Drivetrain Clunking...I'm going to need some help.

[jacob80]

Hey guys,

 

1973 240z

 

Well, it seems as though my attempt to fix my clunk has taken me nowhere (as of now).

 

These past few weeks, I have been working my butt off on this damn car. First of all, we had new floor pans put in and I repainted the entire underbody.

 

Following this, I bought Z31 turbo CV axles, an R200 viscous LSD, R200 280z input flange so I could bolt up my stock driveshaft, modern motorsports CV adapter, 280z 27 spline stub axles, finned differential cover, Arizona Z car solid mustache bar and finned cover brace/uprights, and last but definitely not least, a Ron Tyler differential mount (phew!). With all of this, I thought I would have a completely solid rear end with zero clunking issues...WRONG. Previously, with the completely stock setup (R180, '73 240z), we had clunking. After installation of all these new parts, the exact same clunking has consistantly comes back.

 

As of now, my only thought would be the transmission mount, but I'm confused as to why it would transmit noise all the way to the rear end.

 

A couple things that happens are:

 

1) When the car is rolling and disengaging the clutch, I will cycle threw various gears and every time I hit a different gear, I sound is transmitted through the drivetrain, like something is loose.

 

2) When letting on and off the throttle completely, a clunk will result.

 

3) When shifting gears, the clunk is trasmitted through the drivetrain.

 

As of right now, I'm not sure what to do, other than double check my transmission mount. Any help is appreciated here guys, I'm just not sure what else I can even do at this point. Thanks!!!

Edited April 26, 2010 by jacob80

[hoov100]

check you're u-joints. Also could be, you have to much backlash between the ring and pinion.

[JMortensen]

Probably not backlash. Everyone posts that they think the problem is backlash, I have yet to see a single person fix their clunk by adjusting backlash in a Z car. I'd go after the U-joints or maybe loose driveshaft bolts. If the bolts aren't loose, pull the driveshaft and feel the U-joints by hand.

[jacob80]

One U joint had very very minimal play, almost completely unnoticed unless you were looking for it, but it was there. Would this really cause a clunking/shock through the drivetrain? I'm kind of headed in the same direction here, as well.

[jacob80]

Another thing, there is a little play in the differential, but I was told this was normal by the individual that i bought it from (Dsommer). Is this true? Also, should my rear differential be making any noise at all? I am hearing a kind of noise that sounds like gears meshing and sounds like a small air leak and slowly subsides as I slow my roll. Thanks!

 

EDIT: I did a little reading about back lash, so I suppose this play is normal?

Edited April 26, 2010 by jacob80

[jacob80]

Okay, well it doesn't look as though anyone has much input for me at the moment, so I'll check a couple things.

 

1. I'll ensure that my driveshaft bolts are tight on all four corners.

 

2. I'll double check that my differential mount is solid, as well.

 

I would like to do a test and want you guys to tell me what you think. I was thinking about putting the rear of the car up on jack stands so that the wheels will spin freely, and while I lay under the car and watch for any kind of movement within the drivetrain, I'll have someone sit in the car and go through the gears with the clutch disengaged.

 

I would do this test because when I am simply rolling down the street with clutch disengaged, I can go through the gears and everytime I shift into a different gear, a CLUNK will occur. Could I rule out the fact that my differential mount may be loose, or not yet?

 

THANKS!!!

[cygnusx1]

Good luck.  I have been under my '76 280Z for 20 years, have changed/upgraded EVERY single drivetrain part at least once, and have never gotten completely rid of the clunk.  Mystery to me.  I think it's just a combination of tolerances.  A little here, a little there, and it clunks.

 

My '72 240Z bone stock other than the L28 motor.  ZERO clunk, and I mean ZERO!

 

 

 

 

Here is a little diagnostic tidbit.  Put the car in 1st gear on level ground.  Creep under the car as far as you can.  Have someone roll the car back and forth, bumping it against the engine.  You will physically see where the slop is.  My 76 will roll back and forth an inch or more, in gear!

 

 

 

 

 

 

 

 

Edited April 29, 2010 by cygnusx1

[jacob80]

Hah great! So that slop is most likely the source of my clunk? More importantly, is it a problem? I wouldn't think that parts clunking around and banging into eachother is necessarily healthy

[cygnusx1]

Hah great! So that slop is most likely the source of my clunk? More importantly, is it a problem? I wouldn't think that parts clunking around and banging into eachother is necessarily healthy

 

 

 

Yeah, aside from sounding like garbage when you time a bad shift, it's holding up.  I figure, everything important is in good shape, so it's safe, and when it finally breaks or gets worse, maybe I'll actually pinpoint it.  

 

 

 

[jacob80]

I would think that it would be solid by now, after everything I've done, but I guess not. The EXACT same sound was present before installing everything, so maybe it the transmission, at this point I'm just lost. I guess I won't worry about that noise for now. How about the sound that the rear end is making, should I be concerned???

[sweetride2go]

Good advice cygnusx1! I found my clunk the same way, putting the car in gear on concrete, then pushing it back and forth against the gears, and I could duplicate the clunk. Since the car was in gear and not running, I had no problem getting underneath it and grabbing the exhaust/diff framework and pushing it back and forth. Low and behold I could see the diff rotate a bit on the clunks, it was the two bolts that hold the diff to the mustache bar and they had loosened up just enough to allow the diff to rotate back and forth just a wee bit, but enough to make a clunk. Especially between gear changes. Apparently those two nuts had backed off, or maybe I hadn't tightened them all the way when I reinstalled the diff some time ago. Either way, if the clunk comes back, there's the first place I'm going to check. Maybe locktite this time?

