TH400 Knocking Noise

[zway]

Hey guys......I just wanted to say first that I'm new here and love the site and all the information here.....it's great. I read the technical manuals and searched around and didn't find anything on this, so if I missed something.....apologies.

I just bartered my way into a 1984 CUCV M1009 with 140,000 miles on it and she has a few problems. The most troubling is that their is a strange noise coming from the transmission. When you put the truck in gear, there is a rapid clicking noise as it engages and then after it is in gear, there is a distinct knocking noise coming from the transmission. The knocking goes up with RPM. What is strange to me is that the knocking is there when the transmission is in Park and Neutral both, just not as noticeable. This is happening in both 2WD and 4WD.

Also, there is no vibration at all with the noise.....only audible.

I haven't pulled anything apart yet, and will be doing that this weekend.....just wanted to get some advice from the experts on where to start.

Thanks guys

 

[doghead]

Drop your inspection cover and inspect your flex plate. It may be broken.

 

[Bob H]

Drop your inspection cover and inspect your flex plate. It may be broken.

due to torque convertor bolts coming loose, or it just cracked.
but loose bolts from the flex plate to torque convertor will sound as you described.

 

[Anubis8472]

Loose nut behind the wheel.





...
No seriously, you may want to check the flywheel/torque converter area.
You may have a loose bolt there. A stethescope, or other similar garage invention, would be easy to track down the knocking sound, but if it sounds like it's coming from the trans I would bet flywheel/torque converter.

Does the 'clicking' sound like it is coming from the trans?
There shouldn't be anything there that would produce a 'rapid clicking' except maybe the speedo gear, but if you're not moving yet it shouldn't.

 

[TommyM]

www.neons.org • View topic - Flexplate "flex" (fork rubs with FX700 pressure plate)

Go there and scroll down the page and look at the photos. That's what a broken flexplate looks like. It's happened to my Suburban and looked EXACTLY like that.

(By the way, I have no idea about that link. It was just the first good photo I found on Google.)

Tommy

 

[zway]

Outstanding.....thanks for the quick responses guys. Sounds like I'll be starting at the flex plate.....hopefully it's that easy.

 

[Bob H]

pic mentioned above added

Notice the bolt holes for the convertor

 

[zway]

Alright guys.....I got it taken apart this weekend. The flywheel/flexplate looks fine with the exception of the mounting holes for the torque converter have been elongated some. They're now kind of elliptical instead of round. I suspect this was from an earlier owner having loose torque converter bolts. Do you think just this could be the cause of the noise? Or should I swap the torque converter while I have it out? I'll attach a picture below. Thanks!

 

[dependable]

That could make the noise. I would try just the flex plate if that is the only tranny problem.

 

[zway]

Alright, thanks. I think that's what I'm going to do....just change out the flex plate as I don't have any related transmission problems besides the noise.

 

[timarr]

From what I know the 6.2 flexplate, Converter holes 5 are oblong left to right and one is top to bottom. about it can be warped? keep us posted!

 

[zway]

Alright, replaced the flex plate and put everything together. When I first started it and it warmed up I still had a small noise. I took it for a drive and no noise when I returned. So, I'm a little stumped....we'll see if the noise returns today. I'm kind of thinking I may be headed for a new torque converter. We'll see though.

On a side note, I also installed a set of AC 60G glow plugs....what a difference!

 

[zway]

Alright guys.....just an update. The flex plate ended up solving the problem. Not sure what the noise was right off the bat....possibly the torque converter bleeding out some air.....not sure. No noise now, and running good.

Thanks for all the advice!

 

[TCUCV]

Got any pictures of this new ride?