Vk Rear Suspension

[VK SL 3800]

Ok, i have read all about having to get adjustable panhard rods when you lower you commodore but my VKs rear end has decided to sag recently (about 1.5 inches lower than normal), it has moved the diff over about 15mm to 20mm. Does this mean every time you hit a bump with standard springs the rear end is moving over like this?
They are standard springs.

 

[ari666]

lets imagine for a second that you had no springs at all in the rear. and on the buffer stops your rear passenger side wheel sticks out about 30mm then jacked up to 200mm off the ground, your wheel sticks out 30mm from the drivers side. then half your height and your wheels would be perfectly center.

making sense?

so however much you cut off your spring (or they just "sagged" of their own accord... whatever) expect that to be sticking out of the passenger side wheel. its like an arch. adjustable panhards just re-center your wheels for whatever new height you have decided to cut your springs to.

but yes. the answer to your question is yes, everytime your wheels go up and down, they also go side to side due to solid axles and a panhard rod.

 

[DANNY8]

Could adapt up a watts linkage setup....we're thinkin bout doin that with our race car. Then no matter how far it goes up or down (to a certain extent), the wheels stay in the middle.

Going to all the trouble to do that is prolly a bit o****ill for a street car tho.

 

[VK SL 3800]

mmmmmmm, ok it all makes sense now thanks

 

[Darren_L]

Could adapt up a watts linkage setup....we're thinkin bout doin that with our race car. Then no matter how far it goes up or down (to a certain extent), the wheels stay in the middle.

Going to all the trouble to do that is prolly a bit o****ill for a street car tho.

I've thought about doing the same thing, but have since have sorted out the major bump steer issue I had with the back end. Plus it would need a mod plate etc, which I can't be bothered with. I've seen a couple of live axle street driven Commodores converted to watts link. Good setup. The V8 Supercars all run a watts linkage.

but yeah back to the original post, the panhard rod system used on the Commodore is a very compromised system. The axle will move laterally over bumps in the road - causing 'bump steer' in the rear of the car. However an adjustable panhard rod improves the effect dramatically on a lowered car. My axle wasn't even far off centre after lowering, yet the back end used to jump/skip to the side when cornering over anything that wasn't a perfectly smooth surface. It induced unpredictable handling, really unsettled the car, sometimes it would throw the car into bad oversteer. I finally bit the bullet and fit an adjustable panhard rod (honestly didn't believe it would do much to rectify the problem as my axle was only off centre by a few mm). But the difference was amazing. I think what also helps is most of the adjustable panhard rods are constructed of a much heavier gauge material. The standard rod, when used in conjunction with more solid suspension bushes, I suspect flexes under load which gives a springback effect on the axle, which could account for the radical behaviour.

 

[DANNY8]

I think what also helps is most of the adjustable panhard rods are constructed of a much heavier gauge material. The standard rod, when used in conjunction with more solid suspension bushes, I suspect flexes under load which gives a springback effect on the axle, which could account for the radical behaviour.

The adjustable panhard rod in our race car looked to be of good quality (good welds), but yeah the first time we used it, she bent. That's racing on the dirt, but was at the Port Augusta track which is a very hard surface.

But yeah, just had to bend it back out and re-inforce it. :thumbsup:

 

[vkberlina]

I have been looking into a watts linkage rear end for my VK for my next project.
Dare I say it or even think of it using falcon gear. They runa borgwarner diff same as a commodore so the diff hat swaps straight over, then its just a matter of measuring up mounting points and welding up some mounting brackets maybe modifying the arms off the falcon. I think when i finally get the time to do it I will have it done in a weekend quite easily.

cheers
scott

 

[vkcomie]

my vk commodore has been put on superlows but, the front is really low and the back is sitting up quite a bit still, i want to know what would be a legal way to have it sitting a bit lower without cutting my springs, also have heard about adjustable panhard rods but am just not sure if they are the trick ? can someone help me out cheers

 

[vkberlina]

You need to consult your design rules for your country ie in Aus its ADRs they specify the ride height your car is allowed to be, the lower the car the less suspension travel (unless major work is under taken) and the worse it can handle on bumps.
You may also find your strut top mount/rubbers have sagged which will also cause the front to be lower than normal.

scott

 

[Darren_L]

my vk commodore has been put on superlows but, the front is really low and the back is sitting up quite a bit still, i want to know what would be a legal way to have it sitting a bit lower without cutting my springs, also have heard about adjustable panhard rods but am just not sure if they are the trick ? can someone help me out cheers

you can get springs reset to the height you want, that might be the easiest way as opposed to trying different springs.
an adjustable panhard rod is mandatory on a lowered live axle Commodore. You should definitely invest in one.