Turbo 400 pump converter feed restriction

[Alky V6]

many yrs ago, w/ my first 400. I did the mod, and we tested it out. Found that turbobitt's value of 75 was there. We then changed the drill from 7/64, to 3/32.. PSI dropped to 40's...
We think it may vary, trans to trans, as mentioned by turbo bitt/Bison. Yes? No?....

THANKS Don!

To answer your question, most certainly! One pump specification that contributes to over-feeding and over-pressurization of the torque converter, other than the normal feed passage in the pump cover, is the pump gearset face clearance. Even with the proper restriction placed in the T/C feed passage, if excessive clearance is present at the gearset face, oil pressure will crossleak across that clearance, directly into the feed oil circuit to the T/C. That would explain why some have used the recommended 7/64" orifice in the T/C feed passage restrictor, but still had too high a cooler line pressure. The excessive pump gearset face clearance could easily be labeled a crossleak from the high pressure cavity of the pump pocket directly into the torque converter feed circuit. The potential of this crossleak is directly related to the amount of line pressure that the unit is setup with.

To control this potential crossleak problem, keep pump gearset face clearance to no more than .001". No less than .001". Yes, the specification should be right at .001".

A good example of how important face clearance really is. Back when Chrysler TorqueFlite, lockup T/C, 904 transmissions were around, it was very common to see them kill the engine when the shifter was put into reverse. In reverse, in any transmission, the pump generates higher line pressure than in the forward ranges. The higher pressure in the pump cavity would crossleak directly into the T/C feed circuit, causing excessive fluid flow volume and the lockup clutch in the T/C would apply and kill the engine. If those pumps were not kept to no more than .002" pump gearset face clearance, preferrably .001", this would happen. .003", which is a perfectly exceptable max limit for most transmissions, would most definitely cause the T/C clutch to engage and kill the engine.

I cannot over state the importance of maintaining a proper pump gearset face clearance. The normal flow pattern to feed the T/C goes from the pressure cavity of the pump gearset pocket to the pressure regulator valve, and from there it is regulated by the PR valve and continues on to feed the T/C. A crossleak from the pressure cavity of the pump gearset pocket to the T/C feed circuit is direct. The pressure is not regulated at all except by the face clearance of the pump gearset, bypassing the PR valve all together.

Lots to think about in a transmission. Not the simple beast some think it is.

 

[Alky V6]

Don. I have taken out 2 thrust this year with a glide behind my V8. Never had an issue until I swapped to a tighter converter to transfer the power. I went 400 rpm and tighter. The thrust lasted 5 passes initially with a Castrol 30W oil. I then repaired the engine, swapped to Penzoil Platinum 30W and it lasted 20 passes.

I just got it off the dyno last week. Cooler psi was 65# so I swapped to a ringless input shaft which lowered the psi to 40#. I'm back racing it again to see how it goes.

Something else to think about. This is not a common problem, but the potential is there.

The cooler line is our only way of measuring what kind of pressures are going on inside the T/C. This measurement is being taken after the oil has left the T/C. It is not a direct measurement of the pressures inside the T/C. Think of this scenario. It is perfectly possible for flow to be restricted upon exiting the T/C. Or restricted before it can get to the out flow passage to leave the T/C. Restricted inside the T/C itself. What would this do to our pressure reading at the cooler line. It could very well read normal, exceptable, or even a bit low. So cooler line readings are not the tell all, but it is our best clue.

Dusty. Now that you've controlled your cooler line pressure to 40, if you still experience crank thrust wear, I would look into an internal flow restriction inside the T/C. It's been known to happen.

 

[Alky V6]

Dusty. What has probably allowed your T/C pressure to drop from the change to the ringless input is the crossleak that is now present from the missing sealing ring. That sealing ring seals the normal T/C feed circuit. Without the sealing ring, some of the T/C feed circuit oil is crossleaking directly to the lube circuit. Not a bad thing, but maybe is a bandaid fix for an excessive T/C feed problem that hasn't been addressed.

 

[Alky V6]

guys,

I did the .125 pump feed restriction to my trans and now have 75 psi cold oil pressure in the cooler circuit.Discussed this with Bison and I am theoryizing that the pressure may be high because of the tight thrust clearances and little chance for internal leakage in the transmission. I only have one cooler and I know it is free and clear and no kinks in the line. I am going down on the size to the suggested 7/64.

