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Old 02-17-2007, 10:24 AM
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Turbo 400 Transmission Problem

I have a 1923 ford T Bucket with a Chevy 350. It has a Weiand 6-71 supercharger and a turbo 400 auto transmission. My problem is when transmission is in drive or reverse the car wants to take off and requires excessive brake pedal pressure to keep it from moving. This is a real pain in slow traffic and stop signs. I always have to shift into neutral to prevent the movement of the car. I was told when I bought the car that it has a 2000 stall converter. The trans modulator valve is connected to the carb vacuum source. The car idles around 1100 rpm when warm, and idle is as low rpm as I can get it. Does anyone know how I can fix this problem?
Thanks,
Rich

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Old 02-17-2007, 11:44 AM
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If the converter stall speed is 2000 RPM, then you have a 12" converter. Get an 11" converter (about 2800-3000 stall) and your problem will go away. This converter will need 3.55 rear gear minimum to keep the trans from overheating due to increased stall speed. I would also recommend anti-balloon plates for strength.
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Old 02-17-2007, 01:47 PM
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Rich,
The high idle speed is your problem. I had a 66 chevy big block with a 6-71 and the idle was around 750 with 2x4's and had no problems. You need to get a smaller cam or look for possible air leaks at the carbs. With the idle that high the trans must bang when you put it in gear especially when you go into reverse. With a car thats only 1800# the brakes have a hard time holding against that much RPM. Do you have front brakes?
Wayne
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Old 02-17-2007, 03:24 PM
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Quote:
Originally Posted by 23 T
I have a 1923 ford T Bucket with a Chevy 350. It has a Weiand 6-71 supercharger and a turbo 400 auto transmission. My problem is when transmission is in drive or reverse the car wants to take off and requires excessive brake pedal pressure to keep it from moving. This is a real pain in slow traffic and stop signs. I always have to shift into neutral to prevent the movement of the car. I was told when I bought the car that it has a 2000 stall converter. The trans modulator valve is connected to the carb vacuum source. The car idles around 1100 rpm when warm, and idle is as low rpm as I can get it. Does anyone know how I can fix this problem?
Thanks,
Rich


As Chazmac pointed out , you need a different converter.

As the weight of a car goes down , the stall RPM of the torque converter must go up.

Most T-buckets are very light weight. A 2500 RPM stall converter will act like a stock converter in a light car.

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Old 02-17-2007, 08:36 PM
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I agree with waykoe, the high idle speed is the primary problem. But of course you already know that. Putting in a higher stall converter may help the problem some, but it only treats the symptom. If you go with a higher stall and keep the idle at 1100 RPM, you will still be holding a lot of brake even if the converter is not stalled or nearly stalled. A higher stall also has the potential to run the trans temps up so upping the stall may generate another problem - to fix that you need a numerically higher rear end ratio so the converter 'locks up', but the higher ratio is bad for fuel consumption, and on and on. The cure to this ever increasing stack of band-aids really involves lowering the idle. If you absolutely can't get it to idle any lower than 1100 while stopped in gear, then maybe the next best solution is better brakes - again just treating the symptom. Racing is one thing, but this can get pretty annoying if it is street car. Even with a blower, 1100 rpm idle is too much for a street car - checking again for vacuum leaks makes a lot of sense. I know of a blown T in my area where the cars idles at 2100 rpm - completely unmanageable. The trans modulator is of little concern here unless the vacuum line to it is leaking or the modulator will not hold a vacuum applied to it. The vacuum line is typically attached to an intake manifold vacuum port - not quite sure what you mean by 'carb vacuum source' but there a couple sources of vacuum on the carb that the modulator should not be attached to.

Yes, T's are light and a 2000 rpm stall is many times much less in practice because of the total weight. I have a 2000 stall in my T, and because of manual brakes, it takes slightly more than light pedal pressure to hold it at idle, in gear while stopped - my idle is around 600 in gear. While stopped, if I footbrake stall the converter, the engine will not exceed about 1750 rpm, but my brakes still hold the car in place even though it requires a lot of pressure. Release the brakes and a lot of rubber gets left on the pavement.

TCI has a half-way decent article about stall speed, inertia, and a number of other factors which boil down to the real stall speed.

http://www.tciauto.com/Products/Tech..._explained.asp
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Old 02-17-2007, 09:24 PM
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Someone needs to accurately identify the camshaft in this engine.
Idle speed WILL NOT affect stall speed.
Vacuum leaks WILL affect idle speed.
Re-read what Crosley stated regarding the cars weight and its overall effect.

If this is cammed the way I suspect, idle speed is more an issue of engine efficiency, maginified by the blower and carbs....

There is REAL work and diagnosis needed here. Parts thrown at this problem will only yield a thinner wallet.
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Old 02-18-2007, 11:13 AM
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First of all I want to thank all of you for taking the time to answer my post. I am fairly new to the hot rod hobby and am learning as I go along. I really appreciate all your help.
The car does jump when I put it in gear. I have Wilwood 4 piston calipers front disk brakes and a 10 bolt posi rear end with 373 gears. With the car at idle the carburetor curb idle adjustment screw is all the way out and I have verified the throttle plates are fully closed. I was told the car has a mild cam but the previous owner doesn’t have any specs. I wouldn’t know how to find the specs unless the cam is removed and checked. I really don’t want to get into changing the cam unless it is absolutely necessary. I have removed the blower to repolish the parts and will install new gaskets upon reinstallation. I will also look for any possible air leaks in the hoses and check for flatness on the intake manifold, blower, and carb surfaces. I am using 2 stock Holley 600cfm carbs (These are not blower carbs, the power valves are not boost referenced) The trans modulator valve is connected to a full manifold vacuum port on the bottom of the carb. The other vacuum port will be used for the PCV valve. I will recheck the carb float level and idle mixture upon reassembly. It may be a month before I get the car back together for further testing. This car is for street only and basically for cruising around on nice days. What areas should I be looking in in addition to the torque converter stall speed, idle and cam?
Thanks,
Rich
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