Trunnions? WHy?

[vincereynard]

Sorry in advance if this is asking the ******** obvious, but why did Triumph use trunnions for the front suspension bottom link? Why not a simple ball joint like at at the top?

[john.p.clegg]

I guess part of it is that they are screwed and handed so that ay one turns the steering geometry changes???

John

[billwill]

I guess part of it is that they are screwed and handed so that ay one turns the steering geometry changes???

John

I raised that point before, but most/all of the responses said the change would be trivial.


My guess is that trunions have better wear characteristics.

[rgh0]

The main reason I believe they are handed is so the weight of the car causes opposing torques on the threads so there is no tendency to track to one side or the other which would occur if the same threads were used on both sides

Canley Classics make a ball joint conversion for the trunnion now, so it is possible. I guess it was just cheaper to make the trunnion rather than the alternatives back in the day

cheers
Rohan

[Chancer]

I machined the threads off the (identical) uprights on my Caterham when I upgraded the suspension to a rose jointed lower wishbone, it leaves it a bit weak with the central drilling but as it was a motorcycle engined conversion the dynamic forces are reduced, it has held up to some serious abuse over the last decade.

As to why, well in the early days of ball joints the materials werent as good, they didnt take as much load as a kingpin bush or trunnion and the sealing using non polymer rubbers left a lot to be desired so it was a long time before they were commonly used for the exposed lower swivel joint, they started with track rod ends.

30 - 40 years ago I was forever replacing suspension joints, Mini and 1100 swivel kits were by far the worst especially as people were then getting out of the habit of greasing the suspension, I assume that later Minis used sealed ball joints.

My current car is 13 years old, has done 300000 miles and it still amazes me that all the ball joints and gaiters etc are still in perfect condition, removal of the trunnion for a modern swivel joint would be a real advantage for an Elan.

By the way is the consensus that they should be oiled not greased like it was with the 7 owners a decade ago?

[dougal9887]

This link explains.
elan-archive-f16/trunnion-analysis-t4057.html
However further research suggests that the Elan is light enough not to require the anti dive geometry provided by the trunnion, which presumably was originally designed for a heavier car. No doubt this is why ball joint conversions are acceptable.
Dougal

[gjz30075]

By the way is the consensus that they should be oiled not greased like it was with the 7 owners a decade ago?

No consensus. Ask ten different people and half will say grease and the other half will say oil.

lotus-twincam-f39/oil-grease-gun-t13894.html

[vincereynard]

Thanks for the replies. It is something I have wondered about for quite a while!

Grease or oil. It is certainly my understanding that EP90 was the recommended lubricant for a Triumph. I have had one snap on a Vitesse. The logic being that grease would become too viscous to lubricate properly in that situation.

A similar situation to the early Norton Commando as it happens. The swinging arm, (a particularly dubious bit of design), is provided with a nipple but EP80 / 90 is recommended as the grease may not (i.e. hasn't got a chance) in reaching the bearing surfaces and excess pressure will blow the end caps off!

[stevebroad]

Canley Classics make a ball joint conversion for the trunnion now, so it is possible. I guess it was just cheaper to make the trunnion rather than the alternatives back in the day

cheers
Rohan

I have used these on my project car as they allow me to have adjustable caster.

[The Cyclist]

My view on trunnions is that they are a straightforward & cheap way of dealing with the forces. Don't forget the suspension spring is try to pull the threads off the upright & the trunnion and at the time they were put on the Elan they had only just stopped using the uprights in Formula 1. I don't mean the same set up, I mean the actual uprights. I think Ron Dennis started in F1 filing the casting marks off the original triumph uprights in the Cooper workshop.