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Discussion Starter #1
recent purchase of 74 convert 4spd L-82...fun car...but a lot of heat coming from the drive tunnel.

What is the best way to address this ? Do the cosmetic pieces on the tunnel come off easily to add heat insulation ? It looks like under the floor carpeting has already been done, but only partially, not all the way up the drive tunnel.

Bill C
 

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Discussion Starter #3
c3 tunnel heat

Thanks Nick,

I have not been under the car yet....nor had the cosmetics off the console (do they come off easily ?)

I did order the tunnel heat shield and have it, but not installed yet.....does this go undernearth the car or inside on top of the tunnel under the console cosmetics ? (don't laugh...this is new to me ! )

Was not aware of the foam heat tunnel heat shield...same question...is this underside or installed in the car under the console ?

BC
 

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Heya,

They both go on the outside and above the tranny. The foam collar 'helps' preventing engine compartment hot air from flowing inbetween the transmission and the tunnel, the shield reflects the heat coming from the tranny. I have them both in boxes, but my car is far from ready to assure you it is going to help. When the car still drove, those two parts were not in and yes the center console became very warm. In another box I got a full set of sound and heat insulation, again maybe in a month or two I can tell you if it was worth it or not. C3's are prone to interior heat anyway, as almost everyone in the C3 section will agree on. There have been many threads about, do a quick search to see what other people wrote about it ;)
A good read is also this site from fellow forum member Vettfixr !http://mywebpages.comcast.net/vettfixr/page13.htm
Removing the interior is straight foreward! Also get a Assembly manual http://www.ecklers.com/product.asp?pf_id=38157&dept_id=226 typical for your year of corvette. It shows you exactly where every part goes, and how it is fixed, clipped, strapped etc. It's a must if you are going to DIY!

Hope it helps and if I'm talking rubbish please someone chip in !
Nick
 

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Discussion Starter #5
C3 Tunnel heat

Thanks Nick,

I ordered the assembly manual and the foam piece. I am sure the assembly manual will show me, but does the heat sheild just slip in place underneath?

The way it's made with a square hole in the top, looks like the tranny has to come down, or the shifter needs to come off ? Or can it just be slit to go around that shifter and linkage ?

BillC
 

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'Unfortunally' I have a automatic so there is only a cable running through that hole which can easely be disconnected. My transmission is out, so I have full acces to the underbody. The heat shield is actually held by these little retainers rivetted to the tunnel. You slide the insulation over and bend the tabs (http://ecklers.com/product.asp?pf_id=26952&dept_id=1628)
I'm not sure if it can be done while a manual transmission is mounted, sorry :(
Nick
 

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Discussion Starter #7
heat tunnel stuff

Thanks Nick....i think I will cheat and slice a line to slide it past the manual stick , unless it's an easy disconnect.

BillC
 

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Discussion Starter #9
tunnel heat sheild

Excellent photo !! Thanks for taking it and sending. I did receive a couple of clips with the heat sheild....not sure where they go, but I am sure the assembly manual will help....wondering if I could pop rivet this in place with some washers or metal tabs ?

Bill C
 

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Thanks for the plug in this thread guys. I would however like to add something to the link on insulation. Its a good exercise but I doubt that is where your problem is coming from. I have a 74 also and battled the heat problem for quite a while until I stumbled on to the fix below. I published this fix in Corvetteforum under tech tips and it was also used in an issue of Corvette Fever magazine. Read the cut and paste from the tech tip below and take a look at the pic to see what I'm talking about. This fix removed about 95% of my cockpit heat. BTW, that is not my car but a pic someone gave me to illustrate the area in question.



