Trunnion testing

[ResinRocket]

I've been reading all manner of horror stories about trunnions failing on small chassis Triumphs. ??)
I've had a look at mine and they don't look too clever - the seals look well past their best and when I scraped away the years of muck, I discovered that they didn't have a blanking plug in the oil / nipple hole!

I've ordered a rebuild kit for them, but as I understand it, when they fail it's the threaded shank in the upright which shears - am I right?

So, assuming my trunnions haven't been properly serviced, are there any tell-tale signs of impending doom?! Presumably the shank begins cracking before failure... or have I got the wrong end of the stick and it's the trunnion casing itself which usually fails?

[JohnD]

There's a parallel thread on this at Sideways.  Some have found new-made trunnions to be a tight fit on old uprights, but the word is to 'ease' it by working the new trunnion up and down the threads.  If a new one is loose or esp. if there is any 'wobble', I'd be very worried about the upright.

Trunnions are basicly a bronze tube with a swaged steel plug at one end.   On some new ones, the plug leaks oil!
Prevention is to take the new trunnion, clean the inside with thinners or similar and lay some Araldite onto the inside of the seam.  I suppose that you could use your glue of choice, as long as it's oil resistant, but do it first.  If you wait 'n' see, it'll be too late, the seam will be full of oil and the glue will never take hold.

John

[Nick Jones]

You are right - catastrophic failure is almost always the vertical link snapping around the point where the thread starts.  This usually when a crack, that has been present and growing for some time finally spreads too far.  Cracks start from rough surfaces so any rust up there is a bad sign and if deep enough to cause pitting - time for new links.  If all is visually bright and shiny you can get them crack tested either by Dye penetrant (DIY possible) or MPI (not DIY, but superior) for full peace of mind.

Nick

[Slimboyfat]

JohnD wrote:

  Some have found new-made trunnions to be a tight fit on old uprights, but the word is to 'ease' it by working the new trunnion up and down the threads.  

Bearing in mind I have a vested interest I have been following various threads (no pun intended) on this subject with a great deal of interest.

It never ceases to amaze how many differing opinions, advice, and otherwise uninformed guess work there is out there when it comes to product knowledge for our cars.

So here it is from the horses mouth so to speak.

There are only currently two types of trunnion available throughout the trade.

One type has a plain outside with no 'STANPART' logo on it. They are made in Turkey and should cost you a fraction of the cost of the 'STANPART' branded type.

The other type is the 'STANPART' branded mentioned above. They are finish machined here in Coventry.

There is a problem with the right hand 'STANPART' trunnion that your preferred supplier should by now be aware of. We have been working with the manufacturer this week to try and sort this out. It turns out that the special finish tap that puts the thread down the bore is tapered on it's first few threads (as taps usually are). You may have now worked out what is happening! By the time the tap has reached the last few threads in the bottom of the trunnion it's not really cutting the threads deep enough to accommodate the link threads.

If you have a particularly tight right hand STANPART trunnion send it back to the trader you bought it from and ask him to exchange it. Do not try any other method to get it to fit! By the middle of next week there will be sufficient stock of correctly threaded trunnions with the manufacturer to re-supply whoever you bought your trunnions from originally.

[ResinRocket]

Thanks for the advice, I was intending to take off the trunnions and if they look OK, just replace put a rebuild kit on them. One side I suspect has been greased, not oiled, but I shall take them off and give them a once-over.
I'll check the upright for corrosion and cracking too. :)