TheSamba.com :: View topic

Wed Sep 17, 2008 3:18 am

My newly acquired '74 camper had many issues most which have been attended to but one has really stumped me.
my windscreen wipers stopped and naturally I checked the fuse - -all good, the I checked the arm assembly- flopping from side to side- so the drive from the motor was busted- I took it all apart and found some 'bush mechanic" had drilled the steel shaft and the collar to the plastic worm gear and pushed a steel wire through and this was now broken.
I replaced the wire and all worked well- I connected the wiper / motor assembly to my battery charger just to make sure it worked and - no problemo BUT when I fitted it back in the bus it blew the fuse super fast -short circuit , you say. I pulled off the plug and connected the battery charger directly to the terminals on the motor and - guess what - it worked . 7 fuses later i gave up It does not blow the fuse when the motor plug is removed so its not the wires through the switch - it must be the motor but I don't know where :(

Wed Sep 17, 2008 7:45 pm

From your description; I think that due to the “bush mechanic-ing” and the fact that electric motors have the greatest torque and current draw at start up, the current needed to get the motor going (due to extra maniacal force of non stock setup)is more than the rating of the stock fuse, when connected directly you have unlimited power (all amps that are in the battery charger) to get the motor going…

Thu Sep 18, 2008 12:47 am

Wiper motors are quite a bit more complex than simple DC motors. to park they use a dynamic braking system to make sure the drive stops at the right place.
Make sure you have the connections right. You may need to look at a Bentley book to get the color codes.
Al

Thu Sep 18, 2008 1:06 am

Both comments greatly appreciated :D . My guess is the PO had had major issues with the wiring as well because there is a GREEN wire that does not crossreference with my workshop manual.
This "dynamic breaking" interests me; when I pulled the gearbox appart , is it possible I put the worm drive cog in incorrectly and the brake is somehow causing some "locked armature current" to occur ; i.e its fighting the brake in some way :?: the wipers did work the day I bought it and just stopped when obviously the wire broke that locked the drive to the shaft. :?

Thu Sep 18, 2008 8:09 am

Could be, the brake is the contact on the gear IIRC and grounds both poles of the motor when parked if the switch is off. When you move the switch from off it disconnects this feature. If the gear is in the wrong position or a wire is on the wrong terminal you could get grounding while it's running.

Thu Sep 18, 2008 11:58 am

I wish the p.o. of my bus had half the skills of your "bush mechanic."

Thu Sep 18, 2008 2:29 pm

Maybe the simplest solution is to purchase another motor but, it somehow appeals to my masochistic nature to belt my knuckles each time and pull the whole mechanisim out , strip it down and start again.
There are motors on ebay for $25 that would suffice but I'll give it one more go an the dynamic braking thing - I think thats the problem for sure.