Jump to content

IGNORED

High speed Deceleration clunking/hard rattle 60-70mph


Jmoyet

Recommended Posts

I couldnt find anything that described what I have just the usual clunk at changing gears typical of a bad mount. 

I have an early 1971 Datsun 240z with a 4 speed manual built in 1/71. All original to my knowledge. Besides the clunk at accel and decel (front diff mount that is no longer in production) I also have a loud clunking/rattle when i let go of the gas over 60mph then goes away under 60mph. Sounds like somebody with 2 hammers hitting the bottom of the car rapidly. When I have it up on jack stands it does the same on 2nd and 4th gear at idle. its louder on the drivers side wheel for some reason.. Quieter without the wheels. when i hold the drivers side wheel and let the passenger side spin away (yes its an open diff) it still makes the same loud clank on the drivers same if i hold the passenger side wheel. still louder on the drivers side.. and also jerks at the wheel when holding it.. Bad Diff? 

Link to comment
Share on other sites


2 hours ago, Jmoyet said:

When I have it up on jack stands it does the same on 2nd and 4th gear at idle. its louder on the drivers side wheel for some reason..

When the wheels are hanging the u-joints of the driveshafts/halfshafts have too much angle and will bind.  Clang, clang, clang as they pop around.  If you want to test it on jacks spread the load with some wood under the control arms, to load the suspension and get the drive shafts in a normal position.

If you want to just check u-joints, it's best to use a screwdriver to pry the joint around with a bright light so you can see any movement.  Also look for rust dust around the bearing cup seals.

 

Edited by Zed Head
  • Like 1
Link to comment
Share on other sites

I have a transmission mount ready for install. I ordered a solid mount for the differential. Waiting for it to arrive now to see if it fits the early differential mount without swapping everything out of the 72 model into my early 71. But yeah, I get the normal clunk when changing gear, Accel, deceleration typical of bad mounts. But the heavy pounding rattle at above 60mph only at dice is strange. When I press on the gas again it goes away and let go of the gas and rattles like hell. I won't be able to work on it till next week on my days off.. Yeah it's a daily driver.

Link to comment
Share on other sites

 IMO, Check the drive shaft u-joints first. I've experienced the rattle induced by deceleration in an RX7. It was caused by a front u-joint that had a TINY bit of end play in it. The clunks? A really bad u-joint will do it but trans. and or rear end mounts are probably the culprit. I think if the clunk was coming from the ring and pinion, you'd have worse symptoms than a clunk.

Link to comment
Share on other sites

  • 3 weeks later...
On 1/13/2016 at 9:27 PM, Jmoyet said:

I have a transmission mount ready for install. I ordered a solid mount for the differential. Waiting for it to arrive now to see if it fits the early differential mount without swapping everything out of the 72 model into my early 71.

Personally, I wouldn't go with a solid mount. They will transmit a lot more Noise, Vibration and Harmonics than a rubber mount, especially on a DD . Just my .02c

  • Like 1
Link to comment
Share on other sites

There are eight points of rubber contact holding the engine, transmission, and differential in place.  The two motor mounts, the central transmission mount (called rear engine mount by Nissan), the two ends of the transmission mount crossmember (not readily noticed), the front differential mount, and the two mustache bar ends.  They can all add some looseness to the whole system.  The tail of the transmission is really not very tightly held.  That's a spot for rotational vibration that might be hard to diagnose.  Lots more mass also, small movement = big effect.

Link to comment
Share on other sites

"somebody with 2 hammers hitting the bottom of the car" is exactly how mine sounded when my driveshaft U-joint self-destructed. Happened at odd times though. New driveshaft fixed it instantly. Mechanic I trust said needle bearing was loose in there. I was sure it was something about the right rear wheel but no.

Jalex, maybe install a new trans mount and new differential mount ?  If that doesn't fix it, it's OK, they were probably about shot anyway. So then do the expensive stuff if necessary.  Or if you can afford it, replace rubber at all eight points of contact per post above.

I got my car cheap because it was clunking. Thank you worn out trans mount !

Edited by Stanley
Link to comment
Share on other sites

So I got a solid diff mount and it did for my series 1 240z. Clunk went down but still clunks due to play at the axle hubs at the wheels. And replaced both u-joints on the driveshaft since it had a bad u-joint. Runs smoother but still clunk due to axle hub play and still rattles hard when letting go of the gas going above 60mph like something hammering. Checked the driveshaft it has no marks on it as all that would indicate any rubbing or hitting anything. So I'm still wondering what's causing the rattling/hammering 

Link to comment
Share on other sites

On serious deceleration the rear stabiliser was touching the tail-shaft on my race Z causing the 2 hammer sound.  On careful examination the stabiliser bar joints were cracked and the bar had pushed up close to the tail=shaft uni joint in front of the diff.

Link to comment
Share on other sites

  • 2 months later...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy and Guidelines. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.