Gas Pedal Travel

[38convsedan]

Curious about correct amount of gas pedal travel on my 38 CS with 8BA.
Can’t get carb to WOT (only about 2/3).
(EFV8 Bible calls for 10.44” carb arm— mine is more like 9.5”.)
Pictures below show pedal up and then fully depressed.
Doesn’t seem to be enough pedal travel…

[19Fordy]

Would installing a little adjustable turnbuckle (both sides RH threads) that extends the throttle arm to the carb help? See the little aluminum piece in photo. I think I used a 10-32RH die to cut the threads on the throttle rod. Car is a 40 Ford with an 8BA.

[38convsedan]

19Fordy-How much travel do you have on your accelerator pedal?

[19Fordy]

38: Measuring with a combination square from the top surface of the gas pedal to the rubber floor mat the distance between the top of the pedal and the floor mat when the pedal is all the way up is 4 7/8 in. With pedal all the way down that measurement is 1 7/8 in. That gives a travel of 3 in. These measurements will vary according to thickness of floor mat.

The stock 40 gas pedal set up worked fine on the 8BA when using the stock 8BA 2 barrel carb. It worked fine without modifying the linkage. But, when I changed to a Holley 390, I had to add the turnbuckle. You can cut, drill and tap a mild steel bolt to make the turnbuckle.

I am running a 390 Holley 4 barrel on an 8BA and found that I had to modify the linkage using the turnbuckle because the stock length throttle rod would not provide enough "throw" for the Holley to work properly. I did not need to use a return spring on the carb.

Because the throttle rod is mild steel it can easily be welded back together. Or, buy a used one and make a "practice piece" to experiment on.
https://www.ebay.com/itm/1935-39-For...7/391411142838

You can also cut a piece of small dia. rubber hose and secure it in place with tie wraps to find out what length turnbuckle and thread length you need. My alum. turnbuckle is 3/8" OD x 1 3/8 in. long. Use fine threads for better thread contact and finer adjustment.

I would not "mess with" the rod that inserts into the bottom of the gas pedal and attaches to the firewall linkage. Too much chance of badly altering the gas pedal accuating geometry.
Hope this helps. Jim

[al's28/33]

Someone could have replaced the linkage along the way.

I am having a similar issue with my '33 pickup. It was originally a 4-CYL and someone converted to V8 and thus different carb. The "modified" spoon pedal arm is sloppy on the linkage rod connected to the firewall. I'm trying to measure "full upwards" and "full downwards" positions to weld in the pin hole on the rod and drill out a new hole that will give me full range of motion ....... measure 82 times and cut once.

Or it's possible your linkage from firewall to the carb is too long.

[Terry,OH]

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Your pedal should go nearly to the floor. Appears there is something preventing further movement. If you disconnect the Carb from the linkage how far does the pedal depress? Post a photo of the linkage at the Carb.

[38convsedan]

Using 19Fordy’s measuring distance from pedal to floor (see a post #4).
Pedal all the way up-4 3/8”
Pedal fully depressed-3 1/8”
Travel is 1 1/4”
Something is definitely wrong.

[38 coupe]

If you take the pedal loose from the linkage does the carburetor get full travel or not?
Might help diagnose if the problem is pedal, linkage, or both.

[38convsedan]

Carb has full travel with linkage removed and carb arm moved manually.
Lower gas pedal linkage arm is hitting oil line boss on block when depressed, not allowing for further travel.
Is this correct??
I also notice that the two linkage to firewall studs do not seem to protrude equally as there are more threads showing past the nut on the passenger side compared to driver’s side when viewed from interior….not sure if this is a meaningful variable….

[38 coupe]

I don't remember my gas pedal linkage hitting the engine block, that seems wrong.
It sounds like the rod between the gas pedal and firewall linkage may be too long and the rod between the firewall linkage and the carburetor too short. Or maybe just the carburetor rod too short.

