Lotus Elan

clutch effected by heat?

PostPost by: David tye » Tue Jul 26, 2016 11:54 pm

I've had an Elan built from scratch with everything brand new where required. the car was built for racing so most of the components came from TTR.
when taking the car out for a 6 hour relay recently I found that changing 2nd to 3rd and 3rd to 4th became almost impossible. we've worked out that as the clutch fluid has overheated the clutch ceases to disengage. (the slave cylinder is close to the exhaust).changing down is not a problem because we are double de clutching which has the effect of pumping the clutch.
when the car cools down the clutch is back to being OK. when hot you can be in form up in first gear and the clutch fully depressed and the car creeps forward unless you brake.
we are going to review the fluid that we are using and create a heat shield.
has anyone else had this problem?
how have you fixed it?
david Tye
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PostPost by: Panda » Wed Jul 27, 2016 1:29 am

Hi David, it does sound like the fluid is boiling. We use a Dave Bean internal concentric slave cylinder and have never had a problem. I do change the fluid annually with the highest boiling point fluid available and the clutch hose is shielded up to the master cylinder with hi temp silicon tubing. The master cylinder seals, if worn, can allow the fluid to bypass back to the reservoir with the pedal depressed. Normally this occurs when the pedal is depressed after a few seconds, when the car will start to move if in gear.
cheers Alan P.
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PostPost by: john.p.clegg » Wed Jul 27, 2016 5:09 am

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PostPost by: rgh0 » Wed Jul 27, 2016 10:43 am

The other reason you may have a problem is that as the bell housing heats up under racing stresses the amount of throw required to disengage the clutch fully increases so you need to minimise the free play when cold to less than the factory spec.

I presume you also have good quality new hoses and that the master cylinder is in good condition with its reservoir valve seal working correctly and the overall flywheel and clutch assembly was built to the correct stack height versus the throw out bearing and slave cylinder assembly ( some of the components you can buy are not quite right in this regard) as issues in any of these can be part of the problem also.

With new good quality standard Dot 3 fluid I have never had a clutch problem due to the fluid getting to hot while racing --- and I have done a six hour relay with 3 other cars on a couple of occasions. i have the TTR race exhaust pass close to the slave cylinder as you have. If it is really the fluid getting to hot then use a high boiling temp DOT 5.1 fluid and put a heat shield to protect the pipe and slave cylinder.

cheers
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PostPost by: David tye » Sat Jul 30, 2016 11:30 am

thanks guys, really appreciate the help
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PostPost by: vstibbard » Sat Aug 06, 2016 4:19 am

I've used Internal slave cylinder for my 26R and also heat shield on the flexible lines

On a recent S1 for racing, I used the standard slave arrangement with heat shield over the flexible lines with racing grade fluid, the car was also road tested in 38Deg C conditions in Sydney including being stuck in stationery traffic and I experienced no boiling issues.

Both work

Cheers

V
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PostPost by: David tye » Mon Aug 29, 2016 11:46 am

thanks to everyone, in particular Rohan.
fitted heat shield and duct - perfect.
took 3 seconds a lap off and probably 2 more due to driver.
cheers,
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