Like most of you I've battled the problem of cockpit heat. I think I've finally found a problem in my 74 that may be common to a lot of C3s and which may cause heat to come in to the cockpit no matter how much insulation or sealing is done to the heat/AC system. Over time I've noticed that I always got an "engine" smell in the cockpit. I figured it was air coming out of the hood and being drawn into the heating system through the air intake in the wiper trough or air leaking into the system through the heater box. I put a wiper cover on earlier this year and I could see that the hood sealed really well in this area so this shouldn't cause a problem with air leakage past the gasket. Since I pulled my heat/AC system out last winter and resealed everything I discounted this as a cause for heat leakage also. When doing the heating system I also installed a shutoff valve for the coolant. I also insulated my entire cabin so I'm not getting heat through the floorboards or the body. This left the air intake on the system as a possible source. I removed the right hand dash pad and kickpanel which exposed the flapper mechanism for the inside/outside air control. I removed the vacuum motor and flapper mechanism by unbolting the two bolts that hold the motor, moving it out of the way, and unhinging the flapper. This is done by pulling down the top spring loaded pin, pushing the door into the fenderwell and twisting it so that it can be removed from the inside of the car. I then started the engine with the hood closed and the heat/AC off. I felt hot air coming into the plenum from the engine compartment. This plenum is secured with the same adhesive that holds the rest of our body panels in place and like those the adhesive will dry and crack over time. Anyone who has dealt with stress cracks on the fenders can attest to this. Remember also that air leaking into this plenum will be coming directly off the exhaust system and with headers the problem is exaggerated. To seal this plenum I used windshield sealing caulk. You can get this at your local parts store for around $5 a roll. I used the caulk to seal around the entire perimeter of the plenum, or as much as my arm would reach since you're working through the flapper hole. The most important areas to seal are the forward and lower area since that's where the majority of the heat will come from. The rear area is sealed against the forward door jam and really shouldn't leak hot air. After doing this I repeated the test with the engine running and felt no heat entering the cockpit. I reinstalled everything to complete the job. I've only driven the car twice since then but I can tell you that there was a vast improvement. I took the car to work on a day when the temperature hit about 85 degrees. Before the fix I would have had to have the AC running or the heat would have been unbearable in the footwells and even worse with the t-tops off. I ran the car home that day with the t-tops off and the footwells were no hotter than the rest of the car. I've also noticed that the AC tends to run a little cooler by not having to fight the heat coming into the system. So far I also haven't had that "engine" smell anymore. I'm hoping that as I use the car more, in different situations, I'll be able to report more benefits from this fix but until then I thought I'd give a heads up to everyone. For details on the cockpit insulation go to my website. You'll see the article on insulation and also what you have to remove to reseal the heater box. UPDATE 9/12/03: Since posting this topic in the C3 forum over a year ago I've had time to live with this fix and I can tell you it's completely eliminated the footwell heat common to C3s. I've also recommended this fix to others who have had similar success. One tip that I left out in the original post was to put a soda straw through the bottom of the plenum until it sticks out below the rocker panel. Seal the plenum all around the straw and when you've completed the sealing pull the straw out through the bottom of the rocker panel. This leaves a drain hole that will channel water in the event that it enters the plenum. Other than that it's an afternoon fix that really pays off. Good luck.
 

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billc: purchase the assembly instruction manual for your '74. The AIM is worth the cost. Order a reproduction owner's manual if you don't have an original.

:thumbsup:
 

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Discussion Starter #12
74 heat solution

Interesting write up....Can you describe where that picture is taken from...? What area of the car does the picture show.

Bill C
 

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It's the front right side between the front wheel and the door jamb with the fender taken off, you can see the heater box on the middle right side of the picture :thumbsup:

Indeed a nice write up might wanna check that as well, now that everything is still out of the car !

Nick
 

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Interesting write up....Can you describe where that picture is taken from...? What area of the car does the picture show.

Bill C
Here's a pic with the area outlined. It's where the fender is glued on to the body to create a plenum area for the fan to draw air from. You can see how the original opening at the bottom is inches away from the hot exhaust. This is where the majority of hot air is drawn in to the system. Hot air also comes in anywhere the body separates from the fender due to old adhesive.

 

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Discussion Starter #15
plenum seal

I think I got the idea ....this area is where the cutout in the fender is located to bring in fresh air ? I am wondering if any of this can be resealed from the engine compartment or from below ?

BillC
 

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It creates a space where outside air or recirculated cabin air is drawn in depending on the position of the flapper door you see mounted on the body. This door is controlled by the heat/AC controls via a vacuum motor. The only way you can reach the area is through this flapper door from the inside of the car. It's not that difficult once you remove the flapper. In fact the way I discovered this was by accident. The flapper wasn't closing properly so I removed it to see if something was binding. While I was doing this I had a droplight on the floor just under the front fender. I couldn't figure out where the light was coming from when I looked into this area. I got an inspection mirror and was amazed at the amount of light that you could see from inside this "enclosed" area. I then started the engine and was even more amazed by how much heat was pulled in to this "enclosed" area from the exhaust. Trust me, once you seal all around this plenum and keep the exhaust heat out of the system the cabin will be 20 degrees cooler. Just don't forget to use the straw trick so that any water that may enter the area has a drain.
 

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Discussion Starter #17
c-3 heat

Thanks again,

I plan on doing all the other 'fixes' for the heat, but this may turn out to be the most important. Currently when I drive the car with shorts on, I cannot touch my right leg against the vinyl lower console...it's too hot to touch. So I am fairly certain I need to do some insulating in that area.

Your point on the fender well is important, and now that I think about it, the guy I bought the car from did say he had put in a glass patch to stabilize the fender, so obviously it has pulled away....and I do have a small flaw in the otherwise brilliant paint, on the left front fender...which I guess is a stress fracture ?

BillC
 
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