[38convsedan]

Removing upper linkage from carb arm does not increase pedal travel.
It appears issue is centered on lower pedal linkage having restricted travel…

[19Fordy]

Originally Posted by 38convsedan

Carb has full travel with linkage removed and carb arm moved manually.
Lower gas pedal linkage arm is hitting oil line boss on block when depressed, not allowing for further travel.
Is this correct??
I also notice that the two linkage to firewall studs do not seem to protrude equally as there are more threads showing past the nut on the passenger side compared to driver’s side when viewed from interior….not sure if this is a meaningful variable….

8/14/23 On the 8BA in my 1940 car the gas pedal linkage does not hit or touch oil line boss at rear of block or anything else on the block. Also, the (round) heads of the firewall studs that attach the big spring loaded accelerator mechanism to the firewall mount tightly against the exterior of the firewall in the engine compartment.

The two threaded fasteners that hold this big spring loaded assembly in place extend through the firewall and pass through the firewall insulator and are held in place with a deep dished steel washer and nut on each. Check and make sure your spring loaded assembly is bolted tight against the firewall. Also, make sure the spring is not broken. The gas pedal should "spring back" by itself.

As a side note, I used an 8RT truck water pump and the stock motor mounts to position my engine. Could your engine be positioned too far back towards the firewall? What set up are you using? I know some folks used 1951 Merc water pumps with Merc "U" shaped spacers.

Just curious, Is the problem you are having new or has it always been a problem?

[38convsedan]

The passenger side linkage mounting stud is in contact with back of engine block.
Previous owner did 8BA engine swap—perhaps engine is mounted too far back.

In a correctly mounted engine and pedal linkage, what provides stop of downward gas pedal travel? In other words, is the downward travel stopped when pedal linkage contacts something or is downward travel stopped by carburetor linkage at WOT?

The threads of the linkage mounting studs do not protrude evenly through the nuts when fully tightened as mentioned earlier. There are more threads showing through on passenger side while threads are flush with nut on driver’s side.

Spring is working correctly.

[19Fordy]

In answer to: "In a correctly mounted engine and pedal linkage, what provides stop of downward gas pedal travel? In other words, is the downward travel stopped when pedal linkage contacts something or is downward travel stopped by carburetor linkage at WOT?"

My downward travel of the gas pedal is stopped by carburetor linkage at WOT. I have adjusted the turn buckle so that the spring loaded cup at the end of the linkage rod just slides over the little ball for attaching the linkage on the carb when the gas pedal is not depressed. Then, when the gas pedal begins to be depressed, the carb linkage begins to move and the primaries on the carb begin to open and the gas squirts out of the carb discharge nozzles into the engine. Gas pedal springs back to its original "none depressed" up position when foot is removed from pedal.

This gas pedal and the carb worked together in this same manner when I was running the 8BA two barrel carb. At that time, I did not need a turnbuckle. But, when I installed the Holley 390, I had to add the turnbuckle to achieve the same operational relationship between the carb, linkage and gas pedal movement.


Look inside your carb and examine the working mechanical relationship of how your linkage works in coordination with the discharge nozzles inside your carb as gas pedal is depressed.

[38convsedan]

Thanks--so it appears the reduced gas pedal travel is a function of the lower half of the accelerator linkage. Something is not correct resulting in reduced pedal travel as the lower linkage is contacting the engine block at the oil line to canister boss.

It doesn't seem possible to remove the linkage with engine installed. The passenger side linkage stud is in contact engine block--no clearance to pull that stud out of the firewall.

Any suggestions on corrective measures with linkage remaining in place?

[19Fordy]

38convsedan: Is there any way you could post a bunch of photos showing what you are dealing with? Here are a few photos that may be helpful to compare with your situation.

1st photo shows dished washer that is used to secure firewall accelerator assembly in place on inside of car against firewall insulation mat. There are 2 of these. The other is hidden by the heater. I covered my OEM insulator with fiberglass cloth years ago.

2nd photo shows pencil point with blue tape resting on top of the head of the special oblong round top fastener bolt on driver side that goes thru firewall and holds accelerator assembly in place. It has a special hollow rounded head through which the accelerator spring arm shaft passes. It is secured in place with nut and dished washer on inside of car.

