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EF Ian

Solid Moustache Bar, Disadvanatages/ Advantages?

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EF Ian    10

I'm thinking of running some AZC components in the rear, moustache bar, dog legs and cross brace to enable me to fit a finned diff cover and run a rear mount ARB so I can extend my frame rails.

 

 

What are the disadvantages of running a solid moustache bar? I may be wrong but is the original not designed to be slightly flexible and act as a sort of spring. If this is the case what do you loose by running a solid one? What do you gain? Nothing?

 

 

 

Can anyone running this setup let me know if its heavier or lighter than the stock setup?

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whatnow123    0

I have one, no idea what the disadvantage would be. It's also got to be lighter than the steal MS bar.

 

 I also have the front of the diff pinned with a snubber, that made a difference! The front of a long nose diff moves considerably up with some HP tossed at it. With an IRS rear, I would assume you'd want the diff not to move at all, or very little with rubber mounts. I think the factory mounts were just a poor design but was adequate for the HP the stock engine S30's were tossing at it.  

Edited by whatnow123

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johnc    724

By mounting the mustache bar solidly you are moving the majority of the loads into the mustache bar mounts and the rear diff cover.  Depending on power and tire size/grip you can start cracking in those areas.

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whatnow123    0

Just to clarify my set up, my Arizona Z MS bar is has the poly bushings where it mounts at the body (just like the stock bar) as well as the stock rubber mount at the bottom of the diff nose. It is pinned in place by another poly bushing on the upper nose of the pinion to keep it from lifting much, so it's not a solid mount diff, but it does minimize movement.

 

I do agree with John, it shouldn't be a solid mount as anything that vibrates compounded with mass will eventually crack somewhere.

 

I think the question is the solid aluminum bar VS the flexing of the stock bar. I don't think this would be an issue provided the mounts to the body and front diff mount are allowed some movement via bushings.

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EF Ian    10

whatnow123 - You say its got to be lighter, but its a good bit thicker than the steel one so I doubt there a huge amount in it.

 

I also have a pinion snubber, wouldn't be without one.

 

 

Technically its not solidly mounted as it still mounts with poly bushes, however the bar itself will not flex like the stock ones does. What I am asking is what you said, solid bar vs semi flexible spring like bar both mounted with poly bushes. I would imagine that even if the bushes give some movement, there will still be a lot more load on the parts John mentioned.

 

 

 

 

svMike - I imagine his will be similar to mine, have a look at technoversions website.

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NewZed    56

Didn't Nissan go essentially solid with the ZX system?  Only rubber bushings damping slight movement, with rigid metal attachment points.  The mustache bar system seems unbalanced from a design view - the front rubber-metal sandwich allows much less movement than the mustache bar.  It gets overworked.  Probably why they wrapped a belt over the top of the diff nose, to help out.  Could also be that the mustache bar wasn't put there for the diff, or for ride quality, but to take loads off of the body mounting points.  Maybe it started out solid and they went to the bushed spring as a fix for other problems.  Overall, the Z diff mount system is an odd collection of parts.

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z240    14

By mounting the mustache bar solidly you are moving the majority of the loads into the mustache bar mounts and the rear diff cover. Depending on power and tire size/grip you can start cracking in those areas.

The ZX and 510 semi trailing arm suspension simply makes the long bar that the control arms and diff nose attach to, into the equivalent of the S30 mustache bar, it just happens to be at the front of the diff. Its mounted to the chassis the same way our M-bar is, with bushings on a body pin. Same same, not odd, just kinda backward. ZX ties the suspension hanger and M-bar together, rather elegant I thought.

 

The point of these things, either kind, is to use a long bar to transmit the twisting diff torque to the body. The other end, nose on s30, and tail on zx/510 just need to be held steady from lifting/dropping, so need a simpler lighter mount. The 510 actually has a little m-bar on the back of the diff, total overkill, but that's why they work so well... Oh right, Z forum, back on track, sorry...

 

The bushings at the ends of the Mbar are for noise isolation and vibration damping and to remove the stress related solid mount failures that John alludes to.

Edited by z240

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NewZed    56

The ZX and 510 semi trailing arm suspension simply makes the long bar that the control arms and diff nose attach to, into the equivalent of the S30 mustache bar, it just happens to be at the front of the diff. Its mounted to the chassis the same way our M-bar is, with bushings on a body pin. Same same, not odd, just kinda backward.

Can you really see that rigid cross member as like the loose, floppy leaf spring of the Z?  Seems a stretch.

 

I missed johnc's comment, and repeated something similar in my post.  Funny though, a lot of time is spent on making the unibody more rigid, with bracing and roll cages, but the mustache bar mounting points seem like obvious areas to mount a rigid cross-member to, for stiffening the body.  In the bigger picture maybe the Arizona bar should be mounted rigidly (get rid of the urethane donuts on the ends), and the elastic dampers (urethane or rubber) should be placed at the diff, like in the ZX post mount.  Stiffen the tail of the box, but keep a little bit of damping at the diff.

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TimZ    21

Can you really see that rigid cross member as like the loose, floppy leaf spring of the Z?  Seems a stretch.

 

I missed johnc's comment, and repeated something similar in my post.  Funny though, a lot of time is spent on making the unibody more rigid, with bracing and roll cages, but the mustache bar mounting points seem like obvious areas to mount a rigid cross-member to, for stiffening the body.  In the bigger picture maybe the Arizona bar should be mounted rigidly (get rid of the urethane donuts on the ends), and the elastic dampers (urethane or rubber) should be placed at the diff, like in the ZX post mount.  Stiffen the tail of the box, but keep a little bit of damping at the diff.

One thing possibly worth noting is that the mustache bar arrangement allows considerably less rotational movement of the diff in the roll axis, compared to what you would likely get if you put the bushings at the diff itself.  Not only does the longer lever arm limit the amount of angular movement for a given bushing deflection, the force on the bushing is correspondingly lower with the longer lever arm, resulting in less bushing deflection in the first place.

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NewZed    56

That's a good point.  Considering the extra mounting holes in the front of the long nose that aren't used though, and the modifications to the bar end bushings after a year or two in the 240Z, and the big chunk of iron they strapped on to the bottom of the cross-member later, I'm still seeing a cobbled together system that they never really got right.  If a person has never been under a Z, like I hadn't when I got mine, when you first get a look at all of those parts, there's a lot of time spent thinking "what the heck were they trying to do here".  I'd bet the first prototype cars had a more solid mount but the diff howling and clunking inside the unibody tin can was just too much to stand.  Then they started cobbling.

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EF Ian    10

^^ What is the purpose of that big weight under the diff? I removed mine and never noticed any difference. ^^

 

 

 

Verdict so far seem to be that a more solid bar won't have any drawbacks. Has anyone broken an AZC or similar bar?

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TimZ    21

^^ What is the purpose of that big weight under the diff? I removed mine and never noticed any difference. ^^

 

It's a "tuned mass damper".  Basically they found an NVH issue really late in the game, and this was a quick and dirty way to address it.  Presumably there was something in the rear suspension that was resonating audibly at some speed range.  Adding the mass lowers the part's resonant frequency to a range where it no longer gets excited under normal use.  

This is actually a really common practice and still happens today - it's not the most desirable solution but if it's two weeks to launch it starts to look like a really good idea...

Edited by TimZ

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