Mustache bar bushings

[Captain Obvious]

Here's a dimensioned sketch of the OEM bushing. For those of you who don't want to deal with my chicken scratch, the bottom line is:

OD ~ 1.977
OAL of bushing outer wall ~ 1.575 after installation (1.985 reference before installation)
length of center bolt cylinder ~ 2.565
ID of bolt hole through ~ .677 (clearance hole for 17mm dia bolt shank)

Note that the 40mm after install dimension should be on the inside edges of the bent over flanges instead the outside as it's drawn. I'm no draftsman.

[Captain Obvious]

I copied the bushing info over from the other thread.

Thanks for the links and info. I'm sure there's something that would work. We just have to find it!!

That first bushing from RIdetech looked interesting until I saw the ID. It won't fit over the bolt sticking down.

[Patcon]

9 hours ago, Captain Obvious said:

That first bushing from RIdetech looked interesting until I saw the ID. It won't fit over the bolt sticking down.

I thought it was a little small off the top of my head, but I wondered about drilling it or reaming it out. I believe it was only about 2mm too small...

[Zed Head]

14 hours ago, Captain Obvious said:

I copied the bushing info over from the other thread.

Thanks for the links and info. I'm sure there's something that would work. We just have to find it!!

That first bushing from RIdetech looked interesting until I saw the ID. It won't fit over the bolt sticking down.

That bolt/stud has a taper.  As anyone who got their washers mixed up from the typical PU bushing kit would find out.  Don't know why.

[Dave WM]

maybe a DIY using the old sleeve and inner tube? I tried to find something, could only find people making PU stuff for stiffer bushing. Perhaps a softer rubber compound could be cast into the void?

[Captain Obvious]

Tapered? You got a pic?

My PO put poly in there and I haven't done anything about it yet, so I've never seen it disassembled.

[Zed Head]

No pics but I distinctly remember that the washers that came with my bushing kit had different sized holes.  I put the small one on first and had to take the bar down to swap them because it got jammed halfway up the shaft.

If somebody has a kit they might be able to measure or eyeball.  I think that I have the old factory stoppers out in the garage that might show the same.  I'll dig around.

Edit - found the parts and took some pictures but realize that they don't confirm a taper.  The small  one fits on the step on the end of the shaft, for the nut and washer.  The kits come with a sleeve that fits over the shaft, so the washer with the small hole only has to be smaller than the sleeve hole.  A different system.  Could have been "wear and tear" taper, and the washer that came with the kit, that was only needed to not slide over the sleeve, "almost" made it up the shaft.

Maybe a non-issue.

Edited July 18, 2017 by Zed Head

[Zed Head]

I did measure the hole in the top stopper though.  15.7 mm.  So, approximately the stud/bolt size.

[Zed Head]

Just to add to the possibility, and because it could be a while before anybody gets a chance to actually look at the bolt.  I snipped a few pictures from the carparts site.  The drawing shows line on the mustache bar bolt which seem to indicate a change in diameter, but none on other bolts.  Don't know if it means anything.  Maybe a draftsman knows.  The FSM picture looks like an actual taper, but 2/3 up, with a step.  I've never looked closely at the bolt in the several times it's been exposed.

Now I have good reason to remove one of those bolts if I ever find another Z n a wrecking yard.  They are much sparser now than they used to be just a couple of years ago.

 

[grannyknot]

22 hours ago, Captain Obvious said:

Tapered? You got a pic?

My PO put poly in there and I haven't done anything about it yet, so I've never seen it disassembled.

The 3 Z's I have torn down 1970-72 all had the tapered mustache bar stud like in this pic but I have been helping a guy a few miles from me with his 72 Z and the M/B stud on his is stepped, 2-3 steps, I'll take a pic next time I'm there.

 

[Namerow]

12 hours ago, grannyknot said:

The 3 Z's I have torn down 1970-72 all had the tapered mustache bar stud like in this pic but I have been helping a guy a few miles from me with his 72 Z and the M/B stud on his is stepped, 2-3 steps

The FSM diagram that Zedhead posted is from the 280Z manual, so it's possible that the bolts used for the 240 were stepped rather than tapered.  The fact that Nissan's engineers chose to use a stepped/tapered design rather than a plain old bolt says to me that there's a lot more going on here, NVH-wise, than first meets the eye.  The m-bar 'bolts' are more like pins with threaded ends.  It's an expensive design (compared to a bolt), so it was used for a reason (just like those rubber-ribbed end-washers)

It's a little hard to tell from the FSM sectional diagram, but it appears that only the upper 'special washer' (as the parts manual calls them) bears directly on the shoulder of the pin in the radial direction.  If I'm right, it means that the 'eye' of the m-bar is solidly located (in the radial direction) only at the top, while the bottom 'floats' (in the radial direction) on the rubber of the lower special washer.  It also means that the thick rubber of the big bushing only comes into play (in the radial direction) when the m-bar deflects far enough to bring the inner metal sleeve of the bushing into contact with the pin.  My guess is that this is all about isolating high-frequency differential/gear noise from the chassis under light-load/cruise conditions (via the ribbed special washer), with the bushing only coming into play (laterally) to isolate against cornering-induced vibration (when the diff loads up laterally against the pins).  Kind of a two-step isolator for lateral loads.

In the vertical plane, the special washers and the bushing look they work in unison as a two-mode isolator (that is, they're both at work simultaneously, in series, but have different stiffnesses and natural frequencies and therefore serve to isolate different vibrational frequencies).

Another interesting point (to me, anyway): the FSM refers to the m-bar as a 'transverse leaf spring'.  That suggests that the bar itself is being used as a spring.  The m-bar is only truly flexible in the fore-aft direction, so perhaps it comes into play when the diff is subjected to braking loads.

One final thought:  All of this suggests to me that it's not a good idea to jack up the rear of the car using the diff casing.

 

 

[Captain Obvious]

Thanks for the pics and info guys. I've (thankfully) not yet had to mess with that part of the car and I appreciate the education.

I haven't studied the design at all, but the general concept for all the rubber bushings on the car is that there is no direct metal to metal contact between the two things being connected together. The center metal cylinder would be tightly pinched between the metal of the washers, but the rubber would isolate the outer portion of the bushing.