holding the front plate, which also has the drive shaft protruding through it.

The windscreen wiper “exploded” drawing referred to previously is taken from the LUCAS Technical Services series of documents published as part of the Overseas Technical Correspondence Course.

Ed’s Note: The LUCAS Technical Services series of documents, referred to above, is available on the TTT 2 website under Technical Publications.

The drive pin in the spindle is classified as “sacrificial” should things become jammed in the motor or gearbox.

The Brushes, held within the Brush gear assembly (F), can also wear over a very long period. The Armature (E) and the Field Coils (O) are quite fragile and care is needed if the assembly is dismantled.

The drive spindle is shown below with the “soft iron” sacrificial pin identified. If this pin is broken it is best to identify the cause before replacing. The original pin can be replaced with a small soft metal “panel pin”, or similar, that must be a tight press fit into the spindle.

With the wiper motor cover removed it is now possible see the field coil windings on each side with the armature that rotates in the centre.

Photo 2 – view from rear of motor after cover removed.

At the rear of the motor (see photo 2) is the brush holder assembly with the brass on/off switch contacts just above the back of the centre of the armature.

Remove the brushes by prising aside the small spring and locating into the park slot. This brush holder with on/off switch assembly is removed by unsoldering the two black wires (on the left in photo 2) and unscrewing two set-screws.

It should be noted that the armature is now free to drop out!

I decided it was necessary to carry out a “continuity” check of both armature and field coil windings in the hope of identifying my fault.

With the brush-holder removed, as detailed above, the armature is free to be extracted away from the (front) gearbox and field coil assembly.

Photo 3 – the armature, having been extracted away from the (front) gearbox and field coil assembly.

The armature should be inspected for signs of excessive wear or damage. It is likely that the commutator will have some signs of wear but this may not be significant enough to warrant replacement.

Of equal interest, if the motor has stopped working, is the integrity of the three armature windings. My reading varied from 5.8 ohms to 6.2 ohms, but as long as a similar reading is obtained this should be fine, taking into account the age of the original armature.

If the armature is badly worn or the coils are damaged a replacement may be the only solution.

I found a break in one of the armature coil windings that would account for my wiper motor failing. Although this item is typically classified as “not available” from most parts suppliers, it is still possible to purchase a new armature (with new brushes) from “Complete Automobilist, Vintage Supplies Ltd” in Norfolk. Phone. +44 (0)1692 406465.

The Lucas wiper motor has a long history so be sure to clearly identify your version before placing an order, as a number of different armatures are available.

I should add that this armature comes with two new brushes and although I believe these brushes last a long time it is worth replacing these at the same time.

Having removed the brush holder assembly and armature it is worth taking a moment to look at the two field coils. The two field coil assemblies are held in the main cast housing with four set screws. If it is found necessary to remove this assembly from the gearbox, the two wires in the terminal blocks need to be detached.

Photo 4 – the two field coils

Check the integrity of the field coils with an ammeter. Each of the coils has a resistance in the region of 8 or 9 ohms with a combined total of 18.5 ohms, in my case. However the most important thing is the overall integrity of the windings and any “open” circuit will quickly show up.

If a failure in one of these two windings is identified it will be necessary (in the absence of the availability of complete assemblies – as mentioned previously) to find a way to repair or “rewind” a new field coil.

A repair is an option for the field coil if it has suffered some “contact” damage with the armature, (or a loose drive shaft “soft iron pin” as in my case!). The coil is typically, but not always, covered and protected with a fine linen “bandage”, wrapped tightly around the wires. If the linen covering is damaged, along with the wire, it is possible to remove the bandage, and expose the wire coil to identify any break in the outer windings. Once identified the two damaged open circuit ends of wire may be cleaned and a short length of shellac removed to enable soldering. The ends should be dipped in soldering flux before re- soldering. It might be necessary to “insert” a very short length of fine wire between the break as the coil is typically very tightly wrapped. Once the solder repair is complete, test for the correct 8 ohm resistance of the affected coil, and then re-tape the coil with linen insulation as before.

