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View Full Version : Throwout bearing question - failure mode


SteveH
12-11-2009, 09:01 AM
The throwout bearing on my '98 4Runner is making some noise. Truck has 151K, original clutch (AFAIK) and the clutch seems a bit tired, too.

I'd rather wait until Spring to do the clutch. What's the most damaging failure mode for a throwout bearing? Can it seize and really tear up things? I've never had one get noisy before.

Thanks - Steve

Red_Chili
12-11-2009, 09:47 AM
Me neither, so the answer from me is theory. In theory, theory and reality are the same.

In reality they are not! :lmao:

It will likely continue to get noisier, and I am thinking will give you fair warning. If it grenades however, the results just got more expensive if it damages the tranny input shaft, pressure plate, fork, and little retainer clippie dealeo.

I hear ya on the spring thing. My 97 may be in similar shape but is quiet for now, and the clutch grabs.

DaveInDenver
12-11-2009, 10:19 AM
I'd think the worst likely mode of failure is seizing. It would seem to make more likely to seize than go straight to grenade, anyway (and the step from seize to grenade could be quickly fer sure). That could score the tranny input sleeve and/or break the throw out fork. If it ruins the pressure plate, meh so what, you're replacing that anyway. I wonder if it could weld itself to anything? That might make a heckuva racket.

SteveH
12-11-2009, 11:54 AM
Thanks for the thoughts.

Now that you mention it, the input shaft on my '99 Subaru was badly worn and had an aftermarket stainless steel 'repair sleeve' installed on it, due to a bad TO bearing. This happened at 60K (it's a Subaru afterall).

It would stink to tear up the input sleeve on the 4Runner tranny. I hope it's not the pot-metal that Subaru used. I guess if I hear the TO bearing starting to get considerably louder, or transmit odd vibrations, that's the time to park it, drive the FJ40, and fix it.

Red_Chili
12-11-2009, 12:09 PM
Having been inside an R-series Aisin tranny...
http://www.4x4wire.com/toyota/tech/r151f/
I can promise you the components are of the first order of quality.

DaveInDenver
12-11-2009, 12:32 PM
It's funny that you mention all of this because the past couple of mornings the TO bearing on our Jetta is making noise, too. There at start-up and goes away immediately when I push the clutch, so it's obvious. But after just a couple of engagements it shuts up and I wonder if it's really toast. I am thinking when the clutch is -2 degrees that the grease in the bearing might be really stiff and being German things are designed to silly tolerances that can't take these temps.

Du fahren der Auto unterhalb Temperaturen von fünf Grad Celsius!

teamextreme
12-11-2009, 12:50 PM
Dave, the TO bearing only engages when the clutch is depressed, so if the noise goes away when the clutch is depressed that would indicate internal tranny bearings.

As far as damage from continuing to drive on it, the clutch would be the one component I would worry about the least on a vechicle from doing this. All the pieces that will grenade are being replaced anyway and like has been said the only worry would be damage of the tranny input sleeve, which I think would be highly unlikely. I've seen and driven clutches to utter failure and destruction on several occasions and never seen damage to the sleeve. Likely because as I started out saying, the TO bearing only spins when the clutch is depressed.

DaveInDenver
12-11-2009, 01:00 PM
Dave, the TO bearing only engages when the clutch is depressed, so if the noise goes away when the clutch is depressed that would indicate internal tranny bearings.
Could be, the noise is there sitting idle, tranny in neutral, clutch engaged (pedal not pushed in). Clutch disengaged (pedal pushed) the noise stops and once moving the noise is not detectable. Only makes it when ambient is below zero, so that could mean the bearings are not being lubed or something. Can't buy a break, was hoping to get those gears from Red_Chili but looks like I'll be doing drivetrain work on the Jetta. :-(

Air Randy
12-11-2009, 01:21 PM
Remember to check the adjustment on your clutch before you start dropping everything out to repair it. As the clutch wears the adjustment will get tighter and eliminate freeplay. It's entirely possible your throw out bearing is touching the pressure plate slightly and spinning even though you don't have your foot on the pedal.

Red_Chili
12-11-2009, 01:42 PM
Dunno about Jetta TO bearings, but I have had Toyota TO bearings chirp until they are pressed against the pressure plate - it wasn't really the bearing, but the interface between the bearing and throwout fork and the slightest bit of wobble due to everything spinning. Judicious application of grease solves it. Pretty common.

Maybe it is that simple.

SteveH
12-11-2009, 02:25 PM
Here's another factor - just as the clutch completes its engagement, there's a faint 'shriek' (for lack of a better term). I can't tell if it's from the TO bearing and/or the clutch itself. It's only made this noise for a few months. I've just never heard this kind of noise in 5 'cruisers or the slew of other Toyotas I've driven.

I will check clutch freeplay - that's always a good thing to keep an eye on. I have changed the fluid and replaced the $#@%$^ pedal bushings on this truck. That's about the nastiest job I've done on any Toyota as far as raw frustration - other than a heater core on an '89 4Runner.

Red_Chili
12-11-2009, 03:37 PM
I had a recent pedal bushing experience myself. Kind of a pain... but once you learn the trick you scratch your head wondering how the dealers charge book of ~$200 for it. I would do that all day for 2 bills a pop. OK... for a little while.

Hmmm, could be a glazed clutch plate... could be rivets exposed... could be the throwout bearing near seizing and therefore skipping on the pressure plate fingers... Dunno, I would bet rivets on steel. You probably are about done.

DaveInDenver
12-11-2009, 03:50 PM
Hmmm, could be a glazed clutch plate... could be rivets exposed... could be the throwout bearing near seizing and therefore skipping on the pressure plate fingers... Dunno, I would bet rivets on steel. You probably are about done.
That is what popped into my head when Steve said faint shriek, glazed flywheel or pressure plate or worn out friction plate or pressure plate springs.

SteveH
12-11-2009, 04:01 PM
There's certainly no gripping problem with the clutch, in spite of possible wear. I'll just remove the clutch inspection cover, and,... oh - wait. Darn. ;-)