Transmission: Spring Loaded Input Shaft?

[DogRocker]

In the International Auto Parts video (https://www.youtube.com/watch?v=JPhBXCVu76M), Jake mentions that the input shaft is "spring loaded" and demonstrates.

I noticed mine wasn't. That is, the input shaft bearing was in there very tight and didn't move forward and backward at all.

Anyone familiar with this phenomenon? Would this cause problems if the input shaft bearing fit is very tight (like mine)?

[AndyVAS]

If that bearing isn't moving at all then it somehow became a press fit or is slightly cocked off to a side. A press fit bearing that isn't supposed to be will cause something to wear quickly and generate excessive heat. It being cocked off the side will likely pop back to centered once everything is fully together. Should it not self center then I can only imagine what it will do.

The real answer is to take the transmission back apart and figure out why it isn't going together as it should and correct that.

[DogRocker]

I've had a bad rattling sound when accelerating under load, i.e. up a slight grade or just "getting on" the pedal on any grade. It happens in all gears. It did it before I tore into the gear box and after replacing all seven bearings. All the gears looked great.
There was nothing obvious to me anyway. I'm stumped.

I put this transmission together over the winter, and as I remember, the input shaft was a snug fit where it mated with the inner race of the bearing and the same with the outer bearing race on the case. In the video, it looks like the outer race is sliding in and out.

There's another youTube video (https://www.youtube.com/watch?v=yvK_FXv0QMg&t=450s) that doesn't seem to have the same amount of free play back and forth. It's at about the 4:50 mark on the video.

Thanks for the response.

[AndyVAS]

The 4th gear / input shaft tends to grind into the center case without the spring washer. On deceleration if I remember correctly based on the direction of the angle cut gears. You would have found a LOT of aluminum shavings in the fluid and stuck all over the case.

Did you replace the pilot bearing or release bearing? Have you checked or replaced the center support bearing on the driveshaft?

[DogRocker]

When I rebuilt over the winter there were no aluminum shavings. However, there was brass dust on the cover plate and some in the oil when drained. The syncros looked good. The two internal shift forks looked a little worn so I replaced those thinking they were the source of glitter.

I did not replace the pilot bearing because things were quiet when the clutch pedal was depressed. So, I guessed it was good.

I didn't replace the throwout bearing either. It looked almost new and felt solid.

The center driveline support bearing was replaced when the differential was serviced by a local-ish Fiat specialist last October. In fact, the transmission rattle appeared immediately after that oddly.

A couple of weeks ago, after the rebuild, I re-installed the transmission. It still rattled. I thought I'd try Redline MTL just for fun. When I drained the new GL-1 - that I put in after the rebuild - that had maybe 3 miles on it from a test drive, there was shavings stuck to the magnetic drain plug and the GL-1 looked grey and cloudy.

At this point it's clear the transmission needs to come out again. However, I'm reluctant to replace it with another since I'm wondering if there's something else external (clutch alignment, drive line bearing, or ...?) that would eat up a transmission.

[AndyVAS]

Since the noise started right after the center bearing was replaced I would suspect it was either a bad bearing or incorrectly installed. Check it as best you can or have another shop put the car on a lift and check it.

Very few external problems can damage these transmissions. The pilot bearing can eat the 4th gear / input shaft and the flex disc can explode and take out the rear of the unit.

Cloudy fluid tends to be from contaminates. What assembly lube did you use?

Metal shavings on the drain plug tend to be simple wear or signs of something wearing badly. Since your unit is old and you didn't replace any gears, the shavings are sign of accelerated wear.

[DogRocker]

What assembly lube did you use?

I didn't. I did coat things with GL-1 during assembly.

The rattle sound seems to be coming from more of a forward direction than the drive line support bearing or even the shifter linkage area.

[AndyVAS]

Good job on using the GL-1 as assembly lube.

Noise can travel rather far in a car.