Re-assembly is relatively straightforward, locate the armature shaft into the main assembly and ensure a good clean interference free fit into its bearing in the gear box.

Note. If the armature has had to be replaced, check that the new item runs clear of the gear box and, if in doubt, use small “washers” as shims on the shaft to achieve the necessary clearance for free running. (A number of different armatures are available from The Complete Automobilist so ensure you have the correct one for your wiper motor if you have had to replace it.)

Reposition the armature field coil assembly, complete with brush assembly, on the main casting and attach the 4 set screws that hold the unit in place. Re-attach the two connecting wires back into the connector block located on the gearbox. The flat brass holding plate, on the back of the brush gear, should be just touching the armature rotor shaft and can be adjusted (by careful bending) to hold the shaft correctly in place.

With the brush assembly centred correctly, re- introduce brushes and springs. Ensure a clean free fit so that the brushes move under the pressure of the springs (that locate into a groove at the top of the brushes) and maintain good electrical contact with the commutator.

If all looks good, and the commutator runs freely, it’s time to re-attach the back cover and connect the chrome parking handle with its chrome headed screw.

For a “test run” of the wipers I sprayed the screen with a slightly soapy solution of water and moved the handle into the run position. As the wipers were not under any great load they swept the screen in their usual (slightly ponderous) but effective way.

With a new armature and repaired field winding I hope I will not have to worry about this interesting Lucas device for some time to come!

Jonathan Goddard

Ed’s Note: We still have copies of Jonathan’s book available to order from the T-Shop at £6.99 + postage, from this link: Practical M.G. TD: Maintenance, Update and Innovation

3 thoughts on “Windscreen Wiper Motor – Type CWX

  1. Richard Michell says:

    I seem to have been following in Jonathan’s footsteps. In my recent rebuild of a 48 TC I was fortunate to be able to create one working wiper motor from two non-runners. I have no electrical knowledge but one thing that I did that was straightforward and, I trust, sensible, was that I re-coated the windings with appropriate varnish.

    I was driven to this in part because, one of the field windings had been mechanically “disturbed” and several of the turns were “floating”, waiting to be caught mechanically and destroyed. I used the varnish to help keep them in their correct place, and hopefully to keep moisture out.

  2. Barrie Robinson says:

    This is sort of related to the wiper motor bit. This Club now has the grommet (Lucas 740722) for the Lucas DR1 wiper motor in urethane. We know of no other source – that’s why we had them made. Price is $17 each.

    My first ever car was an MG TD – oh joy!!

  3. Tom Kirkland says:

    The Editor,

    Let me introduce myself, I am a member of the Johannesburg MG Car Club in South Africa, for the past 28 years, and own a 1950 Y-Type Saloon. It is still in very good condition, and still attains prizes on Show Days. Recently I was put out to pasture, and chose to Restore T-Types. August last year I received a Request from a friend to Service his 1948 TC. As it required a Roadworthy Certificate, I knew it would be a tough task.
    However, I have been making frequent visits to your Website, and have gained an enormous amount of Valued Information with this project.
    This weekend, near its completion, I discovered the Windscreen Wiper Motor worked very sluggishly. I referred to your Issue 20 of October 2013. I was then able to dismantle the unit and understood exactly how to open it up, and how to go about servicing it.
    The grease inside was almost rock hard. The wiring showed signs of burnt insulation leading to the armature etc. It then got a thorough wash down in engine cleaner. The brushes were OK, and no rub marks on the Comutator or Coils. The rebuild was relatively easy, with adding fresh grease. Now how to re-insulate the main leads to the brushes etc.
    Here I managed to use a piece of thin electric wire, by pulling the wire strands out of the casing, I used that to thread the fine wire through and re-soldered the wire back onto its original points. I also gave all the coils a coat of clear varnish as a precaution against moisture etc. Once assembled, and connected up, it is working like a charm.
    I have just received your latest edition only a few days ago. and am finding it most interesting as usual. Great to know that so many of these old cars still exist today. And that they are all so well kept. (Due to your fantastic initiative by publishing this regular T-Type 2 publication).
    PS. I have other similar projects lined up for the future.

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