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I’m working my 1968 late build Corvette and have the left dash out and on the work bench, and have a few questions that I hope to get help on.
1) The speedometer trip meter works as designed and when pushing in and turning the flexible cable, the numbers advance. The trip meter and odometer numbers also advance when using a drill to activate the speedometer. However, am I correct in thinking that when pushing in the flexible cable it should reset the trip meter to 000? If so, what could be causing my unit to allow the advancement of numbers but not the resetting to all zeros?
2) I’ve read on the forum that lubricating the speedometer gears should be done very sparingly, but I have not been able to find what lubricant is the best to use. Or does it not matter as long as very little it being used?
3) What is the best way to clean the numbers on the trip meter and odometer?
4) Finally, I’ve got what appears to be a condenser attached to the back of the tachometer, although there is no wire attached to it. Is this the condenser used to prevent radio noise? If not, what is its purpose?
Thanks for any help on these questions. I’ve learned a lot on this forum and really appreciate the information that’s provided here!
1. You push in and turn it to set to zero it is not an automatic reset when you push it in.
2. Use a graphite lubricant which should be available at auto parts stores and also look at this link, gears would be dry lube and pivot points oil. https://www.corvetteforum.com/forums...brication.html
3. Try some rubbing alcohol but try to test it first.
4. Capacitor locations https://www.corvetteforum.com/forums...capacitor.html
Hi wp,
Here's a photo of the trip odometer re-set mechanism.
I don't know if you can spot something that's different on your 68's re-set that's not allowing all zeros to appear.
I'm sorry I can't be more helpful.
Regard,
Alan
MelWff and Alan 71, thanks for your quick reply and the links, very helpful.
Alan 71, sorry if I was not clear. By turning the the flexibel cable I can manually get to all zeros, I was wondering if by push it in fully if the trip meter would automatically go to "all zeros", like on my regular cars. MelWff answered that for me.
As a followup: I've only tried to change the trip meter reading by advancing the numbers. Would it damage the unit to turn the cable in the other direction? I'm thinking it would be easier to turn it "back" to zeros, say from 235 miles, rather than all the way forward to zeros.
If it's like the 69 turning the **** one way resets all the numbers equally then you continue rotating till all are at zero. If you turn the **** the other direction it resets each individual number and is a longer process. Also, be careful when installing the dash back in as the reset cable tends to get stuck and bend on the metal support right behind it resulting in a cable that binds or doesn't work at all. Stick your head under the dash when the left side is almost in and make sure the cable is free and clear.
Hi Canada, the cable was not working prior to pulling the dash out of the car, so maybe that's why. Actually, I was surprised I was able to get it to work on the bench, after just cleaning up the cable. So now, instead of thinking I "fixed" it, I'll just remember to check the routing as you suggest.
And while I've got it out, I'll also check to see if mine will work like your '69. I'm hoping it does.
Thanks for that information,Canada. I just tried turning the trip meter cable backwards and as you suggested, it rolled all the numbers together, but all the 8s are now lined up in the speedometer window. I put a little pressue on it but I couldn't get it to roll past the 8s so all the zeros would be showing.
Do you believe, since I'm probably not the first one to open up this speedo, that they may have been put back together incorrectly? If so, any idea on how I could fix this?
I haven't heard of that one before. Unlike a newer speedo, when all the numbers line up they will rotate past the zero mark and will go around again (and again if you want). You have to stop at all zeros as it won't do it for you automatically like later years. Not sure why it won't go past eights though. It shouldn't stop at all and should just continue round and round with all the numbers lined up the same. Turning it in the opposite direction will rotate the 1/10's forward then the miles forward in increments of 1. When you get to all 8's and it stops, what happens if you turn the **** the other way then back again? Also make sure the **** is pushed in fully.
Last edited by CanadaGrant; Feb 14, 2018 at 06:31 PM.
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try releasing pressure on the cable , then turning it a little further and pushing in again. You could have a burr on your cable that is getting ung up. Mine is a little stiff as I rotate it but I can get through the rough spot and it goes to zero.
