th400 converter pressure questions
th400 converter pressure questions hey guys i have a few questions about th400 line pressure or charge pressure. I have a dynamic converter and transmission built awhile ago. I have found out today there is no trans pump restrictor in the trans. I havent had any issues for about a year but the car wasnt making too much power. went 10.1 at 138 mph. I switch to a different converter which was PTC 9.5 inch and everything was fine, drove it around. went very similar time. swithced tuners and now the car IS WAY faster. prob a mid to low 150 mph 1/4 mile car. after it got tuned i did a couple pulls and noticed my oil pressure drop which was in another post.
Long story short. it killed my thrust bearing but i caught in time to not cause any major damage.
when i pulled the trans out of the car i noticed the snout of the converter was a screw on and was laying in the end of the crank with the threads mushroomed a little on the converter.
NOW, i am a little confused as to wether line pressure is the issue or its 100 percent the converter snout coming off. I really dont want to kill my thrust again. my trans builder said my line pressure was about 200.
Long story short. it killed my thrust bearing but i caught in time to not cause any major damage.
when i pulled the trans out of the car i noticed the snout of the converter was a screw on and was laying in the end of the crank with the threads mushroomed a little on the converter.
NOW, i am a little confused as to wether line pressure is the issue or its 100 percent the converter snout coming off. I really dont want to kill my thrust again. my trans builder said my line pressure was about 200.
I know we talked before but sounds to me like the new converter was working on the thrust as it had an extended pilot. What was your converter pad to flexplate gap with old converter vs new? I have a restrictor in my pump but I had gone without it for quite sometime in the past with no issues. Some guys do it for spool time.
TECH Resident
Joined: May 2006
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The TH400 has had problems with loading the thrust bearing. The "easy fix" is to remove "two" splines 180 degrees apart on the input shaft. GM knows of the problem and has done this modification to the input shaft on a couple of the TH400's over the years, but it is very rare to see one. This modification will save the crankshaft thrust.
Last edited by PBA; Aug 27, 2017 at 07:49 PM.
The method of measuring the converter charge pressure usually leaves something to be desired (rarely in the actual charge circuit, but usually in the cooler circuit after the converter).
And if everyone knew what was actually happening on every GM lockup unit going down the highway they wouldn't be overly concerned with a TH400 making 40-70 or even 100 psi of charge pressure.
Joined: Aug 2007
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From: Turnin' Wrenches Infractions: 005
I took out a thrust, from forward push. Its so funny it developed about 5k miles after installing a name brand converter (i wont name the company) on a motor that had 90k miles, so very obviously Jake wins dumb post of the day because we ALL know that was definitely an "engine" issue that caused it. 
Same trans now has 150k in a buddies car.......hmmm.
Same trans now has 150k in a buddies car.......hmmm. I took out a thrust, from forward push. Its so funny it developed about 5k miles after installing a name brand converter (i wont name the company) on a motor that had 90k miles, so very obviously Jake wins dumb post of the day because we ALL know that was definitely an "engine" issue that caused it. Same trans now has 150k in a buddies car.......hmmm.
Same trans now has 150k in a buddies car.......hmmm.If the converter was at fault, why did it last 5k? If the pressure was enough to cause damage it would likely happen faster. A 90k motor may already have had a developing issue.
Dumbasses like you ruin it for other guys willing to learn.
You have some personal issue with me obviously that you feel compelled to follow me around and spout BS. Are you so experienced in this field that you build and test transmissions and converters daily?
I've done testing that many other shops haven't, and if they have they aren't posting results or talking about it. Some of that might get shared. Internet myths are a pet peeve of mine.
What do you think happens to internal converter pressure when you go to lockup on a 4L60E? 4L80E?
I would venture to guess that you don't know, and that likely none of the other sponsors on here do either (except Greg at FTI because I've told him what we found testing).
Most places aren't going to take the time to measure this pressure pre-converter because it's time consuming and ruins parts.
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Joined: Aug 2007
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From: Turnin' Wrenches Infractions: 005
The great thing though about the internet Jake is, we can both have an opposite opinion.....EDIT: and actually you could have just ignored my response, shared your technical data and the massive knowledge you've accumulated and helped the community of enthusiasts. But all the above response is none of that and pure bullshit, tooting your own horn and giving yourself an out by blaming me and giving you an opportunity to call someone a dumbass. That is why the **** i dont like you, sir.
Last edited by 01ssreda4; Aug 27, 2017 at 10:06 AM.
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TECH Junkie
Joined: Jul 2015
Posts: 3,012
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An easier way to keep a "killer 400" in check, and cost about $0.50 from your local hardware store....a set screw. Tap the converter feed in the pump, drill the setscrew to .110 or greater. From all the issues I've seen from guys killing thrust bearings from newly installed 400s....i took no chances, and restricted it straight off the rip. Bearings are happy thus far.