The other moustache bar bushings - the wavy rubber washers

[Namerow]

This topic picks up on a mini-conversation that I started on Grannyknot's 280Z build thread.

These little washers are an important part of the NVH isolation design for the Z's rear diff.  The design, from an engineering perspective, is a lot more sophisticated than meets the eye, so there's an incentive to try to install a proper replacement if your own have deteriorated (which they probably have, if they're 50-year-old originals).  Unfortunately, the part is NLA from Nissan and none of the primary Z restoration parts suppliers offer a substitute.

There's been some discussion about the need to use vulcanized rubber.  I think that's a red herring (look up, 'vulcanized') and was meant to infer that the rubber part needs to be bonded to the metal part. While the originals might have relied on a heat-bonding process, its now 2019 and we have aerospace adhesives for this purpose.

So:  All we really need is the rubber part.  Steve / Nix240 has cobbledup a wide range of rpreviously unavailable rubber parts for our Z's.  I see nothing special about re-creating the moustache bar runner washers, other than using a suitable durometer rubber and having access to a good-condition original to create a mold.  After that, they could be bonder to a suitable metal washer and, presto, we have another part taken off the NLA list.  I think these washers carry across the entire 240-26-280 series without any differences.  Maybe even the ZX's?

Also:  I'm thinking that the same might be the case for the Series 1's diff front insulator.  Steve creates the rubber piece, then the owner carves the perished rubber out of his insulator, cleans up the metal armature, and then bonds in the new rubber.

@nix240z  Steve:  What do you think?

 

[Patcon]

12 hours ago, Namerow said:

This topic picks up on a mini-conversation that I started on Grannyknot's 280Z build thread.

These little washers are an important part of the NVH isolation design for the Z's rear diff.  The design, from an engineering perspective, is a lot more sophisticated than meets the eye, so there's an incentive to try to install a proper replacement if your own have deteriorated (which they probably have, if they're 50-year-old originals).  Unfortunately, the part is NLA from Nissan and none of the primary Z restoration parts suppliers offer a substitute.

There's been some discussion about the need to use vulcanized rubber.  I think that's a red herring (look up, 'vulcanized') and was meant to infer that the rubber part needs to be bonded to the metal part. While the originals might have relied on a heat-bonding process, its now 2019 and we have aerospace adhesives for this purpose.

So:  All we really need is the rubber part.  Steve / Nix240 has cobbledup a wide range of rpreviously unavailable rubber parts for our Z's.  I see nothing special about re-creating the moustache bar runner washers, other than using a suitable durometer rubber and having access to a good-condition original to create a mold.  After that, they could be bonder to a suitable metal washer and, presto, we have another part taken off the NLA list.  I think these washers carry across the entire 240-26-280 series without any differences.  Maybe even the ZX's?

Also:  I'm thinking that the same might be the case for the Series 1's diff front insulator.  Steve creates the rubber piece, then the owner carves the perished rubber out of his insulator, cleans up the metal armature, and then bonds in the new rubber.

@nix240z  Steve:  What do you think?

 

Steve has been resistant to making rubber pieces for the suspension. I believe the concern stems from liability. However if he were to only supply the rubber section and the owner did the DIY part, then that seems to mitigate that issue. If nothing else, Steve should be able to speak to whether his process would work for these parts.

[Captain Obvious]

How about a couple pics of the wavy washers? That would add a lot to the discussion.

 

[siteunseen]

16 minutes ago, Captain Obvious said:

How about a couple pics of the wavy washers? That would add a lot to the discussion.

 

Just a guess.

Edited June 15, 2019 by siteunseen

[zKars]

Great idea to reproduce these. 

Note that the only difference in the upper and lower washers is the ID of the hole in the middle, as the pin it thicker at the top than at the threaded ended. 

It's fun to visualize how and when those knubs touch and resists the movement of the M-bar as it flexes with diff movement. In the neutral position, the knubs don't touch the bushing eye, but as the bar flexes, the knubs touch and help resist that twisting motion. When the eye bushings wear out, these knubs become primary support for the bar and quickly wear.  

[Patcon]

1 hour ago, zKars said:

Great idea to reproduce these. 

Note that the only difference in the upper and lower washers is the ID of the hole in the middle, as the pin it thicker at the top than at the threaded ended. 

It's fun to visualize how and when those knubs touch and resists the movement of the M-bar as it flexes with diff movement. In the neutral position, the knubs don't touch the bushing eye, but as the bar flexes, the knubs touch and help resist that twisting motion. When the eye bushings wear out, these knubs become primary support for the bar and quickly wear.  

The id's are different on the washers but I was thinking the shape of the washers were slightly different too.

[Namerow]

This snip-out from the 75 280Z FSM provides some insights into what zKars is talking about.  The step at the bottom of the tapered-shank bolt limits the amount of crush/preload applied to the wavy washers...

[Namerow]

A couple of photos, taken by other members, that provide additional illustration of the design and function of these washers...

[CanTechZ]

I find the mustache bar bushing and washer subject quite interesting. The changes that happen over the 1970 to 1973 model years are not very well documented. There are multiple part number for both the bushing and the washers, the later wavy washer part number 55474-N4300 was not introduced until 12/74. The picture in the parts book does not depict this very well. I think the early thin serrated was P/N 55474-21000, only one per side was used, above the bushing.

 

From Service bulletin TS71-18 it looks like the first wavy washer set up was a two piece arrangement using P/N's 55478-E8300 and 55475-E4102, two of each on both left and right sides.

[Namerow]

3 hours ago, Patcon said:

Steve has been resistant to making rubber pieces for the suspension.

As has been pointed out by others, the moustache bar isn't really part of the rear suspension.  It's function is to provide a fixed/flexible rear mounting system for the differential.  None of the (primary) suspension loads feed through the differential.  See diagram below for more understanding.  That said, Steve may find this distinction irrelevant to his overall policy of keeping away from  parts that he feels may have high potential for liability issues.  I guess we'll have to wait to see whether he responds.

 

[CanTechZ]

Here is a picture of the early set up,  thanks @Mikes Z car. Note that the bushing presses into the bottom of the mustache bar. The bottom of the bushing has a flange that is rubber coated and does not have a top flange. There is washer with serrated rubber at the top and a plain steel washer at the bottom.

[Namerow]

1 hour ago, CanTechZ said:

From Service bulletin TS71-18 it looks like the first wavy washer set up was a two piece arrangement using P/N's 55478-E8300 and 55475-E4102, two of each on both left and right sides.

TS71-18 describes a cobbled-up fix that Nissan came up with to address complaints from owners about powertrain noise in Z's with automatic transmissions.  It largely consisted of hanging a big-arse weight off the back to the diff casing.  It also doubled up on the number of wavy rubber washers at each of the 4 places where these are located.  It's interesting to note that the 'teeth' of the new, add-on washers appear to have been designed to interlock with those of the original washers.  That would have really stiffened things up.

Although I haven't checked the parts manual, I doubt whether this dealership service kit ever made it into actual production.  Nissan probably found a more elegant way to solve the problem with the auto-trans Z's (different final drive ratio, maybe?)