Subframe movement?!?!

[S2 Ant]

Just thought i'd put this in a new thread isntead of the other one.....

I put a jack on the front passenger side wishbone where it mounts on the rear of the 2 mounting points for it (dont worry i wasnt gonna lift the car there with the jack)
I was lifting the jack up to this point and when it got there that end of the wishbone all went upward..... surely this bolts to the subframe which shoudl be totally rigid with no movement????

I would have expected it to be solid and not move as surely movement here will affect how the car drives?

Hope that makes sense?
I'll be taking a proper look later in the week but wanted to confirm how all this should be before worrying!

[Keeper of The Kitten]

Was it just squashing of a rubber type suspension bush?

Or do you have harder bushing fitted?

__MDC__

[S2 Ant]

If it was squashing then the bush must be like a bath sponge as it moved very very easily with use of the jack.

The wishbones have Powerflex bushes but subframe i would assume are standard.
It will be on a lift later in the week to look at properly and see why its moving how it was.

[mcandmar]

The subframe bushings are not supposed to take a load in that direction so i imagine they would flex quite a bit. The bushing is fitted to the subframe from the bottom of the car up so in theory jacking the subframe will try and push the bushing out of the subframe.

They are a floating design so the subframe can move about and absorb vibration etc, the alloy subframe mounts will mount it solid to the car and tighten things up no end. There are various opinions on using them, not everybody agrees on using solid mounts. Other option is the poly subframe mounts, never tried them myself but they sound like a good compromise.

[S2 Ant]

Ok, Thanks for that, i'll be checking it out closer tomorrow with the aid of a lift.
Just seemed to be a bit excessive thats all esp as the car feels a bit floaty a lot of the time, like a strong crosswind at times.

We'll see.

[Keeper of The Kitten]

Mcandmar and Ant, that's not quite true about the subframe bushes:

They are always taking an upward load when the car is sat on it's wheels, because the car's weight is exerting a downward load on the same subframe bushes.

Every action has an equal and opposite reaction!

Ant, just to make sure - when you saw the wishbone move upwards, did you see the whole frame moving or just the wishbone end? Also, how much movement are we talking about here? 5mm, 10mm?

Because you are using Powerflex bushes, I would assume that the wishbone is fairly stiffly mounted - which would probably make the subframe the culprit. But even poly bushes wear out and holes can elongate, making movements quite possible.

__MDC__

[S2 Ant]

To be honest, i had the hump with it at this point and bashed my knuckles several times undoing the bottom nut on the drop link.

It looked like just the wishbone and must have been a good 10mm as a minimum i'd say.

I'll have a pry bar handy tomorrow night i think, maybe its nothing, as u say, i hadnt thought that obviously the cars weight is usually down on it, but i didnt expect it to move as it would affect handling, perhaps its just worn subframe bushes.

[Keeper of The Kitten]

I could be peeing in the wind a little, now that I think about it - because most of the downward load is reacted through the strut tower and the spring/damper!

The wishbone will see lateral loadings to hold the bottom of the strut in it's outboard location, and longitudinal loadings as it holds the bottom of the strut in it's fore/aft location - these are much greater when the car is moving, naturally.

Perhaps I should rethink that comment about the subframe bushes, sorry dude! They are most likely encountering lateral loads only.

(Martin crawls back into a hole now...)

__MDC__