Strange clutch problem

[rhdv8]

Guys, firstly sorry for posting a strictly speaking non Monaro related thread here but it’s almost related and I’m a bit lost.

I have a LS1/T56 from and Pontiac GTO (see, almost a Monaro) transplanted into a Mazda RX7. The original clutch operation when transplanted into the Mazda was via a cable operated 7/8ths inch master cylinder due to space limitations. This was fine until the cable broke, so then I thought I would make it completely hydraulic by using a Monaro master cylinder directly on the back of the Mazda clutch pedal.

So far so good, but now I have a problem whereby from cold the clutch engages around half way up its travel but as I drive the pedal engages the clutch further and further up the pedal travel until the clutch slips. I’m not sure if it’s heat related or just time but when the car cools down/switched off, the engagement point returns to halfway up the pedal.

Thinking out aloud about what may be causing this, I was wondering if anyone knew if it was possible for clutch fluid to expand when hot (although I would have thought that if this was the case it would release the pressure into the reservoir? Or has anyone come across a sticking slave cylinder? So each time it moves forward it doesn’t return fully?

Also could it be that due to the adjustment of the master cylinder ( not enough travel in either direction?) it’s acting like a one way valve each time the clutch pedal is depressed? (This is how I’m getting)

Open to all suggestions,
Many thanks.

[MadMaxHSV]

Its most likely down to heat if the pedal comes back, the surroundings when mounted in a Mazda may not be conducive to heat dissapation. First thing would be to try fresh fot 5.1 fluid.
Otherwise i've had this problem because of a rubber clutch line. The rubber when hot would balloon under pressure causing the problem you described. Replaced it with a steel braided line and never had a problem.

Edited by MadMaxHSV on Thursday 14th August 13:04

[MyM8V8]

If the release bearing is on a mechanical fork you might want to investigate a hydraulic release bearing, i.e you pipe straight from the master cylinder to the body of the unit. I had one of these on a big block chev, but setting up the clearance could be an issue. The one I used was made by Tilton but it was specific for a chev aluminium bellhousing and really designed for a Tilton multiplate clutch.

[rhdv8]

MadMaxHSV said:

Its most likely down to heat if the pedal comes back, the surroundings when mounted in a Mazda may not be conducive to heat dissapation. First thing would be to try fresh fot 5.1 fluid.
Otherwise i've had this problem because of a rubber clutch line. The rubber when hot would balloon under pressure causing the problem you described. Replaced it with a steel braided line and never had a problem.

Edited by MadMaxHSV on Thursday 14th August 13:04

Thanks for your reply but it is new clean fluid and I'm using a braded line between the master and slave. From what I’ve read else where It looks like that if the fluid was boiling etc it would be hard to disengage the clutch rather than engage the clutch? If anything it isn’t a lack of pressure it’s too much.
Also it is the standard hydraulic slave and release bearing, any other ideas?

[MyM8V8]

Is the release bearing going over centre and mashing the fingers into the clutch?

[MadMaxHSV]

rhdv8 said:

MadMaxHSV said:

Its most likely down to heat if the pedal comes back, the surroundings when mounted in a Mazda may not be conducive to heat dissapation. First thing would be to try fresh fot 5.1 fluid.
Otherwise i've had this problem because of a rubber clutch line. The rubber when hot would balloon under pressure causing the problem you described. Replaced it with a steel braided line and never had a problem.

Edited by MadMaxHSV on Thursday 14th August 13:04

Thanks for your reply but it is new clean fluid and I'm using a braded line between the master and slave. From what I’ve read else where It looks like that if the fluid was boiling etc it would be hard to disengage the clutch rather than engage the clutch? If anything it isn’t a lack of pressure it’s too much.
Also it is the standard hydraulic slave and release bearing, any other ideas?

Sorry, was getting the problem the wrong way round

Is the engagement point still firm as when cold? Is it a stock clutch and pressure plate?

[rhdv8]

MadMaxHSV said:

rhdv8 said:

MadMaxHSV said:

Its most likely down to heat if the pedal comes back, the surroundings when mounted in a Mazda may not be conducive to heat dissapation. First thing would be to try fresh fot 5.1 fluid.
Otherwise i've had this problem because of a rubber clutch line. The rubber when hot would balloon under pressure causing the problem you described. Replaced it with a steel braided line and never had a problem.

