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Panhard V No panhard rod.

Started by rodomo , Dec 30 2007 09:25 AM

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206 replies to this topic

#76 ls2lxhatch

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Posted 13 January 2008 - 10:16 PM

Did I read this or am I dreaming it? Goes something like:

"If you add a panhard rod to a Torana rear end, you are effectively creating 2 roll centres unless the roll centres are in line with each other. If not, expect something to break."

I'm sure I read this somewhere over the last couple of days but buggered if I can find it.

You will find the post here.
http://www.gmh-toran...&hl=roll centre

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#77 rodomo

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Posted 13 January 2008 - 11:07 PM

So I'm not dreaming? Phew, that�s a relief.

I agree with that theory.

So the rule of thumb would be have the panhard height half way between the upper and lower mounts? Perhaps a whisker towards the uppers due to preportion of movement between uppers (less) and lowers (more)? And run rubber on the uppers?

Edited by rodomo, 13 January 2008 - 11:17 PM.

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#78 _82911_

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Posted 14 January 2008 - 12:10 AM

I will have a go at an explanation..... Warning, this stuff can be complicated. So get a cuppa ready!

The problem with adding a panhard rod to a Torana is that the diverging upper arms ALREADY PROVIDE SOME LATERAL LOCATION.
Because they do, that means that they define a roll centre at the Instant centre's vertically projected location. On a standard rear it is up around the middle of the back seat area. As you lower the car it heads further upwards towards the parcel tray area.
Imagine that this point is the pivot (imaginary) about which all axial loads enter and leave the rear suspension. It is also the point about which the whole rear suspension pivots in ROLL.
When you add a panhard rod, the roll centre is now defined by the intersection of the projected lines through which the Instant centre and the panhard rod intersect.This can be up to 12 inches lower!
NOTHING can pivot through 2 centres in the same plane.... It cant happen. So what does happen is that the suspension goes into bind and locks up, causing an unpredictable oversteer characteristic.(scary) This aproach if used with urethane or delrin bushings will eventually tear the rear uppers out of the floor.
Another related problem occurs when you look at where the front roll centre is.... Usually on or close to ground level.
Now imagine the car is on a skewer, and it rolls (rotates) through the front roll centre and the rear roll centre(roll couple).The skewer is pointed upwards towards the rear at probably 20 degrees, so as the car rolls the greater amount of weight jacking both longitudinally and diagonally occurs at the front. This is cause of the dreaded UNDERSTEER that all Toranas suffer with so badly.
It gets waaaaay more complicated from there on in, so i will leave it at that.
If you want to ask a question , most welcome,make it specific so i don't end up writing a novel!

Cheers Greg..

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#79 _rocket_

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Posted 14 January 2008 - 05:08 AM

I guess this why the HDT A9X s, didnt have panhards, just a torsion bar set up.

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#80 _rocket_

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Posted 14 January 2008 - 05:49 AM

Will a watts linkage have the same effect ?

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#81 _82911_

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Posted 14 January 2008 - 08:02 AM

Yes.
Only in the case of a Watts link the roll centre position is the centre pivot bolt.
But the same thing will result, two roll centres= binding.

Cheers Greg..

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#82 TerrA LX

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Posted 14 January 2008 - 08:17 AM

Similar to RODOMO's suggestion of trialgulating the arms, would a track locator (altho dependant on the lower busher still) be a better choice in this case?

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#83 _82911_

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Posted 14 January 2008 - 08:53 AM

A track locator is a vastly inferior method of lateral location and are only acceptable on drag cars.
Notwithstanding that statement if you choose to use one you will still be dfining another roll centre,much lower and in the same plane as the lower axle location arms.
The problem here is not the lateral location devise. It is those Bloody diverging upper arms! :furious:

Cheers Greg..

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#84 Racehatch

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Posted 14 January 2008 - 11:28 AM

Sam you need to add at least one more upper control arm to the diff preferrably on the passenger side to try and cancel some of the squat.

Hey Greg,

Okay, so we go the "clark rubber" super soft (hehe) option on the top arms (effectively negating them) and run an additional upper arm parallel with the lower arms, the question is would one be enough? I would have thought that you would need one on both side to stop torsional twisting through the diff housing under accell?

The other question is, where do you run them off the floor pan, as there isnt much room around the area in question (esp with a 9inch)?

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#85 ls2lxhatch

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Posted 14 January 2008 - 02:09 PM

If you want to ask a question , most welcome,make it specific so i don't end up writing a novel!

Given the problems caused by fitting a panhard bar which setup would you recommend for a race LX Torana and which setup for a street LX Torana.

