Fiesta clutch fun
Discussion
Hi all,
I'm having a fun time after replacing the clutch master cylinder on my 1998 Mk4 Fiesta. Not a difficult job you'd think, old one out, new one in and bleed the air out but not so.
First bleed was done with a pressure bleeder and seemed to work rapidly, however, every 10-20th push of the clutch pedal was met with no resistance, right to the floor. After this, it went back to normal for another 10-20 pushes. Went old school for the second bleed and got some air out but the same thing was happening and a third bleed with the pressure bleeder pushed half a litre of brake fluid through with no visible bubbles of air at the outlet but still, every so often, no resistance from the pedal and back to normal for 10-20.
Here's the fun bit though, if you're stationary and pump the pedal, no problem, you can feel the clutch resistance every time with and without the engine running. It's only after pulling away or changing gear that the pedal occasionally goes down with no feel to it at all.
Has anyone had this kind of madness before? Was it air, a knackered slave cylinder or possibly a dodgy replacement master?
Any help appreciated.
I'm having a fun time after replacing the clutch master cylinder on my 1998 Mk4 Fiesta. Not a difficult job you'd think, old one out, new one in and bleed the air out but not so.
First bleed was done with a pressure bleeder and seemed to work rapidly, however, every 10-20th push of the clutch pedal was met with no resistance, right to the floor. After this, it went back to normal for another 10-20 pushes. Went old school for the second bleed and got some air out but the same thing was happening and a third bleed with the pressure bleeder pushed half a litre of brake fluid through with no visible bubbles of air at the outlet but still, every so often, no resistance from the pedal and back to normal for 10-20.
Here's the fun bit though, if you're stationary and pump the pedal, no problem, you can feel the clutch resistance every time with and without the engine running. It's only after pulling away or changing gear that the pedal occasionally goes down with no feel to it at all.
Has anyone had this kind of madness before? Was it air, a knackered slave cylinder or possibly a dodgy replacement master?
Any help appreciated.
No replies yet so I'll have a go, though you may have cracked it by now.
The detail that stands out is that it's fine when you pump it stationary but drops after pulling away or a gear change. That points me away from plain trapped air, which usually shows up whenever you press it, and towards something that only happens once the car's moving. Things I'd check, roughly cheapest first:
1. Pedal return. Watch the pedal after a quick release. If it isn't getting all the way back to its stop every time, the master cylinder piston may not be returning far enough to refill from the reservoir between presses, and the next press can feel very different. A tired return spring or a sticky pedal pivot can cause that, and so can the pushrod adjustment on the new master if it differs from the old one.
2. The new master itself. Replacement master cylinders do sometimes come with a seal that lets fluid bypass intermittently. If the problem only started after the swap and the slave was fine before, that's a real suspect. Keep the receipt handy.
3. The slave. If yours is the type that sits inside the bellhousing, look for any dampness at the bottom of the bellhousing or a slowly dropping fluid level. A seal that leaks a little can also let air back in, which would explain why bleeding never seems to fix it.
4. Clamp test. With a hose clamp on the flexible hose to the slave, the pedal should go rock hard straight away. If it still sinks with the hose clamped, the problem is at the master end. If it's firm, look downstream.
Worth checking the fluid level after a drive as well. A level that drops a little each time tells you there's a leak somewhere, even if you can't see it.
Did it behave like this before the master went in, or did it start with the new one?
The detail that stands out is that it's fine when you pump it stationary but drops after pulling away or a gear change. That points me away from plain trapped air, which usually shows up whenever you press it, and towards something that only happens once the car's moving. Things I'd check, roughly cheapest first:
1. Pedal return. Watch the pedal after a quick release. If it isn't getting all the way back to its stop every time, the master cylinder piston may not be returning far enough to refill from the reservoir between presses, and the next press can feel very different. A tired return spring or a sticky pedal pivot can cause that, and so can the pushrod adjustment on the new master if it differs from the old one.
2. The new master itself. Replacement master cylinders do sometimes come with a seal that lets fluid bypass intermittently. If the problem only started after the swap and the slave was fine before, that's a real suspect. Keep the receipt handy.
3. The slave. If yours is the type that sits inside the bellhousing, look for any dampness at the bottom of the bellhousing or a slowly dropping fluid level. A seal that leaks a little can also let air back in, which would explain why bleeding never seems to fix it.
4. Clamp test. With a hose clamp on the flexible hose to the slave, the pedal should go rock hard straight away. If it still sinks with the hose clamped, the problem is at the master end. If it's firm, look downstream.
Worth checking the fluid level after a drive as well. A level that drops a little each time tells you there's a leak somewhere, even if you can't see it.
Did it behave like this before the master went in, or did it start with the new one?
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