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MG MGB Technical - Intermittent and slow wipers

For a while now the wipers on my 79 MGB have been either very sluggish or not moving at all as though the wiper motor just doesn't have enough strength to get things going. Where should I start in my attempts to diagnose the cause of this problem?
Frank

If it were me, I'd start by ensuring that the earth for the wiper motor was 100%. I'd then satisfy myself that the charging circuit (alternator etc) was 100% so it's getting good current (are the headlights a bit dim?). If both these are OK, I'd then bite the bullet, remove the wiper motor, dismantle it, clean the commutator and replace the brushes.
My money's on the earth connection...
T J C Cuthill

It could be the rack mechanism that transfers the drive across the car behind the dash to the wiper spindles. It's a pig to get at, but everything is possible. Then again, I've seen the spindles them selves seizing because the alloy bits corrode. It's not too difficult to disconnect the rack from the motor, then you could (A) try the motor with no load and (B) try pushing the rack back and forwards with your hand - it should move quite freely.

Mike
Mike Howlett

Thanks for the quick responses...will look at these suggestions...also seems that I saw something in the archives about the some brands of wiper arms have too much spring tension... will check to see if things work better with no windshield contact when I get home from work.
Frank

In addtion to what has already been said, it could also be due to the grease having solidified in the wiper boxes and the drive mechanism of the wiper motor.

Regards,
Jerry
Jerry Causey

OOOPs! One more:

Take a look at the switch -- bypass it and note the results, if any, then do a ohm check on the switch terminals.

and as noted, check and clean terminals on motor and check continuity of ground.
glg gimbut

The wipers will *always* go faster with the blades lifted off the glass for obvious reasons. You are doing it with a wet screen, I presume, I have known otherwise.
Paul Hunt

Paul,
When I tilt the wipers away from the glass they do move like gang busters, however, when against the glass (dry) they move poorly or not at all. As I never take the car out in the rain I don't have experience with my new wiper arms with a wet windshield. Should I simply wet the windshield and see how they work or could it still be that the new arms I purchased (Proper MG - made in China I believe) may have too much spring tension. I am planning a long trip and didn't want to get caught with no wipers if I did get caught in the rain. Thanks.
Frank

NEVER run the wipers on dry glass. Either use the washers or pour water on the screen from a hose, watering can etc. Lifting them off removes so much load that it is impossible to use just that to determine the cause of the problem as even if they speed up the real problem could still be either stiff mechanical operation of the motor, rack and gears or bad electrical connections. You really need to measure the current and compare it to a 'correct' value which I haven't done but the book quotes 2.7 to 3.4 amps. More than this indicates excess mechanical load, less indicates bad connections. Of course you could have both problems and draw the correct current and yet still have slow wipers.
Paul Hunt

This thread was discussed between 11/04/2003 and 14/04/2003

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This thread is from the archive. The Live MG MGB Technical BBS is active now.