For those who like to troubleshoot...

[shippman]

Here's a problem I have been working on for several months now. I found the culprit this past weekend, but thought some of you might like to take a stab at it.

Background: '82 C20, 350 SBC, NV4500 5spd trans. Several months ago I installed new GM Performance L31 with serpentine belt setup. I used the 91 TBI setup that was on the old engine but on a new vortec TBI manifold. I also replaced the mechanical clutch setup with a hydraulic clutch setup from a 85-87. The new engine required a new flywheel but I used the same pilot bearing, pressure plate, and clutch disk that was in the 82 because they only had about 5K miles on them. I did replace throw-out bearing.

OK, to the problem... After everything was installed again it was out for a test spin. The new clutch setup worked very well. Engine ran well and I was very pleased for the first 15 minutes or so. Then a loud squeal began from under the truck. It was localized to the bell housing area. I used a probe to try and isolate the noise... it was definitely in the bell housing.

Since the pilot bearing was real sloppy in the crankshaft, I removed the trans and clutch assembly and replaced the pilot bearing. After reassembly and 15 minutes into the test drive the noise reappeared.

Now it is your turn... what you think? Ask any questions you have... let's see if you come up with the same culprit I did.

Mike

[1970pelle]

What style/type hydraulic clutch set up did you use ? Was it a Hydraulic throw out bearing style ? Similar to what Jeep use for so many years ?

[shippman]

It is the original Chevy/GMC master/slave cylinders activating a release arm on the driver side.

[Wrecked1982]

oe or advance adapter bell housing, is the noise when pressing the clutch or all the time?

[1970pelle]

Have you checked the throw out bearing operation? How where the clips that hold the bearing on the arm? Is one possibly weak or bent allowing the bearing to settle down and get hung up?
What about the input shaft bearing ? Input shaft collar?

If you could get it on a lift, and run it up to road speed when the condition occurs. Then have the throw out arm grommet off so you can maybe see something. Get a spray bottle and use some soapy water to see if you an pin point the noise.

Ken

[shippman]

Originally Posted by Wrecked1982

oe or advance adapter bell housing, is the noise when pressing the clutch or all the time?

It is an OE bell housing with an advance adapter trans to bell housing adapter.

The noise starts after about 5 minutes of driving and then remains constant and doesn't vary in tone or pitch much no matter if clutch pedal is in or out. It does hesitate or lighten up while accelerating.

[shippman]

Originally Posted by 1970pelle

Have you checked the throw out bearing operation? How where the clips that hold the bearing on the arm? Is one possibly weak or bent allowing the bearing to settle down and get hung up?
What about the input shaft bearing ? Input shaft collar?

If you could get it on a lift, and run it up to road speed when the condition occurs. Then have the throw out arm grommet off so you can maybe see something. Get a spray bottle and use some soapy water to see if you an pin point the noise.

Ken

This is good... these were the same things that I asked for months proving that I not as crazy as I thought, HaHa.

We checked the release arm and the throw out bearing when we changed the pilot bearing and everything looked normal. As far as input shaft bearing or collar, we did not disassemble but did the yank check to verify there was no excessive play. Trans has less than 5K miles since major overhaul.

[1970pelle]

I would pull the tranny as a very last resort. After exhausting all diagnostic options. Sometimes it helps to get somebody who doesn't know the truck to take a look and listen. It could be a very minor thing. If it was a imput shaft bearing/bushing issue, I would think you would be hearing the noise more as a grinding.
Do you know someone with a Chassis Ear.

http://www.steelmantools.com/chassis...-ii-combo.html


great tool for such noises.

[Chevy_mud_truck]

Input shaft to long bottoming out on the crank causing a clearance issue

[mrolds88]

Does the noise change or go away with the clutch pushed in and you are at a stop? Or when it is engaged and you are driving?

