Clutch bleeding : she turns me mad !

[Chris59]

Hello guys,

 

Sometime, one brain is not enough : I'm fighting with a Stag clutch (clutch system is working the same way as on any TR, the gearbox itself is very similar) who do not want to work correctly

 

On this car, the clutch is a NOS, brand new item, the flywheel has been very slightly skimmed, the release bearing is a very good quality part too, there is no significant play in the clutch shaft bushes.

 

The clutch shaft is new, as are the fork and pin, the clutch master cylinder is new and bigger than the original (0.813 instead of 11/16, ie about 0.687, if I'm not wrong) to improve travel, the slave cylinder is a new 1" item, the clutch flexible hose is home made (no problem, it won't expend under pressure !).

 

There is no play in the pedals shaft, the master cylinder rod is adjusted (the master cylinder work on its entire lengh), and the whole thing is correctly pressure bleeded.

 

So, my problem is : if I use my special tool straight on the clutch fork shaft , the usual 11mm travel is recquired to de-clutch, no problem apparently here.

 

But, whatever I do, the hydraulic system allow only a 7 mm travel : did I miss something ?

 

Before you ask, there is no play in any of the pins, they are new aswell......

Edited February 15, 2017 by Chris59

[TR 2100]

Chris -

 

I hope you haven't got the slave fitted upside down

so the bleed nipple is at the bottom!

I did that once, on my old TR6, long time ago, with

the obvious consequences.

 

Nah - can't believe you could do that!!

 

But - will you admit to going to check ! ! ! ?

 

AlanR

Edited February 15, 2017 by TR 2100

[Peter Cobbold]

Chris, Which side of the engine plate did you fit the slave? Its flange should be bolted to the rear face of the plate, which means feeding the hose through the hole. Peter

Edited February 15, 2017 by Peter Cobbold

[Guest ntc]

Chris

You need 15mm of travel,are you sure the bearing is not binding on the fork? ask me how i know

Edit

Did you fit it dry on the nosecone?

Edited February 15, 2017 by ntc

[Chris59]

Thanks guys for your replies.

 

@ Alan, no, I don't

 

@ Peter, it's on the right size, whatever original pushrod don't allow a fitment to the front face of the "plate" (it's not a plate on a Stag, the slave cylinder carrier is include in the "gearbox to engine" sandwiched adaptator)

 

@ Neil, yes, the travel is to short : 11mm are enough to de-clutch, but 15mm would allow a the clutch disk to be completely free.

 

Here, I have no more than 7mm !

 

What do you mean by "bearing binding on the fork", do you mean the release bearing carrier who wouldn't be free to rotate in the fork ?

 

I always (since +30 years...) use some copper grease on the gearbox input shaft tube.

Edited February 15, 2017 by Chris59

[Lebro]

If you are sure about the cylinder sizes being right, then you must still have some air in the system.

 

Bob.

[Guest ntc]

Thanks guys for your replies.

 

@ Alan, no, I don't

 

@ Peter, it's on the right size, whatever original pushrod don't allow a fitment to the front face of the "plate" (it's not a plate on a Stag, the slave cylinder carrier is include in the "gearbox to engine" sandwiched adaptator)

 

@ Neil, yes, the travel is to short : 11mm are enough to de-clutch, but 15mm would allow a the clutch disk to be completely free.

 

Here, I have no more than 7mm !

 

What do you mean by "bearing binding on the fork", do you mean the release bearing carrier who wouldn't be free to rotate in the fork ?

 

 

Chris

Yes there is not enough clearance on the pins on the fork and it binds going forward

Edited February 15, 2017 by ntc

[Chris59]

@ Bob, yes, the bores size are right, I even tried different combinations, ie standard size master cylinder with 1" (standard firment, as on a TR6) slave, then with a smaller bore slave (8/9) to improve fork travel, now it's a bigger master cylinder + 1" slave, and it's still not working.

 

I've bleed by the bottom, by the top, under pressure or not, it don't change anything, the result stil lthe same, ie not enough slave piston travel...

 

@ Neil, a few minutes ago, I've tried to add some washers to bring the slave piston fully home when the pedal is released, it doesn't make any difference, so I don't think it's a "fork binding" problem, especially if we consider that the fork and bearing carrier are new.

[Guest]

Google image show small difference between the cylinders; a few even look as if they have a different housing length. Did you check that. Second, I see pics of cylinders bolted to the housing with nut stacked upon each other to provided distance where needed.

 

Menno

[Guest ntc]

@ Bob, yes, the bores size are right, I even tried different combinations, ie standard size master cylinder with 1" (standard firment, as on a TR6) slave, then with a smaller bore slave (8/9) to improve fork travel, now it's a bigger master cylinder + 1" slave, and it's still not working.

 

I've bleed by the bottom, by the top, under pressure or not, it don't change anything, the result stil lthe same, ie not enough slave piston travel...

 

@ Neil, a few minutes ago, I've tried to add some washers to bring the slave piston fully home when the pedal is released, it doesn't make any difference, so I don't think it's a "fork binding" problem, especially if we consider that the fork and bearing carrier are new.

Chris

New? thats what I found out on sombodys car on here if by manual push you only have 11 mm it is binding,so sorry box out and file required.

