I received another set of PU lower control arm bushings today, these from Whiteline (Australia). A durometer (hardness) check says they’re significantly harder than the Polybush I previously tested. I haven’t been able to complete a rate (stiffness) test as the test fixture I used for the original bushings won’t hold them steady. That’s probably an answer in itself, I need to modify the fixture to get some numbers. More later (inevitably).
My thinking is they might work well in the front leg (only) of the LCA , where they could add some
steering precision and response. I’d be wary of fitting PU throughout the suspension, I think they would reduce the total damping and could give a rather loose, “rattly” ride feel - less plushness and composure than with rubber bushings. Pure conjecture as usual.
You really need to drive one…as iv mentioned before not all PU bushes are the same…iv fitted Black Polybush to several cars…definatly no “loose rattly ride feel”…Steve
Yes, I really want to get in one, maybe when I go to Utah in the summer to help Peter finish the modified car we’ve been working on.
My speculation about ride feel was based on expectation that the PU bush would have higher stiffness than the rubber ones, added to the lower inherent damping of PU. (High stiffness + low damping implies low control).
My testing suggests the Polybush LCA bush is actually softer than the original rubber so I could believe the damping will be less of a factor.
(That’s not complete guesswork, I’ve worked on similar situations on other cars).
That’s one reason I’d be inclined to keep a bit of rubber in the suspension, to retain some “flow down the road” feel from the natural light damping of the rubber. The upper control arm bushes would be an obvious place as the cornering loads are typically low enough that their stiffness isn’t too important for handling.
I would personally leave the LCA rear bush standard Jaguar rubber, working with a stiffer PU front bush such as the Whiteline to generate some side-force understeer - gives a good feeling to “lean on” as the car tightens in to the turn.
I’d probably put some PU bushes somewhere in the antiroll bar system if they were stiffer than the rubber ones - that typically gives a crisper turn-in feel.
The above steps follow general industry rules of thumb. They could expose some of the weirdness in the E-type suspension, charts available for the truly dedicated.
Not an E but a series 11 XJ the front AR bar rattled like crazy, mostly due to the poly bushes having completely disintegrated. Disclaimer; I was given the car in this condition so never drove it while they were newly installed
Perhaps I should have used the word “rattly” more carefully. I was trying to describe a feeling, not a sound. A feeling. of light “jiggle” over small road inputs such as concrete with rain grooves or coarse asphalt. Small disturbances that can be irritating if not damped. Rubber is good at that so removal of all rubber carries some risk.
That risk would probably be reduced where the Polybush items are actually softer than the original rubber, as in the lower control arm.
A general question, why do people fit PU bushes? I assumed it was to get higher stiffness than typically available with rubber, but that’s not the case with the Polybush items I measured. Is there another advantage?
Largely, and in my humble opinion, it’s because they believe they’re so much better than the rubber bushes.
I’ve run both in my prototypical Datsuns: I can guarantee you that the same car, one with stock rubber bushings, and one with polyurethane, and in some cases, Delrin bushings, provided a much harsher ride, and a demonstrably much more immediate feedback loop.
I think that for what the E-type was intended to be, and that is a grand touring car, what it came with from the factory was optimal.
Going beyond that may increase the handling capabilities of the car, but I’m not convinced that they will do anything but make it a harsher riding car. I know you haven’t driven an E type, yet, but one of its outstanding features is the marvelous and well-controlled ride that it has.
PU/Delrin: Fine for a race car, Ugly for a street car.
Hi Paul…this is why i said more than once that not all PU bushes have the same performance or work in tne same way…the Black Polybush (manufactured by Polybush) are soft material and acording to the manufacturer are as near as equivelant to the original rubber as they could manufacture…they also fit the same as originals so are “gripped” in the wishbones and shaft and twist as the wishbone moves up/down…as Clive found out in his test they were slightly softer that Jaguar originals…they do give a good ride…iv used them on several cars…then we get to the much harder type of PU bush that really does give a harsh ride…,some also fit different they are not designed to “grip” in the wishbones …even supplied with silicon grease so they can revolve in the wishbone and on the shaft…and the reason that some members have had and complain about PU bushes squeeking and needing to grease them…If we just use the term PU bushes then comparing Delrin with black Polybush is like chalk and cheese…Steve
Hi Clive…so why do some fit PU bushes…going back quite a few years the original metalastic bushes became no longer availabel…and the quality of aftermarket “rubber” bushes was questionable. …so alternatives were looked for…so PU became an option…what you need to remember is that most owners are the actual restorer. .they buy an old car that needs a refurb…suspension needs doing…whats being said on forums…orginal metalastic rubber not available,…the rubber option are not good and dont last…so they try PU…if you were lucky you did a bit of research you went for a PU product that resembled the original rubber…if you didnt then who knows what PU product you chose then the chatter on forums with some liking their PU and some not…much the same today…only aftermarket rubber options or PU…Steve
Exactly Clive…lets not forget the thread title…“Getting the best out of standard suspension components for touring driving today”…youve got your E type and refurbing it…you want parts now to get it back on the road…so what options off the shelf do you have to get the best out of it…you look on the forums make you choice and off you go…Steve
I’d say “generally” for perceived handling benefit.
However, PU bushings are often at least advertised as lasting much longer than rubber. In fact I have a 2005 Bentley Arnage in need of some front suspension work, and one of the leading suppliers offers a poly bushing conversion. They have assured me that they are specing the bushings to be identical to factory from a ride/handling perspective, but with 3 benefits vs factory items
Much lower cost
No special tools needed for installation as they slide in vs needing to be pressed in
Much longer life than factory rubber (Arnages are known for quickly wearing front suspension bushings)
