6 Speed Transmission / Clutch / Shifter Issue - any guidance appreciated!

[acoffing]

Hello all - first post! I have a Caterham R400 Superlight in the USA. It has a 2.0L Duratec and Caterham 6 speed. It has been a ton of fun, but I would greatly appreciate some help in diagnosing a transmission / clutch / shifter issue I am having. 

Most of the time, the car behaves normally with no problems. The problem occurs intermittently when coming to a stop then starting off again. When it does exhibit a problem, here are the symptoms:

• Clutch pressed, transmission won't go into gear
• Clutch released in neutral, and an obvious knocking noise occurs from the transmission / clutch area
• Yesterday, while the shifter was still in neutral, releasing the clutch caused the car to be propelled forward very slowly, almost as if it was partially in gear despite the shifter being in neutral. The strange knocking noise persisted while the car very slowly was propelled forward.  Depress the clutch and the noise stops, and forward movement stops (shifter still in neutral). 
• I move the shifter back and forth a bit in neutral with clutch depressed, then all of sudden the issue goes away again completely, it goes into gear just fine, and no more noises (until it intermittently happens again)

Any ideas where I should start to diagnose this? I would love to get it fixed up and get back to driving and some track time! 

Thank you for any help!

 

[Jonathan Kay]

Welcome.

Is that hydraulic or cable clutch?

Any recent work on it that might be associated?

Jonathan

[John Vine]

Hi and welcome. I too have an R400 with 6-speed.

First thoughts...

1 sounds like clutch drag - a variety of possible causes: leaking master cylinder seals, worn driven plate, knackered slave cylinder, maladjusted pedals, obstructive pedal stop, etc etc

2 could be gearbox layshaft rattle - if so, that's normal

3 is puzzling. Sounds as though it could be a problem with the gearbox internals, such as synchros?

Have you checked the oil level in the box?

Do you have a gearbox specialist nearby? If not, try contacting Phil Stewart at Road & Race Transmissions for his thoughts:

https://www.rrtransmissions.com/

JV

[22daz]

I would guess that is a clutch release bearing failing. Check the fluid level first. But it's likely the engine will need to come out to fully diagnose.
22daz

[ScottR400D]

It's more than a clutch issue given the creeping forward when in neutral. 

When I built my R400D/6 in 2015 I had a similar issue after a few hundred miles. When completely cold the car would creep forward when in neutral unless the clutch was depressed. It was also noticeably hard to roll about with the engine off. Once hot the car seemed fine. 

CC fitted a replacement box under warranty and told me there was a synchro issue with the original. 

As a long shot what oil are you using? Not a GL5 is it?

[Wrightpayne]

SPC claim there is an issue with second gear on the 6 speed, in that the internal bore tolerance on the gear is too small and that they seize up when really hot. When he rebuilt mine he honed out the bore to a 'special top secret' size to prevent the problem occuring.

Not sure if relevant here but worthy of mention! 
 

Ian

[Geoff Brown]

Possibly clutch cover cracked & distorted ?  Had similar symptoms when out on a blat. Decided to dash 20 odd miles for home. Then the clutch pedal got higher & higher until I was shifting by revs only. Bit crunchy !

On dismantling the clutch cover had indeed cracked in four different places around the periphery. The flat part was also slightly distorted.

My theory was that when depressing the pedal the centre of the cover distorted so much that selecting gear or coming into neutral was a 50/50 chance.

[ScottR400D]

But how would that allow transmission through a gearbox in neutral, Geoff?

[acoffing]

Thank you all for the help and ideas! I will be giving a fluid change a try first and then go from there with diagnosis of the other items mentioned.