Pressing clutch in makes a knocking noise.

GregLast

GregLast

Member
Well if it's not one thing, it's another.

I drove the car yesterday and didn't notice a noise. I went to start it up tonight and when I press in the clutch, there's a knocking noise. It's consistent, and I didn't think it changed at higher RPMs. The car drove like normal, just a quick down the street and back, but this can't continue.

I did notice a audible change when releasing the emergency brake. Seemed to be worse with it off.

Any ideas?
 
Is it a tinny noise, or more solid like cast iron on cast iron? Does it only do it in gear, with the clutch depressed, or also in neutral? Do you need to be moving? does it start right away as you depress the clutch or only when fully depressed?

Might just be the exhaust pipe rattling, or floor boards, or maybe body work....

Are you missing any wrenches from your toolbox? :)
 
Makes sense. I don't think it sped up at all. If I'm remembering correctly, it was consistent, but only when the pedal was depressed.
 
Yes... Flathead may have found it. Possible indication of rear main thrust bearing failure. You might actually be able to see evidence of it by blipping the throttle from idle and noticing if the crank pulley looks like it moves forward. Or have someone push the clutch in at idle, while you look at the crank pulley to see if it moves foreward. I can't recall off the top of my head what the tolerance is for rear main thrust clearance, but I think it's around 0.004". That's probably not very easy to see with the naked eye, so if you see much movement, you have excess thrust clearance.
 
.003 to .005 I think too so .004 is in the middle I have .016 and pulling the motor this weekend :-( also found pieces of thrust bearing in oil pan Do I need to say don't drive it ?
 
If the noise started all of a sudden, it's more likely that the ring gear on the flywheel has moved forward a bit. It usually does where the starter engages the ring gear, mostly one of two places on the ring gear. That pulls the gear forward from its ledge if the gear is fatigued, cracked or made slightly too big, as off-shore ones were in the 70's and 80's. I have run into this problem numerous times and have also posted here and elsewhere about its possibility, if not probability. I'd pull the starter and check there first. Look for a gap between the ring gear and the flywheel ledge behind it. The ring gear should be right up next to this ledge, no gap between them. You'll have to hand crank the engine 360 degrees to check every place. Chances are, the gear is tilted forward in one place only and that's what's hitting the upper part of the inside flywheel housing. 'Doesn't cost a darned thing to check this out and should only take about 10 minutes.
If the gear has tilted forward, take a big hammer and punch and drive the gear back against the stop ledge all 360 degrees. Should this happen again down the road, you'll have to drill and tap the ring gear and flywheel and use Allen plugs to secure the ring gear to the flywheel.
Marshall
 
GregLast said:
Well if it's not one thing, it's another.

I drove the car yesterday and didn't notice a noise. I went to start it up tonight and when I press in the clutch, there's a knocking noise. It's consistent, and I didn't think it changed at higher RPMs. The car drove like normal, just a quick down the street and back, but this can't continue.

I did notice a audible change when releasing the emergency brake. Seemed to be worse with it off.

Any ideas?
Click to expand...

I had a similar problem a while back. Turned out to be a combination of things: Firstly, my crankshaft thrust bearing is worn allowing a lot of movement; Secondly, the bolts holding the starter were slightly too long. Thirdly, the ring gear had shifted on the flywheel.

I replaced the starter bolts with the correct size after returning the ring gear to its correct position by using a hammer and drift (punch) through the starter hole.

I have not yet taken the time to deal with the thrust bearing, but the problem has not returned since applying the hammer.
 
Ok. I went away for a bit, and then it came back.

It does get faster at higher RPMs. It happens in gear or out of gear. It only makes the noise when the clutch is depressed. I looked at the front of the engine and couldn't see any movement in the crank pulley, nothing noticeable anyhow.
 
Well, I would pull up the carpet/floor mat, remove the transmission cover plate and then remove the access cover to the bell housing and see what is going on in there....you can start it and run it with the access cover off and see just what is happening when you press the clutch and as the noise occurs...You can also turn the crankshaft by hand and look at each of the pressure plate "fingers" and see if one is bent or loose...there are six on a standard A pressure plate...
 
Marshall V. Daut said:
If the noise started all of a sudden, it's more likely that the ring gear on the flywheel has moved forward a bit. It usually does where the starter engages the ring gear, mostly one of two places on the ring gear. That pulls the gear forward from its ledge if the gear is fatigued, cracked or made slightly too big, as off-shore ones were in the 70's and 80's. I have run into this problem numerous times and have also posted here and elsewhere about its possibility, if not probability. I'd pull the starter and check there first. Look for a gap between the ring gear and the flywheel ledge behind it. The ring gear should be right up next to this ledge, no gap between them. You'll have to hand crank the engine 360 degrees to check every place. Chances are, the gear is tilted forward in one place only and that's what's hitting the upper part of the inside flywheel housing. 'Doesn't cost a darned thing to check this out and should only take about 10 minutes.
If the gear has tilted forward, take a big hammer and punch and drive the gear back against the stop ledge all 360 degrees. Should this happen again down the road, you'll have to drill and tap the ring gear and flywheel and use Allen plugs to secure the ring gear to the flywheel.
Marshall
Click to expand...
I had the ring gear move on the flywheel of one of my As just as Marshall describes. I knocked it back into place and put on a few drops of Loctite super wick in (I think it is number 290). That was several thousand miles ago and there has been no sign of trouble since. You don't even have to remove anything more than the flywheel cover to get at it and the starter motor to apply the loctite. Easy, quick and effective. You can't ask for ore than that - so long as that is your problem and I suspect it is from your description.
 
GregLast said:
Well if it's not one thing, it's another.

I drove the car yesterday and didn't notice a noise. I went to start it up tonight and when I press in the clutch, there's a knocking noise. It's consistent, and I didn't think it changed at higher RPMs. The car drove like normal, just a quick down the street and back, but this can't continue.

I did notice a audible change when releasing the emergency brake. Seemed to be worse with it off.

Any ideas?
Click to expand...

1955cj5 said:
Well, I would pull up the carpet/floor mat, remove the transmission cover plate and then remove the access cover to the bell housing and see what is going on in there....you can start it and run it with the access cover off and see just what is happening when you press the clutch and as the noise occurs...You can also turn the crankshaft by hand and look at each of the pressure plate "fingers" and see if one is bent or loose...there are six on a standard A pressure plate...
Click to expand...

And while your in there, give the throw out bearing grease fitting a shot or two of grease! One of the most under serviced grease fittings :-)
 
The trouble with modern throwout bearings is they are no longer made to accept grease from the collar zerk, all you lube is the shaft that slides.
 
I had an experience similar to those who described the noise caused by an improperly-fitted ring gear knocking against the flywheel housing.

Sometimes you can isolate the source of the sound by having someone in the driver's seat depress the clutch while you listen through a stethoscope or wooden dowel held to your ear (be mindful of moving engine parts such as the flywheel). This method helped me determine the knocking sound originated in the flywheel housing behind the starter.

Mike
 
My vote is for the ring gear moving. It is just another part made wrong. I would drive it back and pin it to the flywheel. It happens all the time. You can get to it when you take the starter out.
 
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I don't know if you can see what I was seeing and felt, but the ring had slipped forward. Drove it back in and it's driving like it was before!

Got to inspect the starter and it looks good as well. Bonus!
 
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