[barkerwilliams]

Chris,

If you disconnect the clutch slave link rod from the operating arm there are two things to check.

can the clutch release arm move further than when operated by the clutch slave (might need a bit of scaffold pole as an extension? If so the slave is not pushing it far enough.

Does the slave rod move further when disconnected than connected, if so then the clutch release is binding.

Are you using a “one piece” slave link rod, or the Moss adjustable length one?

Alan

[Waldi]

Chris,

New clutch master cylinders can be delivered with rods in different lengths, this may be worth checking, compare the lenght of the old rod and the new one, if you have a new rod on the master.

Waldi

[Chris59]

@ Menno, adjusting the position (but I've tried various position, been there, done that, you know !) of the slave cylinder is not so important, as the hydraulic system is self adjusting : the piston travel should be only 15mm, far from the entire lenght of the bore.

 

@ Neil, considering that it's easy to completely declutch (I mean press the clutch fully, thus allowing the disk to be free) using an appropriate tool connected to the clutch release arm, should I consider that binding is possible ?

 

@ Alan : "Can the clutch release arm move further than when operated by the clutch slave (might need a bit of scaffold pole as an extension?" yes, absolutly.

"Does the slave rod move further when disconnected than connected, if so then the clutch release is binding" : no.

@ Waldi, no problem with rod lenght, I usually make adjustable rods myself when necessary, it's a 5 minutes job.

[Guest ntc]

What tool are you using? pic?

[barkerwilliams]

Chris,

 

you wrote in the first post that your clutch needs 11mm, but the slave only pushes 7mm. How far does the slave rod move if disconnected from the clutch arm?

 

If there is air in the hydraulics slave rod movement will be reduced, but when the load is disconnected the resistance/pressure that compresses the air is absent so you will get full movement.

If it's air in the plumbing you should get 11mm without a load.

 

ps A wild thought, if you look at the pedals are the clutch and brake pedals the same distance from the floor? i.e. is the clutch pedal returning to it's home position?

 

 

Alan

[Peter Cobbold]

If you are sure about the cylinder sizes being right, then you must still have some air in the system.

 

Bob.

+1

Chris, as a test clamp the slave cylider so the piston cannot move, then see if you can depress the foot pedal. it should be solid- but not if there's air in the system.

Peter

[Chris59]

@ Neil, picture as requested.

 

@ Alan, I'll check again later today, but will need an assistant for this, I'm alone during the afternoon.

 

No problem with the pedal position (or thickness of carpets !), the clutch master cylinder piston on its full bore.

 

I say that 11mm are sufficent, because I have checked with my hydraulic press : this distance is the minimum recquired to freeing the disk, but, ideally, as Neil write, 15mm would be perfect !

Edited February 15, 2017 by Chris59

[Chris59]

+1

Chris, as a test clamp the slave cylider so the piston cannot move, then see if you can depress the foot pedal. it should be solid- but not if there's air in the system.

Peter

Good idea Peter, I'll try this.

[Guest ntc]

Chris

If you need that much force I will stick to my thought ,I hope I am wrong.

[Chris59]

Chris

If you need that much force I will stick to my thought ,I hope I am wrong.

 

Neil, if I need to remove the gearbox, no problem, it's only bolted by a few nuts, so it can be very rapidly done, but I don't want to move it for nothing.

 

Meanwhile, I've made a small (but extremly solid !) tool to clamp the slave cylinder piston in position : I still can push the pedal, so I must have a bleeding problem, as expected in the title of this post (and suggested by previous contributors !).

 

I've bleed this so many time, I really deserve a kick if I've done it wrong all the time !

[Guest ntc]

Then remove the pin and push the cylinder right back get somebody to press the pedal by hand ( do not over do it and see if you can get more fluid in.

[Chris59]

I've tried this too, Neil

 

The slave cylinder piston travel is 7mm when the rod is connected (so, under the pressure of the clutch) and 24 mmm when free......

 

So, no doubt, I've a pressure loss somewhere, but as there is no external leak, the only way is to remove everything and try it on my bench.

 

Because I don't like to waste my time for nothing, I'll take carefull measurements, and check slave piston travel with different sizes of master and slave cylinders, and may check the volume of fluid involved.

 

I'd like to know also what kind of pressure need a clutch diaphragm to do its job ?

 

If nothing work correctly, it may be time, again, for a gearbox out

Edited February 15, 2017 by Chris59

[Motorsport Mickey]

How about reverse bleeding ? connect up to the slave cylinder and pressurise the fluid in from that end ? That will often shift an airlock on the brake circuits.

 

Mick Richards

[RogerH]

Hi Chris,

before you strip the system down

why not disconnect the slave cylinder hydraulic pipe, place the end in a jar and then fully depress the clutch pedal.

 

This will be the max amount of fluid that the master cylinder will move.

What is the volume of the slave to move the piston 15mm.

 

This may give a clue!!

 

Roger

[Chris59]

@ Mick, that's a good idea, so good that I've tried at least 2 times : I often do this when gravity or pressure are not doing the job.

 

@ Roger, to late, every parts are now on my bench, where it will be far more easy (and less dangerous for the car paint) to play with clutch fluid.