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I just did a search on the classicopels list for an old reply I made to someone inquiring about bushings for Opels. Much easier than writing it out again!
Bob
From: Manta Rallye [SMTP
[email protected]]
Sent: Saturday, April 13, 2002 12:54 AM
To: classicopels
Subject: [Opel] Suspension bushings
Could someone please give an unbiased viewpoint the pro's and con's of the
different materials used in bushings? Say... Rubber, Poly-Graphite,
Polyurethane, Teflon, Delrin, etc. Everything from ride quality and
handling ability to inherit flaws that may make the material unsuitable for
this application.
Darrin
*****Unbiased? Well, I'll try.
First of all, rubber bushings. This has the best ability to dampen road
noise, impacts, vibration, etc. It costs the manufacturers the least to
produce (in volume). It moves around the most under hard cornering, which
means it allows the alignment specifications to change constantly.For the
most part, it always returns to its' original state when the load it
removed from it. It also "adds" a little bit of spring rate when used as a
control arm bushing. The rubber is bonded to the inner and outer sleeves of
a bushing assembly, so all rotation is by the deflection or twisting of the
rubber between the sleeves.
Polyurethane is by far the cheapest aftermarket bushing material to work
with. Tooling is less expensive for smaller quantities (oem rubber is
cheaper per unit to produce, but only because of the numbers produced,
tooling costs more). Usually the hardness or durometer of polyurethane is
harder than oem rubber, so ride quality in terms of shock absorption is a
little worse. Polyurethane works different from rubber bushings, the inner
metal sleeve will rotate within the polyurethane material to allow for
rotation at a pivot point. Herein lies the problem. IF the inner sleeve is
perfectly smooth (no seams), and the polyurethane is lubricated, the system
works quite well. There is less bushing deflection, so alignment specs stay
consistent. There is also more "feedback" from the road. Enthusiasts find
this "helpful" for handling, whereas purists may find this as more of a
nuisance, since road noise and road irregularities are amplified. Loads in
multiple planes are tougher on polyurethane than rubber, it tends to bind
up the poly (i.e., rotational loads then lateral loads). Once lubricant is
displaced from a poly bushing, it tends to bind up and squeak. I always
install zerk fittings in poly bushings so I can grease them with teflon
based grease. Otherwise, the sleeves may bind in the bushings and tear the
polyurethane. Still, this material is the most widely used for aftermarket
bushings, as it is affordable for the consumer.
Poly-Graphite is one manufacturer's solution to the problems associated
with polyurethane. They impregnate the polyurethane with graphite so it is
in effect "self lubricating" (boy, this is turning pornographic). This
lessens the effect of binding the poly bushing if the grease is displaced.
It seems to help somewhat (I have these on other cars I own), but is not a
stop-all. Grease is still required.
Hard plastics. A lot of companies, especially in Europe, make hard
bushings for sport use. They use Delrin, Acetal, Nylatron, Teflon, etc.
They all have their ups and downs. Delrin, Teflon, Acetal and Nylatron all
tend to "cold-flow", that is, they eventually will change shape under load.
Also, with the exception of Teflon, they all absorb moisture to some
degree, and will dimensionally change due to expansion. This will bind the
bushing and make the inner sleeve fit tighter. So driving in the rain is
bad with these bushings! But they all are harder than polyurethane is, so
there is even less deflection under cornering loads and therefore more
precise alignment is kept. Ride quality lessens in the sense that impacts
are transmitted more readily, however in some conditions the ride quality
can improve, because in rotation, the friction is lessened (unless wet),
allowing the control arms to move more freely than rubber (which has to
fight the twisting effect of the bushing).
Okay, here's where the bias comes in. I like using Delrin AF. It's Delrin
with teflon. Always brown in color, and always costs about three times the
price of the other plastics mentioned above (for the raw material).
Machining costs are about the same, but the best way seems to be to freeze
the material first, then machine quickly! I guess the teflon makes it
slippery enough to make machining more difficult, freezing it helps out.
This plastic does not cold-flow as much as the others listed, does not
absorb moisture, and lasts WAY longer under duress (racing use).
Technically, it doesn't need ANY grease, but I still add grease fittings
anyway. Does not squeak, and rotates nicely too. I always use new seamless
inner sleeves too. So, the cost is definitely higher overall. BUT, I found
that for (Opel)racing use anyway, rubber moves around too much,
polyurethane wears in 2 - 3 races, Delrin in 8 - 12 races, and Delrin AF in
about 40-50 races. So cost is actually cheaper for my intended use. Go to
http://www.opelgt.com/forums/showthread.php?s=&postid=836#post836 to see
a worn rubber bushing and replacement Delrin AF bushings, as mentioned
above.
