Torque Converter Stall???

[Nicholas]

Good evening everyone,



I need some help understanding the concept of torque converter stall. I understand our 1st gen. trucks (in stock form) are fitted with a torque converter that has a very high stall rate, no means of lock-up, and transmit power by the use of a fluid coupling. Therefore, these torque converters transmit power & torque poorly, and inefficiently. I learned through research and discussion, that it often requires a aftermarket, low stall torque converter like DTT system for example, to correct the high stall problem. My questions to everyone are as follows:



- What happens inside a torque converter when it is operating in a stall condition?



- What is an optimum speed/rpm range for a torque converter to stall in our 1st gen. trucks?



Any information would be greatly appreciated. Thank you.





Respectfully,



Nicholas R. Gajewski

 

[BushWakr - RIP]

Hey hey Nicholas,... .



Good to see you .....



Man that is a tough one to explain, at least for me anyway...



The normal stall for our TC (as per owners manual) is between 1700 RPM and 1900 RPM, if during the 'stall test' the RPM exceeds 2000 RPM then the TC needs replacing... again according to the "book".



Between those RPM's the drive side is moving oil, which in turn is trying to turn the outlet side. At the upper end is the point at which the engine cannot climb any higher in RPM due to the restraint of the TC's internal parts and efficiencies. Either the truck starts to move or the engine RPM "stalls" and goes no higher.



As you increase your HP, the effective 'stall speed' actually goes up. Your engine can literally cause the "stall speed" to increase because it can force the RPM/stall level higher. It could climb into the 2000 + range or more quite easily.

The stock TC is made to "effectively" transfer power from about 1800-1900 RPM (MIN. ) and up. At that RPM the connection is firm enough that load cannot stop power transfer so long as the wheels can turn. Commonly the best connection on a stocker is 2000 RPM.



In our case the Cummins starts to produce it's highest torque numbers by the time we are in the 1600 RPM range. The torque rise begins before that though. Yes both HP and Tq levels can "move" when an engine is tweaked up, but the work starts happening at RPM's far less than a gas engine.

For example my max Tq numbers with a 91% TC was 836 lb/ft at 1480 RPM. That is WAY lower than any stock TC even begins to become efficient.

On our 1st Gen trucks most of the higher HP guys are peaking out the HP at around 2300-2700 RPM, or roughly thereabouts. .

A gas engine is just getting it's wind at that point and the TC is starting to really firm up and do its job... . for us, that's way too late in the curve... .



I hope that makes some sense. . if not, then jump in and help us out here guys... another perspective always helps...



bOb.

 

[phoekema]

stall ratio

Just a quick comment re: stall speed. The actual stall speed is lower (thankfully, since there is no lockup) on the 1st gen automatics. I know my '93 slipped a lot less than my 98. 5 in non-lockup mode. I suspect it was done to make more use of the torque converter at lower speeds, since they could lock it up later. In my opinion, they lost more than they gained by that. It would seem the older non-lockup converters were actually matched to the diesel characteristics better than the newer units. I know I am glad I now have an aftermarket converter on my truck - M U C H B E T T E R !

Paul H

 

[Nicholas]

Good afternoon everyone,



Thank you so much for the great information on torque converter stall. At least I now have a much better understanding as to what is happening inside a torque converter, what rpm ranges it begins power transfer, how the stall ratings can change with added HP & torque, and how it is able to transfer power.



I am still left with two questions:



1. How does a person go about performing a stall test?





2. Do torque converters eventually wear out?





Thanks again for the information.



Respectfully,



Nicholas R. Gajewski

 

[Philip]

Here is some good reading for beginners on how a torque converter works.



http://auto.howstuffworks.com/torque-converter.htm

1. How does a person go about performing a stall test?

You need a tachometer and a stop watch. Put the vehicle into drive. Set the emg brake and hold down on the service brakes as hard as you can. Then put the throttle on the floor. Look at tach and see what the highest rpm you get is. That is the stall speed of your converter.



Do not do this for an extended period of time. Only do this long enough to get a accurate rpm reading. Then let the engine idle in neutral. You need to cool the converter back down. A stall test will make a lot of heat fast in a converter. By doing it for to long of a time you can cause damage to the converter/trans.

2. Do torque converters eventually wear out?

Yes they can.

 

[formula]

Originally posted by Philip



You need a tachometer and a stop watch. Put the vehicle into drive. Set the emg brake and hold down on the service brakes as hard as you can. Then put the throttle on the floor. Look at tach and see what the highest rpm you get is. That is the stall speed of your converter.



