Wishbone Conversion Safety/performance Issue

[Grim]

Having recently failed my mot on my top wishbone ball joints (transit type) i have discovered a design flaw in the style of wishbone conversion my car has (courtesy of Martin @ MK engineering).

The angle that the dummy mcpherson struts meet the wishbone is incorrect, so the top ball joint travels beyond its capability at full lock, which leads to wear of the joint. As a result the movement of the suspension is juddery, which is a bit dangerous as means the road holding / braking over bumps is much worse than it ought to be.

 

To solve the problem for the moment i have had the ball joints replaced and had lock stops fitted, and adjusted the front camber to a more believable setting, but it does mean it has the turning circle of an ocean liner. I'll replace the top wishbones with a new design given the modest price quoted for having new ones made, and because i use it every day (28k on the clock now). I've noticed since that the fronts don't lock up so easily now, and i can get either side to lock instead of just the one. I haven't even braked hard enough to lock up a wheel in the dry yet, I'm too scared!

 

Out of personal interest, is there anyone out there with the same setup as mine that would be interested in replacement top wishbones? I haven't discussed this but i assume a ball park figure would be about £100 for a pair, if a batch was to be made up. The advantage being you wont lose your car for a week whilst they are designed.

 

Have a look below for some photos. Some of you may recognise my suspension from the

video.

 

Andy

 

 

[Grim]

As an example, here's a better design of top wishbone, with the top part of the ball joint sloping downward toward the centre of the car.

 

Taken from the MK sports cars website

[Guest chris brown]

Having recently failed my mot on my top wishbone ball joints (transit type) i have discovered a design flaw in the style of wishbone conversion my car has (courtesy of Martin @ MK engineering).

The angle that the dummy mcpherson struts meet the wishbone is incorrect, so the top ball joint travels beyond its capability at full lock, which leads to wear of the joint. As a result the movement of the suspension is juddery, which is a bit dangerous as means the road holding / braking over bumps is much worse than it ought to be.

 

To solve the problem for the moment i have had the ball joints replaced and had lock stops fitted, and adjusted the front camber to a more believable setting, but it does mean it has the turning circle of an ocean liner. I'll replace the top wishbones with a new design given the modest price quoted for having new ones made, and because i use it every day (28k on the clock now). I've noticed since that the fronts don't lock up so easily now, and i can get either side to lock instead of just the one. I haven't even braked hard enough to lock up a wheel in the dry yet, I'm too scared!

 

Out of personal interest, is there anyone out there with the same setup as mine that would be interested in replacement top wishbones? I haven't discussed this but i assume a ball park figure would be about £100 for a pair, if a batch was to be made up. The advantage being you wont lose your car for a week whilst they are designed.

 

Have a look below for some photos. Some of you may recognise my suspension from the

video.

 

Andy

How do you propose getting over the problem Andrew?

Are you going to put an angle on the outer end so the ball joint sits central when at rest?

I am asking because I have always thought your wishbones sit at a much better angle than the standard 2B ones (mine) that change the camber from -ve towards +ve under compression. Not a good thing IMHO

[Grim]

very good point that i had thought of, and partly why i'm posting this here.

 

If you look at the picture in my 2nd post, this wishbone automatically allows the ball joint to sit at the correct angle. My new wishbone will point slightly downward as opposed to horizontally now, and then have a flick upward at the end, at the threaded section of the wishbone. Essentially the same design as the one in the photo, but with a higher pivot points. There wont be any undue load on the wishbone from this because my dummy mcpherson strut is that much taller than standard.

 

As for correcting the 2b wishbone setup, there's a lot more going on, the top wishbone needs moving backwards for more castor, a longer dummy mcpherson strut (which would solve your problem), and a slightly shorter length wishbone. It worries me somewhat that the angle of the ball joint on the 2b wishbones design is even tighter than mine.

 

 

I forgot to say, the smoothness of the ride has vastly improved after the change, no more crashing about over bumps.

[sylvia.fry2]

Grim, very interested in redesign of top wish-bone-- will your thoughts include a redesined mac-strut tube to get rid of the stupid angled top plate-- then we will be able to ensure the lock-nut is tight with-out loosing a socket per side. I'm in for new struts if they improve safety & handling, regards Bob.

[Bob Tucker]

This is a frequent problem.

It because the dummy strut continues sloping inwards at the top, viewed from the front.

The wishbones usually sit slightly down at the hub end, making the problem worse.

The angle between the dummy strut and the wishbone is far more than the 90 degrees the balljoint is designed to be used at.

A lot of cars (including my RS Jigtec conversion) will lock up the wishbone when the car is raised by jamming the balljoint instead of hanging at the end of travel of the coilover.

 

I managed to get round it by fitting a relatively short coilover, and dropping the car right down.....easier now with the SBD sump on the XE.

 

The simplest solution Ive seen is to weld the threaded tube that the BJ screws into at an upward angle away from the car.

 

The MK site has a good example of this on their NEW CAR part of their website.

 

HERE

[Grim]

Grim, very interested in redesign of top wish-bone-- will your thoughts include a redesined mac-strut tube to get rid of the stupid angled top plate-- then we will be able to ensure the lock-nut is tight with-out loosing a socket per side. I'm in for new struts if they improve safety & handling, regards Bob.

 

 

Does your car have the same design of suspension as mine? I can't tell from what you've said, what's an angled top plate? Can you post a picture?

 

In light of Bob Tucker's comments, if people want a new top wishbone/struts for a standard 2b, and if someone is willing to lend their car to martin for a week, I'm sure i can arrange for a batch to be made up. Martin would be doing the design, and he's a very capable man, so if there's something you want, it can be done.

[Guest timswait]

Andy, is the hole in the top of the dummy mcpherson strut along the axis of the mcpherson strut on yours? On the RH standard design these holes are at an angle so the ball joint is nearer to 90 degrees in the resting position (although it's still not quite right). Wouldn't an easier solution to your problem be to get new dummy mcpherson struts rather than new wishbones? That way you can use wishbones without a kink in them.

[Grim]

good point! I shall find out and think it over, as i would need new cycle wing brackets (which may well help the steering lock problem)

 

 

---edit---

 

yes, perfectly possible and would kill two birds with one stone! Ingenious.

[sylvia.fry2]

Seems like Timswait is answering your Q & my beef-- is the 2007 RH dummy mac strut with the angled plate welded on top correct/better than the unit you are having trouble with? Regards Bob

[Guest timswait]

There's nothing wrong with the RH welded angled plate per se, it's a sensible idea. One problem is that it doesn't have quite enough angle on it, so the ball joint still isn't in the middle of it's travel at rest and it gets pretty close to locking out when the car's jacked up, but that can be set up acceptably. The major problem is with the wishbones being parallel and angled downwards from the car (they should be divergent, with the bottom one horizontal and the top one angled up from the car). This gives less than ideal suspension geometry as Chris says. I know at least one person (Takumi on here) has modified his 2B to have better geometry, but it's not that straighforward, will definitely need a new dummy mcpherson strut and probably a new top wishbone. Also whatever solution Andy comes up with for his car it almost certainly won't fit a 2B on standard wishbones. So yes, the RH supplied angled plate is OK if not ideal and probably better than the bit Grim's having problems with.

[Grim]

yes, the RH one is better than mine.

 

Rich hall has modified his 2b to have a longer dummy strut which improves the angle on the ball joint, and i believe he trimmed his wishbone (3mm if memory serves me correctly)