Lotus Elan

Clutch master and slave cylinder conundrum

PostPost by: Evante » Mon Jun 03, 2019 11:19 pm

Hi All,

I am looking for some practical problems solving. I just rebuilt the clutch master cylinder and replaced the slave cylinder on my 72 Sprint. I have read many posts about how difficult it is to bleed the slave cylinder but I have tried several ways. When I depress the clutch pedal, it goes to the floor with virtually no resistance at all. Needless to say, the clutch does not engage.

Now I am left not knowing if my master cylinder rebuild did not work or if I just have not properly bled the system. It seems to me that I should have some resistance, e.g., mushiness from the clutch, but with no resistance at all, I am not sure which is the problem, master cylinder or slave cylinder.

If anyone has experienced this or has any thoughts about how to proceed, please let me know.

Ta,

Jay S.
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PostPost by: gjz30075 » Mon Jun 03, 2019 11:36 pm

Do you get any resistance after pumping many times?
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PostPost by: Evante » Tue Jun 04, 2019 12:18 am

Nothing.
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PostPost by: 2cams70 » Tue Jun 04, 2019 12:19 am

Sometimes the master cylinder piston during bleeding will hang up in the compressed position. To free up press the brake pedal by hand until you feel contact with the piston. Once there pump the pedal rapidly by hand so that the pushrod is tapping the piston. This will normally free the piston so it returns to the uncompressed position and you can then resume bleeding normally.
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PostPost by: Evante » Tue Jun 04, 2019 12:25 am

Thanks, I will try that.

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PostPost by: billmoore42 » Tue Jun 04, 2019 3:07 am

I built a reverse brake bleeder with a garden sprayer tank (buy the smallest one they have at the hardware store). Fill it with brake fluid, pump up some pressure (maybe 5 pumps), and attach some clear vinyl tubing (I think used 1/4" interior diameter or maybe 5/16" inch.

Then when you pull the trigger on the gun, brake fluid emerges through the clear vinyl tubing and you can watch to make sure there are no bubbles. Make sure your clutch master cylinder is empty, jack up the front of the Elan quite a bit (I have a 67 FHC with Spyder chassis), and attach the filled vinyl hose to the bleed nipple which is a bit of a bear to get at with a Spyder chassis. Open the nipple and press the trigger until the clutch master cylinder is full (it may start spilling on your face). The fluid fills from bottom to top of the clutch system, and at least for me, I had a hard working clutch pedal the first time.

I have used this method with great success also on my MGB, which has similarly difficult clutch to bleed.
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PostPost by: miked » Tue Jun 04, 2019 6:36 am

Is the bleed nipple in the slave cylinder at the higest point. The sandwich plate captivates the cylinder at an angle and one hole sits higher than the other.
Last edited by miked on Tue Jun 04, 2019 9:13 pm, edited 1 time in total.
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PostPost by: joe7 » Tue Jun 04, 2019 1:13 pm

Make sure you have the push rod properly adjusted and return spring attached. Experience on this one!
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PostPost by: Evante » Tue Jun 04, 2019 3:43 pm

Can you clarify what you mean by "the return spring attached?" Is there an external return spring?
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PostPost by: Evante » Tue Jun 04, 2019 3:44 pm

Oh, you must mean on the slave cylinder, right?
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PostPost by: Andy8421 » Tue Jun 04, 2019 3:53 pm

Jay,

Is the first master cylinder you have rebuilt? There is a tricky little valve which is at the end of the master cylinder assembly in a little white plastic cup which is easy to fit incorrectly. If it is incorrect, it won't seal, and all that will happen when you press the pedal is the fluid will go back into the reservoir.

You could look into the reservoir with a torch when an assistant presses the pedal. If the fluid level goes up, then there is a problem with the valve.

Good luck.
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PostPost by: Evante » Tue Jun 04, 2019 5:37 pm

Andy,

Thanks for that suggestion. I have looked and the fluid level does not go up or down. I think that seal is working properly.
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PostPost by: nmauduit » Tue Jun 04, 2019 6:48 pm

Evante wrote:Andy,

Thanks for that suggestion. I have looked and the fluid level does not go up or down. I think that seal is working properly.


You need to look inside the brake fluid reservoir to see if there is some flow front to rear : the level is not going to change as no fluid is going to accumulate somewhere, but in case of malfunction of the return valve (at the front end of the master cylinder) the fluid will be pumped in the circuit via the pressure port(s) and return immediately via the return valve.
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PostPost by: Evante » Wed Jun 05, 2019 1:18 pm

Interesting,

I will have to look at the reservoir more closely.

Thanks to everyone for your suggestions. I will be working on this problem this weekend and give an update as to my progress.

Until then,

Jay S.
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PostPost by: h20hamelan » Thu Jun 06, 2019 2:55 am

Does the master require bench bleeding?

I normally use pressure bleeding on non electric clutches, vacuum on all brakes.
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