Do not do this for an extended period of time. Only do this long enough to get a accurate rpm reading. Then let the engine idle in neutral. You need to cool the converter back down. A stall test will make a lot of heat fast in a converter. By doing it for to long of a time you can cause damage to the converter/trans.

:--) Maybe for a gasser... ... but try that with the 6BT and you'll put the life of your input shaft on the line. Even more so if the engine is modded and/or a lower stall converter is put in



Sean

 

[Philip]

life of your input shaft on the line.

roflmao



If the input shaft can not handle full engine power at 0 road speed doing a stall test then how could it handle it driving down the road. You are applying the same amount of power and torque to it all the time. The drive shaft not turning doesn't have any bearing on it. It isn't any different than doing a WOT launch.



In my manual for a 93 no where does it say to not do a full stall test on a auto with a diesel. If you ever get a chance to talk to someone that has worked in the test drive garage at the trans plant. It will amaze you if you knew what the tests were. A good 40 percent of the tests would break a weak designed input shaft. LOL



They do have diesel powered testing also. I have a friend in the test garage for the car trans plant.







The manual did state 5 seconds max on the stall test. That was the reson for the stop watch. I left that out in an earlyer post.

 

[JStoll]

I agree on the torque being the same rolling or static

its unlikley that the input would be broken but its easy to boil the fluid in the converter

in fact in my current truck the chevy if Im pulling a hill & say Im in 3rd gear doing 30MPH or so if the engine is at stall speed Ill throw it down one gear one shouldent use the converter as a gear reduction especilay pulling a load & not for extended periods either way. Learning how to drive a truck with an auto is important for trans longevity

& by the way the chevy is sold this weekend & the dodge is on the road

JAK

 

[BushWakr - RIP]

The guys are right, the "book" says stall test MAX 5 seconds, then long idle in "N"...



The input shaft can go in the blink of an eye when doing this, but it is literally the only way to test them while they are on the truck. .

I have several tests under my belt, prior to the DTT work. . luckily, no problem. Just don't hold it long is all... The shaft can go if it was crystallized or faulty when cast.

Do it with engine warm and oil pressure is up too of course...



bob.

 

[hdm48]

Hey BOB! I tried that stall test you mentioned here and my neighbors were miffed because I filled the area with tire smoke.

So now what do we do?



Mebe ya soulda mentioned dis only works with stock motors, HUH?





he he he snicker snicker



Dave

 

[BushWakr - RIP]

Ohhhhh,... I see what you're doing wrong... you need someone to hold the wheels still, while you're doing it.

Either that or put the brakes back on your truck, they don't weigh THAT much you know... ... . geeeezzzz...





Bob.

 

[therabbittree]

sounds like a bad idea i have done this and it just starts to burn tire even with new brakes. . on our detriot drag trucks the rule is never step on the brakes and gas at teh same time as it will break the pinion right out of the ford 9" rear. . i haven't done it but my freinds who race have don it and have the broken rears to prove it. .

 

[Philip]

ford 9" rear

Put this axle behind any diesel and you are going to have problems. It isn't rated for the power or torque that a modded diesel can put out. It is border line for anything above a stock 4 cylinder diesel engine. IMHO





In all of my working life as a mechanic. I have only seen one broken input shaft on a 727/518. This one just happened to being one of my cars. But the input shaft wasn't the original problem. It happened a couple of milliseconds after the planetary gear carrier assy got done doing is impression of a grenade. That got pretty exciting also. I was doing 90 mph at the time. I was in the process of showing a BB Chevelle the proper way to look at the tail lights of a built up 71 Challenger.

 

[therabbittree]

not to bust any bubbles but the ford 9" is pretty tough if built the right way . and not used to hual any weight . the worlds quickest diesel truck runs a ford 9" @ 9. 27 in the 1/4 mile also most of the prostocks and promod cars running 2500hp plus and over 1500 ftlbs plus run a 9"... ... i would use on in drag truck but i wouldn';t put one in my 1 ton and go off road with it or load it up under a 5th wheel or gooseneck etc totally different applications

thanks

deo

\x/ hillfolk!

 

[hdm48]

Uh BOB, I asked my wife if she would hold onto the wheels when I do the stall test next time.



Well,,,,,,,,,,, uh,,,,,



I never heard a woman use words like that before.



I told her it was your idea.





You better stay in Canada for a while, dude

 

[BushWakr - RIP]

:-laf :-laf :-laf :-laf ... . ahhhh heck, story of my life bud... . :-laf :-laf



bOb.