1994 Evo II 5th gear rotational sound out of nowhere.

[Gosutag]

I have it at a shop that is unfortunately not very familiar with these vehicles so I'm hoping to get some understanding of my problem. There's a rotational sound that brings in 3rd gear quietly, slightly louder when in 4th, but its worst in 5th gear. There are no power issues. Car runs fine but the rotational sound is concerning. Shop said it's not the throw out bearing though so I'm hoping they're right. They said the sound seems to be coming from the transfer case. Any advice is appreciated. Thank you.

 

[twicks69]

Use a mechanics stethoscope with the vehicle on a lift and listening to components in gear. I see issues like this sometimes coming from a transmission with excessive bearing endplay or failing intermediate shaft bearings and damaged intermediate shafts. The engagement of higher gears is pushing the intermediate shaft further away from the input shaft and center diff resulting in gear damage and more noise.

Drain trans and inspect fluid.

After that, drain transfer case and inspect fluid if trans is perfectly clean.

What kind of mileage are on the drivetrain components?

 

[Gosutag]

The shop found the intermediate shaft? Bearing shot. So they're gonna replace that and all the other bearings. I'm wondering what clutch I should get for the car since it's out and what else to replace. I'm thinking to check the flywheel, resurfaced if necessary, New throwout bearing, New transfer case seals. Just wondering what else I should get done while the transmission is down to prepare it for 450hp give or take. Car is stock with 75k miles.