Bob Legere
Mod edit: Corrected the forum link URL
Bob
From: Manta Rallye [SMTP
[email protected]]Sent: Saturday, April 13, 2002 12:54 AM
To: classicopels
Subject: [Opel] Suspension bushings
Could someone please give an unbiased viewpoint the pro's and con's of the
different materials used in bushings? Say... Rubber, Poly-Graphite,
Polyurethane, Teflon, Delrin, etc. Everything from ride quality and
handling ability to inherit flaws that may make the material unsuitable for
this application.
Darrin
*****Unbiased? Well, I'll try.
First of all, rubber bushings. This has the best ability to dampen road
noise, impacts, vibration, etc. It costs the manufacturers the least to
produce (in volume). It moves around the most under hard cornering, which
means it allows the alignment specifications to change constantly.For the
most part, it always returns to its' original state when the load it
removed from it. It also "adds" a little bit of spring rate when used as a
control arm bushing. The rubber is bonded to the inner and outer sleeves of
a bushing assembly, so all rotation is by the deflection or twisting of the
rubber between the sleeves.
Polyurethane is by far the cheapest aftermarket bushing material to work
with. Tooling is less expensive for smaller quantities (oem rubber is
cheaper per unit to produce, but only because of the numbers produced,
tooling costs more). Usually the hardness or durometer of polyurethane is
harder than oem rubber, so ride quality in terms of shock absorption is a
little worse. Polyurethane works different from rubber bushings, the inner
metal sleeve will rotate within the polyurethane material to allow for
rotation at a pivot point. Herein lies the problem. IF the inner sleeve is
perfectly smooth (no seams), and the polyurethane is lubricated, the system
works quite well. There is less bushing deflection, so alignment specs stay
consistent. There is also more "feedback" from the road. Enthusiasts find
this "helpful" for handling, whereas purists may find this as more of a
nuisance, since road noise and road irregularities are amplified. Loads in
multiple planes are tougher on polyurethane than rubber, it tends to bind
up the poly (i.e., rotational loads then lateral loads). Once lubricant is
displaced from a poly bushing, it tends to bind up and squeak. I always
install zerk fittings in poly bushings so I can grease them with teflon
based grease. Otherwise, the sleeves may bind in the bushings and tear the
polyurethane. Still, this material is the most widely used for aftermarket
bushings, as it is affordable for the consumer.
Poly-Graphite is one manufacturer's solution to the problems associated
with polyurethane. They impregnate the polyurethane with graphite so it is
in effect "self lubricating" (boy, this is turning pornographic). This
lessens the effect of binding the poly bushing if the grease is displaced.
It seems to help somewhat (I have these on other cars I own), but is not a
stop-all. Grease is still required.
Hard plastics. A lot of companies, especially in Europe, make hard
bushings for sport use. They use Delrin, Acetal, Nylatron, Teflon, etc.
They all have their ups and downs. Delrin, Teflon, Acetal and Nylatron all
tend to "cold-flow", that is, they eventually will change shape under load.
Also, with the exception of Teflon, they all absorb moisture to some
degree, and will dimensionally change due to expansion. This will bind the
bushing and make the inner sleeve fit tighter. So driving in the rain is
bad with these bushings! But they all are harder than polyurethane is, so
there is even less deflection under cornering loads and therefore more
precise alignment is kept. Ride quality lessens in the sense that impacts
are transmitted more readily, however in some conditions the ride quality
can improve, because in rotation, the friction is lessened (unless wet),
allowing the control arms to move more freely than rubber (which has to
fight the twisting effect of the bushing).
Okay, here's where the bias comes in. I like using Delrin AF. It's Delrin
with teflon. Always brown in color, and always costs about three times the
price of the other plastics mentioned above (for the raw material).
Machining costs are about the same, but the best way seems to be to freeze
the material first, then machine quickly! I guess the teflon makes it
slippery enough to make machining more difficult, freezing it helps out.
This plastic does not cold-flow as much as the others listed, does not
absorb moisture, and lasts WAY longer under duress (racing use).
Technically, it doesn't need ANY grease, but I still add grease fittings
anyway. Does not squeak, and rotates nicely too. I always use new seamless
inner sleeves too. So, the cost is definitely higher overall. BUT, I found
that for (Opel)racing use anyway, rubber moves around too much,
polyurethane wears in 2 - 3 races, Delrin in 8 - 12 races, and Delrin AF in
about 40-50 races. So cost is actually cheaper for my intended use. Go to
http://www.opelgt.com/forums/showthread.php?s=&postid=836#post836 to see
a worn rubber bushing and replacement Delrin AF bushings, as mentioned
above.
Bob Legere
Mod edit: Corrected the forum link URL