That's usually not the case. I setup my thrust clearances tight also. In the world of transmission hydraulics, a 1/8" orifice is practically free flowing. You must be under 1/8" to offer a significant flow restriction. Just look at most shift kits. If the shift kit designer wants full flow to a clutch pack or band, what size orifice do they ask you to drill to? 1/8".

 

[Dusty Bradford]

Dusty. What has probably allowed your T/C pressure to drop from the change to the ringless input is the crossleak that is now present from the missing sealing ring. That sealing ring seals the normal T/C feed circuit. Without the sealing ring, some of the T/C feed circuit oil is crossleaking directly to the lube circuit. Not a bad thing, but maybe is a bandaid fix for an excessive T/C feed problem that hasn't been addressed.

Fluid has no issue getting out of the converter. Already thought of that I installed the ringless shaft and checked cooler pressure without the bushing in the pump. Pressure was 20# but when power was applied, it blew all the fluid out of the converter....car felt like it had 8000 rpm stall when the boost came in. Now with the bushing in the pump I am back to 40# cooler pressure. The bushing gave it just enough restriction to keep the converter full so no pump mods are necessary. Stall is noticably looser in high gear but I ran my best mph with 4# less boost than earlier in the year.

 

[Alky V6]

Fluid has no issue getting out of the converter. Already thought of that I installed the ringless shaft and checked cooler pressure without the bushing in the pump. Pressure was 20# but when power was applied, it blew all the fluid out of the converter....car felt like it had 8000 rpm stall when the boost came in. Now with the bushing in the pump I am back to 40# cooler pressure. The bushing gave it just enough restriction to keep the converter full so no pump mods are necessary. Stall is noticably looser in high gear but I ran my best mph with 4# less boost than earlier in the year.

For future reference, you would restrict T/C feed at the separator plate on a PG. The PR valve is in the valve body. T/C feed comes off the PR valve. It should have to feed through an orifice in the separator plate.

That's interesting. Does your input shaft have a passage in it, or is it solid? Where is the out flow passage? Is the impeller bushed into the T/C cover? The internal flow pattern must have been shorted circuited by the missing bushing. I'd sure like to see the inside of that T/C and your pump/input shaft arrangement. Sorry for being so curious.

 

[Alky V6]

So it sounds like due to the crossleaking set up by the ringless input shaft, you've actually had to figure out a way to create more pressure in your T/C. Do I have this right?

 

[Alky V6]

And yes, you can run a bushed impeller and the front stator support bushing together. I've been doing it with my 400 for quite awhile now. As long as things are running true centerline and you've accounted for proper flow in and out of the T/C, you shouldn't have a problem. Very easy to check with a bolt together T/C.

 

[Dusty Bradford]

So it sounds like due to the crossleaking set up by the ringless input shaft, you've actually had to figure out a way to create more pressure in your T/C. Do I have this right?

The ringless shaft is solid and stronger than a regular shaft. It's the same shaft you find in the pro-mod and outlaw 10.5 glides. Fluid flows around the shaft. Without the bushing in the tranny pump, the fluid doesn't have enough restriction (too loose of a clearance around the shaft). The bushing adds enough of a restriction to maintain backpressure in the converter once you make power.

 

[turbobitt]

That's usually not the case. I setup my thrust clearances tight also. In the world of transmission hydraulics, a 1/8" orifice is practically free flowing. You must be under 1/8" to offer a significant flow restriction. Just look at most shift kits. If the shift kit designer wants full flow to a clutch pack or band, what size orifice do they ask you to drill to? 1/8".

Don,
If you look at the lub feed in the 400, it needs to jump the clearance between the input and the intermediate shaft to lub the back. Any increase in thrust will significantly increase internal leakage. I am just therorizing and have no data to support this but it makes sense.

 

[jakeshoe]

Don,
If you look at the lub feed in the 400, it needs to jump the clearance between the input and the intermediate shaft to lub the back. Any increase in thrust will significantly increase internal leakage. I am just therorizing and have no data to support this but it makes sense.

Wouldn't the fluid at this junction be "sealed" by the forward hub, so no matter the endplay, the spline fit here would actually be the determining factor of how much fluid loss happens?

On a TH400, aftermarket input shafts can also contribute to the converter charge pressure.

 

[turbobitt]

Wouldn't the fluid at this junction be "sealed" by the forward hub, so no matter the endplay, the spline fit here would actually be the determining factor of how much fluid loss happens?

On a TH400, aftermarket input shafts can also contribute to the converter charge pressure.

