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Old 04-27-2012, 09:56 PM   #1
Working Class Zero
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Default 1930 Model AA Cant Get Her Over 25 MPH

Just picked up a 1930 Model AA. Nice older restore stock original. Got her home, fired right up, sounded great, running strong. Then I go for a drive....... She won't get past 25 MPH. In third gear pedal to the metal and she just won't go any faster, rpm's are not even high, but 25 MPH is it on a flat road, hit a hill and its worse. So I looked her over a bit and found a 1 inch hairline crack in the intake manifold. Could this be the issue? Ordered a new one regardless, but any advice on figuring out the lack of speed is appreciated. I know these don't go fast, but 25 MPH? Also what would be the top speed on a AA? Less than a regular pickup I hear. Thanks for any help guys.
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Old 04-27-2012, 10:07 PM   #2
Bob C
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

I don't know about 3rd gear but if you have a low speed rear axle 35 in 4th is about it, a
high speed rear axle about 45.

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Old 04-27-2012, 10:19 PM   #3
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

There are more than a few items to check so start a list. You already have indicated one so here are a few more.
1. Where was the timing when you were in 3rd gear. It should have been all the way down on the column.
2. Verify the points and the timing at the distributor.
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Old 04-27-2012, 10:33 PM   #4
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

So is there a simple way to determine if I have a high or low speed rear axle?
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Old 04-27-2012, 10:38 PM   #5
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

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Originally Posted by TinCup View Post
There are more than a few items to check so start a list. You already have indicated one so here are a few more.
1. Where was the timing when you were in 3rd gear. It should have been all the way down on the column.
2. Verify the points and the timing at the distributor.
Timing was all the way down on the column in third. Here's some more symptoms:

Have a drip leak at bottom of the carb.

Also in the very short first drives It seems to have dropped from 1/2 a tank of fuel to near empty, as far as the gauge says, in a matter of 4 10 minute drives.

Plugs are blackened around base but clean at gap.
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Old 04-27-2012, 10:40 PM   #6
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

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30-31 AA,s use the 4-speed trans.Low speed RE is 6.6-1 ratio,high speed RE is 5.14-1 ratio. High speed gears increase speed just over 28 %.Hi speed gears are stamped 7-36 in numbers 1/2" high on axle hsg.Only HS ratio is stamped on hsg.Info from page 438 of Model A service bulletins. AA,s had to be low geared in order to pack several tons of freight with only 40 HP.If you could find a 3-speed warford aux trans for an AA,that would give you an under,direct & an overdrive.It replaces the coupling shaft assy.With the OD it may approach a 4-11 ratio which is still a little slower than the average A that is 3-78 ratio.
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Old 04-27-2012, 10:42 PM   #7
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

Appreciate the help guys..... This is my first time with a model A original motor and I'm loving it, however a bit in the dark so far.
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Old 04-27-2012, 10:57 PM   #8
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

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30-31 AA,s use the 4-speed trans.Low speed RE is 6.6-1 ratio,high speed RE is 5.14-1 ratio. High speed gears increase speed just over 28 %.Hi speed gears are stamped 7-36 in numbers 1/2" high on axle hsg.Only HS ratio is stamped on hsg.Info from page 438 of Model A service bulletins. AA,s had to be low geared in order to pack several tons of freight with only 40 HP.If you could find a 3-speed warford aux trans for an AA,that would give you an under,direct & an overdrive.It replaces the coupling shaft assy.With the OD it may approach a 4-11 ratio which is still a little slower than the average A that is 3-78 ratio.
Good info!
Cant see any markings. Dang. They would be on the rear axle where? On the Center or shaft? Wonder how hard a Warford Aux Trans is to find. This was going to be my daily driver shop truck but if I'm locked down at 35 MPH ouch. I don't mind join slow but..........
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Old 04-27-2012, 11:05 PM   #9
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

How about placing the tranny in fourth, taking out the plugs, jacking up the rear and counting the number of enging rotations with the crank to make the wheels make one revolution? This should give you the rear end ratio. (I don't think truck 4th is OD)
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Old 04-27-2012, 11:09 PM   #10
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

heres the stamp on my AA rear diff fastest i can go on this boy is 53 on a downhill slop avg fast speed is 48 comfortable is 43-45 . all brakes in good shape and stops fast when needed . point gap is 20 spark plug gap at 35 timing set at absolute tdc , noted here that when i had my head off i looked at the piston location when the timing pin was set in position and found that the piston was apx 3/16 below deck , rotated the crank a hair more to absolute tdc and set my points to open there , that truck starts right up ! and runs nice ... good luck if you have the high speed rear you will get there . may be your carb too what are you running?
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Old 04-27-2012, 11:27 PM   #11
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

