Second to Third Shift Point

B

Banditorama

Senior Member
The car runs great at any RPM in first and second gear

The problem is shifting into third gear at what I consider a "comfortable" RPM out of second there's a slight (but noticeable) stumble. If I ride out second gear longer I avoid it. But I feel like I should be able to shift into third sooner and don't like revving the engine that high.

From what I've read, Ford recommended shifting from 2 to 3 around 12-15 mph. My estimate (speedo isn't working) is that to avoid stumbling I'm shifting around 18mph +/- a couple mph

GAV is around 1/3 to 1/2 turn out when warmed up and I keep the spark advance about halfway down
 
Revving it higher should not be a problem, but with the Model A, it feels like it would be. There is a wide gap between 2nd and third that means that you either lug the engine a little when shifting up, or you have to rev it higher. Revving it higher is better on the engine than lugging it. I also do 20-25 mph.
 
Number one, 12-15 mph into 3rd works great for me. If you are refering to a "stumble" as a misfire, address the issue now as it will only get worse. Pull the carb and make sure its all clean, then check points and gap. Clean plugs. If its missing at low rpm you probably just aren't noticing it at higher.
 
eagle said:
Number one, 12-15 mph into 3rd works great for me. If you are refering to a "stumble" as a misfire, address the issue now as it will only get worse. Pull the carb and make sure its all clean, then check points and gap. Clean plugs. If its missing at low rpm you probably just aren't noticing it at higher.
Click to expand...

It's not a misfire. I went through the carb and the ignition system just a few months ago

Runs fine right off idle in first/second and idles well. Anything over 25mph (I'm estimating) in third gear runs great. Below that and there's just a very slight random stumble. It doesn't occur in rhythm with the cycle of any one cylinder and isn't accompanied by any pops or out of place noise.

I've tried retarding the timing when it occurs and adding/subtracting fuel via the GAV. It got slightly better with less timing but the GAV didn't have any effect
 
Try adjusting the idle a little richer. If a Zenith then turn the adjustment screw in about 1/4 turn. The car may need a tuneup. Slightly smaller spark plug gaps may help. You could also try a hotter coil. Another thing to try would be a smaller gap between the distributor rotor and the little pegs inside the distributor housing. The specification is 0.025 inch but I found my car to run better with a smaller gap. Just make sure the rotor does not crash into the pegs. New or different plugs may also help.

I use a GPS as a speedometer because my speedometer is off. You could run a GPS off a small rechargeable 12 volt motorcycle or lawnmower battery.
 
Nkaminar, I have a Tillotson carburetor on it and am right around 3/4s of a turn out on the idle screw. I'll try taking it another 1/4 turn or so out and see what happens. How much does the idle circuit affect low RPM operation?
 
Both of my Model A's have Model B motors, 3.77:1 differentials, hi-compression heads and stock transmissions. I avoid lugging the engines, so I typically shift into 3rd gear at 25-27MPH.
 
Adding some thoughts to this as I have never been a fan of a used Tillotson because of their casting issues. The one key thing I read was that adjusting the GAV at the lower speeds made no difference. To me, that is an indicator that you have a vacuum leak somewhere. Is it possible the throttle shaft is sucking air which affects the signal at low RPMs? I think to a certain extent, the Idle circuit does play a role as the engine's RPMs are between 500 - 600 in the 12 - 15 mile an hour range. None-the-less, when the throttle is snapped-open at that RPM range, it should begin accelerating smoothly, ...especially with a Tillotson since it was an economy carburetor with a smaller venturi.

I would adjust the carburetor where it will rev smoothly and very quickly from an idle all the way to 2k RPMs. Then richen the mixture just a tad and go test-drive. If you are receiving any type of hesitation or stumble during the snap-throttle test, then find where your problem is with that first. Maybe a carburetor change??
 
Nkaminar, you are the man (or woman)!

Gave the idle screw a 1/4 turn richer and no more stumble. Seems to rev a little freer at low RPMs in first and second gear too.

Thank you everyone for the help!
 
I am glad that fixed it. Neil (male, last time I checked.)

I had the same issue on a Weber carburetor. In that case it took a larger jet for the idle circuit.
 
My truck loves to shift into second at 8-10 and into third at 16-18 mph, down shifting into second it likes 15-10 into second and into first at 10-8 mph. you can downshift from second back into first easily, just take it out, give it a blip of the throttle, clutch and drop it into first, easy-peasy A model squeezey.
 
Remember 20 miles an hour in high gear on a stock model A with 3.78 gear ratio is only about 1,000 RPM. It's easy to lug the motor if you shift earlier under a heavy load.
 
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