Evening all.

Can anyone advise how much wear is acceptable on this type of joint please? Have been scratching my head as all three of my cars have play of varying degrees but only one is troubling me with excessive vibration and resonance at a certain speed.

Do the 2 blocks absorb the wear or is it also necessary to renew the pin and carden 'female' housing?

I will leave the answer to this to those with real-time experience, but I also have a question on the same subject: Which way does the cardin pin go into the shaft?: With the "flats" inline with the shaft, or across the shaft? As a matter of interest, what purpose do the "flats" serve?

Thanks,
DG

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Dennis

I changed one a couple of weeks ago and set the flats at right angles to the shaft.

Rightly or wrongly my reasoning was that the flats were to allow lubrication space, and that the driving surfaces should be intact.

As an associated question; has anyone ever made one from silver steel - thus available at modest price, and ready ground to size, at your local engineering suppliers?

Mike

Mike, you are correct, the flats, which help with lubrication should face fore and aft in the line of the shaft, the curved surfaces should bear onto the blocks in the direction of rotation.

Not sure on silver steel which is only slightly more resiliant than normal steel, the originals were made from case hardened steel. Case hardening keeps the 'flexibility' of the steel but with a hard working surface. What you should not do is use tempered silver steel as this would make the whole pin hard but brittle and likely to snap under sudden loading.

My Austin has the carden block coupling, with home made block and pins which are case hardened and has done abot 9000 miles with no obvious signs or wear and, as many local A7 people will tell you, I don't hang about when driving. There is obvious slight play when you lift the shaft up and down but I don't experience heavy shaft vibration which may well be caused by either the shaft being bent or, more likely, the flexible coupling at the other end.

I have found that the modern flexible couplings have the fixing holes at approximately 2mm out on the pitch diameter of the holes. although this does not sound a lot, when you assemble the coupling onto the shaft ( or gearbox ) the normal method is to get two studs in and then put pressure on the fabric to get the third stud into the hole which is 2mm out. This distorts one side of the coupling making it out of balance. What you need to do is gently file the inner edge of each hole, as close as possible by the same amount, so that the coupling slides onto the studs without distortion.

By the way, use 3/8 BSF nyloc nuts instead of those awful split pin jobs and the task is so much easier.

Sorry for yet another long ramble, just trying to be helpful.

I once had a ‘brainwave’ that I could put some washers behind the blocks to take up some of the play---result, the whole thing locked up solid on the first revolution.

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I had a similar 'brainwave' to Ian when I fitted the recent replacement unit. I turned up some phospher bronze washers of suitable thichness, but had a good waggle about on the bench prior to actual fitment. Indeed the first pair I considered too thick. Everything now points to a satisfactory job, and yesterday's 'Drive-It Day' went without a hitch. Certainly my transmission is much smoother than previously was the case.

I took this step because the spherical 'lump' through which the pin passes was very worn around the pin hole.

I believe that this a particular mechanism where lubrication is of the essence - even the old unit could be quietened down for a hundred or so miles with a fresh application of grease. I fancy this is one of those applications where Molybdenum Disulphide based grease is a definite advantage.

I am sure that Herbert would have used it had he had it available to him!!!

Mike

OK, so that is the pin problem cleared up. My "original" had no flats, but the "club" replacement had 'em, and the pin was only about a quid (can't remember the pounds symbol), so not worth making.

Now can we get back to David's original question about wear & tear?

Thanks,
DG

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Dennis

These units will still run in a quite apalling condition. The ideal is a nice sliding fit. Between these two you take your choice, but I suggest that you tend towards the later. It probably depends on what is available these days.

Mike

The problem with all 3 cars is that they all have pretty much the same amount of play if you grasp the propshaft and move it back and forth along the plane of the pin, however only one of them produces this ghastly vibration and noise at certain speeds which can definitely be identified as coming from the assembly.

When I assembled the unit first time around, the blocks were a snug fit on the pins and in the block, the only wear I could identify was 'end float' as described above but didnt think any more of it because the other 2 cars were the same.

David, a suggestion,

swap the 'faulty' shaft only ( not the Carden housing nor the fabric coupling ) with one of the two 'good' ones, if the noise/vibration transfers itself to the formally 'good' car then you know it is the shaft.

If no change then try both the 'faulty' shaft and housing on another car, again if the 'fault' does not transfer then the Carden shaft and joint is not your problem, it will then be tiome to look at the fabric coupling.

Not the best 'engineering' analysis but by a process of elimination you may well find the fault.

I have seen some Carden joint pins where thay have almost worn half through yet they still seem to work OK although there may well be a 'clunk' when changing direction from forward to backward. ( similar to a loose halfshaft ! )

happy hunting !

Just a thought, Are you sure you have no up and down play in the chassis ball connection and the spherical joint as this can also make a terrible din, especially if the prop is a touch out of line. Another point is that replacement drive discs are sometimes too stiff and can set the carden end of the shaft wagging about if the blocks are a bit loose. A more flexible disc would mask this effect to a degree.

Thank you very much for the suggestions. I did put a nice new fibre coupling on when rebuilding but now wonder whether that was the right thing to do - particularly in view of Malcolm's comments concerning the holes out of alignment - I remember it was difficult to fit for that reason. I still have the old soggy oily one so will try that out.

With the aid of a good used carden Block with new pin and blocks all kindly supplied by Tony L, and the old fabric coupling back in, I am happy to report that rumblings have ceased!

Thanks for all the advice everyone

I stopped the vibration from the propshaft on one of our RNs by replacing the large jubilee clip which retains the grease bag with two smaller ones connected together putting the screw sections opposite each other.