Stag+RV8, clutch slave cylinder, 1" bore to 7/16"

[Dibnah]

Hi all,

Stag with RV8 and Stag MOD. New clutch, 1" slave (FTC5071) and master (AEU1644) fitted before the RV8 engine was installed, clevis pin was fitted to the middle of three holes on the clutch operating arm. It worked but the action was low, it's now got worse and can't engage gears with the engine running.

Moved the clevis pin to the lowest hole of three, improved but still problematic.  There is immediate movement of the slave pushrod when operating the clutch pedal, pumping the clutch pedal doesn't seem to help.

Clutch operating arm moves from about plus 5 degrees to minus 5 degrees from the vertical, I'll need to measure the  travel distance of the pushrod, my understanding is that 16mm is apparently the minimum.

An option used by others is to fit a 7/16" slave cylinder (591231) for greater travel, albeit at the price of greater effort. If this means that I can put some summer miles on the car without splitting the engine and gearbox then that's fine by me.

A question: will I need to change the slave pushrod to match the 7/16" slave cylinder?

[Russell]

I'm surprised you got a better response on the lower hole of the three, I would expect more movement in the top hole.

To answer your question, no you won't need to change the pushrod for a 7/8 bore slave, (I assume 7/16 is a typo as that would be tiny!).

This may not make you feel better, but I had similar issues with my RV8 Stag, never felt confident that the clutch was working correctly. I solved it by installing an LT77 5 speed box, but that's probably a route you don't want to go down.

Russell.

[RobPearce]

Isn't this the classic symptoms of the usual failure mode - the lock bolt that holds the release fork onto the cross-shaft snapped off?

[Dibnah]

Thanks for the replies, my error re: hole position, I've spent too long laying under the car looking up at the slave cylinder! I moved the clevis pin towards the centreline of the gearbox input shaft, so greater movement of the clutch release fork for the same movement of the pushrod.

Unfortunately, the symptoms do indeed fit a broken bolt for the clutch fork, although would this not cause the operating arm to sit at a different angle?

It is possible that the adapter plate to match the RV8 with the Triumph box has created dimensional issues, first thing I need to do is to measure the movement of the pushrod.

Overdrive is on my wish list, but an LT77 is an option.

[Russell]

I changed mine after speaking with Ian at Monarch Stags. He said he had a customer in Germany that was getting through a clutch a year with the adapter plate set-up.

My experience was it seemed to mash the fingers on the pressure plate. Mine had a crudely extended bearing carrier , along with an extended pushrod to make up for the extra distance on the bell housing caused by the adapter plate. That, coupled with the two sets of bolts between the engine and gearbox (gear-box to adapter, adapter to engine) meant the whole thing was a nightmare.

I miss the Stag box a bit, as it's far more refined than the LT77, but my set-up is so much simpler now and just works.

The whole car is a bit of a mule, and had the RV8 in it when I bought it, so I'm not bothered about the originality.

[Jonny-Jimbo]

Quoted from RobPearce

Isn't this the classic symptoms of the usual failure mode - the lock bolt that holds the release fork onto the cross-shaft snapped off?

I was told this as well when my clutch wasn't working on my 2500 engined mk1, so I pulled it all apart and the fork, cross shaft and pin were all fine. The problem in my case were a few small things coming together to make an ineffective clutch, but it wasn't that. Try using a suction bleeder on the slave cylinder, helps get that fiddly bit of air out of the system.

[Dibnah]

Thanks again for the replies, of course it's a 7/8" slave cylinder not 7/16"! Can't seem to edit the title though.

I have 16mm of movement on the slave piston with the standard 1" slave cylinder, which suggests that external linkages are OK and that further bleeding is unlikely to achieve improvement. I'll try the 7/8" slave cylinder, if that fails then I'll probably drill a hole in the bellhousing to have a look.

[Dibnah]

7/8" slave cylinder and clevis pin closest to the centreline of the gearbox input shaft works, bleeding was a bleeding pain, several useful threads on this forum, thanks. There is some lost motion on the pedal, possibly trapped air, so I'll need to revisit at some stage.

An unknown is "it worked, and then it stopped working", which is nagging me. More road testing required!