Edited by MadMaxHSV on Thursday 14th August 13:04

Thanks for your reply but it is new clean fluid and I'm using a braded line between the master and slave. From what I’ve read else where It looks like that if the fluid was boiling etc it would be hard to disengage the clutch rather than engage the clutch? If anything it isn’t a lack of pressure it’s too much.
Also it is the standard hydraulic slave and release bearing, any other ideas?

Sorry, was getting the problem the wrong way round

Is the engagement point still firm as when cold? Is it a stock clutch and pressure plate?

Yes it's still firm, as far as I can tell, although it's hard to say as it gets higher and higher and you can tell the clutch wants to slip. Yep, standard clutch and PP. The car is now running everything clutch wise that a 04 Monaro would. The strange thing is it never happened with the old cable operated master cylinder and if anything the Monaro master cylinder has less throw now it's on the Mazda pedal than it would have on a Monaro pedal. So I can’t see how it might be pushing the release bearing too far. One last point is that the pedal pressure is always the same hot or cold if that means anything.

[MadMaxHSV]

Strange

Depends what the access is like, but you could try pulling the slave cylinder out of the bellhousing when cold and when hot and compare the extension and/or pushback from the pp when removing. May be able to see whether its pumping up and not returning when hot. Master cylinder is obviously ok if the pedal position stays the same...

Edited by MadMaxHSV on Thursday 14th August 14:39

[rhdv8]

Strange indeed, Can't get to the slave without dropping the gearbox so I'm leaving that as a last resort. As you say it seems like it’s a slave problem some how but that’s been constant throughout, whereas I did swap master cylinders. It seems like the slave is pushing the release bearing and not returning for some reason but what that reason is??????

[MadMaxHSV]

If the cable cylinder worked, its not an issue with the bearing sticking on the shaft or the forks doing something weird, so its is all pointing to the slave. It is possible that the piston is sticking when hot.

Not sure your going to get to the bottom of it without pulling the slave short of any other suggestions.

[Well_Fans]

have you checked the US GTO and Oz Monaro forums for people that may have had similar problems. They've got some excellent searchable tech forums.

[rhdv8]

Well_Fans said:

have you checked the US GTO and Oz Monaro forums for people that may have had similar problems. They've got some excellent searchable tech forums.

Yep, been working my way through them with this one, no luck so far, my problem seems to be unique. Here is a pic of the slave/release bearing just to show what's in there.
http://store.summitracing.com/partdetail.asp?autof...

[MadMaxHSV]

Well that definately rules out any fork problems, and explains why its a pain to get the slave out

The drop would be very small and could be negated by temperature but have you looked at the fluid level in the reservoir when hot and cold. A drop could indicate its sticking open.
If you can get the dust cover off you could also get a dentists mirror in the bell housing to compare the position of the bearing.
Just trying to think of ways you could confirm or deny a slave problem without dropping the box.

[rhdv8]

Yep looked at the fluid level but just to add to the strangeness it looks the same hot or cold! Not sure if the slave can come back but leave the release bearing out if you know what I mean.
I was thinking about a surgeon’s camera etc to have a look inside the bell housing, but the bleed hole is very tight against the trans tunnel. Or even making an inspection cover but I wouldn’t want to risk weakening the bell housing.

Edited by rhdv8 on Thursday 14th August 15:57

[MadMaxHSV]

Is there not a gap beside the sump where the bellhousing mates with the block? Normally a plastic dust cover over it to stop cr*p filling up the housing.

[rhdv8]

MadMaxHSV said:

Is there not a gap beside the sump where the bellhousing mates with the block? Normally a plastic dust cover over it to stop cr*p filling up the housing.

I know what you mean but nope, fits nice and snug up against the sump. Not sure if you can see this but this gives you an idea:

http://dragworx.com/viewtopic.php?t=19&postday...

Edited by rhdv8 on Thursday 14th August 16:18

[MadMaxHSV]

No needs login. Tried registering quickly but no.

[rhdv8]

Here you go, you can just about see the bell housing is a direct fit to the stressed sump

[slackalice]

reading the opening statement that all was fine untill the Master cylinder was changed, then surely that is the first place to look, otherwise you are chasing your tail. Sounds like sh it has got into it, so a quick strip and refurb? as I take it was a second hand MC?

[MadMaxHSV]

hmmmmm, couldn't remember from when I was last under the car.