Front Differential Mount Replacement

[JoelH]

I wish it were that easy. We checked those bolts and bushings in the mustache bar as well. I believe the last thing he wanted to tell me was my diff was bad.

[Zedyone_kenobi]

I think I am in the same situation JoelH.

I think I have excessive play in my R180. I have the clunk your refering to as well. I have checked my arrestor strap and my rear diff mount, and both seem in very good condition. My driveshaft has more rotation than I think a ring and pinion should have. I would like to get mine rebuilt, as it was original to the car, but at the same time getting a used one is FAR cheaper. We will see. I just need confirmation on my diagnosis. Once I get that, I can know how I want to move out. There is a good Z mechanic here in Houston, I may have to let him have a look.

[JoelH]

I had play in mine as well so we replaced it. Still the clunk. In my case we think it may be a worn stub axle. It can cause the clunk as well. I got a used R180 from ZBarn for $180 shipped to my door and I still have the old one.

Replacing the stub axle can be a big deal so I decided to live with the clunk for now and throw $$ at it later. When I tackle the problem I'll probably replace all rear bushings, stub axle, yadda yadda = new rear suspension.

Good luck with yours. From what I can tell, the clunk is very common but not deadly.

[Arne]

I almost hate to bring this up, folks. But I've been through all this on my low miles '71 as well. Took me many months to go through it all piece by piece. And in the end, the clunk from the rear on my car was actually in the transmission. Sound travels in funny ways through the body shell, and what I swore many times was coming from the differential area was actually in the transmission.

In my case, the clunk was much worse when the transmission was warm, and I could make it clunk in first, second, third and reverse, but not fourth.

[Sailor Bob]

I replaced the front mount last year - didn't fix the "clunk". The rubber was separated - so it seemed like a good fix - it needed to be replaced anyway. First drive it was back.

I have replaced every bushing in the rear end (except outer control arms) including the mustache bar bushings, shocks and springs replaced. There is no slack in the drive shaft or side axles.

I have learned to live with it and find that it is definately related to my driving habits. If I am sloppy shifting - it happens every time - when I am in the groove, I will go for a week without a "clunk".

That's my personal experience.

[Arne]

My car now is virtually clunk-free. I have to do something pretty stupid to make it clunk now. But prior to the transmission rebuild, once the car had warmed up it was difficult to make any torque change (on throttle or off) in any of the lower gears without it clunking badly.

During my hunt, I replaced the following parts with new:

• Front differential mount
• Rear transmission mount
• All six u-joints (professionally done, not a hammer and vice job)
• Driveshaft balanced
• Rear struts, with bump stops
• Inner rear control arm bushings
  

I also swapped in the following parts known good from different 240Zs:

• Both halfshafts, several times (from two different parts cars)
• Rear mustache bar (from parts car, which had fresh bushings)
• Differential
• Both strut assemblies, including the bearings and stub axles
  

What I finally found was that the primary drive gear on the countershaft was moving under torque changes due to worn woodruff keys. After replacing those woodrff keys (along with all four synchro rings and all bearings for good measure), my clunk was gone.

Now I expect that my problem was rather unusual. Most clunks will be taken care of by the usual suspects. But if all the normal stuff fails, don't forget to look for the unusual.

[cstew69]

Ok, sorry guys, I'm confused. I actually have already taken what I think y'all call a rear diff mount off the car. I'm aware that this part is the source of much "clunking" on the car, as mine does. But I was under the impression that there is a bushing on this thing, which was likely worn out. No, there is none. So I'm looking at this thing, and don't see anything wrong with it. What am I missing? I just ordered with MSA what they told me is a bushing for this. I'm confused.

[Diseazd]

My clunk was rear inner control arm bushings. You can check the torque on the four large bolts on the rear control arms. Diffs are hardly ever the problem (there is play in all Z diffs).

[Jeff G 78]

Ok, sorry guys, I'm confused. I actually have already taken what I think y'all call a rear diff mount off the car. I'm aware that this part is the source of much "clunking" on the car, as mine does. But I was under the impression that there is a bushing on this thing, which was likely worn out. No, there is none. So I'm looking at this thing, and don't see anything wrong with it. What am I missing? I just ordered with MSA what they told me is a bushing for this. I'm confused.

This is a lousy picture, but it's all I could find in a hurry. The mount has an inner and outer steel "U" with rubber bonded between the two. The rubber and/or bond rips and the diff moves too far up and clunks.

http://www.courtesyparts.com/rear-differential-mount-1970-1978-s30-p-568987.html?cPath=7724_7758&

To test it, take a large screwdriver and try to pry the two halves apart. Look for gaps in the bond.

Edited March 18, 2009 by Jeff G 78
Added info

[f1race79]

Might want to check rear struts...?

[=Enigma=]

This is a lousy picture, but it's all I could find in a hurry. The mount has an inner and outer steel "U" with rubber bonded between the two. The rubber and/or bond rips and the diff moves too far up and clunks.

http://www.courtesyparts.com/rear-differential-mount-1970-1978-s30-p-568987.html?cPath=7724_7758&

To test it, take a large screwdriver and try to pry the two halves apart. Look for gaps in the bond.

That's a diff isolator and mounts to the front diff member. The rear diff mount/member is often referred to as the moustache bar due to it's shape and bolts to the diff cover. This is mounted to the body on two large bolts that protrude down through the rear deck. Each end of the moustache bar contains a rubber bushing which can become worn to the point that it allows the mount/member to move around and clunk, normally upon acceleration, but potentially on decelleration as well if the wear is bad enough.

Edited March 19, 2009 by =Enigma=

[Jeff G 78]

I have had to replace the front mount on nearly every Z I've had. The new mount eliminated the clunk on all but one which had a torn mount and worn half shafts. It took both repairs to eliminate the noise.