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MG Midget and Sprite Technical - Trunnion wear

At my mot today (passed - yay) an advisory was issued that there was slight lift at the lower trunnion. MoT man showed me and sure enough there was up and down movement. How do I remove this play ?
Geoff Mears

Hi see the post lower down called fulcrum pin. I think this covers your query. Bob
Bob Beaumont

Thanks Bob
Geoff Mears

Did that answer your question Geoff? That other thread was only 5 posts long! (two mine!).

Malcolm.
Malcolm Le Chevalier

Sorry for late reply Malcolm. Not been online. Not had the chance to have a look at the problem yet - as it is an up and down movement rather than a loose any direction wobble (which would be wear and need replacement), I'm wondering whether I will be able to take the movement out with shims at the top trunnion. I may be talking out of my you know where, but will check that out when I have the opportunity. Thanks again for your help. Regards Geoff
Geoff Mears

Mixed terms here. There isn't a lower trunion.

The lower link, is the screwed fulcrum pin, that goes through the king-pin and wishbone bushes, and no, you can't de-shim that.

The trunion bolts to the top of the kin-pin and shock lever arm. If there is vertical movement of the trunion, then it's loose on the king-pin. Tighten the nut to circa 40lb, or just good and tight. But not finger tight, it's meant to be properly tight.

If there's vertical movement of the stub-axle, relative to the king-pin, then you may be able to remove shims under the trunion to eliminate the movement. If not, then generally, it's a new oilite washer, or new k-pins, and or bushes in the stub-axle.



Lawrence Slater

PS.

After some, -- and I'm guessing here -- ten thousand miles or so, on new wishbones and fulcrums, there will likely be a slight lift between the fulcrum and the wishbone bushes, as the pin wears it's way into the bushes, and vicky-verky. Grease takes up the slack, and often just greasing prior to the mot, prevents you getting a mention of it.

So how much lift are we talking about here? When were your wishbones last replaced?
Lawrence Slater

Just to add, when checking it is also dependant on where you place jacks. i.e. Jacking under the wishbone will take the weight off the wheel (stub axle) and also absorb the tension of the spring, so wear movement should be more apparent. You may still need to use something like a large flat bladed screwdriver to check for movement. I also prefer to feel for slack with a finger touching across the joint of the adjacent components whilst pushing/pulling/levering. Its easier to determine where most of any slack that is detected is actually occurring
Guy W

I had the same thing on an MOT, tester was a very experienced older guy I have known for years, but I thought he was wrong. Did not argue, but took the car home, and adjusted the King Pin shimming, it then passed no problem.

Dave
Dave Barrow

Hi Lawrence. The wishbones + kingpin assembly were replaced about 20k ago. It looks as though the kingpin itself was moving up and down, as seen from underneath where the mot man was levering - I would say about 2mm lift. I'll do as suggested and check the shims etc and tighten up if necessary, plus also pump more grease through. I'll see what the weekend brings......
Geoff Mears

You know that song? The thigh bone's connected to the etc etc. Well, the king pin is connected to the fulcrum pin, in as much as the pin goes through the eye of the king-pin, and the fulcrum pin is prevented from rotating in the kin-pin by the cotter pin driven into the slotted fulcrum pin.

if the cotter was loose, or missing, the fulcrum could rotate and wear the eye of the kin-pin, and then the king-pin could move up and down relative to the fulcrum pin. It doesn't usually happen that way, but it can. So make sure your cotter pin is present and tight.

Otherwise 2mm movement sounds like wear in the wishbone bushes/fulcrum pin, and de-shimming won't fix that unfortunately.

How often were the wishbone bushes and stubaxles greased in that 20k miles?
Lawrence Slater

Clearly not as often as they should have been..
Geoff Mears

This thread was discussed between 07/06/2013 and 13/06/2013

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