TH400 Charge flow pressure

[turbobitt]

OK, While I'm in the process of rebuilding my engine, I decided to take the oportunity to dial in the converter charge flow pressure since it's a little on the high side. Well, problem is, I am already restricting the flow with a .113 orfice and afraid to reduce it further. This is unchrted teritory for me so I'm a little unsure.
This is what I found with the pump,
1 - Gear clearance maybe a little high, .003" but already at the max available gear thickness. Realize that some flow may be coming froom this area.
2 - As mentioned, orfice is .113"
3 - Line pressure is steady 190-200 PSI
4 - PR valve is not notched
5 - Confident pump halfs are flat. Pump half's been sanded flat on a surface plate.

I am willing to further reduce the orfice size but wanted to see if I'm the only one down this far with the restriction.

Allan G.

 

[chris718]

I dont like going lower than that.During some testing last year I put .721" gears in a pump body that specced out at .7285"and plugged the hole to converter feed completely.Guess what?After about 2 minutes I had 3 psi cooler pressure ,0 flow on the gage on cooler flow volume ?and 1 quart of oil after about 3 minutes.

 

[turbobitt]

So you don't think gear clearance is an issue ? Was thinking of reducing orfice size to .090". I forgot to mention that my cooler pressure was 100 psi w/.113" orfice.
Allan G.

 

[chris718]

I would first install the correct pump gears .The pump efficiency losses generated with incorrect pocket depth to gear ratio are proven to reduce line pressure when hot.Then I would examine what you have for a pr spring and if it is really stiff use something lighter.I have never gone down below .100" on the orificing but correcting pump gear clearances may reduce cooler psi to acceptable level.What is cooler psi when warmed up?

 

[Alky V6]

Get the pump gear face clearance down to .001-.0015". There's no good reason to have it more than that. You can face cut the pump body to get the clearance you need or just get another body.
Make sure there is no hole drilled in the PR area that would provide 'full time lube' or feed to the converter charge. Similar to what a flat on the PR valve would do.
The orifice size is not as important a consideration as the fact that you need a minimum flow of 1 quart in 20 seconds. If you go down in orifice size and have less than 40 psi cooler line pressure, but can still maintain 1 quart in 20 seconds, you're good to go. 100 psi is crazy. Do not settle for a pressure that high. If after all these corrections you still have pressure like that, replace the pump assembly and take a hammer to the old one.
Also, to keep good converter charge and lube circuit separation, make sure the stator bushings are operating with a good tight clearance. Especially, the rear one.
Your line pressure reading looks good. Don't mess with the PR spring.

Above has been edited.

 

[turbobitt]

I never checked the pressure when it was really hot. I can't imagine it changing very much or dropping from 100 psi to an acceptable level.

I have been tweeking the line pressure for some time. I tried numerous combinations of valves, stock springs, and shims to try and get to 160 to 180 PSI. The closest I got was with a stock spring and a thick washer and maybe a horseshoe shim and only got 155 psi. I even tried a different pump. This spring I have now was advertised to give me 200 PSI and I have 195-200 on a calibrated gage. This same gage shows 100 PSI in the converter charge circuit.
Here is another piece of info. When I make gear changes at idle, the converter/cooler pressure doesn't change EXCEPT when it goes into third. While in third, the pressure goes to ZERO. When I bring the engine of idle to about 1200 or so, it comes up to about the 100 PSI mark. I suspect the drilled hole in the direct drum may be causing the PR valve to compensate and sutting down flow to the converter.
I was thinking of reducing the orfice to .090 and checking the pressure. Only problem is that I have a long wait time since I decided to rebuild the engine for next summer.
I will check the rear stator bushing as stated. I don't know if I can have the cover cut to reduce pump clearance but will check into it.
Allan G.

 

[Alky V6]

I never checked the pressure when it was really hot. I can't imagine it changing very much or dropping from 100 psi to an acceptable level.

