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Mushroom adjustment?


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I've obviously got too much time on my hands and can't stop fiddling until I can get out again.

My Sierra based front suspension has the mushrooms. I know rotating adjusts various things but I was wondering what raising them dies? They are both sat at the lowest setting and I've seen several pictures where they are set much higher. Geometry isn't my strong point. If they were higher does this compress the onboard coilovers and therefore raise the ride height? Mine is pretty good but I'll take anything I can get with the state of my local roads Would it also change the camber or caster? I know I could just try it but knowledge is always useful.

Cheers.

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One of the issues with the 2b front suspension is the geometry. They are unequal length wishbones which is good but they have been setup incorrectly by RH.

Imagine a horizontal line.

The bottom wishbone is horizontal but the top wishbone points downward from the car.

When the car goes over a bump the suspension moves upwards.

as they move in an arc the bottom wishbone begins to effectively move inwards on the arc it travels from 3oclock towards 1oclcock. The trouble is the top wishbone as it is below the horizontal line (lets say 4oclock) as it moves up it again swings through an arc but it now pushes out as it reaches 3oclock. 

This means the bottom of the wheel is pulled in and the top of the wheel is pushed out as it swings upwards. This increases positive camber which is entirely not what you want to happen.

The reason people increase the length of the top mushroom is to move the position of the top wishbone from pointing downwards to ideally pointing upwards.

Now if you imagine the above with the top wishbone at 3oclock (if set horizontal) -as it moves upwards it now gets shorter along the arc and pulls the wheel in at the top maintaining negative camber.

Hopefully that makes sense and i'm not talking rubbish but that is my understanding of it. 

I had longer struts made. Scaffold tube is perfect for turning down too fit and has a decent thick wall. 

on a side note you should ideally have some way of locking them in incase the pinch bolt comes loose. If you make them long enough to poke out the bottom you could put a small bolt just though the dummy strut which would stop it sliding up and out.

 

 

 

 

 

 

 

 

 

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I would avoid rotating the mushroom if its to far off centre you could exceed the ball joints range of motion. Lifting would raise ride height, but you could do that with the spring seats. Most if not all of the adjustment is in the top wishbones. Taller mushrooms are to correct the none ideal suspension geometry. There's a kit for the 2B, I've not seen one for the S7.

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oh also you should check that the suspension stops the wishbones not the balljoint. This is why the dummy strut has an angle on which it mounts.

You will have to remove the shock and move the wishbones up and down to see where the balljoint maxes out. Hopefully this will be after the shock maxes out. 

Otherwise on full droop the balljoint is being stressed

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Posted (edited)

Many thanks. That makes perfect sense and is a good reason to raise it. The car is in fact an S7 monocoque mk 2 but I think it still applies as the lower suspension arm is horizontal and the top wishbone does point down. 

Edited by dandan62
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don't think it will effect the ground clearance/ride height. that is more to do with where the suspension mounts to the bottom wishbone. 

I think from memory you want a 2/3 1/3 setup where you have 2/3 of the suspension movement on the up stroke and 1/3 for the downward. Eg I have 13inch open 9inch closed which gives 4 inch of travel (bump stop is about 1inch) so i have about 2inches upward travel and 1 inch down when it's sat normally. 

so you can't necessarily just wind up or down the springs too much as you would potentially be changing the available length of the shock. Ideally you need to move the mounting points. E.g inboard to move up outward to move down. A stronger spring will change the ride height (and the feel) but again it needs to take account of the available travel on the shock.

 

 

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Thank you. To be honest I'm not hugely worried about the ride height as it's not bad. But improving the geometry sounds like a good enough reason to raise the mushrooms a bit. I will double check the top mount end stops but I'm pretty sure I checked when I installed new coilovers last year as I realized the danger of stressing the ball joints.

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Dont forget that moving the dummy strut upwards will also increase any positive camber because its at an angle in the hub.

My wishbone conversion has "ears" welded to the dummy struts. They fit inside the slit in the hub, and are drilled so the bolt goes through it

as a positive lock in case the bolt comes loose.

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I've decided while I'm at it to replace the top ball joints. I'll be doing a lot of fiddling so will check over all the alignment settings once done. Thanks for all the help.

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I found when i made longer struts I had to cut the lock nut on the balljoint as i couldn't find it in far enough otherwise. I think they are an 18mm fine thread so not very common to get hold of.

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