Can someone please explain why i should have the vehicle on the ground with its weight on it before i tighten the front lower control arms and the upper nuts?

 

You will be putting your bushings under stress and cause early failure of the bushings.

 

Ok thank you CQR

 

And the car will ride a lot higher for a while until the rubber in the bushings fail.
These must be tightened when the weight of the car is on the wheels.

 

Is it not true that for the Poly bushings, it does not matter? Thanks

 

The rule applies to poly and solid bushings as well. Entire finished weight on wheels before you tighten and torque the control arms.

 

Thank you also Rob, without having all this knowledge from all of you i could'nt have nor would i have done this work, Again thaks to all who have posted and replied to my threads.

 

Put all four tires on blocks of equal height if you need more space to crawl under the car. Be sure the car can't roll off the blocks. Just jacking up one end (to do the front or the rear) won't get the right height and weight on the suspension.

 

Put jackstands under the rear axles. It's the easiest and safest way to work under the car with all the weight on the axles

 

This is incorrect. Polybushings are not bonded to their shells the way rubber ones are, they are greased between the bushing & shell and will rotate, not bind & rip like rubber.

So poly bushings can be fully torqued to spec without the weight of the car being on them.

 

Well I just learned something then... I thought they were bonded the same way. Cool!

 

Besides early bushing failure the car will ride harsher and not handle as well.

 

I think I'm glad this was question was posted.
I put a jack under the shock mount area in the lower control arm and torqued them one side at a time.

Looks like I need to redo them.