Don't use RTV to seal the transmission tunnel

[Ed_K]

When I was putting my car together last year, I saw that our usual suspects didn't sell the seals needed to install the fiberglass tunnel to the floor and firewall so I convinced myself that I would never have to get under there for years and years and used several tubes of Silicone RTV.
/bcforum/images/%%GRAEMLIN_URL%%/wall.gif /bcforum/images/%%GRAEMLIN_URL%%/wall.gif /bcforum/images/%%GRAEMLIN_URL%%/wall.gif Doooh !
What was I thinking !
I will be spending the next few days repairing the fiberglass bottom lip of the tunnel cover. I have already re-welded and ground smooth the metal knife edge around the floor.
Don't make this same dumb mistake as I did !
PS... Our usual suspects offer a new tunnel cover with a cut out for an ashtray, without the pronounced inner ridge that fits over the floor's knife edge, the length appears to be somewhat shorter than my original. This part must be for an earlier model of the 3000 because it is so different than my original thus I MUST repair my original having sent the new one back for a refund. Perhaps another vendor has a serviceable used one available if I can't fix my original one.

 

[Bugeye58]

RTV is the spawn of the devil!
Get some high density foam strips.
Jeff

 

[Ed_K]

I thought about using high density foam strips but don't they start to decompose above 150 degrees ? I bought some EDPM automotive/marine weather strips from Lowes. I really don't know what their maximum temp rating is supposed to be either. Have your high density foam strips held up OK over time ?
Has anyone used the EDPM automotive/marine weather strips ?
How do they hold up ?
Ed

 

[Bugeye58]

Ed. I used aircraft cowl seal material on my GT6 and Spitfire. I'm not blessed with a big Healey. I bought it at my local aircraft hardware store. It's held up admirably. A 9' roll, 1/8" x 3" costs about 40 bucks, and it's rated to 425*F.
Here are the properties of EDPM.
Jeff

<span style="color: #FF0000">Mechanical Properties </span>
Hardness, Shore A 40 - 90
Tensile Strength, Ultimate 17 MPa
Density 1.50 gcm-³
Abrasion resistance 450 mm3
<span style="color: #FF0000">Thermal Properties </span>
CTE, linear 68°F 576 µm/m-°C
Maximum Service Temperature, Air 150 °C
Minimum Service Temperature, Air -54 °C
Glass Temperature -54 °C

 

[Ed_K]

Jeff,
Thanks for the info. It looks like EDPM is a poor choice as it gets very hot under that transmission cover.
I'll take a look at aircraftspruce.com at their cowl seals.
Ed

 

[Bugeye58]

Ed, I think their P/N 05-00826 is comparable to what I used.
Jeff

 

[Ed_K]

Jeff,
I think this is what you were talking about;
https://www.aircraftspruce.com/catalog/appages/siliconecowlseals.php
Ed
.... We crossed updates

 

[Ed_K]

Dumb question;
what does " w/mat " mean ?

 

[Bugeye58]

I think they have a fiberglass backing material on them, but I'm not certain. You may want to contact them to verify my assumption.
Jeff

 

[Ed_K]

Jeff,
Thanks for the good information and Merry Christmas !
Ed

 

[Bugeye58]

Same to you, Ed.
Jeff

 

[GregW]

I haven't researched this, but here is another thought. Maybe check a boating supply for engine cover seals?

 

[Ed_K]

Greg,
I think that is what I bought at Lowes but it won't last very long under the higher temps found under our transmission tunnels. I suspect that the temps don't get quite as high under boat engine covers due to the ample water cooling of the engine ?
Ed
.... Or perhaps it was just meant for hatch covers and trunk seals ( UV resistant instead of heat resistant ).

 

[vette]

Hi Ed, I'm sorry to hear that you had trouble with the compound that you used. I used a silicone chaulk that I bought from a hardware store. Since then I've had the trans cover off twice and yes it was stuck pretty good but I ran a putty knife all around the edge and it came off pretty easily. I wonder if RTV has much different properties than 100% silicone. I suppose it must because of the temperture of where it is used and the resistance to oil and gas.

 

[healeyneil]

I used silicone to seal down my tunnel, but I smeared some vaseline over the chassis/floor where the cover meets. That way the silicone makes a nice seal, but doesnt stick to the floor

 

[Randy Harris]

I used HD foam insulating sealer last year - basic type sold in hardware stores as 6'strips with adhesive backing. Have had the cover off twice. Works like a charm. So far no signs of heat related failure at all. If it does break down after a few years, no biggie. Just scrape it off, re-apply and I'm good to go for another few years.
Randy '66 BJ8

 

[Dave Richards]

I used HD foam insulating sealer last year - basic type sold in hardware stores as 6'strips with adhesive backing. Have had the cover off twice. Works like a charm. So far no signs of heat related failure at all. If it does break down after a few years, no biggie. Just scrape it off, re-apply and I'm good to go for another few years.
Randy '66 BJ8

I agree with this. I used a HD foam strip from true value hardware store, at a suggestion from someone here. It's very similar to the original material I removed and it's very inexpensive. It was a very simple replacement.

I also installed a "space age" insulating material (from aircraft spruce, also a suggestion from someone here) to the bottom of the tunnel.

I've been amazed at the difference in the heat level in the cabin.

 

[Ed_K]

I used silicone to seal down my tunnel, but I smeared some vaseline over the chassis/floor where the cover meets. That way the silicone makes a nice seal, but doesnt stick to the floor

If one uses silicone or RTV that's the right way to do it.
My brain must have been asleep the day that I decided to do it.

 

[John Loftus]

The original seal along the bottom edge was a J shaped piece of rubber trim that covered the bottom flange and wrapped up and over to the top of the flange. I'm still looking for a good replacement. Silicone or EPDM type materials would have good heat resistance. Might try some U shaped parts from McMaster Carr and trim the one side of the U so that it fits properly. Interested if anyone has found something like this.

Cheers,
John

 

[suprgnat]

Jeff,
Thanks for the info. It looks like EDPM is a poor choice as it gets very hot under that transmission cover.
I'll take a look at aircraftspruce.com at their cowl seals.
Ed

FYI the EDPM is rated at 150 C, which is 302 F. I hope it's not getting that hot under the transmission cover.

Darn metric system. At least our cars were built before THAT was foisted on us...