Did Chevrolet make a major blunder on the grounding of the 1968 wipers?

Look at the standoffs/grommets for mounting of the wiper motor. One has a brass piece that bolts up to the wiper motor ground and connects to the
metal tube of the grommet. (These are aftermarket, but close enough)

To summarize this entire post, that brass strip grounds absolutely nothing. The standoffs, the studs, the reinforcing plate the studs stick out of inside the wiper bay is a metal plate sitting like an island on insulating fiberglass, and is incapable of supplying a ground. Keep reading and looking if you don't believe this is true.


One would ASSUME this is to ensure that the motor is grounded, through the brass piece, through the standoff, through the nut and threads.. Anyone got any heartburn with that?

Here's that brass piece mounted to MY wiper motor, partially painted black with a big scratch in that black paint.




Ignore the blue wire, that's a grounding wire I added once I realized what Chevy MAY have done.

Here's someone else's motor mounted to the firewall, showing the motor, the standoff, and the stud. (And an alligator-clipped grounding wire, interestingly enough!)



Here's the firewall, sans motor, with replacement studs I installed. Notice the 3 rivets that secure the steel backing plate inside the wiper hold to the fiberglass firewall. Fiberglass faces you.



Here's the backing plate, as seen from inside the wiper compartment: You can see heads of two of the three rivets securing it to the fiberglass and the heads of 2 of the 3 new "studs" I put in.



I checked it with a test light; that backing plate is grounded to exactly nothing. It's a metal island afloat on a non-conductive fiberglass sea.

Now let me take you on a short detour.

The pathetically small (10-24?) studs supporting my wiper motor were stripped. I needed to replace them with something beefier, like 1/4-20's.

So I get in there with the Dremel tool to cut the old ones out, which requires cutting THROUGH the fiberglass to the steel backing plate inside the wiper compartment. (This is neither an easy nor a fun job, btw. Access is a real problem)

At which point I realize:

Those studs, and that backing plate, are in no way connected to ground, and there is no way in HELL they're going to provide a good ground to the wiper motor, through the stud, through the little brass plate, etc. The steel backing plate is isolated on non-conductive fiberglass. All by its electrical lonesome.

As if attempting to ground something through the THREADS of a nut or bolt wasn't bad enough.

There's simply no ground for the wiper motor to have through those studs.

Was there at one time a wire connecting that backing plate to an actual ground, inside the wiper bay?

Can anyone explain this --- or is this a genuine Chevrolet electrical design flaw?

Given explanations I've read of how the wiper system works, I'm not sure why it does if this ground is truly missing.

So...choices are, A) I'm an idiot, overlooking something simple B) Some OEM source of grounding is missing on my mostly-original 1968, like a wire to that plate, or C) Chevy dun fucked up!

Your votes, ladies and gentlemen?

 

That's by design. The wiper motor doesn't ground to the car body.
There's a black ground wire that feeds up from the starter bolt to the fan motor then over to the wiper motor.
That wire attaches to a ground lug. That lug then grounds the entire wiper motor case via the strap you see there on the grommet.

 

Could you explain to me again what purpose that brass strap is serving? It appears to me, an EE, to be serving no useful function. The metal sleeve of the grommet contacts (electrically) nothing but the ungrounded backing plate inside the wiper bay via the nut/studs.

The case of the wiper motor only touches the rubber, insulating part of the grommet, not the metal sleeve.

It's not like the General to include a part, even if it only costs 2 cents, that serves no useful function.

Do you suppose some engineer THOUGHT he was going to ground the motor by way of that strap and later realized the grounding wire from the starter bolt was necessary? Or perhaps that strap was used to ground the motor on Camaros / other vehicles with metal firewalls? If so, his coworkers are probably still ribbing him about that -- "Thought you'd ground it against the firewall, did ya??? LOL!"

And on my Vette that ground wire is WAY too small (14awg?) to provide sufficient ground to run the wipers and blower on full at the same time. Looks OEM/original. Poor harness design?

