240z rear end clunk - differential?

[tellis32]

Hello

I'm trying to pin-point the source of my automatic '73 240z rear end clunk. I'm thinking it's the differential. Here's why:

1) I jack up the rear end and put the car in drive. Parking brake is off.

2) I'm noticing the passenger rear wheel is rotating (as expected) but the

driver side rear wheel is nearly motionless. Hardly any power. The half

shaft is connected and I'm not seeing any U-Joint play.

As far as I can tell, it's a stock R180.

Is this normal differential behavior or am I looking at a bad differential?

Any insight is greatly appreciated!

Tony

[Arne]

Pretty normal. The Z diffs are open, not limited slip. Whichever wheel spins the easier will therefore get all the power and the other pretty much none. So if the brakes are tighter adjusted on one side than the other, only one spins. If one of the halfshafts has a tight u-joint, only one spins. Pretty much any reason, if one side spins easier, it will spin and the other won't.

[tellis32]

Thanks Arne! That's great information!

Tony

[=Enigma=]

Welcome to the forums and congrats on your first post.

We'll need a little more info before a diagnosis can be attempted. When does it happen, acceleration, decelleration, when you go over a bump, when you turn left, right, only in reverse, etc.?

That said, the most common source of rear end "clunks" are either the front differential isolator, or your moustache bar bushings.

In the future, I recommend using the forum search feature to see if the question has already been asked and addressed. Most aspects of this general topic have already been covered pretty well.

Cheers,

.

.

.

Enjoy the site.

[beandip]

Well , what happens if you restrict the turning of the spinning wheel? If when you slow the spinning wheel you don't hear any clunking of grinding or such noise, things appear normal. Could be that the brake shoes are slightly contacting the drum on the non-spinning wheel. Since you have the care off the ground and hopefully on jack stands. Go under , never with just a jack alone holding the car up, and grasp the half shaft on one side and see if you can rotate it . Do the same on the other one. Check the ujoints closely for ANY play. There should be zero. There will be a slight amount of movement in the diff. this is normal. Question , does the diff have any whine or howl? hopefully none . have a look at the drive shaft ujoints also. While checking all the ujoints look for ANY signs of rust around the edges of the round parts toward the inner area of the ujoint. Any signs of rust color means the joint is toast. One more thing , hold the half shaft and the wheel and check for ANY play between them. Check the tightness of the two bolts on the back of the diff. where the moustache bar bolts up. The moustache bar should not have any play where it is bolted to the body on each end . this about covers what can cause clunking. You will never remove all of the clunking. This is just the nature of the beast. Gary:knockedou I started this reply an hour ago but was interrupted. ha ha

[tellis32]

Thanks for the welcome Enigma! I have forum searched for this and have

found a wealth of information on this topic! A far cry from the pre-Internet days when I owned my first '72 204z and there was no on-line resource

such as this!

It happens on acceleration. Not deceleration. Not at cruising speed.

Not when I shift from P to D or R or any other gear (automatic). The

frequency of this un-Godly CLUNK increases as acceleration increases.

Right and left turns make it worse. From inside the car, it sounds like it's coming up from between the jack / tool compartments where the differential is located. My thought was to check all the recommended

suspects (differential mounts, U-Joints, etc). But I stopped dead in my

tracks when I spotted this differential behavior which Arne says is normal.

Again, my thanks. What an excellent resource for a Z enthusiast!

Tony

[Arne]

You will never remove all of the clunking. This is just the nature of the beast.

Yesterday I would have agreed with you, Gary. My red 240Z (61,000 miles) clunks pretty noticeably. I've been planning to replace the moustache bar bushings and front diff mount to see if I can reduce it some.

But today I drove my yellow car a bit. Has probably 200,000 plus miles on it. Surprise!! Absolutely no clunk! None! Now that I know it can be done, that a 240Z can be clunk-free, I'm on a mission.

Now, back to Tony's issue. You are apparently describing a noise which is cyclical, frequency increasing with speed (not revs). Not the more typical clunk when changing direction or stabbing then releasing the gas. That being the case, I'd suspect u-joints first.

[tellis32]

Hi Beandip

Well , what happens if you restrict the turning of the spinning wheel? If when you slow the spinning wheel you don't hear any clunking of grinding or such noise, things appear normal.

>No clunking or grinding

Could be that the brake shoes are slightly contacting the drum on the non-spinning wheel.

> I can actually spin the non-spining wheel. No resistance what so ever.

Since you have the care off the ground and hopefully on jack stands. Go under , never with just a jack alone holding the car up, and grasp the half shaft on one side and see if you can rotate it . Do the same on the other one. Check the ujoints closely for ANY play.

> No play

There should be zero. There will be a slight amount of movement in the diff. this is normal. Question , does the diff have any whine or howl? hopefully none .

> No whine or howl

have a look at the drive shaft ujoints also. While checking all the ujoints look for ANY signs of rust around the edges of the round parts toward the inner area of the ujoint. Any signs of rust color means the joint is toast.

> Will do.

One more thing , hold the half shaft and the wheel and check for ANY play between them.

> None as far as I could tell

Check the tightness of the two bolts on the back of the diff. where the moustache bar bolts up. The moustache bar should not have any play where it is bolted to the body on each end.

> These are my next moves!

this about covers what can cause clunking. You will never remove all of the clunking. This is just the nature of the beast. Gary I started this reply an hour ago but was interrupted. ha ha

> Hey, I appreciate the reply and the thoughtfulness behind the information! - Tony

[Carl Beck]

Check the front differential mount !!... lay under the car, put your strong arm/hand under the nose of the differential -PUSH UP AS HARD AS YOU CAN. If you can push the front of the differential up - the front mount is broken - replace it.

Secondly - there is a "strap" that runs over the top of the nose of the differential - make sure that is in place and stoping the upward movement of the nose of the differential - that strap is there to help prevent breaking the front differential mount - by limiting the upward movement of the nose of the differential under acceleration from rest.

FWIW,

Carl B.

[justaZcarguy]

I agree with Carl, it sounds like the diffy mount. The rubber casting fails over time and allows excessive play upon torque.

Gary heard some horrible noises from my rear end about a week ago.

And the Z was bad too!!

Tip your waitresses...

[=Enigma=]

Guys, if this is cyclical in nature and changes frequency with speed, it is not very likely to be any of the mounting points, but is more likely a half-shaft u-joint, wheel bearing, or even something in the diff. That being said, all of the the items mentioned so far should be checked anyway, however my money is on a bad u-joint at this point.

[superfunk]

Just for some clarification, how much play is normal in the diff. With my rear wheels on the ground, how far should I be able to turn to the drive shaft? or should I be able to?