Throttle Rod Seal

Throttle Rod Seal


Here’s a different way to seal the firewall when you have operating rods running through it. Operating rods in the form of hood releases and throttle rods.

These little gadgets do an amazing job of keeping the engine compartment heat out of the*****pit and it looks like they will last considerably longer than the typical thin rubber bellows used on some cars.

I realize that a lot - a whole lot in fact - of hot rodders use throttle cables instead of solid rods. They work well and are a quick and easy answer to an old problem. Even so, I prefer solid rods for a couple of reasons. The challenge of making a good setup, proper ratio’s, solid feel and all the stuff that goes into a good operating throttle system. The other, I like being able to apply pressure in the throttle close direction which is something cable systems can’t do. I am familiar with double throttle cables, one for opening the throttle and the other for closing although the ones I’ve seen have been on bikes and not on hot rods.

The problem you run into with throttle rods is they rise and fall along their length due to they are operating the carburetor arm, which swings in an arc. Throttle rods operate bell cranks as well - this depending on the throttle setup and a bell crank swings in an arc as well Following along with the arc of the carburetor arm and/or the foot pedal is what does it. Throttle rods also move side to side due to engine torque. All of which creates a seal problem where the rod exits the firewall. This little problem neatly solved by the factories long ago with their nice little flexible bellows rubber seals. They do a good job, but most of them that are in cars older than say 20 years, they’re all done. Split, cracked, broken and leaking hot air. Not to mention try to buy one somewhere.


So here’s an easy way out, all that’s required is a small sheet of 1/8" Teflon and a small piece of 1/4" plate. Spinning the aluminum pieces up in a lathe makes life easy, but you can knock them out with nothing more than a drill press, file, razor knife, hole saws, and a home made mandrel to hold the aluminum piece. The mandrel made from nothing more than the proper sized bolt, two flat washers and two nuts with the bolt head sawn off so it fits into the drill press chuck.

To illustrate the typical range of travel between idle and full throttle, here’s a couple of photos.
This first one, throttle at idle.

 

This view shows the throttle rod depressed with the carb*****erflies fully open. Note that the Teflon floater has moved with the throttle rod.

 

There’s a couple different ways to do these. One way requires a lathe in addition to the tools mentioned above, but you can turn out an equally good one without a lathe.
You’re going to have to use your imagination here, because I don’t have all the pictures in as much detail as I’d like, but the few I have oughta do it.

The next photo shows the components of the one made without a lathe and in fact is the heat shield in the 31 roadster.

This first photo shows the basic components for the 31's heat shield. 2 1/4" diameter, but 2 3/8" or 2 ½" would probably work better. That because things get pretty close with the mounting bolts and the floater. Regardless, if you’re careful everything fits.

The undrilled piece upper left is the escutcheon for the inside of the firewall. I drill and tap these for 1/4-20 to give them a little better finish because they are visible from the inside. Regardless, a bolt and chrome or stainless acorn nut would look just as good.

The hole size in the escutcheon is dependent on how much vertical and side to side travel your throttle rod has.

Not seen is the firewall side aluminum outer piece, but it’s under the Teflon pieces. Disregard the extra small diameter Teflon piece. That went to the hood latch rod that also has a heat shield. Not shown as well is the Teflon base piece - same OD as the aluminum piece - which is important for proper function.

Since the retaining bolt holes were not drilled yet, the inner Teflon ring is also not notched for location retainment. Plus you’ll need a notch on each side of the Teflon floating piece. Make these so the inner Teflon ring is captured in place by the retaining bolts through the notches. Cut the Teflon floater a little sloppy so it can move around, but not so sloppy that it moves out of location on the bolts..

The throttle rods in my cars are 1/4" stainless rod. If you’re using the same size, drill the Teflon floater 1/4" as well. It will be a snug fit at first, but after a few days of use it will fit exactly as it should and slide freely on the 1/4' rod. After that, wear is virtually negligible and the throttle rod in the 32 fits as well today as it did several years ago.

You’ll have pay attention to the firewall hole size and make the OD of the entire piece large enough so it will lap over the hole and the bolt holes will fit inside. That’s the reason for the fairly large firewall hole seen on my 31 in the Billet Loud Pedal post from a couple of days back.

The reason for setting it up this way is to allow vertical and horizontal adjustment of the heat shield to accommodate the throttle rod so the shield operates properly as well as allow carb and/or intake manifold changes later on down the line. Not a whole lot of movement is required, but even if you plan for no intake/carb swaps, being able to move the heat shield will allow it to be placed exactly were it needs to go. The heat shield in my 32 can move about 3/8" and that’s enough to allow for the use of three different intakes with three different carb heights.
What you’re gonna end up with is a sandwich of sorts. Starting from inside the firewall, the aluminum escutcheon, firewall, Teflon base, Teflon inner ring with Teflon floater inside it and outer aluminum piece. Incidentally the escutcheon works well as a carpet hold-down and the upholstery guys seem to like em. Better than fooling around with a trim piece, plus the carpet is held down securely.
The only other thing you have to watch is that the floater does float inside the aluminum outer piece and over the Teflon base. Since all the Teflon pieces are made from the same piece of Teflon it can be a close fit, but clearance can be obtained by sanding the Teflon floater a small amount. Which can take some doing due to the slippery aspect of the Teflon.

