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MG MGA - wiper arm skipping on shaft

HI - I christened my full restore with a nice jaunt through a big rainstorm yesterday. I have a 61 1600 LHD. I turned on the windscreen wipers of course and found that the passenger side wiper would head to the right from the left parked position, but when it reached its end of travel, the arm would not return. Rather, it sort of rose up slightly + danced round without traveling back. But it would then catch again once the shaft started its rotation again to the right, thus digging the arm down toward the front hood ... again and again. This is the first time the wipers have gotten action since the wiper motor assembly has been put back in the car. The knurled shaft travels back and forth fine. The driver side behaves fine. I switched the arms and the same thing happens. The arm cap is anchored into the shaft by that clip which moves behind the shaft and keeps it there. The shaft splines appear ok and both arms work on the driver side shaft. When re-installing, I pulled the shaft through the body all the way up and tightened the 1/4" nut. Is there actually an adjustment there that might influence the travel of the arm? Has anyone had to replace the knurled shaft? Since the arm travels fine in one direction, I'm not so sure that it is "skipping" when it returns by worn splines. My replacement blades from moss are 9" - Between the nasty repro arms and the long blades, it sure is a sloppy site with the blade touching the windscreen frame at the bottom. Thanks for any help you might have - -


glenn johnson

Update: my driver side arm is starting to behave the same as well – it now too rotates to the interior but then does not return properly + quickly “skips” out of its alignment rotation. It resumes its grip on the way down and ends up grinding into the lower horizontal frame and beyond into the rubber apron as it fails to return from a rotation, then continues to turn down.

If the spindle shafts rotate back + forth, is that enough to confirm my re-installation of the wiper assembly was successful?
Or is there any adjustment that was necessary prior?

My moss wiper arms were a huge pain prior to the restore, so I took a chance and ordered a couple from vic Brit – I figured there would be a tiny chance that they might come from a different supplier – these do look slightly different than the moss adjacent to the clip area but nothing dramatic.

I’m wondering if their shape or travel might be causing undo friction by rubbing in a wrong geometric angle against the glass.

I might buy a moss arm today and give that a test.

My Haynes manual says to check the limit switch on the gearbox cover and place the projection close to the rim of the limit switch in line with the groove in the gearbox cover if the wipers fail to park or park badly I’m not sure what they are talking about there??




glenn johnson

It is not the wiper arms, it is the repro wiper boxes that are the issue. I had the same problem, constantly finding that the teeth in the wheel box jumped the rack under load or that the wiper arms even fell off the knurled boss. It worked fine without any load, but as soon as the rubber blade hit glass, the problems started. As soon as I found and fitted a set of the original wiper boxes, the problem went away. The wiper arms, blades and rack remained as before.

Be aware also that there are two different wiper box types, with 32 or 40 toothed wheels.
dominic clancy

Dom, I think you are right - i just came in from checking out the pivot shaft.

I can grab the pivot shaft by my fingers and lift, there is a bit of free space or looseness there to move upwards. see pic you can see newly worn bits of metal where there must be churning.

Mine are definitely doing that, so if the pivot shaft does lift, it loses its inside grip to the rack like you say. And only when wipers are in action.

My wheelboxes are original but the car is closing in on 200K miles so maybe time and use necessitates me replacing the wheelboxes. So I should avoid repro wheelboxes, dang.

Can a wheelbox be replaced without taking entire motor and rack assembly out?

Were the wheelbox toothed wheels 32 or 40, a change in config from 1500 to 1600?

Thanks!


glenn johnson

Just remove the nut, bezel and rubber gasket outside, and the two screws holding the plate to the wheel box underneath, and it can be removed with the rack in place
dominic clancy

Dom, what is the reason for the problem which is that the pivot shaft "jumps" causing it to come off the rack? Is it the wheel itself that has worn out and then just pushes the shaft upward?
glenn johnson

I'm wondering if you may have the wheel-boxes connected to the cable rack up-side down.
David Werblow

Am trying to find a picture of one that is correctly mounted so I can compare - here is a picture of mine, passenger side, from under the dash. you are looking almost from behind it.


glenn johnson

If you rotate them 180 degrees, the wipers park on the opposite side of the screen

Your backplate is not tight up against the wheel box assembly. The flared end of the tube should sit in the slot to proven it moving around, and the backplate then acts as a backstop for the cogwheel. The way it is currently mounted, the rack can slip away from the wheel. This is because the spindle can move up with less effort than rotating. If the backplate is correctly mounted, the wheel only has one way to go, around rather than up.

Try moving things around a bit to get the tube flare into a slot, and tighten up the screws holding the backplate to the wheel box. That should solve your problem.
dominic clancy

I'm on it
thanks guys!
glenn johnson

This thread was discussed on 22/04/2012

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