Clutching at straws and beyond

The clutch issues that dogged the final runs at the Gurston practice day didn’t get any better.  And I didn’t want to blog about them until I’d sorted them.  I didn’t envisage it taking this long.

The first thing I did was to flush the clutch hydraulic system to remove all traces of air.  It seemed a bit better, but not radically so.  I entered the May Curborough event, with the idea of seeing if things were better.  Spinning off on the first corner of the first run wasn’t exactly on the planning sheet, and finding the battery didn’t want to restart the engine wasn’t (as an aside I seem to need to replace the battery every season, which is odd.) I managed to put in some semi decent times in the end, but it was evident that the clutch still wasn’t good.  At that point I made the decision to investigate things properly, and that meant removing the back of the car.


I needed to make removing the gearbox and suspension a one man job, so I made a trolley, which with appropriate packing pieces, allowed me to simply undo a few bolts and slide the back of the car off.  It was nearly that easy.  When I got inside what I found was a bit surprising.  The bobbin which actuates the release fingers has a bearing pressed into its ID.  And that bearing had fallen out and was sitting on the input shaft behind the release fingers.  I wish I’d taken a picture of it. This and the resulting millimetres of clearance between the bobbin and shaft may have gone some way to make the clutch of the RF84 a somewhat unpredictable device.  It would also have explained something that happened the first time we ran the car in Bicester.

When I depressed the clutch pedal in those first runs there was an odd modulated grinding noise.  It caused a lot of confusion amongst some pretty experienced people, including one who had made lots of numerical models of clutches and release finger operation in the late 90’s.  I’d say that the bearing had parted company from the ID of the bobbin pretty much instantly.

The bearing and bobbin weren’t usuable, so I had to source a replacement.  And this provided another puzzle.  I measured the dimensions, as Mark Bailey told me that there were two sizes.  Od thing was that the bobbin in the car wasn’t either of the standard sizes.  So it was back on with the rear of the car to measure the freeplay.  Which indicated that I needed the longer of the two options.  So I ordered this and refitted it. The longer bobbin definitely made the freeplay more reasonable.

With the rear of the car reassembled I tested the car in the drive (not ideal but there were few other options.) The clutch felt instantly better.  In fact totally different.  As the car has only ever been driven by myself and my son its possible that the clutch had never been right, and perhaps we should have known that.

Finally I managed, this week, to drive the car round a track; I hired the circuit at Bicester Heritage for an hour.  Again the car felt very different, and when I returned to the pits after the first run, the track manager said “there’s not a lot wrong with that”. He had a point. In that run I’d have to say that the car felt really good, and if anything seemed to be running better.

I’ve got another test session booked at Curbourough next week and am running at Gurston over the bank holiday.  We’ll see if the improvement translates to times by then.



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