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Hi
Just bleading the hydaulic clutch on my Skoda Estelle.
All lines and the master and slave were both completely empty, so bleeding from scratch. I used a vacuum bleeder which appeared to work fine. Got fluid coming through no problem. Clutch pedal was OK but clearly not perfect. I was getting a bit of air coming through but that appeared to be drawn in around the bleed nipple so as a final step I manually bled it with a helper pressing the clutch while I tightened and released the bleed nipple. Doing it this way resulted in loads of air coming out continually. Good fluid flow but loads of air in it.
Clutch pedel was then bad, with no action on the slave. So I vacuum bled it again and got reasonable pedal, manual bled it again to make sure all the air was out but again started getting loads of air in the fluid and no pedal.
I can't see any obvious leaks from any of the unions. I can't see any leaks from the master cylinder or from the slave cylinder.
So in summary, vacuum bleeding feels like it gets be 90% of the way there, but then finishing it off 'manually' results in loads of air and no pedal. I have probably pulled through 2 - 3x total fluid volume repeating this process a few times. Probs a good thing for flushing the pipes out, but getting annoying now as I don't appear to be making any actual progress.
Any ideas? Might it be a sign of a failed master cylinder seal? Res was always topped up.
Thanks for any help.
Lewis
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When you're vacuum bleeding it, you're not using the seals, which makes me think that you're on the right lines with a failed seal.
A couple of systems I've had won't get a decent pedal unless they're pressure bled.
I'm guessing you've checked all the obvious stuff like tight unions, pipe runs and bleed nipple higher than the inlet? Sorry don't know about specific Skoda stuff
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scmick
Posted a lot
Posts: 1,507
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I'm sure some at least part of the problem is it being a rear engined car. I'm into SIMCA 1000s and the related coupes (both rear engined) and they are regularly a pain to bleed often needing several goes at pressure bleeding to get a decent pedal.... i'm sure the extra distance from master to slave cylinder doesn't help. Getting the rear end higher than the front may help too.
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Thanks for the comments guys - yes the clutch pipe run is long, but no worse than, say, the rear brakes.
Comfort - that was my intial thoughts too - vacuum bleeding is not really stressing the master cylinder seals (I am fairly sure the slave is good as I checked it recently when I had the gearbox out). I can't see any leaks from the master cylinder in the car (below the pedal input to the cylinder). Would a failed seal allow air in but not fluid out?
Do you think it is worth buying/hacking together a pressure bleeder? Are they more effective than vacuum bleeding?
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Hi, If This is the existing system that has not been used for a while and has drained it self and there are no obvious leaks then I would say it's the master cylinder seal. What happens is over time a wear ridge form at the normal limit of travel around the biting point of the clutch. When you bleed the empty system you use the full travel and as the piston goes past the ridge it caused the seal to turn over and then doesn't seal properly. So you need to reseal or replace both cylinders because it's doubtful which one it is, although the master is favourite. It's more common on the brakes because the ridge isn't so far along the bore.
Colin
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I've got a gunsons pressure bleeder, in both senses of the word!
It'll bleed systems well, but I've NEVER managed to get it to work without spraying fluid everywhere, and if you reduce the pressure it's supplied with to the point where it doesn't, there's not enough pressure to make it work 🙄
How worried are you about the paint....
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jimi
Club Retro Rides Member
Posts: 2,201 
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Hi, If This is the existing system that has not been used for a while and has drained it self and there are no obvious leaks then I would say it's the master cylinder seal. What happens is over time a wear ridge form at the normal limit of travel around the biting point of the clutch. When you bleed the empty system you use the full travel and as the piston goes past the ridge it caused the seal to turn over and then doesn't seal properly. So you need to reseal or replace both cylinders because it's doubtful which one it is, although the master is favourite. It's more common on the brakes because the ridge isn't so far along the bore. Colin MR2's (mid engined) can have very similar problems, with the master cylinder seal flipping being quite common. Similar problems with vacuum & pressure bleeding, personally I've always (so far!) managed with the manual method & an assist (loosen nipple, press & hold pedal tighten nipple & repeat) One thing I have found to help is to try and block the clutch arm out a bit so you can get a little travel on the slave piston without the having the clutch pressure on it .... if you know what I mean  |
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Last Edit: Feb 2, 2022 16:55:06 GMT by jimi
Black is not a colour ! .... Its the absence of colour
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The marvellous design of a range rover classic clutch system means that the pipe comes out of the master, and goes up, thus creating a great setup for trapping air.
The only solution is to pressure bleed.
Could be similar to yours, particularly if long pipe runs?
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Thanks for the comments. I had a look at the haynes manual for an exploded diagram of the slave and master cylinders, and the seals don't appear to be of a type that might easily reverse. Perhaps they are and the manual doesn't show that level of detail.
I got the brakes bled no problem and had another go vacuum bleeding the clutch. I think I might have got a slightly better pedal feel this time (well the second time of trying this evening) so will leave it for a few days and see if I still have pedal by the weekend - if not there must be a leak somewhere. I think there a little bit of slack I can take out with the relase lever bar so will adjust that as well.
In terms of pipe runs, it comes out the master, drops straight down under car, to the back and then up to the union with the flexi so no obvious air traps in the hard line. I think the flexi does rise up before coming back down to the slave, so will also try and vacuum bleed again while wiggling that pipe up and down to see if there is a bubble I can clear if I still have pedel in a few days. If no pedal, I will just order a new master and slave - not that expensive on ebay and I can't be bothered spending ages tracing a mistery leak!
Cheers
Lewis
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