Author Topic: '68 Speed Warning knob location ???  (Read 3742 times)


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'68 Speed Warning knob location ???
« on: January 15, 2016, 02:59:48 PM »
Does anyone have a photo showing the correct location of a factory installed '68 Speed Warning adjusting knob?

I've owned this car since '78 and it was pretty much a bone stock, never been messed with car when I bought it. The Speed Warning needle on the speedometer was there, the Speed Warning buzzer was there, and the Speed Warning wiring harness going to the fuse box was there......but oddly there was no cable and knob to adjust the needle.....and there was no hole drilled in the bottom of the dash for the knob like the AIM shows.

I have a cable now and will be installing it as my restoration proceeds but where the AIM shows the location of the hole for the Speed Warning knob is a little confusing.

The AIM calls for a 13/32" diameter hole to be drilled .69 inches over from an existing .406 inch diameter hole. The existing hole is there in my car and if I drill the 13/32" hole where they say to, it would actually work just fine........What puzzles me though, is where the illustration in the AIM physically shows these holes. Where it shows the 13/32" hole would actually be covered by the bottom of  the speedometer housing and that can't be right. Maybe it is just an error in the drawing.

I would be fine with using that existing hole but you can't because the the Astro Vent duct would interfere with the cable.

So before I start drilling, I was hoping to see exactly what the factory did.



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Re: '68 Speed Warning knob location ???
« Reply #1 on: January 15, 2016, 05:04:44 PM »
Dave, check your email.
68 05C LA RS/SS U2 712 L34 M21 BR
68 08E LA RS Y2 749 L30 M35
67 11B LA  RS/SS M-1 797-Z L48 M21  Convertible


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Re: '68 Speed Warning knob location ???
« Reply #2 on: January 16, 2016, 12:19:22 PM »
69 Pace (Brian) posted this picture last year on Team Camaro.

Another picture from another car posted there as well.
The thread-
68 Z/28 NOR 01B Orig motor/trans/rear
69 Z/28 NOR 07A Orig Block & GM Cross-ram/carbs
69 L34 Rest. Nova Father/Son Car
69 L78 Surv Nova Purch 4/69 31K miles
67 L89 Corv Tribute
68 Corv 427/400 Orig motor
07 Corv Z06
R 68Z build-


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Re: '68 Speed Warning knob location ???
« Reply #3 on: January 16, 2016, 07:07:38 PM »
STOP!! Do NOT drill any holes just yet!!

The 1968 U15 AIM drawing is INCORRECT. It was taken from the 1967 AIM and simply modified to add the extra hole.

HOWEVER, even though the 1968 U15 drawing indicates a 13/32" diameter hole was "supposed" to be drilled at that location, I don't believe ALL cars actually got that hole. And the reason I say that is because I have pictures of 6 cars in the database with U15 and only 1 of them has that hole (A 03C Norwood car shown below, and to be honest, it appears to be even farther than the .69" indicated in the AIM. Probably located in the existing square hole used for the power top switch on convertibles). The other 5 have the cable assembly installed in the "existing hole" (see below of a good example from a 1968 07C LA car using the "existing" hole and the 03C Norwood car using the "drilled" hole - which probably isn't really "drilled" and is in reality the square hole for the power top switch on convertibles. By the way, the 03C Norwood car is missing the rubber knob, but you CAN see the silver metal knurled cable the rubber knob attaches to sticking out of the dash).

In 1967, only cars with C60 received the outlet ducts, but nowhere in the AIM does it indicate that the U15 cable needs to be relocated because of the interference with the hose. But going by pictures of original cars with C60 and U15 (good example in the link above and the picture shown below), the factory DID drill a new hole to keep the cable from hitting the ducting.

Since all cars in 1968 came with the ducting, they made a note in the AIM dated 9-19-67 to relocate the cable to .69" to the right to alleviate this interference. However, as I stated before, I don't believe all 68's with U15 received this extra hole. I believe, going by the available data (and granted, there's not a lot since this is such a rare option), the cable was simply installed in the existing hole for most installations. Difficult to do because of the hose, but possible.

NOTE: In reality, a hole drilled .69" to the right of the existing hole (just a bit less than 3/4 of an inch) wouldn't interfere with the plastic speedometer housing. The cable would be just to the left of it, so again, the AIM drawing is incorrect.

First picture - 1967 with C60 and U15 (cable installed in a hole NOT indicated in the 67 AIM. Also note the extra washer not called out in the 67 or 68 AIM.)
Second picture - 1968 LA 07C showing the cable installed in the "existing" hole
Third picture - 1968 NOR 03C showing the cable installed in a location that appears to me to be even farther to the right than what the AIM indicates it should be! Probably in the square hole used for the power top switch on convertibles.)

« Last Edit: January 16, 2016, 07:28:19 PM by bertfam »
Ed "Bert" Bertrand
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Re: '68 Speed Warning knob location ???
« Reply #4 on: January 18, 2016, 09:18:48 PM »
Thank to all of you for the pictures and very detailed information on this.

I just checked my cable to Astro Vent duct clearance again and there's no way that "existing" hole work on my car. The Speed Warning control knob and the shaft it presses onto would be sticking through the hole at a 30 degree angle. There's no way it will come straight through because of the duct.

There's only one explanation I can think of as to why that existing hole has worked in other cars and won't on mine. My Astro Vent bezel and ball are reproductions. All of the other pieces of that ducting are original. All the seals are new. I had a heck of a time getting all of those pieces back together and installed. Probably because the original "accordion" section of the ducting has stiffened up over the years and won't compress like it used to. The dimensions of the new bezel might be different too. I had to push hard on the bezel to get it tight against the dash. It's possible that the piece of the ducting that is interfering with the cable is sitting lower than it was originally. It can't be moved now, though. It is in there rock solid.

I really don't have an issue with drilling another hole, especially since that's what the AIM said to do anyhow.  Only problem with that is if you put it where the AIM says too. (.69 inches center to center with the existing hole ), you'll drill right through a spot weld which I don't want to do.

Once I get the speedometer housing installed (a week or two away) and see how everything comes together, I may use that square hole that's for the convertible top switch or try drill a hole that doesn't hit the spot weld.

Thanks again for all the help.......Dave