Spitfire & GT6 Forum

Bleed clutch

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Chuckweasel Avatar
Chuckweasel Charles Hofmann
Tabernacle, NJ, USA   USA
I have not heard or seen reference to this problem before. Rebuilt and installed clutch slave cylinder and new clutch master cylinder in my '78 Spitfire. Have bled repeatedly and get a steady gravity flow of clean fluid out of slave bleeder when open. However, when I depress the clutch pedal, fluid moves back into the reservoir, not toward the slave cylinder. Could there be something wrong with the new master cylinder?

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colodad Avatar
colodad Silver Member Calvin Williams
Grand Junction, CO, USA   USA
you feel the peddle pressure disappear or the car starts moving ?

clutch MC.jpg    49.5 KB
clutch MC.jpg

Smithisretired Avatar
Smithisretired Michael Smith
Wells, ME, USA   USA
Not sure what "gravity flow" tells you. Glenn's Triumph Repair and Tune-Up Guide (Fourth Printing, March 1969) describes the bleeding process as follows:

"Fill the clutch reservoir with brake fluid. Wipe the bleeding nipple at the slave cylinder and attach a tube, the free end of which should be in a glass jar partly filled with clean brake fluid. Unscrew the bleeder nipple a quarter turn and, with quick full strokes of the clutch pedal, pump until the fluid entering the jar is free of bubbles. Then close the bleed screw with the pedal fully depressed."

The Haynes manuals, both UK and US versions, are a bit vague on the subject, saying only to bleed in a manner similar to the brake system, in which case the pedal is depressed fully at which point the bleeder screw is closed after which the pedal is returned to full up before the bleeder is opened and the pedal depressed. This process is repeated until the fluid comes out free of bubbles. For its part, the Glenn's manual describes bleeding the brakes in the same manner as the clutch: simply pump the pedal until the fluid runs free of bubbles. My suspicion is that the Glenn's method allows bubbles that may be in the jar fluid to enter the systems, thus taking longer and perhaps not being as successful as the Haynes method. But in both cases, actively pressing the pedal with the bleeder open is necessary.

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brucejon Avatar
brucejon Bruce Jones
Santa Cruz, CA, USA   USA
1962 Triumph TR3B
1963 Triumph TR3B "Tupperware TR3"
1969 Triumph Spitfire MkIII
1972 Triumph TR6
If you are using DOT5 don't press quickly or you will introduce bubbles. I am also not a fan of pressing the pedal all the way to the floor. I believe this can cause longer than normal travel and perhaps mess up a seal as it rides over areas of the cylinder that are rough.

Sometimes I have found it helpful to bleed at the master cylinder first. I use DOT5 so paint isn't at risk.

Just reread this and realized your question is on fluid moving backwards. Can you describe that more?

Edited 2 time(s). Last edit at 2017-10-12 04:06 PM by brucejon.

lef2wander Avatar
lef2wander Gold Member James Thomas
Hatfield, MA, USA   USA
Gravity flow. Do you mean that after you bleed it. You open the slave bleeder and watch the flow of fluid???? That would introduce air into the system.

Mechanical bleeding of clutch system.
Two man job.
1: fill master 1a: open slave bleeder and let gravity work or pump it a little until fluid comes out close bleeder. Don't let master get low on fluid.

2: 1 person on pedal 1 one bleeder. Start a slowish pump.
Open bleeder. Pedal person tells bleeder guy to shut bleeder before he reaches the bottom of pedal stroke.


3: repeat this process until there are no bubbles coming out. Then do not open the bleeder ever again. Untill you have to bleed it again.

Other than that, if you feel your doing it correctly. Its friggin wierd. You can't compress fluid. However you can compress air. So when you operate the pedal if there's air you compress it. Then it will fight to uncompress the only way it can do that is pushing fluid away. So it has to go back to the master res.

Edited 3 time(s). Last edit at 2017-10-12 05:32 PM by lef2wander.

spitfire50 Avatar
spitfire50 Paul Mugford
Rochester, N.H., USA   USA
If fluid returns to the master cylinder when the pedal is pushed the reservoir cut-off seal in the master is leaking. It is the little seal on the end of the "nail" 512802 in the parts diagram above. Rebuild kits have it.
I haven't seen the position of the bleed screw mentioned. It must be above the supply pipe, not below it. It is easy to swap the bleeder and supply pipe. if the bleeder isn't at the top the system won't bleed.
Good luck,

Chuckweasel Avatar
Chuckweasel Charles Hofmann
Tabernacle, NJ, USA   USA
As I suspected, put the old master cylinder back in and system works fine - no backflow into reservoir when pedal is pushed and clutch disengages. Either I pumped some dirt through to interfere with that seal or it failed new out of the box. Thanks Paul and all who chipped in!

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