Bad thrust bearing or?

A couple days ago my vehicle starting making a loud knocking noise coming from inbetween bellhousing and engine. The knocking increases with rpm in all gears (park,neutral,1,2,3,d) the only Time it gets quiet is right when it shifts to 4th gear.i checked out torque converter and flexplate for cracks and went ahead and ordered a new torque converter and flexplate but upon looking at things through the trans inspection cover the flexplate has back and forth play at the crank. I went to the front to the harmonic balancer and pried that back and forth and the flexplate/torque converter moved with it when i pryed it. I do believe the fp might have cracks where it mounts to crankshaft. I dont have the finances to rebuild the engine right now but i am mechanically inclined and seeing if the problem is the thrust bearings? Is that all i change. Do i need special tools? If it is the bearings why would the knocking quiet down in 4th?

You would need to measure the end play before making any assumptions.

Ok i have a dial indicator would i just mount it to bellhousing then set the tip against the flexplate and move it back and forth ? What is a "ok" amount of tolerance?

FlexJ17 said:

Ok i have a dial indicator would i just mount it to bellhousing then set the tip against the flexplate and move it back and forth ? What is a "ok" amount of tolerance?

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FSM calls for 0.0015 to 0.0065 in.of end play.

I checked there is about 1/4" of play

You have a issue that a bearing won't really fix.

Could be your harmonic balancer is bad. I had that issue a few years ago. I had to replace the crank, crank bearings and I replaced the rod bearings. My thrust bearing was bad. I had 1/8 to 1/4 play. Neighbor had a block with a good crank and reused the bearings. Still, if you can scrounge a good used engine, you would be better off.