 

The lathe cut heat shield works out very much the same except you don’t need the inner ring of Teflon between Teflon base and outer aluminum piece. What you want to do here is cut a relief inside the outer aluminum piece so there’s room for the Teflon floater to float against the Teflon base and the inner surface of the outer aluminum piece. Since the Teflon is .120 thick, cutting the aluminum about .130 deep works fine.
This is the style floater in use on the 32 and it works great. Hot air stays out of the*****pit and there is no binding anywhere. Binding being something you definitely don’t want with a throttle rod setup.
I made a similar heat shield for the 32's hood latch control rod.
Incidentally, making brake pedal escutcheons etc. in a similar manner works very well. You end up with a good heat shield as well as a carpet tie down finish piece.
Brake pedal escutcheons are very easy to make.
A simple disc of aluminum drilled in two places for the mounting bolts, a relief, lathe cut into the aluminum for the Teflon seal and that’s about it. Except for the rectangular hole to accommodate the brake pedal arm. A rectangular hole easily cut with an Exacto knife. Cut the hole right to size. IE: ½ x 1" brake arm, cut a ½ x 1" hole. The Teflon will seat itself after a while and will not scratch the finish on a chrome plated piece. Paint or powder perhaps a different story, but I don’t think so.
The brake escutcheon can also be the same simple disc of aluminum without a lathe cut relief and it sits on top of the Teflon seal.
The 32's brake escutcheon shown in this photo. It’s off center because there is room within the relief for the Teflon to float and the escutcheon shifted a little bit when the bolts loosened. This particular piece reinstalled with allen bolts and nylocks and it doesn’t move now.

 

A nice finishing touch once the carpet is in is to take note of how much of the allen bolt sticks out beyond the drilled and tapped inner aluminum plate - unless you did the bolt and nut bit - and cut the allen bolt so it’s flush with the inner aluminum plate once it’s torqued down.

You’ll note as well the Gennie Shifter throttle pedal in the 32 sits on an aluminum escutcheon style base.

 

All in all a fun little project with big benefits. Running the roadster in our hot summer weather - 100 degrees + - the hot air blowing on your knees got old.
A lot of guys look at and make note of the Teflon heat shields at the rod runs, but few ever ask about them. The ones who have are always surprised to find the Teflon floats within the aluminum disc.

All things are not as they seem I guess....


Just for fun, here's the 32 with its new hubcaps and old mags.

 

.........awesome! Clark, did you get that?? You need to redo the "SoWhat" 999 special with these to get it ready for York!!! (just kidding....neat idea, great instructions and photos)

 

thanks again C9,

I think I'll use your basic design but use painted steel instead the aluminum plate.

Paul

 

[ QUOTE ]
I think I'll use your basic design but use painted steel instead the aluminum plate.


[/ QUOTE ]

Ya know, I bet the right soft plug would work for the Teflon retainer.
I've seen some with a pretty flat outer surface.

Or - and you've probably thought about it already - a very short piece of tubing with a flat piece welded on would do it.

Light weight = horsepower.
Steel weighs more than aluminum.
Course, if you got enough HP, makes no difference....

 

[ QUOTE ]
thanks again C9,

I think I'll use your basic design but use painted steel instead the aluminum plate.

Paul

[/ QUOTE ] I prefer Stainless Steel over aluminum

 

I was thinking,

use one of those stamped steel wiring harness firewall gromet retainer things used on the old cars from the thirties and still use the teflon or some equaly slippery hard material for the seal under it..

Paul

 

Thanks, Jay....I added it to my "favorites" list for future reference. One question. Where did you purchase the teflon material?

 

[ QUOTE ]
Where did you purchase the teflon material?

[/ QUOTE ]

We have a place called Industrial Rubber a few miles south of where I live.
They supply neoprene rubber, UHMW and Teflon.

You've probably seen some of the UHMW stuff I've made in the past and UHMW is an industrial sliding bearing, but not as slippery as Teflon.
Plus, it's about 10- 15% the cost of Teflon.

Regardless, Teflon in the thinner sheets of 1/8" is quite reasonable and I feel strongly it should be used in a sliding situation like the heat shields in this article.
Little or no friction is called for.

Anyhoo, if you live near farms or oil fields you could probably find the stuff in supply houses for these endeavours without too much trouble.
A bearing house should be able to get it, but the best bet is to get it at stores dedicated to farms or oil fields because you can buy as much or as little as you want.

I forgot to mention it in the article and most will probably figure it out, but you want a polished surface for the Teflon to slide on.
Plain steel buffs up just fine as does aluminum if you prefer aluminum throttle rods.

 

[ QUOTE ]
use one of those stamped steel wiring harness firewall gromet retainer things used on the old cars from the thirties and still use the teflon or some equaly slippery hard material for the seal under it..

[/ QUOTE ]

Maybe . . . the key to these little heat shields is that the Teflon can float.
Would the old style grommet retainer allow that?

 

We have a local Tractor Supply store here...thanks

 

C9 -- Thanks for the write-up.

Rocky -- If you can't find the teflon locally, you can get it from McMaster-Carr (www.mcmaster.com) or MSC (www.mscdirect.com)


Ed