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Extended spring perches?
Posted: Tue Mar 10, 2015 10:06 pm
by d_r_1989
Iv been told by a landrover friend that on the series they would extend the perches to help prevent axle wrap, by chance I came across a thread on diff lock and that was debating the need for anti wrap bars. In this thread someone stated that longer perches help but increase the spring rate due to more contact on the spring. Does anyone have any first hand knowledge of this? I like the idea but don't want to lose flex or comfort as I seem to have found a perfect (to me) balance.
Re: Extended spring perches?
Posted: Tue Mar 10, 2015 11:37 pm
by ScottieJ
Yes they can help reduce axle wrap, however in the words of Tim pink, easier than me writing it and he sums it up well (probably from the same thread that you found)
Tim Pink wrote:"Longer perches reduce flex"
True in one sense, longer perches reduce the effective length of the spring increasing its rate thus reducing travel for a given load. Assuming that you increase the load to flex the spring the same you will increase the stress within the spring possibly past its failure point
"Longer spring perches do help as the surface of the perch is spread further along the spring, meaning it will take more torque and leverage to 'twist' the springs"
Separating cause and effect is difficult with this statement, If a short perch has no movement between it and the spring then the only effect of a longer perch is to increase the spring rate as detailed above.
I ran superflexy low rate springs on the racer with 3" perches to reduce the dead zone in the springs. I had a tuned 16v and had no axle tramp even when side stepping the clutch at 3500 rpm. (I used this as a startline technique for a couple of races, in the end I decided it was just too hard on the driveline for the gains)
Personally I would rather run shorter perch and a well made anti wrap bar, it's the best way to maximise spring life and flex.
Re: Extended spring perches?
Posted: Wed Mar 11, 2015 6:57 am
by d_r_1989
Cheers Scottie. Ye that's what I had read, what length are the standard perche's do you know?
Re: Extended spring perches?
Posted: Wed Mar 11, 2015 7:12 am
by mike harris
I'm so against anti wrap bars !
Just fit good quality springs !
All of these setups that wrap always use stock springs, I run missing ok is and don't wrap up !!
Sorry in advance
Mike
Re: Extended spring perches?
Posted: Wed Mar 11, 2015 8:03 am
by ScottieJ
mike harris wrote:I'm so against anti wrap bars !
For what reasons? Without one you will always get some axle wrap on leaf springs no matter what springs you use, it's not something you can often tell is happening from the drivers seat unless it's really bad.
Even if the diff nose only raises or dips a few mm during initial acceleration or changes in speed/torque loads that's still axle wrap.
Maybe we should list the pros and cons of an anti wrap bar and let the individual decide if they want to fit one or not. Yes you don't have to run an anti wrap bar, but there are many benefits and they will increase spring life, especially if you want to run softer more supple springs to help with flex and ride comfort.
Re: Extended spring perches?
Posted: Wed Mar 11, 2015 9:40 am
by timwilks13
Im with Mike, hate anti wrap bars. Part of owning an SJ is the one to one time you get to spend with them in the garage, and not running anti-wrap bars gives you all that extra time in the garage replacing knackered springs!
Re: Extended spring perches?
Posted: Wed Mar 11, 2015 10:54 am
by twiss
You cant talk tim you abandoned your SJ and left it to die.... a truck is for life not just for christmas!
Re: Extended spring perches?
Posted: Wed Mar 11, 2015 4:47 pm
by Anton
I want to make a set of anti-wrap bars. Why are you againt them, Mike?
Re: Extended spring perches?
Posted: Wed Mar 11, 2015 6:20 pm
by d_r_1989
Ok as the 'individual'
I want a list of pros and cons please. My rear springs are bedford rascal springs with the top leaf changed for one of my unknown spares which is slightly longer than standard giving me good flex. Got to say the comfort and flex is really good. Can't say I have wrap at the minute as the axle will pivot because of the spring perche's.
Iv heard that if you use an anti wrap bar it can break the axle casing?
Re: Extended spring perches?
Posted: Wed Mar 11, 2015 6:42 pm
by ScottieJ
Maybe a badly designed anti wrap could, it wouldn't really break the casing but if not made well I guess it could bind and rip the axle case open.
Cons...
1.Takes some time to fabricate
2.A bad design could limit flex (so can remove this if it's designed well)
Pros....
1.Reduces axle wrap and this...
a. increases spring life
b.increases UJ life
2.Reduces axle tramp providing more positive drive.
3.No need to run heavy duty springs
4.No need to run long spring perches that increase the "dead zone" of the springs
5.Less twisting force on the perches during hard acceleration
Anyone think of any others? So basically there aren't really any cons unless it's designed badly.