| [GMCnet] Rear shock calibration [message #110768] |
Tue, 04 January 2011 08:06  |
Gary Casey
Messages: 448
Registered: September 2009
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The shock absorber calibration on most cars is such that there is much more
damping on rebound than on compression, or "jounce." The purpose is to reduce
the shock transmission to the body when hitting a bump, but still controlling
the body motion. So it turns out that stiff damping on rebound is less
disturbing to the occupants than on jounce. Many shocks are "90/10" or 9 times
the force one rebound as on jounce. Race cars often have 50/50 calibration
because they don't care if the driver complains about the ride. Most shock
valve systems have a combination of check and relief valves to accomplish this.
Question: The rear shocks on the GMC work the opposite of car shocks in that
jounce extends the shock instead of compressing it. Do the manufacturers
reverse the valving to increase rebound damping or do they ignore the difference
and just build a standard shock? I suspect the latter, but I have no idea.
Gary Casey
'73 23' with Bilstein shocks
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| Re: [GMCnet] Rear shock calibration [message #110813 is a reply to message #110800] |
Tue, 04 January 2011 18:09  |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
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| Gary Casey wrote on Tue, 04 January 2011 14:21 |
thanks, Charles.
Very interesting - the KYB shocks are of mono-tube design, a very good thing,
and they are very non-symmetric in their performance, another good thing. But
the graphs published don't give a clue as to whether the high damping is during
the compression or extension stroke. The part numbers of the front and rear
shocks are different by only one number, but that probably doesn't mean anything
one way or the other. But a mono-tube shock would have trouble getting much
damping in the compression direction, I think. And that's what we want for the
rears.
Gary Casey
KYB shock information.
http://www.bdub.net/publications/kyb.jpg
Charles
Gary--you're absolutely right about the rebound vs jounce damping. I'm not sure if anyone really knows exactly what the KYB shocks offer us other than most of us like them. The other aspect is that most shocks have different damping settings based on velocity, and although not totally independent, there is a lot of latitude. Years ago, I used to valve shocks myself using take apart units. It's a lot of fun but time consuming. These years I have a lot more fun drinking margaritas by the pool!
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Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Rear shock calibration [message #110836 is a reply to message #110800] |
Tue, 04 January 2011 20:29 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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| Gary Casey wrote on Tue, 04 January 2011 13:21 |
... But
the graphs published don't give a clue as to whether the high damping is during
the compression or extension stroke. The part numbers of the front and rear
shocks are different by only one number, but that probably doesn't mean anything
one way or the other. ...
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I did a web search on the rear shock part number. (KG 5436)
I am surprised by how many sites carry this shock, but the only application I could find was "1973 to 1978 GMC motorhome (4 needed for rear)"
I am thinking as long as the only application is our motorhomes, the shock is set up correctly for us.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] Rear shock calibration [message #110840 is a reply to message #110836] |
Tue, 04 January 2011 20:45 |
Charles
Messages: 455
Registered: January 2004
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Contact KYB. They were very open when I contacted them
several years ago. At that time we discussed venting
and GMC application. It was during that conversation I
acquired the brochure that is on bdub.net. No other
shock manufacture would discuss venting.
Charles
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Charles Wersal
Duncanville, Texas
26 foot 1975 Glenbrook
Pandora's Box
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