Drivetrain Noise Troubleshooting

[Origin7]

I’m hoping someone can help me pinpoint the root cause of a clunking noise that seems to be coming from the rear universal joint or differential. When there is a load on the drivetrain, the noise goes away, but it always comes back when I’m barely tipped into the throttle.

 

I tried greasing the universal joints, but there was no improvement. I also checked the driveshaft for play, and everything seemed okay. Half-shafts seemed alright too. 

 

When I first got the car, it made a loud clunk when I released the clutch. I found that the bottom differential mounting bolts had loosened and backed out. It looked like they had been loose for quite a while. I tightened them, and that particular clunk went away, but this other noise started afterward.

 

I’m wondering whether all that movement damaged the pinion bearing. The noise also changes as the car warms up, which makes me think it may be bearing-related.

 

Hoping to determine what it is before I go through the trouble of dropping the diff. Has anyone else had a pinion bearing fail? If so, did you experience similar symptoms?

 

 

[Scott_]

Have you drained the diff oil to see if there is any metal in it?  If the differential is secure and you are not seeing any backlash in the half shafts  then the problem is either the ring and pinion or it could be at the other end of your driveshaft and it may sound like like the clunk is coming from the rear.    

 

When you say the notice changes do you mean it gets quieter?

 

 

Scott

 

 

 

Edited Friday at 11:07 AM by Scott_

[mccasksl]

Second checking diff oil for volume and metal content!

LSD?

 

I'm going thru a similar noise diagnostic process on my 2008 Roadsport S3 Ford LSD.

Edited Friday at 01:32 AM by mccasksl
typos

[Origin7]

@Scott_I haven't drained the oil yet. That's probably a good next step. That's a good idea to take a closer look at the other end of the shaft.

 

The sound never really goes away. It just gets less frequent. It's really just a problem under light tip-in or lower RPM/load when I am ON/OFF the throttle. It sounds like backlash/clunking back and forth. 

 

@mccasksl Open differential it appears. 

Edited Friday at 11:23 AM by Origin7

[CBuff]

I had a low speed hard turn noise pop up. Assumed it was the titan diff on its way out. Added some redline friction modifiers to the spec'd motul diff fluid. Major noises went away. It's still getting noisier. Have a transport LSD diff standing by to swap over for a winter project.

 

@Origin7 might also want to check you A frame bushes. I have read that those can go and you get a clunk on/off throttle as the suspension loads and unloads. 

 

[Origin7]

@CBuff , A-frame bushings are a great suggestion. That would be a dream come true if that's all it is. 

[Slonie]

Check the middle rear one first (very easy to access!).
 

 I had a clunk coming off throttle and that was the likely culprit as it was the practically the only suspension bolt I found that was noticeably not to torque on my car. You won’t even have to lift the car for this one!

[Origin7]

13 hours ago, Slonie said:

Check the middle rear one first (very easy to access!).
 

 I had a clunk coming off throttle and that was the likely culprit as it was the practically the only suspension bolt I found that was noticeably not to torque on my car. You won’t even have to lift the car for this one!

 

Is it a good enough test to pull on it and look for play, or should I pull it apart and take a closer look? The reason I ask is that I gave it a good tug and everything seemed solid.  

[CBuff]

I have not changed or done this myself. But online seems like if you pull handbrake and push car back and forth that should replicate the clunk of its the bush 

https://www.pistonheads.com/gassing/topic.asp?h=0&f=101&t=1924694
 

[Slonie]

I don’t know for certain but I’d throw a socket wrench on each side of it and give a tug on those, if it moves at all it definitely wasn’t torqued to spec (the spec is I believe 81Nm with a 3/4” socket plus deep socket, ie pretty darn tight)

In my case I don’t think I could identify any movement by hand, but definitely noticed the lack of torque on this one during my bolt check. Scientifically speaking I also tightened every other rear suspension fastener as well as my differential mounting bolts, but this one was both the easiest to access, most loose, and most likely culprit for a clunk. 
 

One of my diff bolts was also loose — these warrant a torque check as well but don’t be like me and trust the modern IKEA manual for torque specs — older diffs have a lower spec and I definitely overdid mine before realizing this. Check the build manual that matches your car! Hopefully not a huge headache for future me.

[Origin7]

1 hour ago, CBuff said:

I have not changed or done this myself. But online seems like if you pull handbrake and push car back and forth that should replicate the clunk of its the bush 

https://www.pistonheads.com/gassing/topic.asp?h=0&f=101&t=1924694
 

 

Thanks, I just tried this. Seems alright. I hear a little clanking, but I'm thinking its slop in the parking brake. 

 

@Slonie The A-frame bolts feel tight. As a test, I put another 1/8 turn on them or so. Will test tomorrow and see if there is a difference. In doing so, I noticed some play/clunk when I tugged on the rear anti-roll bar. These are hard-mounted with no bushings, which I was surprised to see.  Its probably worth going through all the fasteners, like you took the time to do.