[D13]

OK, I'll play.
So, noise is there with clutch in or out.
So my first reaction is that it's not directly related to the clutch system.
It does lighten up when you accelerate? So its sensitive to engine torque. Think about what happens when you torque the engine - the engine rolls to one side, and the trans tries to twist in toque reaction.
Based on your description once it happens it stays, whether moving or not. If you shut the truck off, wait 20 seconds, then restart, does it happen immediately?
If so, I'd yank the serp belt and check. I've seen some weird noise paths....
Does the frequency change with engine RPM, ie more RMP higher pitched noise?
If so, then flywheel rubbing when then engine block expands with heat, rear main seal out of position and binding hot, or a really tight rear main bearing would come to mind.

[shippman]

Originally Posted by Chevy_mud_truck

Input shaft to long bottoming out on the crank causing a clearance issue

We thought that, too. Measured when trans was out and had 3/8 to 5/8 clearance in crankshaft.

[shippman]

Originally Posted by mrolds88

Does the noise change or go away with the clutch pushed in and you are at a stop? Or when it is engaged and you are driving?

Check post #6

[shippman]

Originally Posted by D13

OK, I'll play.
So, noise is there with clutch in or out.
So my first reaction is that it's not directly related to the clutch system.
It does lighten up when you accelerate? So its sensitive to engine torque. Think about what happens when you torque the engine - the engine rolls to one side, and the trans tries to twist in toque reaction.
Based on your description once it happens it stays, whether moving or not. If you shut the truck off, wait 20 seconds, then restart, does it happen immediately?
If so, I'd yank the serp belt and check. I've seen some weird noise paths....
Does the frequency change with engine RPM, ie more RMP higher pitched noise?
If so, then flywheel rubbing when then engine block expands with heat, rear main seal out of position and binding hot, or a really tight rear main bearing would come to mind.

D13... first to your question about shutting down and waiting 20 seconds... if we wait 10 to 20 seconds to restart it returns almost immediately. you wait a minute or more it takes about a minute to return. Also, the noise changes very little with the RPM.

We did yank the serpentine belt and still had the noise. I like the way great minds think the same! We checked flywheel clearances.

I like the way you think outside the box (bell housing)...

[Ol Blue K20]

Is the harmonic balancer rubbing on something ie..timing cover or timing mark and resonating the noise to the bell housing?

[kdh454]

Did you put the throwout bearing spring retainer thingy on backwards?

[shippman]

So far you guys have asked all the same questions that we asked; but, everything appeared to be installed properly with no clearance problems seen. The noise was definitely coming from inside the bell housing.

However, I am a hot rodder/guy and as soon as we hot rodders get to a point that we can test drive a project... we do! I did! Maybe everything was not installed. Everything ran well and shifted well and when the noise came I concentrated on it and not a few lingering items that had not been put back on the new motor.

This help any?

[LeesTruk]

Did you put the clutch disc on backwards ?

[shippman]

Nope... I did check that, though.

[bilfman]

Long shot, but I had a similar issue a few years back. It was the starter drive not disengaging .

[shippman]

Originally Posted by bilfman

Long shot, but I had a similar issue a few years back. It was the starter drive not disengaging .

Starter OK

[shippman]

Well it looks like you guys have run out of ideas... I did too. I went and purchased new pressure plate, clutch disk, and throw out bearing and was about to yank the trans AGAIN when a friend of mine ( a 40 year veteran of a dealership shop) called and said he had these same symptoms back in 1990 and told me to try something before taking the trans out. Here was his instructions:

Drive until the noise returned, stop and remove the oil filler cap and see if the noise stops.... What?

Well I'll be damn!! The noise stopped! I put the cap back on and after a minute the noise was back! The cap off... noise gone!

The thing I had not reinstalled was the breather tube to the valve cover.

This one whipped me for sure... thanks for all the feedback. This was fun.

Mike

[mrolds88]

Sorry for missing post 6. LOL.

[mattcrp1]

That was fun. I love odd ball problems like that. So in short the crank case pressure was "whistling" past a seal in the back? No oil leak?

[Gregski]

WOW, thank you for sharing goes to show the importance of the Positive Crankcase Ventilation system, oh and by the way I would have totally guessed this one right if I saw it in time... NOT!