Determining Existing Torque Converter Stall Speed

DC3

DC3

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Dec 9, 2008
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Lubbock Texas
I'm trying to determine the stall speed of my existing torque converter and wanted to pick some other brains about it. Tranny is a TH400 rebuilt by the previous owner. Rear axle ratio is 3.08.

I stood on the brakes and started giving it gas - not WOT but about half throttle or so. The rpms climbed steadily to around 2200. At that point it leveled off and I had to give it more gas. Rpms then climbed to about 2400 at which point the brakes wouldn't hold any more.

Is there any way to tell from that what torque converter I might have? If not, is there any way to tell by pulling the inspection cover?

Thanks,

DC
 
DC3 said:
I'm trying to determine the stall speed of my existing torque converter and wanted to pick some other brains about it. Tranny is a TH400 rebuilt by the previous owner. Rear axle ratio is 3.08.

I stood on the brakes and started giving it gas - not WOT but about half throttle or so. The rpms climbed steadily to around 2200. At that point it leveled off and I had to give it more gas. Rpms then climbed to about 2400 at which point the brakes wouldn't hold any more.

Is there any way to tell from that what torque converter I might have? If not, is there any way to tell by pulling the inspection cover?

Thanks,

DC
Click to expand...

You were on the right track, but can improve your technique to get better results...
1. Position the car on a deserted street or parking lot so that as it moves no one will be in the way.
2. Raise the rpm to a fast idle in neutral to get maximum engine vacuum for the power brakes and press the brake pedal heavily and hold to get the maximum holding power.
3. Come off the throttle and shift into drive or manual low.
4. Still holding full brake pedal, go to WOT in less than 1/2 second and hold for a second or two noting the maximum rpm attained; and then return to idle.
Note: The car may move a few feet and then abruptly stop when returning to idle - this won't invalidate the results. Important: Don't hold WOT for more than 2 seconds as the trans fluid will heat rapidly in the stalled condition.
 
The flash stall is heavily dependant of the engines output, it's not very accurate at all.

When you move there's rotation so no stall. The only way to get an accurate reading like this is with a trans brake

The wheel brake stall like the initial test he did is lower than true stall speed because the brakes get overpowered before stall speed is reached
 
No, I haven't given it another try yet. Been busy and had a minor electrical problem I had to sort out. I touched base with the previous owner and he told me the converter was a Hughes but he couldn't remember the stall speed. I talked to Hughes and they told me to pull the inspection cover and give them the numbers I found so they could help me identify what I have. Still need to do that and still want to try Larry's method.

TT - is there a way to estimate true stall from data obtained using Larry's method?

None of this is a really big deal to me, more curious than anything. I'm planning for a future swap to a 200-4r and I think knowing what I have now may help me select a converter for the new transmission.

DC
 
DC, as long as the rear tires can be held from rotating, one CAN determine true stall speed. Of course, a trans brake does this job easier, but unless you have a very high torque output, the method I outlined does work quite well to hold the tires immobile.

Bear in mind that no converter manufacturer can tell what the real stall speed will be UNLESS they have an engine dyno readout of the engine that's twisting the converter. When the engine torque line crosses the converters torque absorption line - that's the real stall speed.
When anyone says that they have a 2500 stall converter, it's only an approximation for an assumed engine.

As far as flash stall is concerned, it is very hard to read and is only transitory - if one had automatic data recording and could make a time history graph of the rpm, it would help, but is not as accurate as holding the trans output at zero and reading the limiting rpm.
 
Finally got a chance to try this. Larry - your method worked very well for my car. The trick was getting the maximum vacuum for the brakes. After doing that, the brakes held and the rpms pegged at 2400 when I did the test.

DC
 
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