CV evolution
Nigel chooses a ‘fit and forget’ GT6 rear end upgrade
No sooner is my GT6 back on the road after its marathon body makeover, than I’ve got it back in my garage again! This time, I’m installing the excellent CV joint driveshaft conversion supplied by Alasdair Southall of Classic Driving Development, and binning the old Rotoflex couplings. All who know Triumph’s Rotoflex rear suspension will attest that when it’s good, it’s very good, with far more predictable handling than the old swing axle setup of earlier cars, but the downside is that it’s not the easiest to look after. Specifically, the Rotoflex rubber ‘doughnuts’ perish and split over time, and they require contortionist tricks in order to be replaced. The rear hub bearings are also notoriously fiddly to renew, needing precise shimming to run properly.
While the back end of the GT6 was stripped down to fit the shiny new driveshafts, it was a good opportunity to check the hub bearings. The Rotoflex suspension uprights carry the hub and outer axle shaft in a pair of opposing taper roller bearings, which are generally long-lived. Checking the hubs can only be done properly with the suspension off the car, as when installed pressure from the Rotoflex couplings masks play in the hubs, and it’s impossible to tell if any feeling of roughness comes from the bearings or the meshing of the diff gears.
Once off the car I inspected the hubs and turned them by hand. There was no discernible free play but one side felt gritty as it rotated, a sign that the bearings could be on the way out. Since I don’t fancy stripping and reassembling the rear end of the GT too often, I decided to bite the bullet and replace all the hub bearings. I figure that with new bearings and CV driveshafts, the back of the GT6 should outlive yours truly.
Proper job
Also following the motto ‘do it once and do it right’, I sourced genuine Timken bearings and entrusted the job of pressing in and adjusting the new bearings to Richard at local specialist machine shop Ward Engineering. Alasdair at CDD had a complete set of original Timkens available, so I collected these along with the new driveshafts. I cannot see the point of going to all the trouble of stripping the car down, fitting and adjusting new bearings, reassembling the car, only to find that cheap bearings fail a few thousand miles later. It’s far better to accept the extra cost of decent quality components and execute a proper job that’s going to last. Sermon over!
Serving as my classic delivery van, I hopped in the Scimitar and took the hubs over to Richard’s workshop. He soon had the hubs and old bearing tracks out of the suspension uprights but on inspection, the rollers of the old bearings didn’t appear too bad. Richard finds that looks can be deceptive; old bearings that are quite noisy can often have no wear marks visible to the naked eye. There followed a period of head-scratching over the adjustment of the new bearings. These opposing taper rollers have to be set up in the suspension uprights with just enough shims between the inner and outer bearings to allow free running, with minimal endfloat. It’s like adjusting a taper roller front wheel bearing but without the usual castellated nut and split pin arrangement to set endfloat. Triumph had a special tool to assist in getting the shim thickness correct without repeatedly pressing the bearing in and out and risking damage. Needless to say, said tool is right up the top of the ‘No Longer Available’ List, one line down from hen’s teeth.
Those experienced in the art of such bearing replacement say that usually, new bearings will be fine when simply fitted with the same shims as the old ones. The theory seems to be that the dimensions of the bearings are extremely accurate and don’t vary appreciably between one set and the next. Any dimensional variation will be in how the Triumph factory machined the uprights originally. So when Triumph first assembled the hub the correct shim thickness had to be determined, but new bearings don’t usually require a change in shimming.
Neither of the GT6 hubs contained any shims when stripped down, which was something of a surprise. Richard carried on, pressing in the new bearings followed by grease seals, outer bearing first followed by the inner, without adding any shims. With the hubs built up, both sets of bearings feel just right, spinning with very slight resistance and having no endfloat. As I left his workshop with the refurbished hubs to head back home in my Reliant delivery van, Richard seemed confident the bearings will be fine. I’m hoping the new bearings and CV driveshafts will prove to be of the ‘fit and forget’ variety.