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MG Midget and Sprite Technical - Front Suspension - inner wishbone pivots

Yesterday I was out driving my Sprite; sunny afternoon, dry roads, bliss! I came down a hill on a fast main road and around a long sweeping bend at speed. The tyres gripped and the car squatted enthusiastically down on the suspension as the G forces increased and I followed the sweet line through the bend. Then one front wheel hit a pothole - actually more of a subsidence really - and the front kicked and lurched sideways. Nothing so unusual in that and no harm done.

But it got me thinking again about those flimsy chassis brackets that act as the pivot points for the front wishbones. I have always thought they were a weak design. I have had one mounting begin to tear away from the chassis and another that developed a split running from the edge of one of the larger holes. And neither of these faults from impact damage, just general age and stress.

Apart from the brackets being of quite thin steel I think that the way the stepped washers are expected to locate and stay put in the larger hole is pretty doubtful. And once that washer starts to slip and move around all of the loadings must go through the other single web of the bracket.

Any thoughts on this? It seems a pretty vulnerable and high risk safety item. Have any practical ideas or improvements been tried?
Guy Weller

<<< Yesterday I was out driving my Sprite; sunny afternoon, dry roads... >>>

Lucky you Guy!
I'm trying to learn to drive with webbed feet
David Cox

I have posted this before, long ago.
Especially when they have been damaged, the big hole/stepped washer can be difficult or impossible to assemble correctly. Used to be common to have cars recently rebuilt come in with the inners out of position.

I form a bit of a chamfered bead facing outward. Use a stepped washer (ear cut off or bent) inside the hole (where A arm goes), with a very heavy backup washer, and a chamfered recess (big socket) outside. Strong well lubed bolt to "coin" the edge into a slight bead, maybe 1/16" wide and high. This makes it extremely stiff and very easy to get the stepped washer in the usual position. Especially good when you've had to weld or straighten the web. And it will stay there!

If the web is really bad, replace it with a heavier gauge piece, formed same way.

FRM
FR Millmore

I have replaced the webs with heavier gauge - well, only because I was replacing the damaged one anyway. But I hadn't thought of forming a lip to the hole, if that is what you are describing.

I had thought of adding a larger washer inside the web, larger than the big hole, so that the web is clamped flat between the stepped washer and the additional washer. But it would be difficult to slide into place between the rubber (or polybush) A frame pivots and the web.

The equivalent bottom wishbone pivot points on modern cars are quite hefty items by comparison. Although I guess this is in part due to them usually being front wheel drive so they also counteract drive torque as well as braking torque as for a Spridge.
Guy Weller

I too have had these thoughts Guy, but each time I've removed or changed the inner bushes, I've been amazed at actually how durable the setup is.

As long as the rust has not had a chance to do any damage, I think it's more than adequate, and I haven't read much if at all about problems in this area.

I've also never found any difficulty in locating the stepped washers, but I can imagine if previously someone didn't align them properly before bolting it up, that could cause a future problem. btw, I'm still using the original fulcrum pins and stepped washers. So they can't be that bad.

How about the racers here? Must be a lot of extra stress on a race track. Has it caused a problem there?
Lawrence Slater

>>How about the racers here? Must be a lot of extra stress on a race track. Has it caused a problem there?<<
Not in my experience; remember circuits are much smoother than roads - it's the surface changes, ramps, speedbumps, kerbs and potholes that present the stresses that the designer maybe never thought of.
David Smith

So if I was accused of using the public highway like a racetrack, I could retort, don't be ridiculous, roads aren't smooth enough. And that's certainly true around my way now. I've never seen such crap sufaces. I wiggle all over the road these days avoiding pot holes and the like.

Lawrence Slater

Having taken a FISC race car down a country road years ago (sshhh don't tell) I can confirm that race tracks are smooth and normal roads certainly are not - I thought my teeth (and various other parts of the anatomy) were going to fall out...
James Bilsland

It has occurred to me that the thin webs act as a sort of fuse, preventing more major damage to frame and suspension when people hit nasty bits. Had a number of cars come in with no other damage when I expected it from descriptions. The washers pop out but the pivots can't go far, you can drive home! Smarter puppies then take the car for checking when the steering is off center and the brakes get odd.

FRM
FR Millmore

This thread was discussed on 04/07/2012

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