Mustache bar bushings

[Jason240z]

No I know theres a thread!

So whats your thoughts on going for something like 70Sha poly bushing?

[Namerow]

3 hours ago, Jason240z said:

No I know theres a thread!

So whats your thoughts on going for something like 70Sha poly bushing?

Consider these points:

• The rubber in the OE bushing is softer than polyurethane
• The OE bushing design uses a voided core.  The poly bushing is solid.
• The OE design for the MB mount uses not just the main bush, but also special rubber-faced end washers with a ribbed design.  The aftermarket poly bush set-up uses plain steel washers.

If you go with the poly bushings, they should locate the MB just fine.  However, you'll probably experience more 'gear noise' coming through into the cabin.  More noticeable under highway cruise conditions than around town, I would expect.  Impossible to say just how much more until you try it.  If you do, let us all know how it works out.

[Jason240z]

23 minutes ago, Namerow said:

Consider these points:

• The rubber in the OE bushing is softer than polyurethane
• The OE bushing design uses a voided core.  The poly bushing is solid.
• The OE design for the MB mount uses not just the main bush, but also special rubber-faced end washers with a ribbed design.  The aftermarket poly bush set-up uses plain steel washers.

If you go with the poly bushings, they should locate the MB just fine.  However, you'll probably experience more 'gear noise' coming through into the cabin.  More noticeable under highway cruise conditions than around town, I would expect.  Impossible to say just how much more until you try it.  If you do, let us all know how it works out.

I've thought about those points, the lower shore polybush is an easier fix, most are about 85sha, going for 70 is about 20% softer and comparable to a metalastic arrangement(nominal).  I've got a couple of UK companies looking into it for, to to replicate the oem one.  Might have to be a 'group buy' as I might not need 40odd kits myself

[Namerow]

Some additional photos to support the view that the OE design for the MB mount insulators is 'special'...

[Jason240z]

Interesting.

 

I've got this company on the case for us.

 

http://robush.com/

[Jason240z]

I'm looking to see if you can get those washers also?

[Namerow]

5 minutes ago, Jason240z said:

I've thought about those points, the lower shore polybush is an easier fix, most are about 85sha, going for 70 is about 20% softer and comparable to a metalastic arrangement(nominal).  I've got a couple of UK companies looking into it for, to to replicate the oem one.  Might have to be a 'group buy' as I might not need 40odd kits myself

A few more thoughts before I head off to work...

In the end, it all comes down to finding something that works effectively.  The Shore hardness ratings for the poly bush would be easier to interpret if we knew what they mean in terms of relative stiffness (related, but not the same as hardness) vs. the OE rubber bush.  If there's someone out there who has a good-condition OE bushing and wants to do a little testing for the greater good of the rest of us, they could perform a simple deflection test by clamping the outer casing in a horizontal mount (use a bench vise and a carpenter's bubble-level) and inserting a tight-fitting long bolt or steel rod into the inner sleeve.  Then hang a 2-lb weight off the end of the bolt/rod at a measured distance from the end of the sleeve (i.e. known lever length) and measure the bolt/rod deflection (at a known distance from the end of the sleeve) with a dial indicator.  You could then perform the same test with your poly bushing, to generate some relative-stiffness information.

If the 70sha poly bushing comes close-but-not-close-enough to the stiffness of the OE bushing, it's possible that it could be fine-tuned by drilling some end-to-end holes through the polyurethane (similar to the internal voids in the OE bushing).

If the poly bushing looks promising, there will still be the matter of cobbling up a reasonable facsimile of those special end washers.  As I said earlier, I think this can be done.

[Namerow]

2 minutes ago, Jason240z said:

I'm looking to see if you can get those washers also?

I believe I read that the end washers are also NLA.

[Jason240z]

1 minute ago, Namerow said:

I believe I read that the end washers are also NLA.

it never rains!! I think thats an easier fix though.

[Captain Obvious]

Here's a rough chart that can give you an idea of the relative hardness of rubber and poly:

My thought on poly replacements is they are (obviously) better than nothing,  but will never be as compliant (or quiet) as the original system. With the original system, the only points of contact are through the rubber bridge of the bushing, and the raised tips of the rubber on the flat washers. With poly, you usually have much more contact. At least that's the case with the current design poly bushings.

Also, I'm not sure about the flexing abilities of poly. By that, I mean, I know what happens to rubber when it flexes and flexes and flexes a whole bunch of times... Pretty much nothing. But what happens to poly when you flex it a couple thousand times? I suspect it cracks a lot more readily than rubber of the same durometer.

So the tipping point would be to make it as soft as possible without it being soft enough to bend enough in application to cause it to fatigue and crack.

[EuroDat]

3 hours ago, Jason240z said:

Interesting.

 

I've got this company on the case for us.

 

http://robush.com/

Im interested in hearing what they say. I have used their fkm and isolast products a lot and they have made special parts for the company I work for in the past. Set-up costs will be the main hurdle.

Captain Oblivious posted a schetch of the centre bushing, but has anyone made a schetch of the washer ends? I have a set of washers that are still in good condition.

[Captain Obvious]

I've never seen a good dimensioned sketch of the washer ends. I'd be interested if you want to make one up!

Are the two stock washers the same, or did they have different hole diameters in the middle to account for the bolt they ride on?