[68ragtop]

In looking at the design of most torque converters, is it safe to say that the converters push against the flex plate when under load? Honestly not something I ever really thought much about until just recently. If this is the case, is this why it connects to the "flex" plate?

[242177P]

Originally Posted by 68ragtop

In looking at the design of most torque converters, is it safe to say that the converters push against the flex plate when under load? Honestly not something I ever really thought much about until just recently. If this is the case, is this why it connects to the "flex" plate?

I suspect it's more of a harmonics thing? Convertor is filled with fluid that's churning
about. If you think about it, the convertor has to be slid forward to get bolted up, so
it'd have to balloon at least that much before all that slack is gone? Dunno.

[Brian Baker]

You're thinking in the right direction. I have seen cases where the thrust bearing on the crankshaft was wiped out from a convertor that "ballooned". This is typically only experienced in high-HP applications, especially with nitrous or boost.

[Schurkey]

Yes, it's possible for a converter to "balloon". Doesn't happen all that often.

Yes, the converter is free to slide on the stator support within a limited range of motion.

The REAL problem with converters and crankshaft thrust bearings is that the converter is pressurized with oil. The FRONT of the converter is solid metal. The REAR of the converter has a big hole in it for the input shaft and stator shaft. Therefore, the FRONT of the converter has more area for pressure to act on than the rear. Therefore, when pressurized the converter tends to push forward, in the direction of greater force. When that pressure is beyond design limits, it overloads the crankshaft thrust bearing.

If you wipe a thrust bearing on an engine driving an auto transmission, you need to verify pressure in the trans cooler hydraulic circuit.

[68ragtop]

Even though centrifugal forces would seem to keep most of the oil that is doing the work to the outside, it seemed like some pressure could come back towards the transmission and push it outward because of the stator? I wasn't sure if it was completely full of oil when in operation, or just from the center opening outward.

What got be thinking about it is I have a work vehicle that had a cracked flexplate. Call it lucky I suppose, but I have never had a vehicle with that problem, so I didn't even know what the symptoms were. I have heard of it happening, just never happened to anything I ever owned.

Basically it was ticking at idle, sounded exactly like valve train issue, but would go away with a touch of the throttle. after about 3K miles, that turned into knocking on the fist couple seconds of start ups & would go away when in gear, but would come back when I would get on & off the gas. But never hear a thing when under power. After pulling the cracked plate & looking at it I could see it was getting pushed against the crankshaft & must have been why it wasn't making noise all the time.

Doing some research now, & it turns out this is somewhat of a common problem on the 3.6L Chrysler engine with the T62 Transmission, especially in the promaster van. So much so, that many owners replace them more than once. Crazy thing is there is no recall & no updated part numbers. Ram just keeps stocking the shelves. If it fails under warranty they cover it, but after 5 years or 100K your on your own.

If all other things are equal in the drivetrain, the biggest difference between the Promaster & passenger vehicles is weight & the amount of weight they can haul.

[steve25]

Look at it this way, the input seal on the snout of the converter would be leaking fluid like mad long before a thrust Bearing in a motor would get overloaded due to pure transmission pump pressure alone!

It's a combo of things ballooning the converter like the pump pressure , centerfugal force, and the magnified fluid force ( 2 to 1 or greater! ) in the converter that overloads the thrust Bearing.

As posted, once bolted to the flexplate the converter can not move back anymore and use any of that installation gap that's there, so if it's going to expand due to whatever forces it can only be driven that .005" or do forwards before placing all of the load action on it into the thrust Bearing.

[Cliff R]

The factory took steps to limit converter feed and control converter drain to prevent the flow of fluid from shoving the converter forward and taking out the engines thrust bearing. You can't build pressure (or much of it) in a hydraulic system without a resistance to flow. Even with that said you wouldn't want a partially filled converter either.

They didn't always get it right, so make sure when you go thru your TH400, for example, to make sure to size the converter feed hole accordingly as outlined in my book and on threads running here on that subject........Cliff

[gtohunter]

Originally Posted by Brian Baker

You're thinking in the right direction. I have seen cases where the thrust bearing on the crankshaft was wiped out from a convertor that "ballooned". This is typically only experienced in high-HP applications, especially with nitrous or boost.

My kid had a Thunderbird Super coupe, and we'd put a new crate engine in it. Within 20K miles, motor was trashed, and turns out converter was ballooning to the point of taking out the thrust brg, and had left an imprint of the flex plate bolts in it! Was running about 12lbs of boost.

[Schurkey]

Originally Posted by steve25

the input seal on the snout of the converter would be leaking fluid like mad long before a thrust Bearing in a motor would get overloaded due to pure transmission pump pressure alone!

