I took the old cracked dash out in preperation for a new one thats on its way. While everything is out I plan to fix the hvac control system, replace dash bulbs, and a new speedometer cable.

What else should I do while everything is easy to get to? Im considering a new fan and heater core even though they work. I'm just trying to avoid ever having to take it all apart again.

Thanks,

John

 

I've got the dash out of my 70. In addition to your list, and to expand, here's what I'm thinking about doing.

- replace some of the dash lights with LEDs. The dimmer switch on my 68 burnt out because the incandescent bulbs just drew too much current and heat damaged the switch. On my 68 I didn't replace all the bulbs, just enough to reduce current draw. With some incandescent bulbs still being used, the dimmer function works...it won't with all LEDs.

Rebuild the tach and speedo and install all new cables.

Rebuild the radio. (May change my mind since a radio restore and rebuild for my 70 will be about $500. Whats the condition of the underdash speakers?

Install all new vacuum lines for the AC controls. Also, the vacuum line selector switch that's mounted on the AC contol wheels in the shifter faceplate. (Dr Rebuild)

Replace all underdash vacuum lines going to the headlights and windshield wiper door solenoids.

Also, I build a seperate harness with multipin connectors that allows me to reconnect all the speedo/tach light bulbs by just snapping the connector halves in place after the speedo/tach dash panel is in place.
Install extra ground wires...just in case.

Replace plastic oil line tube going to the oil gauge (if you have an early year C3)

 

I agree with 68/70vette plus the dash wire harness.

Gary

 

Under dash speakers for sure! I love mine I use them alot.

 

On the 1980 I would replace the heater core! This is a major pain job to do with this car. On the 1968-1977 cars you have the luxury of taking the passenger side dash pad out of the car. On the 1978-82 cars this is not an option.


68/70: I not trying to sound like I’m going against the grain on you, but the car is an 80. If I were doing a 68-77 I would be on board with all your suggestions since the speedo and tach can only be serviced with the pad out of the car.

The speedo: The speedometers on the 78-82 cars were less prone to failure than the old W series head used from 1953-1977 (design changed) so I would leave it alone unless you know there is a problem with it. If there is a problem down the road this is easy to remove after the fact. I have instructions on this on the site for how to do this with the pad in the car.

The Tachometer: The tach on a 1978-1982 car can be removed from the car by taking the front lens cover off the speedometer tach cluster. There are three screws on top and two on the side. Once this lens is removed you can remove the three screws that hold the tach to the plastic housing and then remove the tach by pulling it out from the front! I know. . . I wish the design was so easy on the earlier C3 cars. This can be done without removing anything but the lens cover. So unless you know there is a problem with the tachometer I would let it slide too! It’s too easy to remove should you have a problem down the road and in fact about a 20 minute job to remove and install at most.

Vacuum line repair is a must! There is a schematic on our site that will show you how they operate at what control position. http://willcoxcorvette.com/repairand...lp.php?hID=247

The one on the site is for a 79 and they are the same. If you have an assembly manual it will be in this book too. If you want me to post one specifically for the 1980 this is not a problem either. Just post back or better yet shoot me an email to willcoxcustomerservice@willcoxcorvette.c om

Speedo Cables. . . Again a must! It’s to easy to feed them in place with the pad out of the car.

Now I’m going to go out on a limb here. . .

If you take heater box out to do the core, right behind the center plenum is a vacuum pod. This vacuum pod controls the main distribution duct. In the diagram it is called the A/C air valve. This valve is connected to a little section of plastic on the flapper door! This plastic breaks and will not allow the AC to distribute air properly in the car. Easy fix with the dash out if it is broken. Hard fix with the dash pad in the car.

I would inspect the main windshield frame for rust! This is a sign of a windshield leaking or a windshield frame leak problem.

The upper speakers should be replaced and it's easy to install them in the new pad before it goes in the car. It can be done from the top un-like the 68-77 cars. It is easier to do this when the pad is out. I would consider speakers some where else in the front too. Possibly the kick panels?

Check the vacuum pod on the right hand kick panel for proper operation. Make sure the vent door is sealing up properly when closed.
.
Good luck,

 

Cool, thanks for all the suggestions. That vaccuum diagram is exactly what I needed. I should be able to figure it out as I just replaced all the vaccuum lines for the headlights. The more I think about it I probably will replace the heater core. Heres a couple of follow up questions...

Where does the vaccuum source for the hvac attach to the engine? I don't see anything that will fit a tube that small. Do I need an adapter?

Do the headlight control switches fail often? That thing looks like a pain to replace also.

On the hvac doors that open and close to redirect air flow the rubber around the doors is falling apart. Where can I find replacements? I'm not even sure what to call them.

