Tuesday, 19 April 2016

Vibrating Propshaft and replacement woes

My GT6 has had a bit of a vibration that comes in at about 65mph for some time now, not severe but annoying. After investigating a while back I found that the propshaft had some wear in the sliding splined joint which would need a new prop to cure, as the vibration wasn't that bad I've lived with it for a few years now!

However, a couple of weeks ago driving to a local club meet the vibration got much worse and pretty unbearable. I investigated and found I had wear in a propsaft UJ, so I bit the bullet and purchased a brand new propshaft.

Fitting a new prop is fairly straight forward, the only pain is having to remove the dashboard support and gear box tunnel. One bit of poor triumph design is that there is a small extension hatch behind the gearbox tunnel to allow for the overdrive, If this had been made a bit longer so that it encroached on the gerabox cover rear this would make the job much easier as the propshaft flange bolts would be accessible without removing the tunnel. However Triumph weren't that sensible! I think this is my old mechanical designer and production engineering background from the late 70s/ early 80s coming out. I like to think that I always tried to make my designs consider future maintenance!

If Triumph designers had been sensible they would have made this access hole longer going forward to allow access to the propshaft bolts without removal of the tunnel...
Anyway I removed the tunnel to provide better access. dropped the exhaust down and unbolted the prop.

Inspection once removed confirmed a worn out UJ at the front along with the worn sliding joint, this would seem to be the reason behind the vibration.

The new prop supplied by Canley Classics is of a slightly different design to the original, firstly the prop tube is a smaller diameter, secondly the flanges are a different design to the originals, more about this later in the blog!

Old and new props, note the thinner tube on the new one. 
The other point I noted was that the new prop had grease nipples fitted in place. Normally the grease nipple holes have blanking plugs and nipples are only screwed into place during maintenance. However I suspected the prop would have been balanced with the nipples in place and replacing them with plugs may have upset the balance. I checked with Canley Classics and they advised me to fit with the nipples in place.

Original prop with blanking plus in place
New Prop with grease nipples in place.

I then went to fit the new prop. The diff end was bolted up with no issues.

However, the overdrive end had a problem the joint between the overdrive output flange and the propshaft front flange won't quite locate fully home.

I took some careful measurements with my digital caliper and I  determined that there was a clearance issue. The new prop has a different design of flange than the OEM prop. There is a clearance hole in the centre of the new prop flange that measures 28.5mm diameter. The OEM prop had a flange with a much larger diameter bowl shaped recess to provide more clearance.

Old prop flange has a bowl shaped recess for clearance in the centre

New prop flange has a smaller hole for clearance

The overdrive flange has a large castellated nut that sits proud of the overdrive output flange by approx 2.9mm. The nut is 31.4mm across corners and therefore fouls on the clearance hole on the propshaft flange. Taking into account the recess of 1.6 mm , the flanges sit proud by approx 1.3mm.


As a solution to the issue I filed chamfers on the corners of the castellated nut, this provided enough clearance to be able to allow the flanges to fully engage. I've emailed Canleys to advise the issue, they really need their supplier to ensure that new orders are fitted with flanges with larger clearance holes or OEM flanges so they are fit for purpose going forward.

Anyway, prop is now bolted up. I'll spend another evening later in the week rehanging the exhaust and replacing the tunnel, carpet, dash support, radio and trim .