turbo 400's, flywheels, and Thrust bearings

[karolko]

Alright, i was speaking with my transmission builder and he brought up a good point that i would like to share and ask your opinions/experiences on.

I am going with a turbo 400 transmission and as we all know that these had issues with over pressurizing the torque converter and thus whipping out thrust bearings.

flywheels, or flexplates are suppose to have some lee-way to flex around a bit, especially during high load conditions, and with a JW wheel being a solid flywheel, such as the one i and most others have, could hinder the amount of flex that should be seen in the flywheel, thus MAYBE also contributing to thrust bearing failure.

What do you guys think? What have you experienced? What flywheels are you running with you turbo 400?

Thank guys,

Adrian

 

[Chuck Leeper]

I used Mondello's reactor plate, and Don Wang's orifice mod.. No problems.

 

[Scooter3800]

Read this entire thread!
http://www.turbobuick.com/forums/transmission-talk/255286-th400-build-pictures.html
You'll find your answer.

 

[ijames]

In order for the flexplate to flex the crank has to see the force pushing on the plate so it doesn't change the crank thrust loading at all. Think of a coil spring like a valve spring - in order to compress it you have to push on one end and anchor the other end. If the other end isn't anchored it just moves and the spring doesn't compress, right? So the anchor (crank thrust bearing) sees whatever force is applied to compress the spring.

 

[asloan5]

Read this entire thread!
http://www.turbobuick.com/forums/transmission-talk/255286-th400-build-pictures.html
You'll find your answer.

X2 and I use a jw flywheel

 

[Alky V6]

In order for the flexplate to flex the crank has to see the force pushing on the plate so it doesn't change the crank thrust loading at all. Think of a coil spring like a valve spring - in order to compress it you have to push on one end and anchor the other end. If the other end isn't anchored it just moves and the spring doesn't compress, right? So the anchor (crank thrust bearing) sees whatever force is applied to compress the spring.

Yep. What he said.

Think of it like this. You're laying on the floor with your arms straight up. You are holding a round piece of 1/4" plywood up with your hands. Your hands are located at the center of the round piece.
Another person is above with his hands located at the outer edges of the round plywood piece.
The person above begins to push down. The plywood may deflect a little, but does it lessen the amount of load that the person underneath is feeling trying to hold the wood piece up? No, it doesn't.
If the round piece is changed to a 1/2" thick piece of steel, the round piece won't deflect as much, but has it changed the amount of load the person underneath is feeling? No, it hasn't.

The only thing that is different is the amount of deflection between the two round pieces. The amount of load transferred to the hands and arms of the person underneath, trying to hold the plate up, is the same. You thinkers out there, don't confuse the issue by bringing the weight of the round pieces into the scenario.

 

[karolko]

Ijames and DonWG, that is a very good explaination for the thrust/flywheel issue.

i guess the next question of mine would be why do people use the solid JW wheel? Is it because it is SFI approved? Mine came with the car originally, so it has since stayed on.

 

[turbobitt]

I use the JW wheel for the SFI certification, flexability/options in torque converter mounting pattern, and It is neutral ballanced.
Allan G.

 

[Alky V6]

I use a lightened JW for the SFI cert, and the increased durability over the OEM flexplate.

 

[karolko]

funny you guys should say that, I had to get my flywheel balanced. The machinist sadi it was off quiet a bit.

 

[Hutch]

In order for the flexplate to flex the crank has to see the force pushing on the plate so it doesn't change the crank thrust loading at all. Think of a coil spring like a valve spring - in order to compress it you have to push on one end and anchor the other end. If the other end isn't anchored it just moves and the spring doesn't compress, right? So the anchor (crank thrust bearing) sees whatever force is applied to compress the spring.

Thats great but you are assuming the forces on the "flex" plate are constant and they are not so this is not the case.

Hutch

 

[Alky V6]

Thats great but you are assuming the forces on the "flex" plate are constant and they are not so this is not the case.

Hutch

I don't see where he made the assumption that the forces are constant.
The forces being constant or not, and you're correct that the forces are not constant, his statement is true.

