Th200-4R: Ok to run in OD with converter unlocked?

J

jthomas

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Joined
May 24, 2016
I tried searching but couldn't find the answer. I know some early GM overdrives should not be run in OD with the converter unlocked because it starves part of the tranny for oil, but which transmission and years does that apply to? I have a TH200-4R with lockup. It is a CZ from an 86 Monte Carlo. I am running a 9.5" PI Vigilante converter. I don't run it unlocked in 4th, but there are times that would be useful. Is mine one of the ones that has to be locked up?
 
jthomas said:
I tried searching but couldn't find the answer. I know some early GM overdrives should not be run in OD with the converter unlocked because it starves part of the tranny for oil, but which transmission and years does that apply to? I have a TH200-4R with lockup. It is a CZ from an 86 Monte Carlo. I am running a 9.5" PI Vigilante converter. I don't run it unlocked in 4th, but there are times that would be useful. Is mine one of the ones that has to be locked up?
Click to expand...
Do you run a manual lock up toggle switch to lock it or not? That would give you complete control of that issue , I have the kit from tcc and a switch plate in my ashtray but havnt installed it yet or are you having a problem with your lock up? I'm no expert but lockup is for fuel economy
And it cuts down heat I personally would do the tcc lock up solenoid kit
It's easy to install and just hit your switch in 4th and your lock up will engage when you want I know that was some rambling but I hope it is helpful to your question
 
I ran my brand new '86 GN for 1000- 1500 miles with the converter NOT locked. The brake pedal switch wasn't adjusted properly from the factory and I didn't discover it until stretching my feet with the cruise on and raised the brake pedal slightly to engage the switch.
The car has 70k on it now and is running fine.
I believe the lock up is for fuel economy as well.
I hope this helps.
 
Thanks. Here's more information.

I'm running the Bowler Total Cure/TruShift system. In that system, there is a module that plugs into the case connector which monitors OD gear engagement. Once IN OD, it waits 8 seconds for a change in speed or load and if none is detected it locks the converter. If I brake, the brake switch unlocks the converter, or if I accelerate, the module unlocks it. I also have an "unlock" switch on the dash in case I want to turn it off without tapping the brake or want to prevent lockup.

Sometimes between 40-50 mph it locks when I would prefer to use OD without lockup. The lockup gives me a 300-400 rpm drop and is like having a "5th" gear. I can prevent lockup with the switch, but wanted to be sure that won't hurt the tranny before I start doing that.
 
Last edited:
If it's a lockup converter it shouldn't be run continually unlocked while cruising


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bison said:
If it's a lockup converter it shouldn't be run continually unlocked while cruising


Sent from my iPhone using Tapatalk
Click to expand...

Maybe it would be better to run in 3rd gear with the converter locked when looking for more rpm, like trucks do for tow mode?
 
Last edited:
jthomas said:
I tried searching but couldn't find the answer. I know some early GM overdrives should not be run in OD with the converter unlocked because it starves part of the tranny for oil, but which transmission and years does that apply to? I have a TH200-4R with lockup. It is a CZ from an 86 Monte Carlo. I am running a 9.5" PI Vigilante converter. I don't run it unlocked in 4th, but there are times that would be useful. Is mine one of the ones that has to be locked up?
Click to expand...

Interesting.

It is fine to run it unlocked in OD. The trans will run a little hotter unlocked because of converter slip and it will be less efficient. Make sure to have an aux cooler installed. The cooling circuit return is the transmissions lube circuit and it will not be starved of any lube because it is run unlocked. When unlocked, all hot oil exiting the converter is directed thru the cooler and it doesn't matter what gear you are in. This is the same as Non Lock-up. When the converter is locked, converter feed oil is used to force the lock-up clutch on and no oil exits the converter. The converter clutch apply valve will direct converter feed oil thru an orifice to the cooler to lube the trans. So either way, the trans will get lube.

I do recommend using lock-up when cruising as this will allow the transmission to run much cooler which will help longevity of the trans. The number one killer to a trans is heat, so why not keep it cool. Some also like the lock-up function for better miles per gallon...
 
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Thanks David. That is the information I needed. Guess I got some bad info about starving part of the tranny for oil. Anyhow, I have a large auxiliary cooler and I use lockup all the time when cruising. There are just some times when I am on a short stretch of road where OD locked is too low RPM-wise and 3rd is a bit high. In those cases, leaving it unlocked in OD would be better. Now I know I can do that without hurting anything for those short sprints. I know about the heat generated so I will lock up again as soon as I'm back at cruise speed.

And thanks again for helping me get my Servo fixed. No more downshift clunk.... Love it!
 
jthomas, the 700R4 reduces cooler feed when the converter is unlocked. Supposedly the early ones ('83-'84) have no cooler feed when unlocked. With the later ones reducing the cooler feed by about 50% when unlocked.

I didn't know anything about the 200-4R cooler feed so didn't post.

RemoveBeforeFlight
 
Thanks RmvBfrFlght...David answered my question about the 200-4R. Now that you mention it, I recall hearing about the oiling issue when a friend of mine was putting a 700R4 in his Street Rod and we were trying to decide on best lockup system. It sounds like I got my information crossed about the earlier 700R4s and the 200-4Rs.

Thanks to everyone for the replies. Now I can run this thing the way I want to without worrying about an occasional unlock in OD. Appreciated!
 
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