I have been tweeking the line pressure for some time. I tried numerous combinations of valves, stock springs, and shims to try and get to 160 to 180 PSI. The closest I got was with a stock spring and a thick washer and maybe a horseshoe shim and only got 155 psi. I even tried a different pump. This spring I have now was advertised to give me 200 PSI and I have 195-200 on a calibrated gage. This same gage shows 100 PSI in the converter charge circuit.
Here is another piece of info. When I make gear changes at idle, the converter/cooler pressure doesn't change EXCEPT when it goes into third. While in third, the pressure goes to ZERO. When I bring the engine of idle to about 1200 or so, it comes up to about the 100 PSI mark. I suspect the drilled hole in the direct drum may be causing the PR valve to compensate and sutting down flow to the converter.
I was thinking of reducing the orfice to .090 and checking the pressure. Only problem is that I have a long wait time since I decided to rebuild the engine for next summer.
I will check the rear stator bushing as stated. I don't know if I can have the cover cut to reduce pump clearance but will check into it.
Allan G.

I think you meant pump body, not pump cover to reduce pump gear side clearance.
If the PR is shutting down conv feed, you may want to drill a very small full time lube hole (.060") like I stated above to work in conjunction with your orificed feed. You will be fine at .090".

 

[turbobitt]

Do you mean a .060 hole across the pump seperator chanels from converter feed to main line? I could definetly see this desensitizing the PR valve position but would seem to be counter productive since the theory revolves around maximizing the effort to keep these circuits seperated. I still like the idea though, since ultimatly the main feed orfice will govern flow.
Allan G.

 

[Alky V6]

Do you mean a .060 hole across the pump seperator chanels from converter feed to main line? I could definetly see this desensitizing the PR valve position but would seem to be counter productive since the theory revolves around maximizing the effort to keep these circuits seperated. I still like the idea though, since ultimatly the main feed orfice will govern flow.
Allan G.

Now you're thinking. :wink:

 

[matt69olds]

What is the deal with converter charge pressure? How do you check it and why would you want to reduce it? What happens if its to low or high? I have built transmissions for almost 20yrs, this is the first of heard of this. Im not anywhere near the level of Chris, Don or Jake, just wondering if Im leaving some stones unturned.

 

[Alky V6]

What is the deal with converter charge pressure? How do you check it and why would you want to reduce it? What happens if its to low or high? I have built transmissions for almost 20yrs, this is the first of heard of this. Im not anywhere near the level of Chris, Don or Jake, just wondering if Im leaving some stones unturned.

Have you ever heard of Motorhomes with big block Chevies and TH400s taking out the crank thrust bearing?

 

[turbobitt]

Got home late tonight and decided to double check my gear clearance. It seems that the gear clearance is more like .0015-.0020 . I am theorizing that since my charge flow pressure drops to near zero in third gear idle that the gear clearance is a non-factor(zero pressure because of direct clutch bleed orfice taxing PR valve). I would also think that the rear stator bushing clearance is a non-factor(Any leakage in these area's should have keeped the pressure high. Didn't take any actual measurments of the stator bushing clearance but feels good and tight).

I think I will try this,
1 - .060 constant feed near PR port upstream from the main restriction orfice.
2 - reduce .113 orfice to .090 ( approx. 25% reduction in flow area)

Allan G.

 

[chris718]

More than likely the low cooler pressure in third at idle is a result of the lack of pump speed.Low pump rpm results in lack of volume .Volume and pressure are interwoven.Trying it @1200 rpm will yield different results.Combine this with the orifice bleed in the hi drum and the pr valve is favoring its downshifted position to generate enough pressure to cover up the leak.At this point the converter feed land of the pr valve can be shutting off or restricting the oil flow into the passage that pees oil into the converter to keep it full.I suggest going on line to HELMS service manuals and getting a th400 principle of operations manual.The pr valve system is way more involved than it appears.It is never in the same place for long except when then engine is off,and it has a means of hydraulically understanding when it has enough pressure ,and returning unused volume back to the reservoir.

 

[turbobitt]

More than likely the low cooler pressure in third at idle is a result of the lack of pump speed.Low pump rpm results in lack of volume .Volume and pressure are interwoven.Trying it @1200 rpm will yield different results.Combine this with the orifice bleed in the hi drum and the pr valve is favoring its downshifted position to generate enough pressure to cover up the leak.At this point the converter feed land of the pr valve can be shutting off or restricting the oil flow into the passage that pees oil into the converter to keep it full.I suggest going on line to HELMS service manuals and getting a th400 principle of operations manual.The pr valve system is way more involved than it appears.It is never in the same place for long except when then engine is off,and it has a means of hydraulically understanding when it has enough pressure ,and returning unused volume back to the reservoir.