3rd photo shows pencil point with blue tape resting on top of the head of the special oblong round top fastener bolt on the passenger side that goes thru the firewall and holds accelerator assembly in place.

There is about 2 1/2 inches between the head of the special oblong round top bolt on the driver side and the top edge of the engine block. It looks like it could be loosened from the inside car and removed.

The same bolt on the pass side is about 1/4 inch away from the top edge of the back edge of the engine block. It might be possible to remove it if you first loosen the nut all the way and then tilt and turn the round head so it clears the block. If that doesn't work, my intake manifold would have to be removed.

Four more thoughts. Is you gas pedal bolted in the correct OEM location on the wooden toeboard? Could the accelerator pedal rod be rubbing on the edge of the hole? Are you using the OEM toeboard or a replacement? Is it the correct thickness? I recall when I replaced mine I had to make one edge beveled (like the original)so it would fit like the original and lay flat.

[38convsedan]

I’ll add photos … but I think I’ve found the problem, and it’s also why my horns don’t fit!

The carb requires an amount of arc or free travel to go from idle to WOT.
This is achieved by a corresponding arc or travel by both the upper and lower linkage arms.

There are a couple of hints that something wonky is going on with my car.
First, the carb arm (which attaches to the upper linkage arm/ball) is supposed to be 10.44”. The carb arm on my car was bent down at about 9 3/8” by previous owner. This resulted in carb never fully achieving WOT with pedal fully depressed.
Second hint was pointed out above, which is clearance between linkage studs and engine block. Passenger side stud on my car is in contact with engine block when there should be about 1/2” of clearance.
The 8BA conversion resulted in engine being placed too far back.
That’s why lower linkage arm hits the block preventing correct amount of free travel AND why the carb arm had to be shortened to fit reduced distance AND why the linkage studs are too close to the block.
Reduced distance equals reduced arc or travel of linkage and carb arm: gas pedal stops too soon and so does carb arm.
And THAT’S why my horns didn’t fit when I tried to install them six months ago! The horns didn’t have required clearance from fan belt because the engine is too far back.
(BTW: this all occurred to me at 3:30 this morning…)

[38 coupe]

It is hard to install an 8BA too far back. The transmission mount in the frame dictates where the transmission and engine go front-to-back in the car. If you have the original type transmission, torque tube, and rear axle in place then the engine is pretty much guaranteed to be correctly place front-to-back.
As already said by others earlier in this thread I suspect the front of your engine is too high. Stock 48-52 truck type water pumps with stock 1938 front motor mount hardware should get the front of the engine where it needs to be. What water pumps and motor mounts are in your car?

[38convsedan]

Not sure about water pumps/motor mounts--previous owner did 8BA install.

Hmmm...so it's too high and not too far back?

Given wonky nature of motor placement...any thoughts on how to achieve correct carb/pedal travel??

[19Fordy]

38consedan: At this point it would really be helpful to post photos of your water pump/motor mount set up along with photos that show your present carb linkage configuration. It would be super great if you could post a video describing and showing what you are dealing with.

As to: how to achieve correct carb/pedal travel? I would "start from scratch" and straighten out the bent carb linkage rod to its correct length and work backwards from the carb to see what length rod you need both at WOT and at idle. Take measurements and install various length carb linkage rods to see how it affects gas pedal travel in relation to WOT. You may have to buy a spare carb linkage rod.

You may find you also have to modify the ball location on the carb itself in order for it to operate better. Below are photos of how I repositioned the ball hookup on my 390 carb to accomodate the carb linkage rod with the turnbuckle.

The first photo shows the stock Holley linkage arm. I handmade the little aluminum piece so it could be screwed to the stock Holley linkage arm with the repositioned linkage ball to accomodate the stock Ford linkage arm. Last photo shows final solution hook up when viewed from the firewall.

This was a "trial and error" process to get the travel correct. I know your carb is a 2 barrel but this is just to give you another idea. Look at your carb and see if you could do a similar modification. I would say you are at the experimental prototype stage of your solution. Like I said, it would be super great if you could post a video both verbally describing and showing what you are dealing with.

Now, get back to work, post photos and get more 3:30 AM ideas.