As you may have read in my previous article:
I had several issues with urethane suspension joints. They don’t work like some people think and because of this there are extra considerations to take into account, which means they often don’t work very well at all.
- They require regular lubrication
- They jam or judder as the suspension moves
- Cheap ones use the wrong materials
- Tolerances on cheap ones aren’t good
I had several problems to solve and the answer was actually a lot more simple than I thought.
The standard central crush tube on a urethane setup, is only a fraction of a millimetre longer than the urethane setup.
The central crush tube is made out of polished stainless steel (possibly of H6 grade). The finish of the tube is important so that the urethane bush does not grip and rotates smoothly over it’s surface. The crush tube is not a rotating part of the assembly.
I have changed the length of the tube, the material used and its action.
The length of crush tube has been increased so that it passes through the mounting bracket. The hole in the mounting bracket has been increased from 12mm (tight clearance for the M12 bolt) to 20mm (ample clearance for the Ø19.05mm – 3/4″ new tubes). I increased the hole size with a cone cutter drill, as they no longer need to be super accurate. Instead of expensive polished stainless, I used some scrap stainless, but I could have used standard steel. The central crush tube now sits perfectly flush with the outside of the bracket.
NB. The central crush tube has to be inserted or removed in situ.
On the other side of the mounting bracket is a 6001 2RS Silicon Sealed Roller Bearing.
These bearings are so cheap, I went for the top of the range items (6001 2RS-SS). The standard 6001 2RS bearing uses steel balls and is open (left image). It is widely available for around 75p. The rubber sealed bearing on the right is waterproof, sealed for life, has a stainless body, rotates with no noticeable friction and is much more heavy duty (£2 each). I found mine on fleabay, but no doubt they are even cheaper from your local bearing stockist.
Because the urethanes no longer have to slide over the central crush tube, the finish on the tube is immaterial. In fact, if the urethane doesn’t move at all, that is perfectly fine. This means that you can use the really cheap urethanes and not the hyper expensive high tolerance ones. I bought mine from Pop Browns. I bought enough for the whole car for under £35. I had to make my own crush tubes out of 19.05mm – 3/4″ bar as I could find tube suitable.
At this stage, the whole assembly is just rattling around with nothing holding it in place. This is where two extra bits of short tube come into play. I used the same tube as I used for the urethane sleeves on the end of the arms. This was 32mm tube with an inside diameter of 28.5mm. I heated it and rapidly cooled it. This made it shrink and instead of being loose, the bearing races needed to be tapped in with a lump of wood and a mallet. They now sat squarely and solidly against the ends of the extra long crush tubes.
These mounting tubes were 32 O.D. x 28 I.D. x 18mm long.
To make sure all of the 32mm tubes were going to be welded into the right positions, I used a long piece of 19mm bar, passed through all of the joints on each arm. I attached a magnetic laser x/y pointer to the bar. The resulting dot/point was marked on the end wall of the garage, amplifying any error a couple hundred times. The laser pointer arrangement also made it easy to match one side of the car to the other and to the central line of the car. After 30 minutes of probably over perfectionist tweaking, I was able to weld in place the 32mm tubes. I bought a couple of these laser pointers from LIDL for under £7 and they are brilliant.
To bolt the whole assembly up tight, I used M12 x 100mm bolts. These bolts had a 60mm un-threaded shoulder section. I then cut them down to 80mm. I used flat washers and nyloc nuts.
To seal the whole bearing and bolt assembly from the elements I used some 32mm Ferrules (rubber table leg ends). Hopefully, that should help come IVA time.
See Below (Before I cut them down)
The new set-up runs as smooth as silk with barely any friction, it will hardly ever need maintenance or lubrication; yet has all the shock absorbing properties of the standard urethane setup. The new set-up adds about 400g to the total weight of the car and about £50 to the build. To me, this is a price well and truly worth paying.