Wiper arm linkage assembly parts

[SurferD]

I'm rebuilding my whole mechanical assembly and have a question about the spring in the main crank. What's it for and how does it work? I can't figure out if it's in torsion or compression. It's just laying between the sheet metal part the looks like the millennium falcon and a flat washer. It  looks like there's a hooked end that's worn off that maybe fits in the slot. Anyone know? I have a spare one and it's the same except for a plastic ring around the spring. 

Edited September 6, 2017 by SurferD

[Captain Obvious]

That spring is a rotational "clutch" that engages when the motor rotates in the reverse direction to "park" the arms.

You might ask... Rotates in reverse? Park? WTF is that all about?

Z Trivia - An almost long forgotten feature of the wipers is the "park" function. When you turn the wipers off, the motor spins one extra final rotation in reverse and that spring clutch engages (like a Chinese finger torture grabber) and "parks" the wiper blades in a lower position than they normally wipe in.

However, at this time, everybody's springs look like your do and have the little tab has rusted and snapped off, and the park feature no longer works. At this point, I believe just about 100% of Z owners has had his wiper arms off for some reason over the years and they all have just repositioned their wiper arms so the at rest position is where they want it, and never even ever knew there ever was a park function.

Why and how do I know? Because a buddy of mine and I went through the same thing a couple months ago and he dug into it and turned up the existence of this long lost function. He re-formed the broken off tab on his spring and I bet at this point, his park function is the only one on the planet that works.

There are a coupe old threads on-line on one of the forums (don't remember which) that talks about the park function. Might be someone who changed over to the Honda wiper motor and was wondering what all the wires were. There is also some talk about it in the FSM.

[Captain Obvious]

Oh, and forgot the real point... Unless you're really digging originality and crave the park function, I would just clean everything up and put it back together and forget you ever saw that spring.

Make sure you take apart and clean all the crusty grease and corrosion out of the wiper stalks. That's where the real problem probably lies. Use waterproof grease and get new rubber shoes-booties.

[SurferD]

Thanks Cap'n! That's exactly what I wanted to know. I know about the one more wipe feature but never knew about that. I don't care one lick about it so back it goes. The clean one is the original and I'll pack it well with grease. I have already cleaned and repainted all parts. I'm reusing the rubber that goes over this assembly as mine's not bad. I did get new ones that go over the arm shafts.

[Captain Obvious]

I've been into two cars now (my local buddies, and then mine) and I believe the most problematic part of the whole system is where the arms pivot right where they poke through the cowl. Make sure you pop off those little C clips and take those parts apart and clean and grease everything. One all (both) cars I've messed with, those pivot points were very stiff, and they shouldn't be. They should be almost free spinning. There is a little wave washer that takes up the slack, but there should be no rotational resistance other than a tiny bit of friction from the wave washer.

I suggest the ZCCA judges use the existence and proper working of the park function as a tie-breaker at future judged shows.  Z trivia!  

[SurferD]

Yes I had everything off. my pivots were terrible and took about 10ftlb of force to turn. I cleaned/painted/regreased and now they're like butter. I'm sure about 99% of Z owners don't know about that and it would be a real gotcha of the judges held back points for that. 

I made new rubber parts to go between the sheetmetal and the pivots too.

Edited September 6, 2017 by SurferD

[Captain Obvious]

Yeah, those things! That's where most of the problem was on the cars I've been into.

Cleaned and greased, went from 10ftlb to darn near zero!

[Namerow]

On 9/6/2017 at 10:45 AM, Captain Obvious said:

That spring is a rotational "clutch" that engages when the motor rotates in the reverse direction to "park" the arms.

So, CO, I have a question, then:

You haven't really explained how the 'rotational clutch' action actually works.  We know (because you told us) that the motor is supposed to spin backwards when the wipers are turned off.  We also know that:

• the 'park' position for the wiper arms can't be any lower than what the crank arms will allow, meaning that they won't park any lower than their lowest point of travel during regular operation.  That seems to be at odds with what you're saying, but maybe -- with a bit of encouragement from some reverse wind-up in the rotational clutch -- the arms might appear to tuck a bit after the motor shaft stops at its 'park' position.
   
• the spring seems to only be engaged at one end (i.e. the end where the tang locks the 'shield' plate (millenium falcon piece) to the end of the linkage arm.  I can't find any evidence that the other end of the spring engages with anything.  It seems to just push against the underside of the washer that sits on top of it (and even if it did, that washer has no tangs or indents, so it's rotationally free and can't transfer any torque from the spring to the linkage arm)
   
• the keyed center hub is free to turn on the centre shaft but it doesn't engage with the spring.  In fact, it only engages with the keyed washer that sits on top of the parts stack and that washer looks like it has the ability to rotate +/- 180 degrees, with end travel limited by the raised edges of the linkage arm.

