1948 Mk4 windscreen crank mechanism

Well not sure if the worm gear or the sprocket is the issue as have not taken it apart yet but my windscreen crank has stopped working. The crankhand turns but the windscreen does not move.
I’ve tried assisting the mechanism by pushing/pulling on the windscreen and can move it.
Any help locating parts is appreciated.

Hello James,
I have 2 cars with this mechanism in place. One of them needs to be helped along because the chain wore through the aluminum box/frame. You will need to take it apart to find out what is wrong. I have heard that a good metal guy can weld teeth into gears and then grind them into shape, although I don’t know if these gears are too small. Waiting for someone to part out a car would also work.
Best of luck,

Tks for the info, will be dismantling the crank in a week or so.

Here are some pictures to show what to expect. It is a simple but fairly heavy duty design of a worm and pinion - heavy because of the weight of the windscreen it has to wind out. The pinion has an integral sprocket that engages the chain and it is of forged brass. The pinion is the sacrificial part, as it will wear much faster than the other parts.

I assume from your description that the handle is not slipping on the splines of the spindle. The problem is then internal and is likely to be a stripped pinion which means you will have to source a spare from someone. This could be a frustrating endeavour.

You could try a test. Wind the handle and push the window out steadily with the other hand to see if there is engagement elsewhere.

Just a few notes for the pictures. The rectangular plates are packers to fit under the winder block so that the handle doesn’t contact and scour the fascia veneer. Note the rivet near the end of the chain to prevent winding the chain completely out. The attachment cleat at the end has a lip on its lower edge which bears on the edge of the windscreen frame. This is important as it is needed to ensure the screws don’t take the considerable lifting force.


Peter, thanks so much for the photo’s and description. Looks about how I expected. Now I just need to get the wood cover off the dash without damaging it. Have not quite figured out how it is attached as there are no surface marks to indicated screws or tacks.
I beleive the teeth on the pinion are striped as the crank turns and can feel the teeth slipping. Pulling on the windscreen does help but no real positive engagement.

Hi James,

The upper part of the dash is screwed through from the outside with wood screws. The screw heads should be visible in the recess exposed when the windscreen is open. The lower part is bolted to two metal struts that you will see underneath on either side of the instrument / switch area.


Peter, tks again, “you da man”.

Just a hint for reattaching the dashboard. Hold the top of the dashboard hard against the windscreen frame and tighten the wood screws. Don’t use the screws to pull the dashboard into place as there is a lot of weight and it is easy to strip the threads in the wood.

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