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heres the stamp on my AA rear diff fastest i can go on this boy is 53 on a downhill slop avg fast speed is 48 comfortable is 43-45 . all brakes in good shape and stops fast when needed . point gap is 20 spark plug gap at 35 timing set at absolute tdc , noted here that when i had my head off i looked at the piston location when the timing pin was set in position and found that the piston was apx 3/16 below deck , rotated the crank a hair more to absolute tdc and set my points to open there , that truck starts right up ! and runs nice ... good luck if you have the high speed rear you will get there . may be your carb too what are you running?
ok i definitely don't have that stamping. the previous owner said he would get it going 45 MPH easily but thats about it. Liar? Unfortunatly I had it shipped to me from afar so no test drive. I can only get 25 MPH. That is sloooow. Even for the low geared AA. Running the Zenith Carb original. But she leaks. All I want To go is about 45Mph, not looking for anything more, but less is not ideal. Anybody got a high speed diff for sale? shoot.......
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Old 04-27-2012, 11:29 PM   #12
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

check timing for sure, as too retarded will rob top end power.. Its not an uncommon situation. Your leaky manifold will decrease power too. Check it when you get the new one and be sure both manifolds are flat and with the ports in a straight line. You might have to have them surfaced. Check that your brakes are not dragging. A compression check never hurts, and it will give you a starting indication of the internal condition.

Once you get it running right, you can make it stronger with high compression head, cam, better breathing.

Once you get it up and running strong, you can always get a Mitchell Overdrive for it. I know someone around here with a 31 AA flatbed that goes 70.
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Old 04-27-2012, 11:41 PM   #13
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

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check timing for sure, as too retarded will rob top end power.. Its not an uncommon situation. Your leaky manifold will decrease power too. Check it when you get the new one and be sure both manifolds are flat and with the ports in a straight line. You might have to have them surfaced. Check that your brakes are not dragging. A compression check never hurts, and it will give you a starting indication of the internal condition.

Once you get it running right, you can make it stronger with high compression head, cam, better breathing.

Once you get it up and running strong, you can always get a Mitchell Overdrive for it. I know someone around here with a 31 AA flatbed that goes 70.
Ok now I'm getting some hope back. lol. This girl does have a '32 head on it, don't know if that is an improvement or not. Gonna look into the mitchell overdrive. Does it screw with the stock look at all? 70MPH? Whoally Crap.
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Old 04-28-2012, 12:14 AM   #14
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

Wow Mitchell overdrive is not cheap and will really look unoriginal under the truck. Sounds like a nice unit though. Is it not possible to just get the higher gears for my diff, and switch em out?
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Old 04-28-2012, 12:18 AM   #15
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

Model B head is 4.6 c/r,A head is 4.2 c/r,so there is a slight improvement.If engine is in good condition,install a 5.5 or 6.0 c/r head and you will notice a real increase in power.
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Old 04-28-2012, 12:22 AM   #16
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

a 32 head makes little difference. It breathes a bit better, but only raises the compression from 4.2 to 4.4 or 4.5 ( can't remember right now), not much.. A Mitchell OD has another shift lever in the cab, which is the give away. Two shift levers in an AA cab is not as unusual looking as in a car. The undercarriage will look different. The OD unit replaces the intermediate shaft behind the transmission. They'll have to know which shaft you have, short or long.

before you start adding power accessories to the engine, you must determine if its basically sound. That is, strong crankshaft and bearings, good compression, good valves, good cooling system, good steering and brakes etc. Beefing up a worn truck will just cost you money and increase the stress on the truck. But if you want to learn more, join the AA Truck Club. Website here:
http://www.fmaatc.org/
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Old 04-28-2012, 12:24 AM   #17
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

high ratio ring and pinions can be found. Ask around the AA club site.
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Old 04-28-2012, 12:27 AM   #18
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

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Wow Mitchell overdrive is not cheap and will really look unoriginal under the truck. Sounds like a nice unit though. Is it not possible to just get the higher gears for my diff, and switch em out?
You can paint the box black so that it doesn't stick out. Trust me, once you have an overdrive, you'll never regret it.
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Old 04-28-2012, 01:25 AM   #19
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

Did you really have it in 3rd gear?
4th gear is to the right and back and is straight through, just as third gear is in the cars.

As mentioned to check the rear end ratio, jack up one rear wheel, shift to 4th gear, and count how many engine revolutions it takes to turn the rear wheel exactly two full turns. It takes two full turns because one wheel is on the ground and the differential then turns the loose wheel twice as fast.
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Old 04-28-2012, 01:33 AM   #20
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Default Re: 1930 Model AA Cant Get Her Over 25 MPH

What are you calling 3rd gear? In an AA with a 4-speed transmission, 3rd is not "High" gear. It would be equivelant to 2nd in an A with a 3-speed transmission, notwithstanding the rear end ratios. Back in the '50s I had an AA 280A with a 4-speed transmission and on flat ground had no trouble cruising at 50-55 (in 4th gear). I was a teenager then so it was usually "pedal to the metal" wherever I went.

(Tom beat me to it!)
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