Finally Decided to Put Spherical Bearing in deDion To A-Frame Connection

[aerobod - near CYYC]

After getting fed up in replacing the deDion to A-frame bush every couple of years and the limit washers every few track days (having tried PowerFlex bushes and custom washers), I finally put in a spherical bearing today.

I used a standard 1" x 0.5" bearing and machined a couple of cups to mount it and extension tubes to mimic the length of the Caterham bush:

The mounting cups are 16mm deep and 27.08mm diameter, the same as the diameter of the Caterham bush to give 0.08mm interference fit in the 27.00 hole in the deDion tube. They have 4.94mm deep recesses that are 25.40mm diameter to fit either side of the spherical bearing body that is 9.88mm thick. A drop of red loctite is used between the bearing body and the cup recesses. The cups have a hole diameter of 19.00mm at the bearing end, tapering to 21.00mm diameter at the outside end.

The spherical bearing centre is 12.66mm thick, so two spacer tubes of 11.17mm length are used either side to bring the overall centre tube length to 35.00mm. They are made from the PowerFlex centre tube that is 12.70mm inner diameter and 19.00mm outer diameter, but I turned it down to 17.50mm diameter to give me a bit more clearance (it is also then the same diameter as the centre tube in the Caterham bush).

Here is the whole assembly put together:

 

When pressed into place I needed to use about 60Nm of torque on the bolt that pulled the assembly into position, equating to about 3 tonnes of force. This is similar to what is required to insert or extract the Caterham bush. I decided that at the moment I won't add additional clamping mechanisms, such as  grub screws or other retention methods, waiting to see if lateral shock loading will exceed the 3 tonnes insertion force and cause the cups to move.

Comparison with the Caterham rubber bush:

 

Pressing in to place:

Maximum angle that inner mount can be misaligned with outer mount is just over 6 degrees:

 

Everything complete and ready for use at the next track day on Thursday:

[ECR]

Neat..

let us know how it works out in practice....

[timb2117]

Looks like a great bit of work, and thanks for documenting.

 

[7 wonders of the world]

James 

You beat me to it - my tame engineering guy is stacked at the moment so my list ot bits for him is on hold pretty much identical to mine I was looking to taper the outer tubes to allow more movement.

 

 

[aerobod - near CYYC]

Hi Neil, what material are you having your tame engineering guy use? I decided to use 6061-T6 aluminium for the cups as I had some scrap and didn't want the corrosion issues with bare mild steel. I was also contemplating stainless steel, but it is just that much more difficult to machine easily with the basic lathe I have.

I decided to go with a 5 degree taper inside the cup, any more would have left a wall thickness in the aluminium that would reduce the interference force due to the lower Young's Modulus of the aluminium compared to steel, but a thinner wall would be fine with steel. The taper and overall clearance to the 17.5mm centre tube is good enough for 175mm of suspension height difference from left to right, measured at the outside of the tyres.

This is the spherical bearing I used: https://www.emfrodends.com/collections/uniballs/products/com8t-spherical-bearing

[7 wonders of the world]

Hi James,

I asked him to make them in stainless (he did draw breath as stainless it seems has gone up in price a lot !) because of the wall thickness.

Same bearing albeit an NMB one https://www.mcgillmotorsport.com/1/2-nmb-stainless-steel-plain-spherical-bearing-abwt-c-60-p-2091

Option 2 if this does work was to mill the lug off the tube and weld on a new one to permit a larger bearing with more articulation secured with a pair threaded retainers - I've got an old tube which I could play with if I need to.  possibly using something like this with a pair of long top hats https://www.mcgillmotorsport.com/5/8-nmb-stainless-steel-high-angle-plain-bearing-abyt-c-60-p-2093

I'm seeing him tomorrow as he's promised to have my rack clamps machined for then - dropping 3.5mm off the lower one to drop the rack and get the bump steer corrected - wont be a lot of material left !

 

[simon_h]

That's very neat. I guess it might transmit a bit more harshness into things but would anyone notice it over everything else? 
Should make it nice and smooth in use 

[aerobod - near CYYC]

I was thinking Simon it should eliminate the couple of millimetres of movement in the back end with various degrees of clunking, as the limit washers wear or completely fail as the de-Dion hits the welds on the A-frame (I had a couple of witness marks and indents that had to be filed smooth).

There are still rubber mounts for all suspension components to the chassis - I have PowerFlex bushes on the outer A-frame mounts and standard Caterham ones on the chassis end of the radius arms with the standard spherical joints on the Watts linkage ends.

[7 wonders of the world]

I already run adjustable radius arms with spherical joints and there's no discernable difference in harshness over the OE metalastic bushes

[simon_h]

#8 yeah I think it looks like a good idea. Especially if those washers wear regularly and it needs pulling apart for repair. 

[aerobod - near CYYC]

After 150km of road use and 265km of hard track use yesterday, the spherical bearing fix works well. No sign of any movement of the aluminium "cups" I used to hold the bearing in place, no increased noise or harshness and the slight twitch in the backend that the movement of the stock Caterham and the PowerFlex bushes caused under initial heavy cornering, is gone.

I'm very happy with the result.

[Rattie]

Hi James

Just a quick note to say I copied your homework and did the same mod to our SV which as also on a Powerflex centre and was slopping and clunking. I used the NMB bearing and turned aluminium for the cups, then turned down the Powerflex centre to 17.5mm

My puny Axminster SIEG had to be nannied with that centre tube!

My quick road test proved satisfactory. None of the unpleasant twitching or knocking and no movement of the cups. I used the same interference dimension, so hopefully Bedford GT next month won't unsettle it.

[aerobod - near CYYC]

Hi Rattle,

Sounds good. My car has about 10 hard track days on it with this "fix", with no issues so far, was one of the most satisfying mods I have done. I was only getting a few track days out of the nylon "Race" washers (whether with Caterham original or PowerFlex bushes) and it was becoming tedious swapping them so often, besides the annoying twitch of the backend as the tube moved against the washers. Unfortunately my car is off the road now due to my engine failure at my last track day earlier this month, so no further field testing for a while.

[7 wonders of the world]

Mines been in since last summer though got minimal.moleage until this year done no issues and it also take a lot it the rotational torque out of the A frame itself.