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MG Midget and Sprite Technical - Are my king pins bending??
Ive just fitted -ve camber trunnions
Everything is shimmed properly and all the suspension components are in good order.
I noticed that when tigenting the top trunnion bolt (the horizontal one)the stub axles seemed to stiffen up and didnt swivel as easily as before, it was also evident that there was a slight gap (3mm)between the face of the trunnion and the face of the lever arm, which closed as the bolt tightened.
On driving the centreing is not as good as I would have hoped for and the steering is a bit stiff
Back in the garage, slackening off the trunnion bolt makes the stub axle move more freely (yes, i do mean the trunnion through bolt and not the nut on the top of the king pin)
Is it possible that by tightening the trunnion bolt - closing the gap between the trunnion and the lever arm - I am pulling the king pin in to a nerarer to vertical position and therfore looseing some castor and affecting the self centreing . In doing this am I also putting some stress on the king ping causuing it to bind slightly on the stub axle bushes?
I plan to fit a washer between the trunnion and the lever arm to shim the gap. Hopefully this will stop the king pin binding and maintain the castor angle when I tighten the trunnion bolt.
I must stress that without the horizontal trunnion bolt tightened the stub axles swivel smoothly and easily.
(BTW toe in is set to 1/16 using the string and stick method (thanks)- I went to the tyre centre but they said they couldnt set the tracking as I had minilites with two eared spinners fitted that stuck out too far and would foul their equipment, in the end this was a bit of a result as I ultimately saved some money and had the satisfation of doing it myself!)
Any thoughts, does this seem a reasonable explanation.
|S G Macfarlane|
The most obvious possibility is tightening the king-pin nut is clamping the hub tight. Check there's no binding between the trunion/scintered washer and the hub.
The shim washers are there to ensure there's a tiny amount of vertical movement available to the hub on the king-pin; add more shims to increase this movement; remove shims to decrease movement - but too few shims will tend to clamp the hub and prevent swivelling.
HTH - maybe you know this already in which case, please ignore.
Can you post a picture and let us know which negative camber trunnion you're using. I doesw sound like something is missing to leave the gap.
SG mentioned the trnunnion bolt specifically not the shimming adjustment at the top of the kingpin.
Thanks - Im ok with all that. Its tightening the trunnion through bolt that seems to be giving me the problem, I seem to be pulling the king out of line (closer to the vertical) when i do it, which I suspect is the cause of my problem. Ill fit the washer and see what happens. For clarity, the picture below shows the proposed washer. The picture is an old one - bfore i fitted the -ve camber trunnions.
|S G Macfarlane|
Is this a heritage shell?
To me the problem sounds like the shocker (Top link) mount is not linecd up correctly. And as you described that when the trunion is tightened up to the shocker then the "kingpin" will become bent and stiff as a result!
I ask about the shell simply because I have seen 2 heritage shells with similar issues.
|Bob Turbo Midget England|
|Is it possible that these -ve trunnions are also designed to alter the castor angle, and that you have them swapped side for side? Or alternatively that the trunnion link itself is wrongly machined such that the horizontal hole is not at a true rightangle to the vertical king pin hole?|
The shell is an original.
The trunnions are Peter May items, I dont believe they are handed or designed to alter the castor angle.
Both sides of the car are the same (ie they both have a gap). I'll try swapping the trunnions over tonight to see if it makes a difference and take some photgraphs of the gap etc.
I'll also try the washer theory to see if it improves things.
I'm probably going to have to refit an original trunnion just to satisfy myself that the gap wasn't there to start with.
|S G Macfarlane|
|Did you change the a-arms?|
|I've got a set of Peter May -ve camber trunnions fitted to my 1500 midget and they fitted fine straight out of the box (wrapper).|
|I've encountered the gap with PMay trunnions, fitted a selected washer and no problem. I did not tighten before fitting the washer so can't comment if it solves your problem but without the washer it's obvious (to me) that you are stressing components 'not as designed'.|
|>>> Did you change the a-arms? <<<|
Trevor beat me to it... is there a chance your A-arm is twisted?
Yes, I have changed the wishbones for Barry King units, I didn't want to mention this for fear of complicating things.
Ill refit the original trunnion and report back.
|S G Macfarlane|
Are the PM trunnions you have fitted with bronze tophat bushes?.
|Heres the trunnion in place|
I tried a packing washer but it just caused more troubles, the castellated nut wouldn't go on far enough to get the split in and the flat for the pinch bolt didn't line up with the hole in the damper.
Its possible that the trolley jack was twisting the wishbone, making the gap larger than it actually was.
It still doesn't seem right though
Anyway, I've put it all back together and decided just to drive it.
Thanks to all for your input
|S G Macfarlane|
you seem to be resigned to just see how it goes now, but just a few points,
I have had this same problem many times over the years, following various component changes.
We must bear in mind that these cars are based on a budget family saloon of 1953 ? vintage [ A 30 ] and basically are a pile of junk. Don't get me wrong, I love these old beasts, but Jaguar engineering it ain't.
Looking at your pics, you have a great looking car, and look like you know what your doing, at least you realized that winding in the nut to close the gap isn't a good idea !
I believe that what happens has something to do with replacement bushes
in the inner wishbone lower links. Poly bushes vary a lot, some having
quite thick shoulders, and take some effort to fit convincingly, resulting
in a tight squeeze fit, which may leave the wishbone very slightly biased to the front or rear. Certainly thick shouldered poly bushes when used
in the trunions often leave the problem of too little gap !
This thread was discussed between 28/03/2011 and 02/04/2011
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.