 

Thank you bringing this to my attention as I rebuild my 70'. I'll make sure to look into it.

 

Maybe it has something to do with the cast aluminum housing not being a good ground, even internally, or poor with dissimilar metals (causing corrosion) running to a proper ground. The firewall isn't a ground. Under the dash on these things is a good example. Failure to run a ground from anything under there even though it might be bolted or screwed to metal is asking for trouble. Wiper switch is a good example.

 

Because it's a simple system:
The case must be grounded for the motor components to function and that strip/bolt grounds the case.
Wiper motor speed is controlled by grounding terminal 1 & 3
See Wilcox video

Mister Willcox, 68 wiper motor

68 wiper problems

 

its got muliple grounds, multiple issues and was a one year only system. The switch gives it another ground.Read the AIM troubleshooting addendum and you'll realize how excited they were about that motor

 

My 68 with a build date of Jan/68 does not have a wiper override light in the dash. My under the dash wiper override switch was not functioning. Upon investigation Bubba had spliced into the wiper override limit switch wire ( on firewall) and grounded it to a valve cover bolt. Removing this wire stopped the operation of the wiper motor. Under the dash I found the wiper override switch was mounted to a metal plate. There was a grounding wire that was not attached to this plate. Once this wire was attached the wiper system including the under the dash override switch all functioned properly.

I am no where near an expert, but It is my understanding that 68 wiper systems are grounded thru the under the dash override switch.

 

Theres more than 5 different grounds in the system. What your talking about is a ground that bypasses the motor so that it stops the blades in the up position instead of parking them so you can work on them. Even if you shut the car off in the normal position with wipers running, they will park if the system is functioning properly.

If you arent aware if you leave the switch in the bypass position it will slowly drain your battery

 

Not slowly. Quickly 2.6 Amp draw on my vehicle.

I spent two weeks, tore out the entire dash looking for the current drain on mine after (apparently) playing with that switch and leaving it in the wrong position.

After all, my parasitic drain couldn't be in the wiper system because I'd pulled the wiper fuse, RIGHT? RIGHT???

Who would fuse HALF of a circuit. Lucas, not The General. Did the Prince of Darkness do an internship @ Fisher Body during C3 design?

After I discovered the little vacuum solenoid under the dash (connected to the override) was warm to the touch even though the ignition was OFF, I got on the track of the wipers.

Pure luck I discovered that.

I've considered removing the entire bypass system from my car --- all it does is catch my foot / pants leg getting in or out. BUT.... I read where it's intended purpose is to allow you to change the wiper blades.

I hadn't thought about that.

I have always loved the wiper bay door on the '68-72 Vettes. I saw one guy driving around with the door stuck open and thought...that looks cool!

I never realized I would have to become an expert on the whole damn system, vacuum, mechanical AND electrical -- to make it work. FWIW I tested the wipers on the test drive before I bought the car just to make sure they worked. They did. Once.

Just shoot me!

 

That is also consensus, and removing the ground depowers the armature in the motor. (or so I've read) preventing it from spinning. But it apparently doesn't depower the solenoid which holds the door open, etc.

 

If you'll re-read my post, a little more carefully, you'll see that strip / bolt grounds absolutely nothing.

But thanks for reposting the Wilcox material, great stuff, which will I'm sure help some other victim of the 1968 wiper disaster in the not too distant future.

 

Read your post:
GM used this exact same wiper motor assembly on MANY GM cars.
They ALL use the exact same grommet set.
They ALL have that exact same ground strap running to the park module where it is grounded to the case via the retaining bolt for the park module.
On "non-fiberglass" vehicles that strap grounds the case to the vehicle body at the wiper bay.
On fiberglass cars, as stated previously, there is a separate ground wire that runs from the starter, to the blower, and over to the wiper motor to provide a ground circuit.

BTW: this is a frequent topic on all the Chevy, Chevelle, Camaro, Nova, what have you sites.

 

Hello wadenelson!

