DR3A Wiper Motor Problem

[Monty-4]

I'm trying to coax my wiper motor back to life. I've gotten it to spin a little bit, but I think it might be jamming or have a dodgy earth as it gets hot? I really don't know what I'm doing here though, it could be a worn armature or commutator but I wouldn't know what to look for!

Photos of various parts: https://imgur.com/a/gPKhK

[geoberni]

Hi
I don't think it will be an earth, since that should just make it run slow or not at all.

Before you took it apart, could you turn it by hand easily enough?
Was it clunky as it rotated?
What's the depth of the insulation like on the Commutator?
Is there carbon dust filling the gaps?
Those brushed do look like they are getting quite worn, though not totally duff.
Is that actual scoring around the Comm or just 'marks'?

I'd have been doing some continuity/resistance checks with a multimeter before I stripped it down so much.
It could be something as simple as insufficient brush tension on the comm.

You might have a read of this topic I found when I was looking to see what a DR3A motor was (my Moggie is a Splittie).
http://www.lotuselan.net/forums/lotus-e ... 34-15.html
It's quite interesting

[Monty-4]

Will go through all of those points!

On another note - does anybody know what size the cover screws are, I keep dropping them into the gravel driveway!

[Monty-4]

Got it working after cleaning all the internals and soldering a new parking earth cable on.

However it's now really noisy and stops occasionally. Whipping the motor cover off and turning it by hand seems to free it up again. What could cause it to jam?

[geoberni]

Could be play in the bearings, which I assume are just phosphor bronze bushes, or misalignment of the rotor/stator in relation to each other.

Or, the alignment of the brushes, it depends on the type of noise; if it's a chattering, it could be one or both brushes bouncing as they run around the Comm.

[mogbob]

Well done on getting it going again, first of all.
A few things to double check :-
1.Were the bushes lightly oiled on re-assembly
2.If new brushes were fitted ,they may take a few operations for the surfaces to wear down ( only fractionally ) to assume the curvature of the armature. Please note geoberni's points on brushes.
3.Was the adjusting screw assembled with the correct " end float " before the locking nut was tightened ?
( The correct end float for a Lucas DR3A wiper motor should be between .008 and.012 inch ( .20 to .30 mm ). You weren't over zealous
tightening up were you ? Once the motor heats up, inevitably the metal expands a little , hence the need for end float.
4.The gear wheel / final drive wheel , connecting rod was re-greased on assembly.

Jamming
Did you check the movement of the cable by hand , before replacing the wiper motor back in the car. A screwdriver through the cable rack yoke helps to move it slowly back and forth. Just a small length , otherwise it will disengage from the wheelboxes !! Very much like the motor itself the grease in the cable ( Bundy ) tubes and wheel boxes would have gone hard over the decades. With lack of decent lubrication , the wheel box gear wheels may have worn ... generally contributing the lack of "smooth ", non sticky or catching of the drive cable. The screws holding the two halves of the wheel boxes might have loosened and need retightening. Rust could have got a hold in the wheel boxes.
The two rubber angled grommets , holding the splined stem through the bodywork @ the base of the windscreen , deteriorate / degrade
over the decades and let water into the car.

Test procedure
The windscreen was clean and you wetted the screen , before operating the wipers. Wiper blades are in good condition i.e still flexible rubber not hard ?
Bob

[Monty-4]

Really useful posts chaps, thank you.

I'll oil the brushes lightly and set the end float as I just guessed at it before (turned until I felt resistance and then back a smidgen). This isn't covered in my blue workshop manual so I've been flying blind! Also my motor has no locking nut, that part has been replaced with a single screw at some point.

Edit: the rack seems fine, the system turns very easily by hand.

[mogbob]

Sounds as though you've got a plan /things check out OK and that you're on the home straight. The locking nut would help tremendously.
Screw the adjuster right up tight , lock nut finger tight up to the casing , back off , until you can get a feeler gauge under the
lock nut, remove gauge and tighten the lock nut up.
I stumbled across the end float figure for the Lucas DR3A motor elsewhere , some years ago.
Bob

[taupe]

Really useful posts chaps, thank you.

I'll oil the brushes lightly and set the end float as I just guessed at it before (turned until I felt resistance and then back a smidgen). This isn't covered in my blue workshop manual so I've been flying blind! Also my motor has no locking nut, that part has been replaced with a single screw at some point.

Edit: the rack seems fine, the system turns very easily by hand.

I presume you mean oil the Bushes not Brushes!

[Monty-4]

No guarantees there but it works!