The forwoard hub sits in the splines of the intermediate and flush with the input with a thrust washer. The pilot on the forward hub is sloppy and not meant to be a close fit or it would rub. I spent some time anaylizing this area and trying to determine if its an influence on converter charge pressure as well as excess lub oil in the forword/direct clutch drum.

 

[Alky V6]

Don,
If you look at the lub feed in the 400, it needs to jump the clearance between the input and the intermediate shaft to lub the back. Any increase in thrust will significantly increase internal leakage. I am just therorizing and have no data to support this but it makes sense.

When the lube circuit has working pressure in it, the forward drum tends to be shoved rearward. So any clearances rear of the forward drum will be tend to be closed off. Plus their are plenty of thrust washer grooves and other bleed offs of lube flow on down the line through to the output shaft.

Speaking of the lube circuit. Here's another tip. Dang! I'm giving it all up lately.

 

[Alky V6]

Pay attention to this next tid bit of information. It will prevent mysterious overheating of the transmission. Even though you have auxiliary coolers mounted.

Oh! The wife caught me playing on the computer at work. Later.

 

[Alky V6]

OK. Let's trace the path of the lube circuit in a 400.
Starts at the PR valve,
moves through the T/C feed restriction,
up along the outside of the stator support,
through the T/C,
exits the T/C through the tip of the input shaft,
down between the input and stator support shaft to an exit passage just ahead of the rear stator support bushing,
through a passage in the pump cover to the case,
through a short passage in the case to one of the cooler case fittings,
through the cooler lines and cooler(s),
back to the other cooler case fitting,
through a short passage back to the pump cover,
through the pump cover to an exit rearward of the rear stator support bushing,
through the forward clutch housing,
and onward to lube the rest of the internals.

Note the 2 phrases in bold. The lube circuit is separated in the pump cover by the rear bushing in the stator support shaft.

If there is any appreciable wear to this bushing, the lube flow will crossleak across the bushing, bypassing the cooler system. The fluid will go on to lube the transmission geartrain without first being cooled. The fluid then drops to the pan to be picked up by the pump again, flow through the converter to be heated, and bypass the cooler again.
Not all the flow will bypass this way, but enough will to show up on the transmission temperature gauge.

Dusty. The sealing ring on the input shaft of the PG does the same job as the stator support rear bushing in a 400. I have to wonder how the ringless input may have upset the normal flow patterns in the PG. If you are running a solid bushing at the front end of the stator support and the input shaft has no oil passages in it, what exactly is the flow pattern of oil into and out of the T/C?
Without proper flow through the T/C, the fluid will overheat and most likely explode and blow fluid out the breather.

 

[chris718]

Don most of those ringless shafts completely bypass the cooler circuit.Some of the better ones have the rings inside the stator tube,very trick stuff.ATI.As for the bushings ,i agree all should be replaced during an overhaul.I use the grooved 4l80e drive tube bushing from the late center lubed 4l80e in the nose of my 400 pumps,im sure you can understand why.

 

[turbobitt]

When the lube circuit has working pressure in it, the forward drum tends to be shoved rearward. So any clearances rear of the forward drum will be tend to be closed off. Plus their are plenty of thrust washer grooves and other bleed offs of lube flow on down the line through to the output shaft.

OK, I'll buy that explanation..

 

[chris718]

alan when you have the trans apart stack everything from the output shaft up to the center support on the table and blow 40 psi of pressure into the main shaft.next install the direct drum on the support and blow air .now do it again with the output shaft to case bushing feed hole covered with a finger.

 

[Alky V6]

Dusty. The sealing ring on the input shaft of the PG does the same job as the stator support rear bushing in a 400. I have to wonder how the ringless input may have upset the normal flow patterns in the PG. If you are running a solid bushing at the front end of the stator support and the input shaft has no oil passages in it, what exactly is the flow pattern of oil into and out of the T/C?
Without proper flow through the T/C, the fluid will overheat and most likely explode and blow fluid out the breather.

Continuing this thought, If you have flow going into the T/C, but have choked off the exit for this fluid flow, then over-pressurization of the T/C is assurred. You won't get evidence of this on the cooler line pressure gauge because the oil is having a hard time even getting to the cooler line. Most of the exit flow is being blocked and whatever can get past the bushing at the front of the stator support, some of that will bypass the cooler system and crossleak past the ringless input directly to the lube circuit, leaving little to be measured by the cooler line pressure gauge.

 

[Alky V6]

Dusty. I hope you're taking a real close look at that. I'd hate to see you chew another crank thrust.