So I bought an 87 22RE 4Runner with 256k a few weeks ago. I've been doing a ˟˟˟˟load of routine maintenance/replacements (new radiator, brakes) and customization (dropped the lift a little, smaller tires, stereo, inverter, tach install) and all the while have been conscientiously ignoring the single most worrying part of the whole thing.

I have a loud sound upon idle. This sound does not exist when I depress the clutch, but if I release the clutch in neutral, the sound starts. I can depress the clutch any number of times and it will stop the sound each time, and it resumes when I release the clutch. If I rev the engine in neutral, you can hear the sound revving with the engine. If I rev the engine with the clutch depressed, there is no sound. I can only really describe the sound as a loud motor noise, not quite a rattle, since it is in time with the engine idle... but there is also sort of high pitched sound to it (like a very very very tiny engine is being worked at high rpms).

A few people who know their way around trucks have heard this and have gotten puzzled and concerned looks on their faces. Any ideas?

I can take a video if I need to....

 

Does the noise go away if you put very light pressure on the pedal(not pushing the clutch in)? If so, might just be the clutch fork squeaking against the slave or pivot. If not, maybe trans input bearing.

 

Ok does it do it with the vehicle in gear and while driving or is this all at idle?

 

Sounds like the throwout bearing

 

Hm, probably not. Throw out bearing is only spinning with the motor when the clutch is depressed.

OP's problem has to be in the tranny since it happens when the clutch is engaged (pedal not pushed). In this situation the flywheel, clutch, and pressure plate are spinning together and spinning the tranny input shaft. When clutch pedal in and the only things spinning are the flywheel, pressure plate, and throw out bearing.

 

Usually an input shaft bearing will make noise at all times when in gear, since this bearing is spinning all the time when the clutch is released. Most signs of a throw out bearing making noise starts when the clutch is released. The bearing face of the throw out bearing is still in contact with the pressure plate spring. When the bearing starts to wear it will get loose, and tends to rattle and make bearing noise when it is not under a load.

As the clutch is depressed, the slack is taken out of the bearing, and the balls begin to hit the race in an underscored area, hence the change in sound. Much like a wheel bearing that is roaring, but stops under a slight turn.

Now granted anything is possible, it is terribly difficult to diagnose something over the internet. But what he describes sounds like a typical symptoms of the early stages of a throw out bearing failure.

The first question that was asked of the OP is an important one, since the TOB marking a noise would likely go away with slight pressure, whereas an Input shaft bearing would not.

 

Good post, I'll buy that. So it would make noise in gear then too, right? Guess we'll see what op says.

 

Yes since the input shaft is turning relative to engine speed anytime the clutch is released. But sometimes drive train harmonics and noise can mask an input shaft bearing problem, so it is not always possible to hear it when driving down the road.

The other problem is noise seems to gravitate towards any large reciprocating assembly's. Since a noise is effectively a vibration, the large rotating mass will act to amplify sounds, much like a wheel amplifies brake vibrations causing a squealing noise. So internal bearing noises will seem to emanate from the bell housing by ear.

This is where a mechanics stethoscope or ultrasonic ear come in handy.

 

if it makes a whistling noise or more like a cricket sound when your foot is off the clutch pedal but as soon as you add a little pressure to the pedal the noise will stop if the TOB is the only prob.

 

And now the question everyone has been waiting for me the answer... no, just light pressure on the clutch does not make the noise go away- you basically have to send the clutch all the way to the floor.

It doesn't really make these sounds when I'm driving, but 1st, 3rd, and 5th gears are just damn noisy gears in this truck.

 

I googled this and found this youtube video

This sounds an awful like what's going on in my 4Runner. Now I'll google "how much to repair" and "what if I don't repair".

 

How noisy is it? Is it getting worse? My brother's 99 taco has had a noticeable input bearing noise for over 100k miles. It started around 75k or so and he's now at 200k. Its never gotten any worse so we just didn't worry about it.
If you decide to fix it, Marlin Crawler offers a complete tranny rebuild at a reasonable price.

 

Just got it a few weeks ago. It's pretty noisy, but I suppose once you get used to it it doesn't seem as noisy. I wouldn't fix it for the noise level, anyway, only if there is a detriment to the overall transmission performance or longevity.

 

No way to know for sure

 

What might be the consequences of a failed input shaft bearing? I suppose a rebuild is my only option to fix it, realistically... My buddy told me the day I bought the truck to put aside $1500 right here, right now, for the tranny that I will one day inevitably have to put in this truck. (Original tran, 256k)