 

[Hutch]

The original post was about having a flexplate that was flexible. Originally he stated he had a solid no hole style flexplate which is very ridgid. Assuming the converter charge pressure was 60psi we can then calculate the force upon the flexplate at which time based on the diameter of the bolt holes the flexplate would then flex as stated to a point where the pressure was exerted onto the thrust bearing. When the trans gets used there will be that force (constant 60psi) and at times the cooler pressure will see less pressure and for short bursts will meet line pressure (eg. 165-200) regardless of the feed orifice. At that exact time the "flex" plate acts like a shock absorber (providing the converter doesn't bottom in the pilot or hit crank bolts) and flexes instead of transferring the load instantly to the crank which starts the galling process on the bearing leading to the failure.
So as some members here have mentioned they have a flexplate with holes rather than the solid to offer some flex during these events. The proper way to fix the trans pressure is with an external cooler regulator valve and of course the regular internal converter feed mods and exhaust mods.

Hutch

 

[Alky V6]

The original post was about having a flexplate that was flexible. Originally he stated he had a solid no hole style flexplate which is very ridgid. Assuming the converter charge pressure was 60psi we can then calculate the force upon the flexplate at which time based on the diameter of the bolt holes the flexplate would then flex as stated to a point where the pressure was exerted onto the thrust bearing. When the trans gets used there will be that force (constant 60psi) and at times the cooler pressure will see less pressure and for short bursts will meet line pressure (eg. 165-200) regardless of the feed orifice. At that exact time the "flex" plate acts like a shock absorber (providing the converter doesn't bottom in the pilot or hit crank bolts) and flexes instead of transferring the load instantly to the crank which starts the galling process on the bearing leading to the failure.
So as some members here have mentioned they have a flexplate with holes rather than the solid to offer some flex during these events. The proper way to fix the trans pressure is with an external cooler regulator valve and of course the regular internal converter feed mods and exhaust mods.

Hutch

The solid flexplate is more rigid, but still has its own deflection rate. Similar to a light spring compared to a heavy spring. The less rigid flexplate may soften sharp pressure peaks and valleys that the crank thrust sees, but it will not lessen the amount of applied pressure. And the amount of that cushioning affect will be small in terms of automotive flexplates. For every action, there is a reaction.

If an external cooler blowoff valve is necessary, then either there is something wrong with the cooler circuit design, or the feed to the converter is excessive.

The converter should never see full line pressure. An orifice restrictor may see a line pressure spike at the entrance to the orifice, but if the restrictor is sized right, that pressure should never be seen at the exit of the orifice.
Even in an unmodded state, I have never seen cooler line pressures reach a true line pressure reading. Even with a malfunctioning PR valve, some control of TC feed oil is maintained.

 

[turbobitt]

In engineering terms, if you made a free body diagram and sketched the forces, regardless of the flexplate stiffness it would still transmitt the load to the crank thrust. There is no way the flexplate can isolate or dampen the load.
Allan G.

 

[Alky V6]

In engineering terms, if you made a free body diagram and sketched the forces, regardless of the flexplate stiffness it would still transmitt the load to the crank thrust. There is no way the flexplate can isolate or dampen the load.
Allan G.

I wouldn't say no way. I think that any force dampening of pressure spiking as it relates to the transmission situation would be miniscule, but it would be there.

Think of this extreme example. You have a drum that you're going to hammer a new bushing into sitting on a bench top. The bench top is a thin steel gauge and is not supported well for a distance of 3 feet in any direction of the drum underneath the bench top. When you strike the bushing driver with the hammer, the peak force of the blow is ultimately transferred to the table top. The table top gives a little, and due to that deflection, the bushing is driven into the drum a certain distance relative to the amount of hammer force.
Now take that same drum and lay it on a thick piece of steel that is sitting on a concrete floor. Using the same amount of hammer force, there is much less deflection of the support table and thus the bushing is easily driven into place with more distance of the bushing traveled relative to the same hammer force.

Another example can be using an air impact wrench with a long extension to loosen bellhousing bolts. A long small diameter extension will deflect a certain amount as the impact hammer works on it. The deflection can absorb enough of the impact to prevent the bolt from loosening. Now grab that heavy monster, large diameter extension hanging on the side of the tool box and see how much less force is absorbed by the extension and is transferred to the bolt. So much more that the bolt easily loosens.

