I’m looking for technical help or recommendations on: Front Suspension Lower Control Arms
Last September I got an MOT advisory on the front lower control arm bushes, and thinking about replacement…but feeling will have to go to the garage for this.
I’ve read a few times about suspension work being tightened up while jacked up causing “twisted bush syndrome” and if I have the arms replaced slightly concerned about this.
But then I got to thinking surely the suspension pivots on the bushings so can this actually be a genuine issue?
Surely the tightened bolts shouldn’t prevent rotation in the bushes? That suggests all the suspension rotation is provided by bush flexing which doesn’t seem right to me.
The centre steel insert is bonded to the bush, so if the suspension is at full droop when the bolts are tightened clamping these in place the bush will already be under a tremendous amount of static twist just by lowering the car to the ground, worse still when further loaded.
The stock suspension I took off my nc mx5 had a large range of movement from full droop to fully compressed. This will amount to quite a bit of twist.
The correct method is to fit the suspension components back on and leave every nut on a bolt that goes through a bush slightly loose but the bolt all the way home. Then once the wheels are on the ground give a few bounces on the front and rear for the car to settle. Then tighten up. This means the bushes will be neutral with no load and ready to twist in either direction whether compressing or rebounding. It always helps to mark the alignment bolt positions with a paint pen as well to set it all back to roughly what it was, then once you’ve driven it to settle, take it for alignment.
Here is the nc sport tech rear at full droop, it’s a big distance from here to fully compressed.
Easy way to retighten is to note the wheel center to arch distance and replicate this with the wheel off by jacking the hub. A piece of wood with the curve of the hub cut out helps stabilise the fronts which are free turning of course.
This is what I do but normally with a block of wood under the bottom ball joint or outer lower arm. Just thought it more explanatory ‘with the cars weight on the ground’
So the bush is a piece of rubber with a bonded tube through it, yes? And the fixing bolt goes through that tube. Surely the tube/bush is supposed to rotate around the bolt? Sorry just trying to understand this fully.
When you tighten the bolt it pinches the metal tabs of the subframe/arm/brackets into the metal sleeve, pinning it in that position. Any movement from that point on is through the bush twisting as the suspension works.
Ok so the tube isn’t a bearing at all then, it’s only function is to stop the bush being compressed by the clamping force of the bolt then?
I’m amazed all the rotation is provided by the bush twisting, I thought the primary function of suspension bushes was to provide a bit of "give"out of the normal suspension axis to improve NVH.
So yes, a standard bushing consists generally of an outer steel sleeve, bonded rubber and an inner steel liner sleeve. The outer sleeve is pressed into the component/arm with an interference fit. The inner sleeve is where your bolt goes through and fixes it to the car.
Polybushes are slightly different, they tend to have no outer sleeve and can be greased and pressed in with much less force as one piece or sometimes in two halves that meet in the middle. Then you grease and install the steel sleeve. These can rotate slightly depending on how tight the fit. They also are tougher than rubber so can sharpen things like steering and suspension at the expense of comfort and a little noise.
Rose joints are another alternative but not really for a general use road car. A lined metal bearing and come as a complete unit to press in replacing where a bush once was. These are fully articulated so move freely with the suspension but are the least forgiving in noise and vibration and most susceptible to attack from corrosion. They do sharpen the car up as much as is possible but I have tried them in another car and wouldn’t use again for a road car as the downsides are worse than the upsides in my opinion.
It’s the method been used for many years so it must work. Suspension bolts can be among the hardest to get undone in my experience so it does do the job.
I remember reading somewhere years ago that designers do choose the rubber compounds carefully as they are designed as part of the actual suspension and assist in controlling the movement of the shock assemblies. This may be why pattern parts can sometimes be an improvement over a worn out genuine item but not as good as oe because they may use generic compounds.
IIRC, RX-7 FD had what Mazda described as passive 4 wheel steering whereby different hardnesses of bushes used in the rear suspension allowed the rear wheels to alter toe angle during cornering. I think that MX-5 NA (maybe NB too) rear lower arm inner bushes offer a similar benefit.
Nissan did the same with their super hicas rear wheel steer system, but as they often failed and were expensive to fix people would just remove or lock the rack out. Not sure what bushings were used though, may have been rod ends on those.
Many have done it over the years I think. Honda had it on some preludes, maybe accords as well and I believe mitsubishi had it on the gto, Nissan on their skylines and silvias as an option. Never really saw the point though as it’s a whole other steering rack to fail (which they did) and the steering angles were always so slight.
It’s irrelevant how the top arm operates when it’s the lower which needs doing. All you need to do is make sure the people doing the job are aware of it (if the job goes that far) and leave it at that.
