Mustache bar bushings

[Namerow]

Kudos to Kats for being able to finally produce for us a well-organized set of clear photos and graphics, c/w parts numbers.   I still have a few questions, though.

1. The M-bar mounting/isolation scheme for the Early S30's with the angled halfshafts (SoP to until 71-06) appears to use a unique isolator design, in which the rubber core extends out around the lower end of the metal outer shell so as to provide a soft lip for the plain-metal-washer lower 'stopper' to sit on.  This apparently didn't work very well  (the rubber lip probably sheared off over time).  Does any one have a photo of this early-version isolator (PN 55476-E4100 or 55476-E4101).
2. In the section view of the early-version isolator, the clearance gap marked as 'A' is intriguing.  In the FSM, it's called 'B' and comes with the following explanation: "Replace differential mounting rear insulator if the dimension 'B' is less than 5mm."  I believe that the lower 'stopper' (washer) is supposed to sit on the hard stop created by the square step machined into the bottom of the tapered mounting stud.  Then the securing nut gets torqued to 60 lb-ft.  The lower stopper doesn't even touch the insolator.  So that means that the 'A' (or 'B') gap is intentional and the hanging weight of the Diff would be entirely taken up in shear by the rubber core of the insolator.  This would be quite different in principle from the later style arrangement with the rubber-faced lower stopper.  In that later design, the hanging weight of the Diff would be taken through the rubber stopper and into the tapered mounting stud.  Makes me wonder why they even retained the rubber core for the isolator in the later design.  Comments, anyone?
3. As Kats photos demonstrate so nicely, there were at least three different M-bar mounting/isolation schemes used over the life of the 240-260-280 models.  The early #1 version (angled-halfshaft 240) and the final #3 version (280Z) are easy to position in the Z's chronology and well-documented in Kats' photos.  The 'middle' #2 version, however, is puzzling (it's the one that uses the thick/concave rubber-faced stoppers with no ribbing, top and bottom).  Depending on how you read the parts numbers, this version may (or may not) have applied to the entire run of later 240's and the 260 and we should be seeing photo evidence of this style of stopper frequently.  But that doesn't seem to be the case.  Most of the suspension/drivetrain photos I've seen over the years show the deep-ribbed stoppers that were used on the 280Z.  Comments?  More specifically, does anyone know the production dates over which this 'middle' version (thick/concave rubber-faced stoppers with no ribbing) was used...
    

• 71-05 to 73-07?  (i.e. later 240Z only)
• 73-08 to 74-11?  (i.e. 260Z only)
• 71-05 to 74-11?  (i.e. later 240Z and 260Z)

To add to my confusion, the FSM for the 260Z continues to show the early-style insulator design (ref. Figure RA-13). 

 

 

 

 

 

Edited March 19, 2018 by Namerow
made it better, then fixed the new mistakes

[Zed Head]

Somehow I missed Kats's post.  There's a lot of new things in it that I've never seen before .  Too bad we don't have sticky's on this forum.  This could be the mustache bar sticky.

Seems to me that Nissan got stuck between the differential whine and the mustache bar clunk/thunk.  Under acceleration the diff twists, driving one end of the bar up and the other end down.  So you can't have too much free space for the bar ends to gain speed or you get a thud/thunk/clunk noise.  But if you have things too close, then you can get diff whine as the rubber compresses.  If they had just made a less whiny diff, they probably could have avoided a lot of work on the mustache bar.

[Zed Head]

I hereby nominate this thread for "Promotion to the Knowledge Base".  Can I get a seconding motion?

[Acemon]

I definitely think this thread should be preserved given the lack of replacement parts.

I found a moustache bar on eBay (kinda rusty and perished bushings) for $50 with shipping. The 2-part rubber compound is about $30 with shipping, so It's temping to spend a little cash and do some mad scientist experiments. The bushings on mine seem OK, so if I mount the bar on my workbench and use a 6' long pipe as a lever, I can determine how many pounds it takes to deflect the bar 12", then do the same with a set of urethane bushings, and finally with the 2-part compound. It might not be the most accurate method but at least it'll give me a baseline.

My beer budget will be impacted, but science is important, right?

[Patcon]

I second...

[Namerow]

2nd second.

[Namerow]

Over the years that I've been following this sitier, I've been collecting info by 'cut-and-paste' into Word docs and building my own reference library that's organized by categories and topics that make sense to me.  As this particular thread began to build, I discovered that some of the territory that we've covered here had already been addressed some time earlier.  Here are a couple of early contributions made by a couple of well-known voices on this site:

From Zed Head:

"The washers are supposed to bottom out on that inner metal sleeve. It leaves the bar kind of hanging in between, with the web of rubber of the bar bushing supporting the weight. The scalloped layer of rubber on the washers is more of a final damper for any movement. That's my take on the design. I think that the idea is to minimize pathways for the high frequency vibration (specifically, diff howl).  But the rubber gets weak over time. If you've compared a new rubber transmission or diff mount to an old one, you can actually see the difference in rubber stiffness.

I've had good luck with the urethane mounts, with 2-3 washers added to the inner sleeve to leave a small air gap between the urethane and the washers. Basically, extending the sleeve length. The same general concept of the Nissan design. A little bit of float. My diff noise is less than when I got the car and had old worn clunky stock mounts. I had pretty bad clunk and howl. I also added an RT-style front mount now. I think that most of the urethane mustache bar bushings are designed to clamp the bar tightly, race-car mentality.  Therefore, they transmit a lot of noise and vibration to the body. Another opinion."

and from ZKars:

" The mustache bar bushing rubber is likely old and soft or beginning to break down. Tightening down the nut just locks the bushing's center steel tube and the steel face of the washers to the frame. You rely on the hardness of the "eye" bushing rubber and the hardness of those "nubs" on the upper and lower washer to prevent the rotation/twisting of the M-bar that might allow it to touch those up-rights or anything else. Squishy bushings will let it twist all over the place. I'd love to have a Go-Pro and a light back there and take the car for a good spirited drive to see just how much that M-bar twists around."

 

[Jason240z]

So, to add some fuel to the fire.

I've a 1970 10/70 build 240z.

Bar has the number450e4102

I managed to find bushings part number 55476-n4300 also thanks to a good friend, some insulated washers.

However it seems my bar is the earlier type, which is 'double flanged' from the factory. 

has anyone cut a flange off and pressed the rest out with this earlier bar? its only got 45.75mm ID, compared to the 50mm bushings. I measure the flange/insert thas been press flanged at a thickness of  1.9mm.

so basically it looks like theyd press fit nicely.  it seems nissan changed the part design for the bar bushings?

 

[Captain Obvious]

I'm not sure I'm understanding what you have going on there, but...

Are you sure it's not just the old remnants from previous factory bushings still installed in the moustache bar? Lots of people burn or grind out the rubber portion and leave the outer metal shell intact as preparation for installing poly bushings.

Have you got any pics?

[Zed Head]

I think that he's referring to post #42 which shows a design that only has one flange, or folded over edge.  They probably worked their way out of the bar so Nissan added a post insertion flange later.

[Captain Obvious]

I know what you're referring to, but if that's the case, then I can't explain this:

"However it seems my bar is the earlier type, which is 'double flanged' from the factory.   has anyone cut a flange off and pressed the rest out with this earlier bar?"

It sounds like he's describing a later style bushing which is flared on both sides. If it wasn't flared on both sides, you wouldn't have to cut anything to press it out.

Picture is worth 1000 words   

[Zed Head]

I thought that he mixed his bar description with his bushing description.

Either way, "yes, cutting the flange off and pressing the bushing out is how the the two flange style bushings are changed" is the answer, I think.