The infamous stag twitch

[stagwingnut]

Hi all , I can't say I have ever experienced the stag twitch in the 20 yrs of owning my stag , so I'm just wondering is this a problem only to manual cars as mine is auto ! Can automatics suffer this too ? Also do tr6 and the 2000 and 2500 range of cars suffer the twitch as they have the same rear set up ? Regards Graham

[Motorsport Micky]

Unless your car has a modification that presents it the "Stag twitch" is the sliding yokes and shafts at the rear overcoming friction when you come off the power after applying it through a corner. It takes the form of a "lurch" or shimmy from the rear as the shafts realign themselves, if you come off the power midway through the corner rather than when the car has straightened up it is much more pronounced. It doesn't matter whether you have a manual or automatic gearbox the twitch is caused by the rear driveshafts which are the same.

If you are constantly in "Driving Miss Daisy" mode when driving it's unlikely you apply enough power entering and through a corner to apply enough torque to the drive shafts to make them "bind" and they will slide smoothly taking up the variances in length of the driveshafts and so you will not experience the twitch.

Micky

[stagwingnut]

Thx for that Micky , I always keep my splines well greased with graphite grease ,!! We'll explained answer !! Cheers Graham

[Mike Stevens]

Definately affects the big saloons too. Maybe even more so that the Stag. I've been driving Triumph big saloons since 1974 and I know when it's going to do it and automatically adjust for it without even thinking about it!

Clean and well-greased driveshaft splines certainly reduce the effect dramatically, maybe even to nothing.

Cheers,
Mike.

[Andrew S]

I think one of the big factors is the condition of the rear bushes and suspension that allows enough flex and movement as it should rather than expetcing the splines to do all the work. This can be proven by replacing the rear trailing arm bushes with superflex ones or simialr, it goes

[Mike Stevens]

I think one of the big factors is the condition of the rear bushes and suspension

Yes, probably true. Certainly, if you clean and grease the splines the 'twitch' gets better as it also does if you change out the old bushes. So maybe both have an effect.

My Stag doesn't exhibit the effect at all at present. Mind you, it's only done 1000 miles since the rebuild when it had cleaned and greased splines and poly bushes everywhere!

Cheers,
Mike.

[Stagsongas]

Rilsan coated splined shafts have cured it for me up to now, but that's only 500 miles yet, there's time....

At least the shafts also come fitted with grease nipples (a big omission on the originals) to make things easier and another difference - the producer refuses to refit the rubber boots over the new inner couplings.

After looking at removed shafts, the rust all over those inner joints and the complete lack of it on the outer joints (no boots fitted as standard) I have to say I think he's probably right on that one.

Regards

Steve

[stagwingnut]

I have to say the boots around the inner uj s are a nuisance when working in that area ! I wonder why inner joint with the boot, is more prone to rust , I'd have thought it would be the outer ! Hmmmm food for thought on that one !! Regards Graham

[jleyton]

I have a theory that hydraulic lock could contribute to the problem.

The outer yoke has what looks just like a core plug that prevents the entry of water into the sliding joint. However, as the joint slides it is compressing the air trapped in the cavity which is sealed by the grease. This will impede the free movement of the sliding joint.

I've drilled a very small hole (1/16") in the core plug to relieve this compression and to allow the sliding joint to slide more easily. It seems to work on mine at the moment and is small enough to prevent anything untoward getting in.

Just my theory (Ah,huh, ah huh for the Python fans out there )

Cheers

Julian

[Stagsongas]

I have to say the boots around the inner uj s are a nuisance when working in that area ! I wonder why inner joint with the boot, is more prone to rust , I'd have thought it would be the outer ! Hmmmm food for thought on that one !! Regards Graham

Graham,

It just never dries out when covered with a boot, for 10 months of the year anyhow.

Regards

Steve

[Stagsongas]

I have a theory that hydraulic lock could contribute to the problem.

The outer yoke has what looks just like a core plug that prevents the entry of water into the sliding joint. However, as the joint slides it is compressing the air trapped in the cavity which is sealed by the grease. This will impede the free movement of the sliding joint.


I've drilled a very small hole (1/16") in the core plug to relieve this compression and to allow the sliding joint to slide more easily. It seems to work on mine at the moment and is small enough to prevent anything untoward getting in.

Just my theory (Ah,huh, ah huh for the Python fans out there )

Cheers

Julian

Julian,

I think this is a very good idea.

Unless the entire void is filled with grease, that will not provide a hydraulic lock. What it will do is compress any remaining air with the grease providing the final seal (like oil does with piston rings).

The Air will compress of course, but only to a degree. Eventually the resitnace of the compressed air will equal the force moving the shaft, in which case the shaft won't move any further. The Air 'exhaust' hole idea is a very good one which cannot do any harm even if it didn't work, unless anyone is given to driving their Stag in the Sea!

Regards

Steve