Any measureable deflection is an absorbtion of some force. Though, it may be very small in some cases. Open wheel cars, such as IRL, use this fact to build a safer chassis.

 

[ijames]

Hutch, you are right that maximum force isn't transmitted to the crank until the flexplate finishes flexing - while it is in the process of flexing the force is steadily building, and as it unflexes the force steadily drops. The spring action of the flexplate does spread out short impulses in time and reduce the peak amplitude. I can't comment on how strong those impulsive forces are or how much they get spread in time by a given flexplate/converter, but in the case of a t400 with excessive pressure in the cooler circuit which puts excessive steady state pressure on the crank and thus slowly wipes out the thrust surface on the crank (as described in the posted link above), the flexplate does nothing to reduce that problem. That's the situation most think of first when someone says "t400, crank thrust wear", and that's what I was thinking of when I posted .

 

[turbobitt]

I wouldn't say no way. I think that any force dampening of pressure spiking as it relates to the transmission situation would be miniscule, but it would be there.

Think of this extreme example. You have a drum that you're going to hammer a new bushing into sitting on a bench top. The bench top is a thin steel gauge and is not supported well for a distance of 3 feet in any direction of the drum underneath the bench top. When you strike the bushing driver with the hammer, the peak force of the blow is ultimately transferred to the table top. The table top gives a little, and due to that deflection, the bushing is driven into the drum a certain distance relative to the amount of hammer force.
Now take that same drum and lay it on a thick piece of steel that is sitting on a concrete floor. Using the same amount of hammer force, there is much less deflection of the support table and thus the bushing is easily driven into place with more distance of the bushing traveled relative to the same hammer force.

Another example can be using an air impact wrench with a long extension to loosen bellhousing bolts. A long small diameter extension will deflect a certain amount as the impact hammer works on it. The deflection can absorb enough of the impact to prevent the bolt from loosening. Now grab that heavy monster, large diameter extension hanging on the side of the tool box and see how much less force is absorbed by the extension and is transferred to the bolt. So much more that the bolt easily loosens.

Any measureable deflection is an absorbtion of some force. Though, it may be very small in some cases. Open wheel cars, such as IRL, use this fact to build a safer chassis.

Don,
I don't wish to debate this any further but your logic does not apply here. The table top absorbs shock through giving up momentum thus not being stiff. In the case of a crank and bearing, it is infenitly stiff and the last anchor point in the series of parts. If The block and bearing were not stiff and had a spring constant, then your logic would apply.
Don't wish to wast my breath arguing on weather a flexplate should be used as a "shock obsorber".

 

[turbobitt]

Hutch, you are right that maximum force isn't transmitted to the crank until the flexplate finishes flexing - while it is in the process of flexing the force is steadily building, and as it unflexes the force steadily drops. The spring action of the flexplate does spread out short impulses in time and reduce the peak amplitude. I can't comment on how strong those impulsive forces are or how much they get spread in time by a given flexplate/converter, but in the case of a t400 with excessive pressure in the cooler circuit which puts excessive steady state pressure on the crank and thus slowly wipes out the thrust surface on the crank (as described in the posted link above), the flexplate does nothing to reduce that problem. That's the situation most think of first when someone says "t400, crank thrust wear", and that's what I was thinking of when I posted .

Again, Not correct, the flexplate would never "Flex" unless there was an APPOSING force. The RATE may change due to the spring constant of the flexplate but there must be an apposing force.
Does anyone remember Newtons laws ? Every action has an equal and opposite reaction ?

 

[Alky V6]

Don,
I don't wish to debate this any further but your logic does not apply here. The table top absorbs shock through giving up momentum thus not being stiff. In the case of a crank and bearing, it is infenitly stiff and the last anchor point in the series of parts. If The block and bearing were not stiff and had a spring constant, then your logic would apply.
Don't wish to wast my breath arguing on weather a flexplate should be used as a "shock obsorber".

I'm sorry if you got the impression that I was arguing that a flexplate should be used as a shock absorber. I was merely trying to convey what ijames did a good job of doing in his latest post.