So it seems that the assembly can only exert clutching action if the free end of the spring engages with something under certain circumstances.  One possibility comes to mind:

• when the motor spins backwards, the free end of the spring bites into the underside of the washer enough to make the spring coil expand to the point where the free end of the spring bites into the raised lip of the shield plate, at which point the spring starts to exert some actual torque into the linkage.

This sort of makes sense to me.  I have two of the units disassembled on my workbench at the moment and on one of them the shield plate has four or five ragged holes poked into the lip at random locations around the periphery.  The holes are just about the same diameter as the spring (in fact, if you look at the picture that SurferD posted at the top of this thread, you'll see exactly the same kind of hole in his shield plate.

And then there's a cryptic note that somebody made somewhere (I don't remember where) that said that on later units there is a 'plastic ring' that been added that sits around the outside of the spring (can anyone verify?)

So, Captain Obvious:  How does this thing really work?  What happens to the spring when the motor turns backwards?

 

p.s. On both of my springs, the tang has snapped off.  When I tried to bend a new tang onto one of them, it just snapped off so no joy that way.  I'm going to see today if I can maybe put a sleeve made of brass tubing over the end of the spring and then bend the tubing to form a substitute tang.  Might work.  We'll see.  I have other ideas if it doesn't.

Edited September 30, 2017 by Namerow
added some words

[zKars]

As a proof of concept, simply cleaning and servicing both the wiper linkage and the electrical connections to the wiper motor and primary electrical system, have rendered countless "slow and in supposed desparate need of a Honda motor upgrade" Z's in these parts to perfectly respectibly functioning wipers. 

[Captain Obvious]

The trick is that the spring and the eccentric cam that the spring winds around... Ready for this...effectively changes the length of the wiper linkage so that the park position IS lower than their lowest point of travel during regular operation.

The spring only positively locks into one end. The end that is bent to fit into the Millenium Falcon is the only positive engagement. The other end of the spring does not lock into anything.

It's a one-way clutch. Like a Chinese finger torture grabber toy. You can slide your fingers easily into the toy, but can't pull them out because the toy contracts on your fingers and prevents removal.  Easy in, friction out because of the clutch. The spring does the same thing, but in rotation.

In the direction of "normal operation" the spring unwinds a little getting larger and slipping. Other direction, it contracts a little and when it gets smaller, the center hole grips the eccentric cam. That friction rotates the cam a little and makes the linkage a small amount longer which in turn makes the park position lower than normal operation.

I'm hoping I got that right... I'm at a little disadvantage here since I don't have the parts lying loose anymore. I've got access to my buddies linkage which is not yet back in his car, so if there are still questions, I can take his apart again.

As for fixing it, my buddy GGR (you met him in Toronto) was able to make a new bend in the end of his spring. Unlike yours, thankfully his did not snap off again. But prior to that success, I had identified what looked like a suitable replacement spring on the HELP rack at the parts stores. I didn't have a caliper with me, but there was a blister pack with a couple springs in it and one of them looked very close. I was thinking it could be used to replace the original. If you're interested, I'll take another look next time I'm at the store.

[Namerow]

Thanks, CO.  I hadn't thought of the spring coil/uncoil in terms of it cinching down on the hub of the eccentric cam.  Brilliant! 

A few minutes before I read your post, I found this in the 1974 FSM:

That made me remember the eccentric cam, and then I suddenly realized that its purpose is to change the effective length of the linkage arm by about 1/4" when it rotates from one stop to the other (by way of the torque applied by the spring.

Another S30 mystery solved!

BTW, I've had good luck making my own helical and hairpin springs from music wire.  The OE spring in the wiper linkage is made from 0.065"-diameter wire.  I have some (OK, a lot of) 0.040" music wire.  Not perfect, but maybe close enough.  I just need to make sure that my coil that has the right 'grabbing' diameter.  If it works, I can start selling them for $50 a pop and retire.  Let's see:  100 buyers @ $50 each = $5,000.   No good.  Guess I'll have to keep my day job after all.

[Captain Obvious]

Yup. That verbiage is in all the FSMs I think. But nobody in the past thirty years ever saw it or cared.

I think all of those clutching springs broke thirty years ago, but since the wipers continue to pretty much work just fine without it, nobody ever looked into it. Unlike most things, it's a convenient failure.

Back when I had my first Z, I hated the double wipe thing. Now, after all those years, I at least understand the "why"!!

As for replacement, I suspect the ID isn't incredibly size critical as long as it drags enough to start to engage the clutch. Once it starts to engage, it snowballs. But you have to have enough friction to get it started. I'd be more concerned with the wire diameter. A smaller diameter might only last five years.