1970 Triumph TR6 PI Running Report

Working on the premise that the Alternator ought to have enough oomph to supply the car's electrical demands on its own in normal circumstances I decided an upgrade was in order. Decided against going for an A127 as I found a supplier selling upgraded 18ACRs which visually are indistinguishable from the standard 15ACR fitted.

New alternator arrived during the week and it was a straightforward job to swap. Quick test drive revealed the ammeter went strongly into charge initially before dropping back to neutral and no combination of electrical demand could push it into discharge for more than an instant, apart from the Indicators interestingly. I'm guessing that's because the alternator doesn't have chance to stabilise before the intermittent nature of the demand disappears.

It may be wishful thinking but the car felt like it was idling better with less fluctuation. I wonder if the original alternator was struggling to supply enough volts for the pump at idle.

Next incident of note was an excursion to Stokesley Classic Car show.

This was a two car job as we were 5 plus Puppy so Oliver my Son had the job of driving the TR6 and the rest of us followed in the modern. On the way Oliver had used the screen wash and on arrival reported that the Wipers weren’t working. My initial instinct that it would be an electrical issue were quickly dashed when it transpired what he actually meant was the Driver’s side wiper wasn’t working, Passenger side was happily doing its thing as commanded. Back home after an awful lot of dismantling due to the Rack and Wheelbox seemingly being the components Triumph started with on the production line it transpired that the Gear had fallen off the Spindle in the Wheelbox. They are only staked on and once again the curse of the Classic Car owner strikes, it was clearly not the original being much too shiny and clean for a 50 year old component. New one ordered and fitted restored normal service. Fast forward a year or so and caught in a shower I reached for the Wipers, this time the Passenger side decided not to play ball. I think I have an idea what that’s going to be I was heard to mutter. Another new Wheelbox was ordered on spec and fitted rather more easily than the Driver’s side requiring only the Glovebox to be removed along with the heater ducting. As expected failure mode exactly as predicted.

If you are unfamiliar with IRS Triumphs you may not have heard of the “Triumph Twitch” The system is not very complicated, it comprises of an Alloy Trailing arm secured at two points on the Chassis or Bodyshell for location. The hub is part of the casting so basically the Driveshaft’s only role is to provide drive unlike some more sophisticated arrangements where it can play a role as a suspension arm. In Triumph’s case the Driveshaft is essentially a very short Propshaft having a Universal Joint at each end and a sliding joint in the middle to cater for the varying distance and camber change that the shaft has to deal with. The system works when everything is new, but wears quickly leading to (if you are lucky) knocks and clicks, or worse when wear creeps into the sliding joint it ceases to slide when under load and the Driveshaft becomes unable to change length to accommodate the demands of the upright and stop it moving. This usually manifests itself when you are giving it beans, probably in 2nd out of a tight bend or similar, everything locks up and then as you reach for 3rd it all relaxes, unlocks and resets itself to where it wants to be with a resulting change of direction, the “Twitch” You will have probably guessed by now we have the “Twitch”


For many years upgraded Driveshafts of various types have been available, ranging from better Universal Joints, Teflon lined sliding joints, both and at the top of the Tree come joints that replace both with modern CV joints as used on every front Wheel drive car on the road today. I elected to go for a pair of the latter. Available from a number of suppliers the word in the TR world was that the best come from Classic Driving Development from whom a pair were duly delivered.


Installation is relatively straightforward, especially as they are supplied with brand new Hubs which is a double win as:-

a) You don’t have to remove the original Hub from the old Driveshaft which requires an especially butch Puller (which I didn’t have) and

b) There are numerous tales of Hubs failing so new ones give added peace of mind.


It probably took 90 minutes to get the car up on stands, remove the Brakes and pull the Driveshafts out. No surprise that the Passenger side exhibited significant slop in the sliding joint. Reassembly was slightly more complicated on the Driver’s side in that the CV joints are quite a bit larger in diameter than the universal joints and due to the Exhaust occupying some of the space meant that the exhaust needed to be dropped to allow the shaft to be lifted into place before re-attaching the Exhaust.

Another foible of the Triumph IRS system is Triumph’s slightly perplexing decision to use fine threaded studs to secure the Hub in the Trailing Arm. Again when new this probably wasn’t an issue but after 50 years of corrosion and careless over tightening of the associated Nuts means that you will almost certainly be dealing with a number of stripped threads. Classic Driving Development do an updated Stud kit which uses stepped coarse threaded studs to address this issue. Supplied with a jig and correct Taps its a straightforward job to drill the existing holes out to the correct size with the Drill bit supplied and cut new threads before fitting the new Studs. As it turned out all my Studs were fine but you can be certain if I’d not made provision my experience would have been otherwise!