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MG MGB Technical - Are kingpins matched to stub axle?

I'm just about to put my stub axle assemblies back together after a clean up and paint. while doing a dry assembly I notice that one kingpin is very stiff in it's housing. Offering the other kingpin to the same housing shows a little stiffness there also but not as much. Both kingpins are ok in the other stub axle. I'm pretty sure I kept the sides separate when refurbishing them. I'm wondering whether I need to relieve the first housing or the kingpin. the top bearing surface has no stiffness (if I put the kingpin in upside down) so I assume the problem is at the other (larger) end. When assembled I can turn it by hand (no trunnion) but there is some definite resistance there.
Steve Church

They aren't actually matched to the stub axles, as the bushes should be reamed with a stepped reamer, so they should be identical.

If one of yours was reamed with a worn reamer, or even an adjustable reamer, you may have a slight difference.

By the sound of it, one of your kingpins is also slightly smaller than the other. I would fit that one in the tighter stub axle.
Dave O'Neill 2

Not matched as Dave says, and in theory they should be identical. But if they are 'old' units i.e. not rebushed and reamed as you seem to indicate, then the differences could just be down to different units replaced at different times with different wear. Use the less tight king-pin in the tight stub axle, and hopefully the other pair will not show excessive play.
PaulH Solihull

Thanks Steve for asking this question, because I also have a pair of re-furbished stub axles on exchange from MG Parts and service in Australia. I did warn them, it would be a while before I can get round to getting the old ones off the car and the new ones in. What I was a slight query, was that they did not offer me a 'king pin' kit if there is one? ie the king pins the thrust washers the dust seals, and distance pieces. Or do these pins not wear and all the wear is at the stub axle bearings? Mike
J.M. Doust

King pins and bushes do wear, quite probably more than wheel bearings, especially if any owner has been tardy or lazy in greasing them i.e. taking all the weight off the wheel to do it.
PaulH Solihull

On the issue of greasing the kingpin when reassembling the dust tubes do they need filling with grease before assembly? Or do I assemble dry and just pump in some grease?
Steve Church

Grease after assembly I'd say, less messy.
PaulH Solihull

If I swap the kingpins around (to get best fit) will I also need to swap the shims at the trunnion? I've just measured them and one set is about 5 thou thicker than the other.
Steve Church

You'll have to check the end float of the king pin and perhaps swap shims accordingly. Aim for two thou and you won't be far off. Alternatively I like to shim until the king pin just starts to bind in the trunion with the nut fully tightened. Then grease and assemble.
Iain MacKintosh

There must be some free play in the trunnion shims and hence vertical play in the king-pin, or you will not get any grease through, even if you take the weight off the wheels. The workshop manual calls for a maximum of 2 thou. I recently went though these looking for a clonk under braking, and the vertical play seemed more than that. I bought new thrust washers and shims, only to find the thrust washers were *thinner* than the originals, and five out of the six shims were all the same size even though they were stamped with the three different sizes! Even when I got the correct shims I couldn't get a combination that gave less than originally, but didn't bind. Even if made to the original specs each shim size has a spread of 5 thou! But having lost the original groupings you are going to have to go through a repeated process of finding which combination gives the most equal vertical play in each, which may or may not need new thrust washers and shims to get down to an acceptable level. At the end of the day apart from when the wheel is hanging on the suspension, the swivel axle is always pressing the thrust washers and shims up to the trunnion for zero play.

Oh yes, the clonk - turned out to be coming from the rear slave cylinders!
PaulH Solihull

I've kept the thrust washers and shims grouped with the stub axle. Its just the kingpins that may have gotten swapped over. Guess I'll have to do a few trial assemblies with the old nylocs (makes me think the kingpins are replacements) to see what play there is. And I thought the front hubs were tricky.
Steve Church

This thread was discussed between 12/02/2011 and 18/02/2011

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