25 mph in high gear?

[mjdunn]

I have a 1939 Ford Tudor Deluxe. When my speed drops to 25 mph in high gear and I accelerate it "hesitates" or you might say, "misses out" until it reach 30-35 mph. Other than that the runs and idles perfectly. Is this normal or is there something I could do to eliminate this? It does the same thing at low speeds in second gear. I have recently had the carburetor rebuilt by Charlie NY, coil rebuilt by Skip, distributor rebuilt by Bubba's Hot Rod Shop, New gas tank and fuel line, new fuel pump, and new spark plugs.

[oldford2]

What is the rear end ratio?

[38 coupe]

It sounds like your accelerator pump isn't putting out enough fuel. Check the operation with the engine off and the air cleaner removed. When you open the throttle you should get a nice stream of gasoline. If you need a more, move the linkage to the outside hole in the throttle shaft.

[Shoebox]

There might be more to it but perhaps you're just lugging it a bit. I have a 90 degree turn near my house that I regularly take with my 39 Merc in high gear, I feather the throttle coming out of the turn, if I would put my foot in it it would buck...... just saying.

Shoebox

[mjdunn]

Originally Posted by oldford2

What is the rear end ratio?

I don't know. I assume it is original.

[48 coupe]

Sponsored Links (Register now to hide all advertisements)

How's the plugs?

[46ford]

Originally Posted by mjdunn

I have a 1939 Ford Tudor Deluxe. When my speed drops to 25 mph in high gear and I accelerate it "hesitates" or you might say, "misses out" until it reach 30-35 mph. Other than that the runs and idles perfectly. Is this normal or is there something I could do to eliminate this? It does the same thing at low speeds in second gear. I have recently had the carburetor rebuilt by Charlie NY, coil rebuilt by Skip, distributor rebuilt by Bubba's Hot Rod Shop, New gas tank and fuel line, new fuel pump, and new spark plugs.

Sounds normal. Have you tried shifting to second at that speed? 25 is about where my '46 would want to downshift especially on a corner. 28 in a 25 zone was about right for 3rd, albeit illegal

[Brendan]

maybe its lugging, shift down

[mjdunn]

Originally Posted by 46ford

Sounds normal. Have you tried shifting to second at that speed? 25 is about where my '46 would want to downshift especially on a corner. 28 in a 25 zone was about right for 3rd, albeit illegal

When I down shift at 25 it runs normally.

[mjdunn]

Originally Posted by 48 coupe

How's the plugs?

Plugs have recently been replaced and I just took them out to make sure they were clean.

[mjdunn]

Originally Posted by Brendan

maybe its lugging, shift down

It seems like, in the past, I didn't have to down shift at 25 mph.

[Andy]

Vacumn leak. Check hoses and gasket under carb.

[rotorwrench]

The carburetor has two systems for acceleration. The accelerator pump has been mentioned but there is also a power valve. If either system has a problem, it will be very well noticed when lugging the engine and trying to accelerate. I agree with 25 mph being a low speed for high gear so it might be lugging too much at that speed. An 85-HP engine should accelerate smoothly if the speed range is correct for each gear during normal operation.

The later Mercury cars with 110-Hp and overdrive transmissions could start from a stop sign in second gear but you can tell it lugs the car a bit. It could then be shifted into overdrive around 25 mph by the governor for a semi-automatic type drive around town. It you stomp on the accelerator it will shift back into 2nd so that it won't lug.

You may have a problem with the ignition system's distributor vacuum brake retard too. All this stuff works to keep the car running at a happy medium state but if any problems lurk there it will deteriorate performance to some degree. A vacuum leak could also cause problems there.

[JSeery]

Might be a good idea to figure out the rear axle ratio so you have some idea what is going on. Should be able to just check under the center section to see what the numbers are. Not 100% prof, but most likely still original gears.

Not sure why you would want to drive 25 mph in high gear in a heavy car?

[40 Deluxe]

Went looking for the proper idle speed for my '40. Original owner's manual only said "5-7 MPH in high gear". And it will pick up speed smoothly in high, if everything is in tune. The trick is not to floor it completely, just gradually feed in power and away you go.
A bad accelerator pump only causes a momentary hesitation as you step on the gas. If it keeps on hesitating and missing, it's something else. Check voltage at the coil while it is running- should be something like 3.8 V. if I remember. Could be bad switch or bad connection somewhere. Could be dirt in he carb.

[mjdunn]

Thanks guys, I appreciate all of your suggestions. I will check into the things that have been suggested.

[G.M.]

You should be able to get down to 8 or 10 MPH, slowly push the gas pedal and increase speed with NO bucking. In most cases this is caused by sticky valves.
While running drizzle MMO down both sides of the carb for about a minute, put
a 1/2 quart in the fuel tank and drive about 10 miles. You should now be able to drop to 10 MPH and pull out smoothly. G.M.

[Talkwrench]

Agreed my little 21 stud with 28 gearset, 3.78 rear and big 16 x 7.50 will pull from 15 mph no probs. Sounds like its a small problem, tune all will be good.

[mjdunn]

Hey Guys, I found the problem. It was a vacuum leak. I pinched off the vacuum line going to the windshield wipers and it performs perfectly. Thanks for all your help.

[Mart]

Cool. Nice one. Must have been causing a lean condition.

Mart.

[AnthonyG]

Even though you found a vac leak and kudos for finding it, I'm still in the "down shift it camp". 25mph in high gear is too slow S/B a downshift point.

[Bubba]

Back in the 40s my uncle had a almost new 41 Ford PU. Going down the street at 4 MPH as he turn on the side street give it full throttle when we crossed the next street we were at 44 MPH smooth all the way. On that same street my 39 pulls Smooth all way but I have not got it down to 4 mph without it bucking about 5.5 if I get down around 5 it starts bucking. Bubba in Texas

[40cpe]

The '41 PU probably had a lower speed rear ratio, so your '39 DeLuxe meets specs.