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Top trunnion confusion
Posted: Sun Jun 28, 2026 2:01 pm
by gridgway
I had to do some maintenance of my front hub bearings. In taking off the the upright, I noticed that the U bracket was bent in quite a lot and that the poly bushes were badly squished. I thought I would get some new bushes and sort it out. I ordered new MG midget bushes from MGOC (here in the UK), but they are the wrong size. The originals on the car have a 5/8" OD crush tube for a 1/2" bolt (ID in the poly bushes 5/8"). The MG midget ones have a 1/2" ID.
Then I also wanted to change one of the stub axle assemblies as it had an issue, so I got one from MGOC (sent the old one back as it was an exchange unit).
So now I notice that the top trunnions are different dimensions. The original is a bigger (tapered) ID than the replacement MG Midget one.
So there's clearly stuff going on that I don't understand! I can't ask the factory for the obvious reason. Is it something like an MG Midget upright assembly with a different top trunnion - MGB maybe?
Any and all help gratefully accepted - thanks!
Graham
Re: Top trunnion confusion
Posted: Mon Jun 29, 2026 11:15 am
by gridgway
So to update a little. I have been checking with the MGOC Spares people.
In summary I have two stub axle assemblies with different size top trunnions. They say that there was only ever one size on the Midget - the smaller tapered ID one. I sked if the bigger one could have come from something else like the MGB, but that has a different king pin size, so it's not that.
So not much further on really!
Re: Top trunnion confusion
Posted: Mon Jun 29, 2026 7:55 pm
by Euan Hoosearmy
If MGOC supplied you with odd replacement parts that don't fit, surely it's on them to supply the right bits.
When I received my bushes, I was confused as they didn't have a crush tube but one was mentioned in the instructions - this is the reply I received from MGOC on the subject:
"Autobush only include distance tubes where required. You should find that the bushes supplied are a snug fit on the fulcrum pin.
Unfortunately, they include a generic instruction sheet, which confuses." The bushes are a very snug fit on the 1/2 inch bolts.
Re: Top trunnion confusion
Posted: Mon Jun 29, 2026 8:00 pm
by gridgway
I'm pretty sure what I have been supplied is standard MG Midget kit. It's what I had on the XI that is not standard!
Re: Top trunnion confusion
Posted: Fri Jul 03, 2026 2:22 pm
by jonclancy
I’m afraid I can”t add any more to this, because I didn’t build my car. Is there any possibility of adding some photos, please?
Can they return your original stub axle assembly and you replace the kingpin etc?
Re: Top trunnion confusion
Posted: Fri Jul 03, 2026 3:45 pm
by gridgway
Looks the same as a standard one, just a bigger internal taper
Re: Top trunnion confusion
Posted: Fri Jul 03, 2026 3:51 pm
by gridgway
I have a solution that will work. A fabricator friend has turned down a standard set of MGB polybushes to fit the MG Midget trunnions so I'll get a standard MG Midget trunnion and put it all back together. If I ever solve the mystery of the bigger trunnion, I'll restore to what it was.
Re: Top trunnion confusion
Posted: Sat Jul 04, 2026 3:20 pm
by jonclancy
Glad you got that sorted,Graham.
A quick question: do your trunnions have different part numbers cast into them, please?
Just wondering if there is a (significant) difference li.e. as there is with the BTA 648/649 Fat Rack steering arms, and the later AHA Thin Rack Triumph items).
I see you have 2A4005 in the pic.