The fresh air door has been sealed shut by someone. I've read that many people do that as too much heat from the engine gets in. What are your thoughts on that?


Thanks again,

John

 

C3dude,
Willcox was on the mark with their advice. Also if you are putting in the heater core, BE SURE that you really have alot of solder at the points where the two tubes are soldered to the core tank. Reghardless what inspector says that it "passed". In many cases the two tubes will tough and will not be soldered together and if you flex it to much, well you will be doing it again. Also if you are changing the heater hoses, get the hoses that have a 90 degree formed bend in the end. This bend will make it so you can route them to where they need to go and not put to much pressure on the tubes of the heater core. You can use bulk hose off of a roll, but I find that on some years the 90 degree bend is very useful.
If you are putting in a new fan blower . Think about upgrading it to the wider fan. This allows about 20% more air and does require you in making a 1 inch spacer to go between the motor and the housing. I do it often and it does help greatly. Also seal up all ducts with adhesive backed foam tape that you can pick up at any hardware store. This makes sure that the air get to wher it IS supposed to go. The way GM sealed up the systems on the 84-96 is proof that the earlier Corvettes need this to be performed. In fact I believe the fan motor I use is out of a 84-85 vette when doing the upgrades but on the NET there are other choices. So check it out. If you do the fan motor, and depending on the size of your hand. You can reach through the hole for the fan from the wirer cowl and feel if you have leaves and debris on the air entering side of the air conditioning evaporator core. I do not have to do that anymore because I now have access to a borescope. If you have a buddy who has one, use it. Leaves and crap get in there over time and cut off the amount of air that actually can pass through the evap core. Modifing a vacuum cleaner hose and using air pressure from the other side, (due to the heater box being out) can allow you to blow and vacuum the crap out. That is if you have much. Around where I have my shop, I see it alot.
If you are wanting to cut down on the heat fron the firewall and transmission floorpan area, you should seriously think about using DYNAMAT EXTREME and the EXTREMELINER. With you having the dash out and summer coming. It is the best time to do so. I do on the average about 4-6 cars a years It does take some time but is well worth it and I have tried other products but I feel it works the best. If you need info just PM me.
Good luck, sound like you are wanating to do things RIGHT! GMC "DUB"

 

Here is a better dia. for the 1980 It's pdf and better quality.

http://willcoxcorvette.com/repairand...lp.php?hID=273

 

Does your clock work?

 

Another good point!

Willcox

 

Just finished interior overhaul on my 81. All good suggestions above. Heater core is a must. Try to get a US built core. First one I got was from autozone made in china. I tested it out of the box and it leaked. Like others have posted, new gage bulbs, speedo cable, check the printed circut boards for cracks, headlight switch resistor coil for the dimmer. I also installed new vent louvers and seals. Wilcox supplied 90% of the parts for my car. Very pleased with ther results.

 

Hey Wilcox,

If you take heater box out to do the core, right behind the center plenum is a vacuum pod. This vacuum pod controls the main distribution duct. In the diagram it is called the A/C air valve. This valve is connected to a little section of plastic on the flapper door! This plastic breaks and will not allow the AC to distribute air properly in the car. Easy fix with the dash out if it is broken. Hard fix with the dash pad in the car.

My '73 has this problem with the broken plastic part on the center plenum door. You say that this is an easy fix. Can you please give us some detail about this fix?

Thanks,
John

 

Is this the broken part you are talking about? This is on my 71 and I also need to repair it.

 

Rosco,

Yep, that's the piece I'm talking about. There's a guy in Illinois called Piper Corvette that sells them used for about $50.

I just discovered that my "Defroster" plenum door is supposed to be double acting, spring centered. As it turned out, the spring lever was a little bent and caused it to not travel thru its full motion. All it took was a little tweek with some needle nose plyers and now it's working nice.

There is ssoooo much detail with these cars. I'm having a ball!!! All this began with a simple replacement of the A/C wiring harness. I'm trying to stay strong and not pull the body off the frame

John.

 

[QUOTE=JohnRR;1574100856]Rosco,

There's a guy in Illinois called Piper Corvette that sells them used for about $50.Wow $50.00 I think I will wait to hear about the "easy fix" first. For what its worth I can't find a replacement anywhere.
Thanks

 

Have a good look at the two printed circuit boards (mylar) behind the gauges. If they are looking brittle tired, add that to the list.

 

would also be a good time to check the bolts in your drivers door TOP hinge. Make sure they're tight. If they become loose, you MUST remove the instrument cluster to gain access. But with the dash out, would be really easy to check the torque on these bolts..while ur at it,check the pass. door top hinge bolts too. the shop manual says you can reach the pass side easliy, but why wait- do it NOW. mj