Bleeding Clutch

[Chris]

For anyone who's interested, turns out my problem was heat.
Re-routed the clutch line and added heat protection and hey presto a working clutch.
Now on to that oil leak......

Thanks for reporting back,
you can now enjoy driving with ease once you have sorted the oil leak, I'm sure most of us have minor leaks with
our machine .

[GDCobra]

I've had a quick physical check of my pipe sizes, the brake pipes are as mentioned above, in my case in old money, 3/16 '' inside diameter in copper, o d measures 4.9 mm in the decimal form for these .
As for clutch pipe also in copper measures 6.2 mm outside diameter, that being a 5/16'' inside diameter from recollection thirty plus years ago.
I seem to recall the pipe nuts were a bit more difficult to source at the time and would think would be easier with today's on-line availability ?
Chris.

Apologies if I sound pedantic but just want to make sure no one gets confused by this.
3/16" = 0.1875" - =  4.763mm so if your OD is 4.9mm it is not possible for the ID to be 3/16" (would probably be easy to bend though!
Similar story with the larger pipe (in-fact 5/16" is 7.938mm).
I suspect when a pipe is specified as an imperial fractional size this is the outer diameter which is being quoted.

[GDCobra]

For anyone who's interested, turns out my problem was heat.
Re-routed the clutch line and added heat protection and hey presto a working clutch.
Now on to that oil leak......

Great to hear you have your problem solved and thanks for reporting back.

[incey1966]

For anyone who's interested, turns out my problem was heat.
Re-routed the clutch line and added heat protection and hey presto a working clutch.
Now on to that oil leak......

[Chris]

That's interesting, I recall hearing this a while ago but long after I built my car.  As I didn't know it when I built my car I used the same size for brake and clutch (3/16") and even when I swapped to a concentric type I hadn't heard of this.  I can't say I have any problem with it but then I don't know what I'm missing.  Presumably this is due to the larger displacement of fluid compared to brakes and so the clutch line will be larger?


Anyway looking at the bleeding and loss of it.  I would first look at making sure I have all the air out.  One thing I have done in the past with both brakes and clutch is to push the slave cylinder fully back and clamp/wedge it, this removes a lot of hiding places for the air so makes it more likely to get is out and when you think you have it out and close the bleeder the pedal will be solid if no air present and remain solid while you keep pressure on it.

If it goes soggy after that obviously air is getting into the system, the only place I can see that happening without fluid coming out is if the feed from the reservoir is getting uncovered.  Is there plenty of fluid in there  so that the pathway to the cylinder cannot become uncovered?

I've had a quick physical check of my pipe sizes, the brake pipes are as mentioned above, in my case in old money, 3/16 '' inside diameter in copper, o d measures 4.9 mm in the decimal form for these .
As for clutch pipe also in copper measures 6.2 mm outside diameter, that being a 5/16'' inside diameter from recollection thirty plus years ago.
I seem to recall the pipe nuts were a bit more difficult to source at the time and would think would be easier with today's on-line availability ?
Chris.

[GDCobra]

The other thing is to make sure the the pipe is of the correct bore size, they are not the same size as standard
brake tube .

That's interesting, I recall hearing this a while ago but long after I built my car.  As I didn't know it when I built my car I used the same size for brake and clutch (3/16") and even when I swapped to a concentric type I hadn't heard of this.  I can't say I have any problem with it but then I don't know what I'm missing.  Presumably this is due to the larger displacement of fluid compared to brakes and so the clutch line will be larger?


Anyway looking at the bleeding and loss of it.  I would first look at making sure I have all the air out.  One thing I have done in the past with both brakes and clutch is to push the slave cylinder fully back and clamp/wedge it, this removes a lot of hiding places for the air so makes it more likely to get is out and when you think you have it out and close the bleeder the pedal will be solid if no air present and remain solid while you keep pressure on it.

If it goes soggy after that obviously air is getting into the system, the only place I can see that happening without fluid coming out is if the feed from the reservoir is getting uncovered.  Is there plenty of fluid in there  so that the pathway to the cylinder cannot become uncovered?

[KevinW]

I'd also suggest checking the simple things first, like battery voltage, earth connections, and any connectors that may have loosened over time. Those little issues can cause surprisingly confusing symptoms and are much easier to rule out before replacing parts.

Bot.

[StellaHong]

I'd also suggest checking the simple things first, like battery voltage, earth connections, and any connectors that may have loosened over time. Those little issues can cause surprisingly confusing symptoms and are much easier to rule out before replacing parts.

[incey1966]

I'm starting to think it's a heat soak problem.
After having another look I've noticed the clutch pipe is only about 35mm above the header at it's closest point.
That would explain why it's ok when first bled and then gradually gets worse.
I'll look at a cable re route and heat shielding, an re-bleeding yet again....

[Chris]

My slave is of the 5/8, not the 3/4 variation and is also reasonably heat shield wrapped due to close proximity of headers .
Chris.

[Simon]

Had a nightmare getting my setup to bleed for the first time. I eventually had to remove the slave (whilst still connected) and hold it above the master while I vacuum bled it. I've just changed the slave (clutch was too heavy) now I've got to bleed it all over again!

[JON1D]

First check the travel of the fork which should be 25mm/1"inch. You only need to be moving lews than 20mm to start giving you issues and the usual cause is air. Air can get trapped if your slave is not horizontal and an air pocket is trapped. Try the dry tissue check to see if you have a small leak from either pipe fittings to see if any fluid is leaking with a poor joint face. Is the routing of your pipes close to exhaust headers which might benefit from heat insulation.
Since you have replaced both master and slave yet experiencing the same problem did you replace the hydraulic pipe?
Things worth checking out.

John

[Chris]

Hi,
If your happy that the both the cylinders are good, I mean no air or fluid leaks and the pipe work to slave is
suitable, then you should be good to go ?
On my SD 1 set up the cylinder bore sizes are the same as you have, for information my set up can be a bit
tricky to get correct but no real deal .
The last time my system was bled was quite a few years ago to date !
My method was to fill the system then connect an easy bleed to the master cylinder, be carefull with these and
don't go to mad with the air pressure otherwise you will have brake fluid all over the place !
I have also carried out a manual bleed just to be sure, this may not be necessary .
The other thing is to make sure the the pipe is of the correct bore size, they are not the same size as standard
brake tube .
Hope this gives you something to go on ,

Chris.

[incey1966]

I'm having trouble bleeding my clutch and I'd be interested to hear if anyone else has had similar issues.
After passing IVA last summer there wasn't quite enough travel at the slave, so I re-bled the system.
Took the car out everything was fine did about 80 miles and the gear changes were nice and smooth, 1st and reverse were easy to select.
Went out later in the day and the changes got notchy and 1st and reverse were really difficult to select.
To cut a long story short after several bleeds the same thing kept happening so I replaced both the master and the slave as I concluded that air was gradually getting in somehow.
After replacing them I bled it took it road the block and put it away for winter, still not happy with the gear change. I thought, I'll sort it in the spring..
Well spring is here, took the car out, 1st is very hard to get and reverse almost impossible.
I'm pretty sure I've got air in the system somewhere so I could do with some advice on how to best bleed the system.
I'm thinking is it worth taking the master and slave off the car and bench bleeding the system?
The setup is 3/4 master and 7/8 slave so the travel should be plenty to operate that clutch.
Any suggestions would be appreciated.