Re-setting torsion bars on a 406

[David C]

My 406 is dragging its exhaust over speed bumps and the torsion bars are at full adjustment. I think the next step is to remove the torsion bars and move them round one spline. Can anyone offer any advice? Do the front and rear have the same number of splines?
Any constructive suggestions welcomed.

[Roger Morrall]

There’s a lengthy discussion on this topic re adjusting 408 torsion bars under the V8 section. I’ll repeat the advice I gave then based on my experience with a 410.

"You may find that the torsion bars have sagged beyond the range of adjustment available, if so you’ll need to have the car on a lift on the chassis (ie not on its wheels) and a friend with a large Stilson wrench. First screw the adjustment bolt right out so that there is little or no tension on the torsion bar. You might need to remove the axle rebound retaining strap to achieve this happy state of affairs. You then need to dismantle the torsion bar mounting, which will allow the torsion bar to drop to the point where the adjustment arm can be taken off and moved by one spline. You’ll then need the friend with the stilson to pretension the torsion bar slightly so that you can reassemble the mounting. That needs some strength on the part of your friend but by no means a great deal of brute force. This might all sound rather alarming but in my experience it is all very well made and comes apart and goes back together again easily - given a good previous dose of penetrating oil.

[Roger Morrall]

Perhaps I should clarify - I’m talking about the front torsion bar mounting

[David C]

Very helpful and thank you for clarifying. My first instinct was to start at the back so you have probably saved me a lot of work.

[Sam410]

How many times can this be done before it becomes advisable to replace the bars?

And if you have a pair of used but unmarked bars is it possible to tell which side they should go?

[Roger Morrall]

David.

It might be worth your while to replace the adjustment arms while you’re at it - these were carried over to the much heavier V8s initially, proved a bit too fragile in that application and were then beefed up. If that is you can easily get hold of the later arms.

When you’ve done the job all you need to do is to set the adjusters so that the chassis is parallel to the road both fore and aft and side to side. It might just be worth taking the trouble to load up the car appropriately to your normal use per mile travelled.

It’s all very well worth doing, it improves the handling no end and makes the car feel much more agile

(There is I think a description under the V8 resources section of this site re the trials and tribulations encountered whilst doing the same thing on I think a 412, (rather oddly filed under 407) but the 412s originally had self levelling suspension which left all sorts of bearings behind which aren’t present on the earlier cars so don’t get put off by it)


Sam

As to how often? - it seems to be something like a once in 50+ years event (and more for the 6 cylinder cars) so I don’t think it’ll worry most current Bristol owners

As to whether they are handed? I note that the parts lists implies they are but if they aren’t marked I do wonder. Not least how BCL differentiated. It’s also been my understanding that a torsion bar has exactly the same characteristics whether twisted clockwise or anti-clockwise.

[Roger Morrall]

Having done a little bit of research I find I must correct my previous comment regarding the handing of torsion bars. It appears to be essential that they are put back on the side they came off. It appears that some are deliberately handed during manufacture, others not, but the latter then become handed in use. I learn for example that Jaguar E Type torsion bars are not handed during manufacture but are helpfully stamped R and L (and accordingly carry separate part numbers) only so that one knows which side they should be put back on. No help to Sam I’m afraid.