Pressure above a mere 120 psi can do it. Lip seals in the transmission clutches see more than that, and they're much larger in diameter.
https://www.chevelles.com/threads/co.../post-10827865

The force on the crankshaft from the torque converter is simple. It is the same principle as a servo piston or any other hydraulic component: Pressure, multiplied by area, equals force. The pressure part is easy; it's simply the internal torque converter pressure. The area is a little trickier. The area that is part of this equation is the difference between the area of the front half of the converter and the rear half. The oil pressure does exert a force that tries to expand the converter like a balloon (which is why converter ballooning is probably often blamed), however, it is the fact that the front of the converter has more surface area than the rear (the converter neck is open) that causes the forward force on the crankshaft. This difference in area is equal to the area consumed by the inside of the converter neck. The most common scenario is the THM 400 used behind a big-block Chevy. General Motors claims that this engine is designed to sustain a force of 210 pounds on the crank shaft. The inside diameter of the converter hub can vary from 1.5 inches up to 1.64 inches. The area of the inside of the hub can then vary from 1.77 square inches to 2.11 inches. 210 pound of force, divided by these two figures offers an internal torque converter pressure of 119 psi to 100 psi, respectively. That is to say, that depending on the inside diameter of the hub, it takes between 100 to 119 psi of internal converter pressure to achieve a forward thrust of 210 pounds. The best place to measure this pressure is the out-going cooler line at the transmission because it is the closest point to the internal converter pressure available. The pressure gauge must be "teed" in so as to allow the cooler circuit to flow. Normal cooler line pressure will range from 50 psi to 80 psi , under a load in drive.

All it takes is a kinked cooler tube, or a restricted trans cooler.

[Half-Inch Stud]

Conver pressure is low, in the 20 PSI range, yet higher (40 PSI?) under hard accel, but i dunno what PSI occurs with Race Mods. Line Presssure is for Clutch packs.

Total internal Converter Pressure cancels in all directions except for the Neck PSI. Do the calc for "bottlero ket" Force in Pounds at the neck = Square Inch area x PSI.

Total Internal PSI does cause balloning due to the Fluid Whorl mode: Fluid is thrown forward, drives the Driven fan (Turbine) and gets thrown AFT into the Drive fan (Impeller) welded into the Case. Stator deflects fluid in the direction of engine rotation to lessen engine drag. Torque multiplication occurs therein from lessened drag on the Drive fan Impeller, so engine RPM can go up for a given load TQ. A liguid gear ratio! around 2.0:1 to 2.4:1. Light loads allow the luquid gear ratio to be around 1.1:1. Locking Converters are cool but maybe not-needed in most highwat car use.

Ahem, balloning also gets some contribution from case distortions under l oad. When the flexplate tries to potato hip under TQ, the converter case may try to potatochip but ends up with some small balooning, like when Slammed/Flashed into TQ transfer, the Converter Case and Flexplate try to wrinkle for a moment. BOOST or Nitrous will make Case distortion moreso. Anti-ballooning plates is a cool upgrade.

Thrust bearing failure get blamed on Converter Balooning. I reserve opinion that Clearance setting, PSI mods may play a saving-role per application to avoid Overloading the Thrust BRG. Thrust bearings do not have ability to survive much load beyong 200 Lbs. Talk about HOT surfaces! Seems to me a much larger Thrush BRG Flange for PMS engines would have been Developed by now. If so, the crank flexure may get noticed?!

Cooling line outlet flow would be a fine place to monitor Converter PSI under Flash and hard acceleration. I have not done that. Bruno has made a tuning variable of the internal PSI.

Done bloviating.

[Schurkey]

A "ballooned" converter CAN NOT wear the thrust bearing unless it's also pushing against the trans pump gear. As long as there's clearance between the converter hub and the pump, the "ballooned" converter is free to slide rearward instead of applying forward pressure to the crankshaft thrust bearing.

If you wipe the thrust bearing but DON'T damage the trans pump...the converter isn't ballooning (enough to cause a thrust-bearing problem.) Consider how much clearance you have from converter fully rearward, to the flexplate. That's how much the converter would have to expand in order to harm the thrust bearing. This does not mean that a somewhat-ballooned converter won't cause stall-speed, vibration, or power-loss problems--just that it won't overload the thrust bearing.

However, the converter can thrust forward under hydraulic pressure as stated--which could wipe the thrust bearing but NOT damage the trans pump.

[iceman411]

It happened to me.... for fun I ran a COAN 2800 converter behind a mild 455 with E-heads for a few months... I didn’t realize it at the time but it did balloon. I ran this car pretty hard for maybe 500 miles of late night, deserted industrial roads... hint, hint... on a simple cruise home across town, the oil PSI was slowly dropping... like every mile, just a little bit less... made it home, limping, literally with about 10 lbs on the Autometer gauge.... pulled the engine and yes... the thrust bearing was GONE and the crank was damaged ....Time for a rebuild. On the defense side of the COAN, I had it awhile and even loaned it to a friend for a bit and it saw some extensive abuse... Now with the fresh engine full of parts from KRE, the power level was upped probably another 150-175 horse... So I bought a converter with anti ballooning plates. Ran the car at the track a few times and ran low 11’s at 126 in the quarter... 4100 lbs. after a summer and maybe 800 miles, I pulled the engine and there were wear and contact marks on the TCI flexplate where the converter ballooned... Engine checked out fine and the thrust bearing was still in spec to the clearances I assembled it to.... from there I spent some stupid $$ on a beast of a converter(Neil chance) and didn’t experience that again... Transmission never had a brake in it either... I always staged the car at 1200-1500 and on the last amber I let the converter flash to simulate a brake... had to soften it up a bit on the street though...
Mike...

