86 K20 292-Knocking noise, but stops when press clutch?!?!

[thefarmboy21]

*Scroll down for quick version

I just acquired an 86 Chevy 3/4ton 4x4, with a 292 4-speed combo, from my 93 year old Grandpa, who bought it new and it has 78,903 actual miles on it!!! It's lived it's whole life on a farm never traveling further than about 30 miles from the farm. It's in exceptional shape considering it's Always been parked outside. Well it's been sitting since 06-07 (tags say march of 07) and I finally talked him out of it and started tuning it up. Well it runs great but I started noticing a slight knocking noise while I'll let it idle and stand back to admire etc. I got my handy harbor freight stethoscope out and started listening. No noise from motor or inside tranny, but is very loud comin from inside the aluminum bellhousing....

*Well basically it knocks at idle in neutral or in gear with the clutch engaged. When you shove the clutch in it stops and runs smooth and quiet like a new one. This tells me most likely a throw out bearing or possibly an inputshaft problem. Also clutch has hydraulic master/slave cylinder combo and the master cylinder DOES leak slightly inside the cab. It runs seeps out the little rubber boot and runs down the pedal.

SOOOO....1. what do you guys think it really is and 2. How long do you think itll safely hold up.
Currently it is NOT road legal but will be today or tomorrow if it's not going to fly apart til I get a chance to fix it. I don't plan on driving it alot, but it will be for the next month or so because, let's face it, it's a new toy to play with and has lot of old memories!  Thanks guys!!!

[Captkaos]

It could be the throw-out bearing or it could be the input bearing, no way to know 100% sure.  As for how long it it will last there is no telling.

[starkey]

Hey Farmboy.. my gut instinct points me towards loose clutch/flywheel bolts. Second thing that comes to mind is Pilot Bearing and Input Shaft Bearing failure.

Check the grease in that box yet?


Stark

[thefarmboy21]

No, I haven't checked the grease in the tranny yet (btw, what kinda fluid does it take in the tranny and transfer? Transfer is aluminum, so 208?) but I will. Wedging I've talked to and most of my googles searches all said throwout bearing. Idk. Have to dig deeper I suppose

[DustyRusty]

What Stark said.

The t/c should utilize ATF.  The trans uses gear oil although I don't remember what weight.

[starkey]

I agree with Rusty on the ATF. The SM465 uses 80-90w gear oil, non synthetic.

[bake74]

Hey Farmboy.. my gut instinct points me towards loose clutch/flywheel bolts. Second thing that comes to mind is Pilot Bearing and Input Shaft Bearing failure.

     If it was loose clutch/flywheel bolts they would grind when the clutch is engaged, not knock.  (As the clutch turns and mates to the flywheel.)

It could be the throw-out bearing or it could be the input bearing, no way to know 100% sure.  As for how long it it will last there is no telling.

      Most of the time it is the throw-out bearing making that noise, the bearing itself gets loose in it's holder and rattles.  You depress the clutch and take off the pressure and no more noise.

[thefarmboy21]

Bake: That was pretty much what I suspected, now I just can't decide whether to just drive it around for a few weeks or to go ahead and tear into it. Because 1. I eventually wanna do a 350 swap and 2. I don't wanna have to drop the tranny or pull the motor righ now because I have another truck torn down. So I'd rather just wait til I'm ready to swap motors before I have to change it. It's not loud just noticeable. Most people probably wouldn't. Rev the motor and you have no idea it's making noise.

So, should I tear into before I even tag the truck and insure it, or just drive it easy and have some fun until I'm ready for a bigger motor?

Also what's the best way to change the throwout bearing in these trucks? I know plenty of guys that would rather pull the motor as drop the tranny and transfer case, driveshafts etc...

[Blazin]

I have had thoughout bearings, a single loose flywheel bolt, and broken springs in the center of the clutch plate all make knocking noises at an idle with clutch engaged before.
I wouldn't drive it to much. If it fails it could damage other things.
As far as changing the bearing, you should cahnge the clutch disc, and presure plate as well.

[thefarmboy21]

Man, this sucks! I was so pumped about getting the old thing back on the road and just driving it for a while before I tore into it too deep. Oh well, guess that's what happens when things just set for years in a field lol. Thanks guys

[thefarmboy21]

So what's the best way to go about this? Drop tranny or hook a hoist to the motor and slide it forward?

[starkey]

I have had thoughout bearings, a single loose flywheel bolt, and broken springs in the center of the clutch plate all make knocking noises at an idle with clutch engaged before.
I wouldn't drive it to much. If it fails it could damage other things.
As far as changing the bearing, you should cahnge the clutch disc, and presure plate as well.

X2. If you're gonna pull that heap of cast iron, do it once and do it all!

It's not that bad of a job. Just get a good jack and a couple of buddies.

[Fairlane514]

You may also need a new front bearing retainer on the transmission. It looks like a tube with a flange on it that covers part of the input shaft. The throw out bearing slides back and forth on it.

Get a floor based transmission jack if you don't have access to a lift. Unbolt it from the bell housing and slide it back, then you can remove the bell housing, clutch etc...  You can try and remove the bell housing  and transmission as one unit if you want.

[thefarmboy21]

But would it just be easier to hook a cherry picker to the motor and slide it forward about 8 inches?

[Fairlane514]

No,  you would have to remove the cooling fan, shroud, fuel line, possibly some wiring harnesses, exhaust.............why do you think it gives you any advantage moving the motor forward?

 Removing the transmission gives easier access to the possible problem parts.