Motor/Transmission issues, help needed!

[TXBoudy]

As some of you have seen in my build thread, I'm having fits with my SB400/TH400 package which was rebuilt by the previous owner and has less than 50 miles on it. After pulling the setup during the restoration we noticed crankshaft end-play to the tune of about 100+ thousandths. The shop found that the thrust face of the crankshaft had been destroyed, something was pushing forward with extreme pressure. They also pointed out that the high dollar ATI converter was also showing signs of scaring on it's front surface. Worried about the tranny, I had it looked at as well. They found the front drive gear destroyed but it wasn't installed backwards. The trans otherwise checked out fine and they noted that it was built well. Both have since been repaired and are ready for installation.

However... The root cause is still undetermined. The converter could have been ballooning but it was brand new and high quality. I just sent it to a shop to have its stall modified and they passed it with colors. The front drive gear was not installed backwards. The previous owner who assembled it is an experienced hot rod builder certain that the converter was installed properly as he did it himself. Sure I could simply call BS and reinstall it but I'd prefer to exhaust all possibilities before rebuilding the truck to have the issue repeat itself costing thousands to repair. Again!

My engine builder nor the transmission shop can determine the cause definitively, no smoking gun! Anyone have any additional ideas before I just bolt it back in with my fingers crossed?

Boudy's wonderful rebuilt engine! YouTube

[TXBoudy]

If a mod could fix my title, that'd be greatly appreciated. Ugh, icing on the cake...

UPDATE: Thank you whomever you are!

[AussieinNC]

Check inside the end of the crank and make sure the manual trans clutch pilot bush is not there...I have seen these bushes push back against a convertor and destroy both the pump gear and housing and the thrust surface of the crank...

That pic of the trust surface almost looks like it has been machined and radiused by a shop process...do you have a build sheet with crank end float specs listed?

I have seen aftermarket convertors that are too tall...mounting flange to end of pump drive height...check your high stall unit against a standard convertor...

I have also seen aftermarket convertors that have incorrect pilot surface diameter, putting excess pressure on both pump and crank...

Easiest way to check is as follows:

Install convertor into trans ensuring the convertor is fully clocked with the pump gears...

Install trans and convertor to engine...there should be a small gap between the flexplate and the front face of the convertor...

More important is you should be able to slide the convertor forward to close up the gap...easily...not have to force it together with the convertor mount bolts...

Also...suggest you use a one piece neoprene pan gasket rather than those cork sets...

[TXBoudy]

Thanks Aussie. The crank was a new SCAT unit when the engine was built so it should have never seen a pilot bearing but I'll double check next chance I get to the shop. When I mate the pair I'll measure the converter play before bolting it to the flywheel. But the previous builder told me that this was done the first time and it was fine. That's why I'm worried. While searching for answers I found this guys video. He indicates that a blockage in the tranny caused his issue but my tranny shop said mine ready to go.

Torque Converter Pushing Thrust Bearing - YouTube

[AussieinNC]

That video shows a classic convertor ballooning scenario...

The crank in that video is really past saving...it looks to be moving back and forth at least an 1/8th"

Cooler line blockages or block off...(yes I have seen these totally blocked off ! bad idea) will usually push the front pump seal out...

I would be suspicious of the ductile value of that crank...it could be "soft" leading to increased wear...either way, how do you intend to fix the end float issue...to me it would be a new crank...

stay safe

[TXBoudy]

My crank thrust surface was welded then machined back to spec. I was well prepared to purchase a new one but the shop indicated no need to.

[AussieinNC]

I really hope that reweld and remachine process hasnt softened the crank...

I am a bit obsessive with engine parts...It would have been replaced but lets hope it works out for you...if it does it again, you know what to do...

Good luck...

[TXBoudy]

Originally Posted by AussieinNC

...if it does it again, you know what to do

I do. Stroke it, stroke it, stroke it. We were actually planning on building a 427 stroker short block until the machine shop assured us the crank would be fine. So I decided to save $3,500 bucks for now.

[AussieinNC]

You will need a nice pair of heads to feed that monster mouse...

Good luck...

[Steeveedee]

Make sure that your trans cooler line circuit is flowing well. I've been told that a blockage in that circuit can cause pressure that can cause this. Interestingly enough, if you've ever seen a video of the flex plate when an engine is revved up, you can see it move as the engine speed increases, and transmission pressure increases. Guess it's called a flex plate for a reason.

[leddzepp]

Originally Posted by TXBoudy

If a mod could fix my title, that'd be greatly appreciated. Ugh, icing on the cake...

UPDATE: Thank you whomever you are!

You're welcome.

I just drove through Southlake the other day. Had to stop and get my middle boy a t-shirt since his name is Tyler