Chris,
This is my point. At idle and in third gear, the PR valve has closed down and cut flow to the converter. This is obvious in the gage pressure reading. So far I think we are on the same page. At this point, I am drawing the assumption that the PR valve has FULL athority over the charge flow pressure. Becasue of this, my assuption is that the pump gear clearance may not be an issue. If there was excessive clearance and leakage, it would maintain charge flow pressure in any condition. Am I missing anything ?
The drop in pressure in third gear idle doesn't concern me since it would never see this condition during any type of driving. It is just another piece of evidence that paints the overall picture.
I remember you telling me a story about some bread trucks hauling heavy loads and the owners thought that they had blown there transmissions. I also remember you telling me that the actual problem was that the transmissions were running hot and the PR valve in that situation cut the flow and gave the sensation of a blown transmission. If I remember correctly, your fix was to supply constant oil feed to the converter circuit.

BTW, own mutiple books on TH400 stuff. Matter of fact I have Ron Sessions book with me at work today. Owned this book for about a year so I can't remember if the info was any good. It will keep me buisy during luch today. Wouldn't claim to know every little detail but enough to be dangerous. I am looking forward to your own book...
I do appreciate the discussion. I just want it to be the best that it can be without wrecking something. It is cheeper to experiment with the transmission then repairing a billet crank thrust surface on an engine.
Allan G.

 

[turbobitt]

Woops, didn't mean to post twice.

 

[chris718]

Here is what we need to do.When you and Brian can kill 1 day I will make time and we can spend 8 hours on and off the dyno to get real data again.Im seriouys.When the 2 of you have the time,(dont put it off) I will do it on my end and we can get real world data to reconfirm what I have already or dispute it.Let me know.

 

[Alky V6]

Here is what we need to do.When you and Brian can kill 1 day I will make time and we can spend 8 hours on and off the dyno to get real data again.Im seriouys.When the 2 of you have the time,(dont put it off) I will do it on my end and we can get real world data to reconfirm what I have already or dispute it.Let me know.

I don't get it. What do you think he is so far on that you think you need to run dyno experiments?

 

[turbobitt]

Here is what we need to do.When you and Brian can kill 1 day I will make time and we can spend 8 hours on and off the dyno to get real data again.Im seriouys.When the 2 of you have the time,(dont put it off) I will do it on my end and we can get real world data to reconfirm what I have already or dispute it.Let me know.

Chris,

I would love to come up and kill a day. Would be even better to do an A/B comparison with my set-up. Don't know how universal your dyno is. Testing with my converter and trans against your baseline would be very informative. I would almost be willing to bet you may learn a thing or to. I would obviously learn more since I'm just a backyard hobbiest. I don't know when i would ever get a chance to do it though.

This is another thought. Is it possible that we are completly off base and should be looking elsewhere ? Example, If I took my current set-up with the 100 psi charge flow and disconnected the return line to the transmission, we would expect the pressure to drop to near zero and have a lot of flow. So if we take this one step further, it would almost look like that something internally is a bigger restriction in the lube circuit. I have no idea what end play will do with espect to charge flow but I can tell you that all the bushings are new and the clearances are minimized. Could this be the contributing factor ?
So million dollar question, would it be more benificial to keep the charge flow rate up and reduce the pressure by adding a bleed somewhere in the transmission downstream of the cooler ? This would mean that I could maintain a minimum flow for cooler/heat exchange efficiency while reducing pressure. This doesn't seem to be the "Main stream" way of dealing with this issue but could be a alternative solution.
Allan G.
Allan G.

 

[chris718]

I am always willing to learn as well.I have alot of things we can go over beyond what is posted here.A Saturday is fine .Bring the trans and converter.Testing by me has shown differences as much as 20 psi with the same trans and different converters.Trans can be loaded and unloaded in minutes on the dyno and we can do pr valve spring changes instantly on the dyno.3 minutes tops.Talk to Brian and set it up if you are interested.I am finishing up the 400 manual and this info will be added to the book .

 

[Alky V6]

By measuring the cooler line pressure, we're trying to get our best clue as to what the pressure is inside the torque converter. That is the most important consideration here. I hope by now we all know what excessive T/C pressure does. Bleeding off pressure after the fact seems useless to me in terms of trying to determine what the internal pressure of the T/C is.
I've always set clearancing tight on the 400s I've done. Didn't seem to affect cooler line pressure.

What you really need to do is set up some pressure taps in the T/C feed circuit after the feed restriction and at the T/C outflow circuit before it gets to the case fitting. Now that would peak my interest.