Like staed above , be careful cleaning the numbers, the odometer may be embossed into the plastic so it may clean easy, BUT I tried wiping the dust off of an old speedometer faceplate and smeared the numbers. If you have to clean that part I would use canned air
Hi RR, thanks for that little process you go through. I tried it on mine but it didn't work as how I understood the steps in your post. However, as I was trying it, I discovered that if I advanced the 1/10 a few numbers and stopped on the 0 in the 1/10 column, and then reversed my turning, all the trip meter numbers would start to turn and when all the zeros lined up they would end up in the speedometer face window. It seems a round-about way to get there, but as long as it continues to work, I'm good with it. Thanks for the lesson!
Regarding the cleaning of the sppedo faceplate, I learned a long time ago on another car that I've got that they must have used water based paint on them because of the smears I created. I ended up cleaning most of the smears off with a damp Q-tip so now it's hardly noticeable.
As a follow up question, does anyone know why my speedometer case/shell would have seven holes for lights bulbs rather than six that I’ve seen in the pictures I’ve viewed, including the diagram in the 1968 Assembly Instruction Manual? The seventh hole is right above the one labeled “GRAY” that is in the lower passenger side corner near the trip meter flexible cable. In fact, the hole cuts out the “G” in the GRAY stamping. The hole appears to be "punched out" just like the others in the case, not drilled out by a previous owner. The tachometer case has six.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
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you should have 6. 4 marked gray, one at the center bottom for the signal(blue) and one up top for the brights. Can you post a pick so we can see which one isnt being used? I have an early 68 so maybe yours is different.
If you look in the hole is it partitioned off from the case like the turn signal, if you shine a light in it does anything light up?
Last edited by Rescue Rogers; Feb 16, 2018 at 10:47 AM.
Since you have your speedo out, there is a gear that fails fairly often. I believe it's from lack of lubrication.
It's the main gear that is driven from the speedo input shaft to advance the numbers.
It's very difficult to see it's condition without removing the shaft for inspection.
I'm in the process of replacing that shaft as mine failed last summer. The lubrication had literally turned to dust and the gears wore out.
Hi Barry, thanks for the photos. What issues/symptoms did you have to make you want to get deep into your speedometer? Mine actually works well with the exception of being able to easily bring the trip meter numbers back to all zeros. Is that one of your issues as well?
Also, did you follow any instructions sheet to break down all the pieces, or just carefully start taking it apart? I’ve looked for that information online and in YouTube but I’ve come up empty. I'm not sure I've got the courage to completely disassemble the inner workings of my speedometer... yet.
Hi RR, I got so wrapped up in trying to upload the picture of my speedometer case (after many failed attempts) I didn’t answer your questions. Sorry.
There is no partition that separates this extra hole light bulb hole in my case, that’s what has me wondering why it’s there. I also checked the wiring harness schematic and the AIM but found nothing.
[QUOTE=CanadaGrant;1596591004]I haven't heard of that one before. Unlike a newer speedo, when all the numbers line up they will rotate past the zero mark and will go around again (and again if you want). You have to stop at all zeros as it won't do it for you automatically like later years. Not sure why it won't go past eights though. It shouldn't stop at all and should just continue round and round with all the numbers lined up the same. Turning it in the opposite direction will rotate the 1/10's forward then the miles forward in increments of 1. When you get to all 8's and it stops, what happens if you turn the **** the other way the
oops
Last edited by lvmyvt76; Feb 16, 2018 at 04:17 PM.
RR, I thought the same thing but the stamped date on the back of the speedometer face is Jun 11, '68 which is just prior to the build date of my car. Of course, that doesn't rule out that this case could have been a replacement for some reason by a prior owner.
At this point I think I'll just put a piece of duct tape or some other material ove the extra hole to close it off. When I took this speedometer apart I found a very large mosquito (dead) in there, so I'm guessing that may be how he/she got in.
I THINK you are supposed to pull on the **** to reset the meter
In an older C3 if you pull it down the only thing that will happen is you will end up with the rubber **** in your hand. Push up, turn clockwise to reset, counter clockwise to set the numbers where you want.
1968 Speedometer Questions