I too have a 1968 C3, it was an L71 convertible with four speed originally. I ran into many problems when I had my engine rebuilt. I had Tony's Corvettes in Gaithersburg, MD re-install my engine and that is when the fun started. We found multiple parts that are from C2 Corvettes under the hood. My radiator support and shroud were all 1967 parts as were several other little pieces. It seems that GM used up the leftover parts on the early 1968 C3 Models.

I can't tell from the picture but it looks like the car in your Avatar is a T-Top. If it is then it was made post Jan 1968 I suspect as all the early 1968 Corvettes were convertibles.

There are so many one year parts on the 1968 as you no doubt know by now. My car had new (Dr. Rebuild) vacuum hoses installed about 25 years ago and they still seal well. When I open the wiper door it "pops" open and my headlights jump up and down upon commands. In my case the vacuum part has been great. My wiper motor works great (so far) and after reading your post I hope that it never has any troubles. If it ever does I will be sure to use what you have taught us here. I can't understand the brass support bracket either when the horn bracket is made from aluminum. It does not make any sense to an engineer (I am as well) to use these materials unless you need them for a particular reason.

I have a pretty clean example of a 1968 and would be happy to help you out in any way I can. I guess I shouldn't tell you how long it took for me to find out about the little ***** that make the wiper cover pop up or the headlights. Then I had to figure out how to stop those darn wipers while in motion to change the blades. Fortunately I have a cousin who knew Corvettes was able to tell me where the switches were.

Having a 1968 Corvette makes you special in my book. The 1968 model Corvette has not been desirable because of the hood gaps and other unique features. I love my 1968 Corvette because it is "unique". I do not like unique problems or issues however, they just become challenges....

I wish you the very best working with your beautiful Corvette!

 

Theres many 67 parts that change over to the 68 but stop there, some off the top of my head

1. Steering box
2. Steering wheel
3. Front spindles
4. Hand brake
5. Frame

Theres more I'm sure that didnt change over the years like motor parts, muncie, rear diff, brake calipers, etc so it's not really a surprise. The spindle size for bearings can screw you if the parts supplier just grabs a 68-72 part. I've seen them listed that way in many supplier lists. You really have to be wary of anything listed as 68 -XX.
The longer you own one the more you discover by searching for parts. It's the true one year parts that are a hassle to find or afford if you're restoring it.

 

I'm watching this thread... but guys.. I'm sorry.. I'm wiper'd out.... Chevy didn't make any blunders on the motor it was a horrible system for 1968. Wade, if you don't figure this out the info you need is on my tech site..... Just go step by step and you should be able to figure out the issue.

I'm sorry guys, but after doing all this tech work, from 1963-1967, then doing the 68 stuff, then doing the 1969-1977 stuff... then doing the 1978-1982 pulse wiper stuff... and after publishing it.... The answers for all the systems is there if the customers will just take the time to read through it and watch the video's and other items available.

Again, I'm' sorry for not being poofy about working the wiper threads as hard as before but I get probably 10 emails a day on wiper motors...

I can't answer them all but what I can say is the info needed to fix the system is published on my tech site. (I even get emails from Chevelle and Camaro people on that 68 system... }

So... here is all the info I have on the 68 system... and Wade... if you don't figure it out... go head and send me a message to Service@Willcoxcorvette.com and I'll see what I can do for you.

Ernie

http://repairs.willcoxcorvette.com/?yt=1968&s=wiper

The link above should show you everything I have on the wiper system.. including the tech page

http://repairs.willcoxcorvette.com/w...-schematic.pdf

Wiper Motor Bench Test 68 Ver 1


Wiper Motor Bench Test 68 Ver 2 "Follow up"


Great threads on 68 Wiper motors can be found here:

Mister Willcox, 68 wiper motor

68 wiper problems

 

Thanks Ernie, I've got it figured out. I was just surprised to discover that strap weren't doin' nothing, and wanted to confirm I wasn't a total idiot for thinking so!

Your bench test video and other stuff is just fantastic. Thank you SO MUCH for all the effort you put into it.

 

My pleasure... I can't take it with me so I may as well make it available to those that need it...