Questions regarding the function of rubber vehicle body mounts

Hi everyone,
I have some questions regarding the functioning of vehicle rubber body mounts in general, & specifically, rear cab mount bushings for
Chevy K1500 series pickups having conventional two door cabs.
I have included a rapidshare link to a GIF image of an exploded view drawing for reference here...
http://rapidshare.de/files/40737081/Cab_Mount_Bushings_2.gif.html
Referring to the drawing
Part # 58 = Upper rear rubber cab mount bushing or cushion Part # 59 = Lower rear rubber cab mount bushing or cushion Part # 60 = Round steel retainer that goes under the lower rubber cab mount bushing Part # 61 = Cab mount bolt
You can see that the upper rubber cab mount bushing (58) sits on the top side of a steel support bracket that is integral with the vehicle frame. The upper rubber bushing is integral with a steel portion of the bushing. A round / oval shaped steel portion of the upper cab mount bushing extends downward from the underside of the bushing. The downwardly extending steel portion of the upper bushing fits through a hole in the frame support bracket.
The lower rubber cab mount (59) is installed under the frame support bracket, a round steel retainer (60) is positioned under the lower rubber bushing, and a cab mount bolt (61) is used to secure the system to the vehicle frame. The cab mount bolt is torqued to approximately 55 foot pounds.
Regarding the steel portion of the upper rubber bushing which extends down from the underside of the bushing, is this portion of the upper bushing supposed to bottom out on the round steel retainer (60) which is installed under the lower bushing, when the cab mount bolt is torqued down ? Are the two steel components supposed to be in contact with each other when the bolt (61) is torqued down ?
I would appreciate any feedback.
Thanks John
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...
Sad to say, I cannot access the image on account of its sexually explicit nature (!) mount?? bush?? keywords?
Vibration isolation takes two common forms:
cab bracket with through bolt: washer rubber isolator truck chassis rubber isolator washer securing nut
OR
securing nut washer rubber isolator cab bracket rubber isolator truck chassis Through bolt.
Either arrangement is intended to provide no metal to metal direct contact between cab and chassis. I expect your image shows some point of metal to metal contact between the two, which is presumably a drawing error?
Brian W
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Hi Brian,
I uploaded the drawing to a different host, and changed the name to "vehicle". Please see if you can download the file. You will have to actually click download and download the file and then open it. The drawing that shows up when you first go to the page cannot be read, but if you download it, it looks fine.
http://www.mediafire.com/imageview.php?quickkey=scdoztdnzov&thumb=5
I could also email the file to you direct if you still have trouble.
Thanks John
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On Wed, 22 Oct 2008 14:49:56 -0700 (PDT), John2005

I looked at it - it's difficult to be sure but it looks like the rubber doughnuts go round the chassis bracket and the bolt connects to the cab bracket above. Is that what you expected?
Brian W
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Hi Brian,
Thanks for your message.
The upper bushing (58) sits on top of the steel support bracket which is part of the vehicle frame. The lower bushing (59) goes under the support bracket that is part of the vehicle frame. The lower retainer or cup (60) goes under the lower bushing (59). The bolt (61) then goes through the center of the retainer and both the upper and lower bushings, and threads into the weld nut (56) which is mounted to the cab floor.
I did not expect that the lower portion of the upper bushing (58) would be in contact with the retainer (60) after the cab mount bolt (61) was torqued down to specs. However, based on some feedback I have been getting, apparently, the lower portion of the upper bushing is indeed supposed to be in contact with the retainer (60) when the cab mount bolt is torqued down.
Is this correct & is this how the bushings are engineered to work ?
Thanks John
P.S. The bottom of the upper bushing (58) which sit on top of the support bracket that is part of the vehicle frame, is comprised of rubber merged with steel at that point. Therefore, you have metal to metal contact where the upper bushing sits on top of the support bracket that is part of the vehicle frame. I just thought that was interesting as it does not really seem ideal for metal to metal contact at that point, but perhaps with the weight of the cab and forces involved, you need the steel in the upper bushing at that point for strength, as well as the rubber.
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On Wed, 22 Oct 2008 20:24:08 -0700 (PDT), John2005

If I'm getting the right picture, the lower metal piece of the upper doughnut is stationary against the frame, so is not a concern. If it is cup shaped, it can even help prevent squeeze-out on a hard bump.
The more worrisome feature of an antivibration deal is where the through bolt passes through structure - the rubber sheath at this point is thin - and if its worn or cut, the squeaking starts.
Brian W
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