Torsion bar - how slack is slack?

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ColinChandler
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Torsion bar - how slack is slack?

Postby ColinChandler » Thu Jun 27, 2019 7:55 pm

Hello all,
I wonder if someone could give me some advice please. I've dismantled the front suspension and with no load in it, the big cast front suspension arm has a little play in it when mounted on the torsion bar splines.
i.e. if I hold the torsion bar firmly in my hand, I can waggle the outer end of the arm and feel some looseness. It's only a mm max of slackness radially at the other end of the arm but is that acceptable? I'm not sure how tight a fit it should all be. There must surely be some slackness in there to get the arm onto the splines in the first place but have I too much.
Any advice would be much appreciated.
Many thanks, Colin.
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les
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Re: Torsion bar - how slack is slack?

Postby les » Thu Jun 27, 2019 8:00 pm

You’re going to get a little ‘slack’ which is multiplied at the end of the lower arm. If you’re only talking a millimetre that’s to be expected.


ColinChandler
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Re: Torsion bar - how slack is slack?

Postby ColinChandler » Thu Jun 27, 2019 8:10 pm

Thanks Les, you're a lovely man. That's just what I was hoping someone would say.
Many thanks, Colin.

RobThomas
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Re: Torsion bar - how slack is slack?

Postby RobThomas » Fri Jun 28, 2019 6:30 am

Mine moves quite a bit. Not a worry for me since both sections still had lots of teeth left on the spline and no signs of distress.
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ColinChandler
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Re: Torsion bar - how slack is slack?

Postby ColinChandler » Fri Jun 28, 2019 8:07 am

Thanks Rob,
Its the same with the splines on mine. They all look fine too.
The rear splines at the cross member end have no slack in them at all so it was just a case or wondering if there was too much wear at the front for it to be unacceptable. I've tried a few different arms on the torsion bar all with different amounts of play so basically I ended up totally confused and in need of some guidance.
Thank you both for your comments.
Best wishes, Colin.

don58van
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Re: Torsion bar - how slack is slack?

Postby don58van » Fri Jun 28, 2019 8:34 am

I'm glad the OP raised this question because I have been wondering about the same issue for some time.

My question for Rob, or whoever has some info on this: wouldn't the slop in the splines cause a clunk when going over bumps? :roll:

Don

RobThomas
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Re: Torsion bar - how slack is slack?

Postby RobThomas » Fri Jun 28, 2019 9:03 am

The torsion bar remains under torsion even at full rebound (hence difficulty in removing trunnions) so there isn't any noticeable slop.
Cardiff, UK

philthehill
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Re: Torsion bar - how slack is slack?

Postby philthehill » Fri Jun 28, 2019 9:32 am

From new the splines are meant to be a sliding fit but that does not mean that they slide in use. The sliding fit does mean that play can be determined especially at the outer end of the thick front suspension arm when the suspension arm is disconnected.

It should be remembered that the torsion bar was designed to be slid out rearwards (once the horseshoe washer was removed) through the cross member so the splines need to have some clearance/wiggle room - but it is more often easier to knock off the thick arm and remove the torsion bar forwards.

The torsion bar should be adjusted fore and aft with suitable washers at the rear of the torsion bar so that the max spline engagement should be achieved at the front and rear of the bar.

I always recommend discarding the horseshoe washer and fitting stepped washers either side of the cross member for positive torsion bar location.

There is sufficient loading on the torsion bar to always hold the torsion bar male splines against the female splines of the front and rear arms so alleviating the possibility of knocking between the splines.

Because they are held under load it is often difficult to disengage especially the front thick suspension arm from the torsion bar after prolonged use and exposure to the elements.

I would not recommend using grease on the splines but a light spray of anti-seize compound would not go amiss.


don58van
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Re: Torsion bar - how slack is slack?

Postby don58van » Fri Jun 28, 2019 10:14 am

Thanks Rob and Phil for the further information you have provided.

The thick arm (front) is quite a sloppy fit on one side of my Traveller (which is off the road for a full restoration). The spline on both components look fine. I have been wondering whether I should replace one or both components, but based on your advice there is no need.

Apologies to the OP for elbowing my way in. :wink:

Thanks again
Don

ColinChandler
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Re: Torsion bar - how slack is slack?

Postby ColinChandler » Fri Jun 28, 2019 11:57 am

Hello all,
Its not really an elbowing in, more a broadening of ideas and experience. Always welcome unless we now start talking about wiper motors. :D That is a hijack.
Coming back to the subject...almost. What is the purpose of the horseshoe washer? I assumed it was to clear the corner radius of the torsion bar's threaded portion and allow the bar to be pulled up tight to the crossmember but I do like the idea of the extra location given by two stepped washers either side.
Cheers, Colin.

philthehill
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Re: Torsion bar - how slack is slack?

Postby philthehill » Fri Jun 28, 2019 5:51 pm

Removing the horseshoe washer allows the torsion bar to be drawn rearwards through the cross member.

If you fit the extra stepped washer make sure that the step is square and fits snugly into the cross member hole. Some stepped washers do not have a square step and therefore do not fit nicely into the cross member. I have had to true several in the lathe before fitting.


philthehill
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Re: Torsion bar - how slack is slack?

Postby philthehill » Fri Jun 28, 2019 5:57 pm

Don
Try changing over the thick front lower suspension arms from side to side and see if there is any improvement.

Phil


Rust bucket
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Re: Torsion bar - how slack is slack?

Postby Rust bucket » Sun Jun 30, 2019 9:20 am

Also I would say make sure the tie rod rubbers have not gone soft and spongy, if so this will put extra wear on the cast iron splines in the arm. Polly bushes are good for this, bit of a tight fit thow.

philthehill
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Re: Torsion bar - how slack is slack?

Postby philthehill » Sun Jun 30, 2019 11:05 am

If you fit new bushes to the tie rod - I would recommend fitting a Poly bush to the front for braking resistance and a rubber bush to the rear for articulation.



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