1. Panhard with standard arms and rubber bushes.
2. Panhard with boxed arms and rubber bushes.
3. Standard arms with rubber.
4. Standard arms with nolathane.
5. Boxed arms with rubber.
6. Boxed arms with nolathane.
7. Something else

Edited by ls2lxhatch, 14 January 2008 - 02:10 PM.

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#86 A9X

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Posted 14 January 2008 - 10:34 PM

Hi Greg.

I appreciate your short but concise explanation.

You left out the end lines...............

The easist way to fix this divergence and its accompanying high roll centre is to........................

feel free to finish the sentence

Welby

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#87 rodomo

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Posted 14 January 2008 - 11:01 PM

The easist way to fix this divergence and its accompanying high roll centre is to........................

Drive a Commodore? :tease:

Runs and hides>>>>>>>>>>>
Who started this dumb thread anyway? :huh:

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#88 _82911_

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Posted 15 January 2008 - 08:59 AM

355LX..... about an inch lower than the centreline of the axle is a good place to start.
Sam.... ring me... 0417 556 202.
LS2LX hatch....
For street:
Urethane lowers (boxed)with rubber uppers (not boxed)
For race....
Depends on the rules???? But if you were allowed to replace all the pick ups then I would just put a Parallel 4 bar under there with a Watts for lateral location.
If you weren't allowed to replace the pick ups..... well that's when the compromises start.
Welby..... who would buy my book if i told you all the how to's here... :tease:

Cheers Greg..

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#89 A9X

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Posted 15 January 2008 - 11:16 AM

Don't worry about the book, tell me where to send the money and pm the answers

:spoton:

Welby

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#90 _Baronvonrort_

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Posted 16 January 2008 - 11:04 AM

The problem here is not the lateral location devise. It is those Bloody diverging upper arms!
Cheers Greg..

Is the geometry of these upper arms better with the UC or A9X?

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#91 _82911_

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Posted 16 January 2008 - 11:27 AM

Welby,
you can PM me with the troubles that your car is having and I will have a look at a possible solution.
Baron,
The whole design is funamentally flawed.
As Rodomo said earlier, it turns your rear end into a set skate board trucks. As the rear end rolls in a turn the outside wheel toes in, this is called roll understeer, something that the factories used to like to build into their cars. It is a SAFE approach as it causes the front to slide before the rear.Most drivers can handle a front slide, it is the rear slides (oversteer) that scares the shit out of people.
The only way this design has any chance of working is to make the top arms parallel to the centreline of the car and make the lower arms the diverging ones. Having done that the lower arms can now be at least 3 times the length of the top arms and roll steer will decrease, but not be eliminated. This is known as the "satchell link"

Cheers Greg..

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#92 _Chamois hatch_

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Posted 16 January 2008 - 08:47 PM

god this is giving me a headache! can someone draw a rough diagram of the above post so i (and others) can wrap my head round it.....

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#93 TerrA LX

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Posted 16 January 2008 - 09:04 PM

Well I've learnt something new out of this thread.

Here is a link with diagrams that shows the basics http://www.afcoracin...s/panhard.shtml

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#94 _Chamois hatch_

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Posted 16 January 2008 - 09:13 PM

just did some googling, all good now sort of......this is one stupid question but if you installed a watts linkage setup would that me you could remove the upper trailing arms all together, or would they have to be retained to hold the diff in place?

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#95 rodomo

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Posted 16 January 2008 - 09:29 PM

It needs them to stop the wheels from driving the axle forward (rather than the car) and twisting the pinion groundwards if that makes sense?

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#96 Toranamat69

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Posted 16 January 2008 - 09:52 PM

You only actually need 1 top arm parrallel with the centre line of the car to stop the diff rotating if using a panhard or watts - infact the 3 link with watts link is the only true zero bind live rear end setup - provided you also use spherical bearings everywhere. 4 link with parallel arms is the next closest.

3 links don't seem as popular as 4 links in racing - if you break a contol arm with a 4 link - you still have a diff which is attached to the car - it would get pretty messy with a 3 link.

GM used the 3 link during the 80's (torque arm setup) before finally going independant.

Now for some more bad news, the top arms are also too short and result in too much change of the instantaneous centre as the suspension moves - rule of thumb is the top arms should be minimum half the length of the lowers which they are not and when you swing them round parallel, they will be poking somewhere into your rear seat passengers' backs weather you use a 3 link or a 4 link - this is fine if you have no back seat in a race car, not so good for round town.

M@

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#97 _rorym_

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Posted 16 January 2008 - 10:32 PM

Thanks [email protected] usual..your knowledge just bamboozles me...I read that 3 times until I got your drift....your talent is wasted...you should be in an F1 team somewhere. :clap: