alangraham wrote: ↑Sat Jul 23, 2022 6:45 pm
Clutch judder (hot engines) is a topic that's come up before on this forum when I searched, and the consensus was that it's just an old car thing that happens to many old classics but I can't accept that. They didn't do it on Dollies I had in the past that were new or newish, and so it's an issue with a mechanical cause that I believe can be sorted. How do I determine how much "lash" there is and should there be any?
This ISN'T a new problem at all, or even an old car problem. Marinas, which share this gearbox and some clutch components with the OHV Triumph engine, were prone to this, even from new. I was working for various BL dealers throughout the 70s and experienced it first hand, along with the many (mostly) fruitless attempts to cure it, which included 2 clutch plate redesigns, 1 change of cover design and lots of experimenting with prop shaft angles. It even has a name, "clutch thrash vibration" and is thought to be induced by more than one harmonic working in concert at certain points or temperatures. If it's any consolation, several Fords also suffered the same issue, from MKI and MKII Consuls though to the MKII Granada. I should add here that most of my PERSONAL experience with actual cures was on the MK II Granada with 2.0 Pinto motor or 2.3V6. For which a revised driven plate was actually marketed by Ford. However, to get one, you had to know it existed and ask for it, the info was not published, nor was the revised plate standardised!
Back in the 80s (and when self employed) if I was faced with this problem, i'd toddle off down to the main dealer and buy a genuine clutch (and hang the expense, I wasn't paying!) Which probably isn't an option anymore.
There are probably very few or no genuine BL driven plates left, only aftermarket stuff and we ALL know and distrust that!
Another thing you have to take into consideration is that, in the 60s and 70s, clutches were lined with asbestos, which, of course, is no longer the case. Asbestos is the perfect material for clutch or brake linings, it's a crying shame it's so b****y toxic! Nothing they've come up with since is anywhere near as good!
I find it concievable that the revised cluch plate merely masked the symptoms and wasn't an actual fix. In any case, it would have been another asbestos lined plate, if you COULD find one it'd probably be illegal to use it!
Whilst the single rail BL gearbox seems particularly prone (and it may have inherited this tendency from the earlier 3 rail small saloon gearbox) I've had clutch thrash vibration on Sprints too (different gearbox) and, of course, numerous Fords and other makes too. The ONLY common denominator is RWD, not even a split prop is common to all sufferers. So I think if a particular design feature (though I don't know what it is) makes a car more prone to this condition and modifying the efficient asbestos lined drive plate helps, the very fact that they've done away with asbestos may well make things worse and there may no longer be an effective fix.
Steve