[ponjohn]

I was inexperienced and replaced my converter and the pull up distance was in excess of 3/16".

After a short amount of miles the thrust bearing was gone.

[Half-Inch Stud]

Schurkey; good point (that i missed). Taking that point further:

so most younz know i've done a few TH400s. Well, when going through the Front Pumps, i have NEVER seen a gouged front pump from a Ballooned Converter.

Yet i have seen 2 or 3 front pumps where the Conver tangs pulled out of the Pump Gear , landed on the great a rodef the pumpgera into the cover. As it would appear to happen a bunch of times if it happens ones in a combo. So puliing a Converter too far forward means risk of disengaging the Pump gear tang from Converter Neck and THAT will grind the thrust bearing to nothing.

Well, when giving instruction on Install, I say Seat Converter, pull forward 3/16" not 1/8, not 1/4". add 3/8 washers ( equal stackheights duh ), to fill the remaining space. Could be 1 oe 2 or 3 SAE 3/8 Washers. 4L80 with Afaptor Plate will make tou a believer in custom spacings. Some Performance Converters get Re-welded to a lesser install height than their original shells provided.

[many birds]

Originally Posted by Schurkey

A "ballooned" converter CAN NOT wear the thrust bearing unless it's also pushing against the trans pump gear. As long as there's clearance between the converter hub and the pump, the "ballooned" converter is free to slide rearward instead of applying forward pressure to the crankshaft thrust bearing.

If you wipe the thrust bearing but DON'T damage the trans pump...the converter isn't ballooning (enough to cause a thrust-bearing problem.) Consider how much clearance you have from converter fully rearward, to the flexplate. That's how much the converter would have to expand in order to harm the thrust bearing. This does not mean that a somewhat-ballooned converter won't cause stall-speed, vibration, or power-loss problems--just that it won't overload the thrust bearing.

However, the converter can thrust forward under hydraulic pressure as stated--which could wipe the thrust bearing but NOT damage the trans pump.

^2

Also, agree with HIS

[Schurkey]

Originally Posted by Half-Inch Stud

Some Performance Converters get Re-welded to a lesser install height than their original shells provided.

I've never had a converter apart. Wouldn't that screw-up the internal clearances? I have a vague memory of checking stator thrust as part of doing a converter flush; the converter guts would move back and forth less than .050. But that was so long ago that I don't really trust myself to get that part right.

If converter thickness/height variations are true, it adds a whole new layer of complexity to converter installation, as you've detailed.

For that matter...how do we know the hub-and-drive-tangs welded to the rear have the proper dimensions?

[Half-Inch Stud]

So Performance Converters were made mostly from 4- cyl and 6- cyl converter cores. Yea the big converters from V8 cores. Process to cut-open used a fixture. Process to reweld, duh used a similar or same fixture. Not a precise Depth RQMT on the reweld fixture that i inspected. Bit of tribal custom on Factory depth vs Shell gap for excellent reweld.

Radial clearances are well-set by design. Stack clearances good enough for tight, non mushy converters where the Stator redirects 100% well. Re-machine or Re-angle the Stator and those clearances allow detached fluid flow to grow for mush. I think.

You can shake a dry converter to assess the internal stack play. I shook a few at (xyz) and heard weld balls banging around. The owner kicked me out soon after that. THAT and the fact he refunded me on a mushy Converter Return meant he was done with my pickyness.

Spacing may have been too much on factory units, and getting the Stall up involved a different Stator angle, perhaps machine the original or use a custom stator.

Well the mushyness would be the matter of Stator efficiency is redireting fluid return AND where that fluid ended up. If it redirects to the DRIVE Fan, then the driver feels tightness. If Stator fluid redirects to the Whorl at fan-to-fan gap, at the weld-zone: mushy, crappy.

I bothered to try a Converter re-design where a TH400 planetary is set inside (it fits), and provides Overdrive when under light load, and TQ multpily under Acceleration. It would work well but I'd need to spend money to mechanize the planetaryinstall, and the Re-Weld.
Fluid force on Stator would control the OD hold vs OD being overwhelmed. Deal would need "tuned for best feel" which means many reweld cycles: so not purpued. Switch-Pitch Control had a chance but i did not cut that puppy open.

I have cut 3 converters open: all 3 were minty inside and gave me regrets for doing so. 70 455 Big Car Converters and 1 GTO 400 Converter. all same...identical.

GM did an excellent job at Converter design-for-strength and production. Weakest aspect is the Sprag fine-splined into the Aluminum Stator. That could get dicy in cycling from extreme hot to extreme cold. The Sprags and splines in the 3 units i opened were perfect.

[Schurkey]

Thanks for that.