ZF, TOB or something else?

[Kizer]

Rotational movement like that is pretty normal. There will be a clunking when you get to each stop - again pretty normal.

When you say you are hearing this rattle, is it while you are turning? Do you think that it's the same noise you are chasing while engaging reverse?

I makes the noise regardless of turn.

I do believe that it's the same noise. I believe that it's a spring (or 4) trying to jump off the DMF

 

[onetonjohn]

So you twist the driveline by hand and can hear the rattle? Unless you are strong as a Gorilla, I don't think you can get DMF to move by turning the driveline.

 

[Thewespaul]

You can pull off the flywheel inspection cover and check the play in the dmf and look for broken springs when you take the cover off. I typically use the needle bearing setup, never had one fail. The Kevlar bushing holds up well with a lot of power with an engine that needs the upgraded clutch.

 

[Kizer]

So you twist the driveline by hand and can hear the rattle?

Unfortunately the "twang" is harder to hear in the video than in person ... maybe you have better speakers than me.
I performed the same test on another ZF (with LUK SMF conversion) and get about the same movement but a very different sound ... no "twang that sounds like a rattle when the truck is taking off in reverse".

Here's a link to video because I'm tired of trying to get one embedded:

https://photos.app.goo.gl/E9Mp5thQ2QotXEsw6

 

[Kizer]

You can pull off the flywheel inspection cover

That's the plan (now). I couldn't go to my shop today. I had to get some work done so I can sacrifice my $ to the Truck Gods.

 

[onetonjohn]

This is 5sp? From the video it kinda looks like it could be 4sp.

EDIT: Sorry, thrown off by the seam and color. It doesn't look like my 4sp. That said, I get some pretty loud gear noise that is similar when twisting t-case output as gears mesh and clunk. I don't think you are getting the DMF to turn. This sounds like gear noise in the trans as the gears come together and load. I can't comment on if this is normal or not. Wait, I have a couple out the the shop. Let me check them for gear noise. This is 2wd - no transfer case, right?

 

[onetonjohn]

Trans in neutral when doing this test, or are you in gear? IF in gear, reverse? Same noise/slop in 1st?

 

[Kizer]

Thank you for checking yours.

I'm working on (about to be) the '93 CC IDIT that's in my sig. It's 2wd.

Trans in neutral when doing this test, or are you in gear? IF in gear, reverse? Same noise/slop in 1st?

Trans, in both tests, was in 2nd (SOP when I park). I didn't try any other gear or neutral since:

I performed the same test on another ZF (with LUK SMF conversion) and get about the same movement but a very different sound ... no "twang that sounds like a rattle when the truck is taking off in reverse".

 

[onetonjohn]

I tried it on my trans only. Very little swap if input shaft is held (trans in gear), and very little noise. I had much more noise on the 4speed with transfer case. If you pull the inspection cover you can see if you are turning the DMF friction surface or not. It took me a bit to come around, but I'm starting to think your right. Strange that it would only make noise in reverse - but I usually don't understand something till I understand the system completely. The good news is that DMF is way cheaper than something wrong in transmission.

 

[Kizer]

Strange that it would only make noise in reverse

I agree. I've been around 2 failed DMFs ... rattled "like a milk truck" at idle, in neutral.
Pic of one of them:

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