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700R4 Torque converter stall speed too low?
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1great40
New User
Apr 4, 2017, 6:22 PM
Post #1 of 5
(2977 views)
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700R4 Torque converter stall speed too low?
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Hello all, this is my first post here. I'm running a bone stock Chevy 4.3 V6 with a rebuilt 1989 700R4 in my 1940 Ford pickup. The transmission was rebuilt by a shop and the rebuild supposedly included a rebuilt converter. I had no knowledge of the function of this transmission before I had it overhauled except that the vehicle did move forward and reverse but I never drove it anywhere. Once the transmission was overhauled and installed, It would never go into 4th (OD). The original rebuilder didn't know (or didn't want to)how to fix it. I drove it for a few hundred miles hoping that it would somehow "free up" but that was just wishful thinking. I took the truck to another transmission shop and he determined that there was a stuck valve in the valvebody and had the thing fixed in about 2 days.
The problem (or symptom) I have also experienced since I assembled the truck is that it doesn't launch smoothly...you would have to be a magician with the gas pedal to keep it from lurching from a stop. Some of the problem was due to spring wrap when I accelerated. I corrected that problem with a set of traction bars. From there I experimented with gas pedal ratio modification so as to require more travel of the pedal to move the throttle plate. While that has helped immensely, It shouldn't have had to been modified, the pedal, cable and all of the linkage and throttle body all came from the same donor vehicle.
Last year I installed a tachometer in the truck. The engine idles at 1000 RPM in park and that drops to 600 RPM in drive. The strange thing is, unlike any of my other vehicles with tachometers, the engine doesn't "rev up" when you start from a stop. The truck starts to move at about 700-800 rpm and if you try to take a guess at the stall speed by locking the brakes and pushing the gas pedal in drive, you would be lucky to get 15-1700 rpm out of it until the wheels break loose. I know nothing of the history of this converter, if it's malfunctioning or there's a different problem or if it's not properly matched to the truck.
I'm beginning to think that the torque converter is either defective or something that never should have been installed in this trans to begin with. I'm also aware that torque converters with a low stall speed problem is quite uncommon.
Anyone have any light to shed on the situation?
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gsferraro
Veteran
Apr 5, 2017, 7:34 AM
Post #2 of 5
(2955 views)
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Re: 700R4 Torque converter stall speed too low?
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That is low stall, stock stall is about 2000-2200, a low stall may give you more power on takeoff verus a high stall would not give you power on takeoff. Does the trans operate ok? Gary
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1great40
New User
Apr 5, 2017, 10:19 AM
Post #3 of 5
(2944 views)
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Re: 700R4 Torque converter stall speed too low?
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The transmission works fine, smooth shifts and the converter locks up fine. From what I have read, I would have thought the opposite of what you're saying since the engine is never getting onto it's optimum torque range while launching. I'm still learning. Thanks.
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Hammer Time
Ultimate Carjunky
/ Moderator
Apr 5, 2017, 1:06 PM
Post #4 of 5
(2938 views)
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Re: 700R4 Torque converter stall speed too low?
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I think the OP is correct.
Remembering back to my racing days, the higher stall speed gave you more torque on acceleration with the higher rpm.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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1great40
New User
Apr 6, 2017, 7:22 AM
Post #5 of 5
(2919 views)
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Re: 700R4 Torque converter stall speed too low?
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So now my question is: can a torque converter be defective in such a way as to cause a low stall speed?
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