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Stupid Clutch

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Morris

Morris

Yoda
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After rebuilding both master and slave cylinders, my clutch hydralics are now sucking air from somewhere. Everything was working fine for months, then it started doing this out of the blue.

Any ideas on how to trouble shoot and fix this? My Midget is a '79.

Thanks,

morris
 
Is there fluid in the footwell or running down the clutch pedal? recheck all fittings and lines for tightness. is the flex pipe original? are there any leaks? has the clutch master run low at all? Have you rebled the system? over time any air bubbles can tend to accumulate in one spot.

sorry for all the questions but the answers can help figure out the problem

mark
 
Hey Mark,

No drips or leaks that I can see. I am going to try to pull the slave later today and have a look at it. The flex line is original, but the slave and master cylinders are rebuilt. I bled the system yesterday, and took on more air after a very short drive. The resevoir was low when this problem started, but not low enough to get air in the line.

Thanks for your help,

morris
 
well lets see what you get after you pull the slave. it may also be worth a look into the pedal box.

mark
 
Well, the slave was clean, as is the pedal box. I bled it again, and it seems to be holding steady so far. Gotta love a mystery.

morris
 
Hopefully you have your problem solved. To me, it sounds like the slave cylinder. The seal inside it may need to be replaced.

Are you using Castrol LMA (or other DOT 4 fluid)? DOT 3 will affect the rubber used in both the clutch and brake systems.

Mike
 
I will have to double check the DOT rating, but it is Castrol Synthetic fluid (if that helps narrow it down). There were absolutely no signs of leaking when I pulled the slave cylinder.

Thanks Mike,

Morris
 
FYI, DOT 3 is fine for a '79 Midget, and the owner's manual for mine (a '77) confirms this. The "natural rubber" argument for using DOT 3 is pretty much limited to ones from the 50s that actually did have pure rubber instead of the nitrile used later. Still, they do have latex in them, so you don't want to get anything petroleum based on them or you will ruin them. Can't explain why after several months it would have started sucking air, but the one thing I did discover is that the clutch pushrod makes a tight seal with the dust boot on the slave cylinder, so if you have to remove the slave you will likely have to bleed it even if you didn't open the hydraulics. When you put the slave back in the pushrod acts like a piston and builds up an air pocket which burps its way past the seal once you work the clutch a few times. This happened to me a couple of times before I figured out what was going on.
 
Get rid of the synthetic stuff now before you waste more time and money trying to get a British car to use Syn. for any length of time they need Castrol LMA fluid. unless u started with a brand new system lines/cylinders/piping etc.it's never going to be right.
 
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