Transmission Growl (revisited)

I've posted this before but I have a little more information. I have a stock '59 F-head with T90 tranny. Clutch, throwout bearing, pressure plate, and pilot bushing all new. Transmission was not rebuilt but it was inspected by a transmission shop and given the green light before I put it all back together.

After driving for a while (never seems to happen until everything is warmed up) the transmission will start to growl. Happens when idling and ONLY when the clutch is pushed in, such as when I'm sitting at a traffic light. It sounds metallic and I can feel it in the floor and shifter.

I can make it stop by putting it in neutral and releasing the clutch. Put it back in gear and its fine until it repeats itself later -- very intermittent, does not do this all the time but it does seem to be happening more frequently.

I used to think it was the throwout bearing. Even though it's new, it is Omix-Ada (just saying.)

But now I notice that while it is doing this, if I put it in neutral, it will not go back into gear without releasing and then pushing the clutch back in -- the gears will just grind. This tells me that it's in the transmission.

Could this be a bearing? If so, which bearing would be the likely culprit?

FYI, other than that, the transmission works great. The shifter rattles in second gear but it never pops out of gear or give any indication that there is a transmission problem. Maybe next time it does it, I can get a recording (but like I said, it's intermittent so I never know when it will happen.)

 

^That.

Or... And this could be a stretch, but it could be that the adjustment is in too far, and the noise is from the pressure plate tongs are hitting the clutch disc.

When your foot is on the clutch to the floor, how far (in inches) do you let it out before it starts to engage and move the jeep?

 

Excellent thought, I hadn't considered the clutch drag. And it kind of makes sense that it would happen only when hot -- heat expands the components.

When my foot is to the floor, the clutch doesn't engage until the pedal is almos

 

If it's in the transmission, the two bearings that keep turning with the clutch in are the front main bearing and the pocket bearing in the input shaft. Did the shop disassemble the transmission to assess these bearings? If not, I kinda doubt they can detect a bearing failure just by feel. Maybe you can look at the input and see galling on the races, but it's hard to feel damage there unless you remove the bearing and wash the oil out.

Gear oil thins out with heat too, so borderline wear in the bearings would be louder once you have traveled a ways.

 

Terminology ... yes, you are right Glenn. Push in the clutch and the input gear stops spinning (typically).

With the clutch pedal pressed to the floor, the throwout bearing spins and the input shaft pilot turns in the pilot bearing. The drag of the transmission bearings should be larger than the drag from the pilot bearing, so the input shaft should stop turning.

You would first suspect either the throwout bearing (more likely) or the pilot bearing (less likely).

 

Agreed, Glenn. When in nuetral and clutch pedal depressed, transmission isn't spinning, so I'm pretty sure we could rule that out.

When it is making the noise, move your foot in and out through the range between the floor and where it starts to engage. Is there a point where it is more/less or quieter/louder? If yes, I'd guess it's an over- or under-travel issue. If no, and it happens at any point while the clutch pedal is pressed, that would point to a throw out bearing issue.

 

LOL yes, a little computer hiccup there. I was going to say "almost all the way up."

 

I took it to them mostly disassembled because I made the embarrassing rookie mistake of separating the transfer case without securing the transmission shaft. I figured I would take it to a transmission shop (owned by a friend of a friend) for them to inspect it and reassemble. I told them that if it needed anything to go ahead and do the work. They reassembled it and told me it was in a-one shape and didn't need anything. They are a reputable shop that's been in business for many decades so I took their word for it (especially since I gave them a blank check, so to speak, to rebuild it if necessary.)

 

If your clutch does not engage until the pedal is near the top then when you push the pedal down it is over traveling the throw-out bearing. This would push the pressure plate fingers into the clutch disk. That forward pressure would force the clutch disk to remain tight against the flywheel which in turn would keep it spinning thus turning the transmission input shaft. (I think I have that right but if not I will for certain hear about it ).

 

Thanks, guys. I will start by adjusting the clutch and go from there. Hopefully it is something that simple and I don't have to pull the tranny out. I admit, though, I'm a rookie when it comes to clutch adjustments.

 

I have to leave on a business trip tonight but will work on it next weekend and take photos. The linkage all feels tight. I rebuilt the crosspiece with all new bushings and grease so there is no slop there.