After a decent day one of the 2015 Circuit of Ireland Rally, the Tuthill Porsche 997 R-GT failed to leave the start line at the evening’s special stage around Newtownards town centre. The car was pushed out of stage on to a trailer and recovered to the service area.
By the time we got back, it was dark. Spectators surrounded the tent, with plenty of work ahead of us. The boys set the car up on jack stands and set to work on removing the gearbox. Just over half an hour later, the transmission was out and the clutch was exposed. It took engine builder Anthony just a few seconds to spot the issue: one clutch plate had lost all of its friction material.
Single Clutch Plate vs Mutiple Clutch Plate Pack
The clutch kit in most road cars consists of three main parts: single pressure plate, single friction plate and a release bearing. In competition cars like the 997 GT3 Cup on which the R-GT rally car is built, the cars run a set of multiple clutch plates, arranged in a clutch pack.
The advantage of a multi-plate clutch is that it can transmit higher levels of torque through a smaller diameter unit. The more plates there are, the more torque it can transmit, or the smaller the pack needs to be: Formula 1 clutch packs are about the size of your fist. The clutch pack in the 997 R-GT is a bigger diameter than an F1 pack, but smaller than a single plate road clutch.
With a carefully calculated number of plates in the assembly, the failure of one plate does not leave enough friction to drive the car. This is what happened to R-GT. As the team carries spare clutch packs, it was straightforward to fit new parts and get the 911 ready to restart day two of the rally.
Chief Engineer Graham Moore also decided to change all four dampers on the Porsche, to make driver Robert Woodside more comfortable behind the wheel. The car enjoyed a trouble free run through Day 2 and the team came home satisfied with a job well done.
Circuit of Ireland Porsche Rally Video
I put together a short video of our experience on the 2015 Circuit of Ireland Rally, which you can watch below. Enjoy the sights and sounds of the first modern Porsche to start this great rally for almost thirty years: it was cool to see it in person.