Lotus Elan

New trunnion stiff to turn on wishbone

PostPost by: david.g.chapman » Sun Dec 04, 2022 9:58 pm

I've just assembled a new trunnion and vertical link to the lower wishbone, but when the wishbone bolt is torqued up the vertical link/trunnion combination is very stiff to turn on the wishbone.

Is this normal?

I've not lubricated anything apart from some copper grease on the bolt, and I believe the bushes, seals and metal washers are correct. The inner washers rotate against the outer washers and nothing else is rotating.

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PostPost by: david.g.chapman » Mon Dec 05, 2022 9:14 am

I think I've worked it out. The inside of the wishbone holes have worn large over the years, and the central tube is nosing into the outer washer and pushing it into the hole entrance either side.
This will make the whole thing bind up on assembly. I can increase the effective length of the tube to compensate.
I had already fitted metal plates to the outside of the wishbone holes to take up the ovality.

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PostPost by: Elanman99 » Mon Dec 05, 2022 2:01 pm

The holes in the wishbone should not have worn oval as once tightened up and gripping the tubular insert there is no relative movement (so nothing to wear).

Other than replacing the wishbone, a better fix would be to weld up the hole and make new one, obviously involves more work and painting etc.

With your worn holes, because the tubular sleeve only has a thin wall its going to deform the thin stainless dust shield (lubricant retainer?) as it tries to enter the oval hole. For a less long term repair you could put your repair 'plate' on the inner faces of the wishbones and fitting corresponding washers at the inboard ends of the wishbones, this might require slightly longer bolts.

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PostPost by: Craven » Mon Dec 05, 2022 4:04 pm

Well known Elan problem, replacement both original and improved style e.g. Spyder readily available, do well to fix it long term as a favourite MOT failure.
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PostPost by: david.g.chapman » Mon Dec 05, 2022 7:25 pm

Yes, a good repair would be to weld up and re-drill - or change the wishbones!

However, the holes had worn oval-ish a long time before I get the car, and I made up semicircular plates many years ago to fit into the wishbone recesses on the outside of the holes (I didn't have the means to weld). The plates are an interference fit in the recesses and cannot move about or rotate once the bolts passes through them. So when bolted up the wishbones and tube form a rigid unit.

I've done one side now and the trunnion rotates in a satisfying way with a poke from a finger. The tube is still wider than the elongated hole, so the outer washer just bells out a bit into the hole and stops. If the holes had been really large the tube would be drawn into the hole onto bolt pressure and bolt torque would drop off.

I will check the bolt torque over time to make sure anyway.

Cheers,

Dave Chapman.
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PostPost by: Donels » Mon Dec 05, 2022 7:30 pm

I’ve seen this problem progress to wishbone failure, not my car I might add. It’s time for new wishbones.
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PostPost by: billwill » Mon Dec 05, 2022 7:51 pm

To me, your symptoms seem to imply that the washers are too big and are gripping on both the steel tube in the centre of the bush and ALSO gripping the outer tube that keeps the rubber bush intact.

I think the rubber there is supposed to flex, otherwise why is it rubber instead of a solid steel tube with fat walls.
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PostPost by: david.g.chapman » Mon Dec 05, 2022 9:12 pm

Hmmm. Food for thought there.

The only reason I replaced the trunnions and vertical links was that there was too much rock in the trunnion. There was no problem with the wishbone bolt due to the plates I fitted back in the early 2000s, so I don't see any progression in my case after 60000 miles.

However I do want to check on what should be rotating and was shouldn't be!

Here goes, from the outside in...

1. Outer washer. Fixed to wishbone. Non rotating.
2. Square o ring fitted around nylon bush. Rubs against both washers. Rotates?
3. Top hat nylon bush. Rotates around inner tube and rotates against outer washer.
4. Inner washer. Rotates with trunnion body as if glued to it.
5. Inner tube. Non rotating as clamped to wishbones.

Is this right?

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