 

However, I am running a v8, t56, new drive shaft, and R200 with a RT front mount and poly mustache bushings and rebuilt/stock halfshafts.

 

Good luck!

Ryan~

[jacob80]

I am running the ron tyler mount, VLSD R200, AZC mustache and brace. I'm going to try this tonight and get back to you guy.

 

Say, perhaps, I do this and all the movement is in the driveshaft/transmission? What then? The transmission was just rebuilt, also.

[jacob80]

Ok, so here is a video that hopefully shows you guys how much play is in the drivetrain. Is this too much?

 

[sweetride2go]

It doesn't seem excessive to me, but I'm not an expert. My car has a bit of slop in the tranny and the diff, and that adds up to almost an inch or so of movement on the tires/ground. I think my car has at least that much slop and it hardly ever produces a clunk now. Did you try that with the car on the ground? The extra weight of the car would/should help reproduce the culprit.

 

Cheers

Ryan~

[jacob80]

It doesn't seem excessive to me, but I'm not an expert. My car has a bit of slop in the tranny and the diff, and that adds up to almost an inch or so of movement on the tires/ground. I think my car has at least that much slop and it hardly ever produces a clunk now. Did you try that with the car on the ground? The extra weight of the car would/should help reproduce the culprit.

 

Cheers

Ryan~

 

I did, but I need to do it again because I was laying under the car pushing it myself (if that makes sense). I guess my question while does this test again is; what exactly am I looking for? I know that if the differential rocks around then it has to do something with either my Ron Tyler Mount or the mustache bar nuts. But, at least from what I saw last time, it looks like the driveshaft is just turning along with the wheels and all that when I rocked it back and forth. It didn't look like anything was necessarily loose, does that make sense? Just looked like movement in the driveshaft/pinion back lash/transmission?

 

I'm so lost

[sweetride2go]

You have poly or rubber mounts all around? I've heard of noise complaints from people that have used solid mounts in their diff/engine/etc, as it transmits drive train noises throughout the chassis. When I spotted my slop in the diff/mustache bar, it was moving less than 1/16 of an inch, so it doesn't take much. Other than that I have no other suspects for the time being. I am curious as to what it may be though...

 

Good luck!

[cygnusx1]

Use your ears and your hands to feel around for vibration, knock, and movement.  Grab each part of the drivetrain while someone else rocks the car.  Your hands will "feel" slop much better than your eyes can see it.  You ears will help pinpoint the location.  I agree it does not look excessive but the noise it makes in your video does sound like something is loose.  Check the two big nuts on the back of the diff.

[jacob80]

Alright, will do. I'll probably have some time to work on it later this week, school has got me pinned down right now. I'll let you guys know if I discover anything else suspicious in my diagnosis process. Thanks for all your help, I'll keep you updated!

[jacob80]

Just another thought.

 

I've come to the conclusion that the clunk that was evident prior to installing my new drivetrain components is the EXACT same clunk that was occurring before. The only thing that I can even possibly think of that I didn't replace is the transmission insulator.

 

Could this be the culprit that is causing my clunk? I kid you not, the sound is identical, I was so disappointed when I pulled out of the driveway for the first time to hear that clunk!

 

I haven't heard anyone suggest the transmission insulator, but its the last thing I can think of other than the differential back lash. From there, I would have to go so far as to say the transmission is the problem SOMEHOW. Ugh I just wish I could get rid of this sound! Ahhh!!

 

EDIT: There is one last thing that may or may not be a factor. We did have our stock 4 speed rebuilt, which is what is being used as our transmission, and even since we've had it rebuilt, if you don't shift into first and then reverse, it will grind if you go directly to reverse. Perhaps this could be a factor?

Edited May 7, 2010 by jacob80

[datsunlover]

 

EDIT: There is one last thing that may or may not be a factor. We did have our stock 4 speed rebuilt, which is what is being used as our transmission, and even since we've had it rebuilt, if you don't shift into first and then reverse, it will grind if you go directly to reverse. Perhaps this could be a factor?

 

 

The grind thing is normal in my exp, just the nature of some transmitions; if they are still spinning forward internally and you try to jam in reverse, it won't go. Putting it in first 'stops' the trany. And I don't think that has anything to do with your driveline clunk.

 

Trust me, cause my rear diff just exploded yesterday :/ Was trying to get rid of the clunk and a weird noise sometimes when I took off... kind of a clunk clunk clunk/rattle, but it would go away after a few seconds. I figured it was u-joint related, and changed all the u-joints; seamed to be better but then some noises came back and out of nowhere BANG! Felt like some one hit the bottom of the car with a sledge hammer! This was at about 60kph and the noise that it started making THEN, I figured the driveshaft had come off or something... Pulled over, reached under the car and could turn the driveshaft about 90* So I limped the car home in 2nd gear (any higher speed the noise would get louder and scary) Pulled the drain plug on the diff and it's not fluid anymore, it's grey/metalic sludge and I have never seen so many metal filings on a drain plug magnet... Havn't got it out of the car yet to disasemble and trouble shoot, but my guess is a bearing let go, or maybe lost a tooth on one of the spider gears... Either way, I would consider at least checking your rear diff fluid I had at least that much play at the wheels too..