Clutch sometimes releases while pedal down

[Deane]

In my 2017 Atom 3S the heavy duty clutch has slowly developed a strange problem. (Now 10K miles on Atom.) It happens only about once or twice per hour of drivinig: When the pedal is being held down but trans is in gear, like at a stop light, the car starts to creep forward as the clutch starts to engage by itself! This causes a bit of panic and sometimes I shut off the engine, pump the clutch once or twice, restart and then it is usually back to normal.
It is like the hydraulic fluid is leaking past the seals in either the master or slave but no fluid is seen leaking out anywhere. Is it possible that fluid can leak past the O-rings and drain back to the resovoir (at the master cylinder)? Seems if this happened at the slave then it would have to leak out on the ground.
Has anyone else experienced this problem?

[John Scherrer]

If you say there's no evidence of an external leak of clutch fluid, then it looks like you have an internal leak in either the master cylinder or slave cylinder.

The internal seals have either worn or the actual cylinder lining has become pitted due to corrosion or contamination, allowing the fluid to seep past the piston seals when you're holding the clutch pedal in for a length of time.

You should be be able to get rebuild kits for both master and slave cylinders, so hopefully you won't need to replace the whole units.

As to whether the problem lies in the master or slave - I don't know how to establish that - good specialist garages should have a pressure gauge that they could apply to the output to measure where the pressure loss is occuring.

Keep us posted on what you find and good luck ..

[Deane]

Thanks. There really is not much else that could happen other than the seals leaking internally but I don't know where the fluid would go. It is a puzzle. I have emailed TMI Autotech in Virginia to see if they know who makes the racing pedals and cylinders. The other problem is I can't see how much fluid is in the resovoir and there is no way to even access the cap on the resovoir as it seems to be hard against the windhield base body panel! Has anyone checked or filled this resovoir and if so how?

[John Scherrer]

Not too sure about the TMI-built cars but on the UK ones, you need to remove the windshield/horizontal "tea tray" (one unit).

It comes out in about 5 minutes - remove the 2 wing mirrors and about 3 other smaller stainless nuts/bolts.
Disconnect one cable harness for the wiper/washer motors and it lifts out.

Here's what the clutch and brake reservoirs look like on a UK 2011 Atom 3 :-

[John Scherrer]

This difficult access was addressed in the Atom 4. - A single hydraulic remote reservoir that supports the 2 brake master cylinders and the clutch, including a low fluid sensor is located in the front compartment under the bonnet.

[33bravo]

I had the exact same issue! Replaced the clutch master cylinder.

Tilton Engineering 74-625U

Less than $100

[Deane]

@33Bravo, Thanks for the part number! Also thanks for confirming that you had the same problem! Good to know before I start digging into it. TMI did get back to me and suggested a new cylinder. I see that Tilton also sells rebuild kits which include a new piston for $27. Might go that way too. In any event we would have to bleed the air out of the system, correct?
Does anyone have a diagram showing where the slave cylinder is located? Is it easy to get to the bleeder valve without removing stuff?

John S.: Glad they corrected the resovoir access on the Atom 4.

[Atlarge]

The slave cylinder on the atom3 is a real pain to get to, it’s tight between the fuel tank and the back of the engine in the middle of the frame at the bottom. Bleeding it solo is a PITA but doable, I also replaced the master (easy job) but for another reason. If you google a Honda k20 diagram you’ll find it easily…

[Curves Junkie]

I'm not sure what kind of engine [mention]Deane[/mention] Atom have installed. He has an Atom 3S - so it's a US model.
If you have the K20 engine, the clutch slave cylinder is circled in red in the picture.

IMG_6226.jpg (1.69 MiB) Viewed 2365 times

It is very tight. The bleed nipple, see green circle, is under the black rubber cap. To open it, use a 10 mm open-end spanner.
If you bleed the system by vaccum, you can also loosen the two screws marked in blue, pull the slave cylinder out to the left and thus access the bleed nipple much more easily.

IMG_7831.jpg (1.44 MiB) Viewed 2365 times

[Deane]

Thanks for the pictures. The Atom 3S model has a Honda K24Z7 engine. Yeah, that clutch bleeder valve does look difficult to get to. I hope it is somewhat easier on mine. Anyone have a photo or diagram for those? I have ordered the new cylinder so will probably attack this soon.

[flying phil]

This was a problem I had back when my car was delivered in 2009. Basically, the master cylinder was not suitable for purpose...too small a capacity. The factory sent out a higher capacity master cylinder and the problem was solved.