Clutch master quiz

[NLcoopermk1]

Hello gentlemen, hope you can advise me on a clutch master cylinder question.

I just finished the (5 year) restoration of my '66 cooper (will post a topic soon). It sailed through its MOT BUT there seems to be air in the clutch system. The slave cylinder is new as is the hose and all the pipework. I've saved the original master cylinder by using a Minispares repair kit. I've bled the system several times, but the problem remains: Once i'm on the road i can't get it in gear without pumping the pedal several times. Now i'm suspecting the master cylinder. I took it out and compared the cylinder in the repair kit to the original one. They are different in length. Could that be the problem? Or did i fit something the wrong way ?


The shiny one is the new cylinder. It's considerably longer.



I'm thinking of buying a new tin type clutch master cylinder, just to be sure, but is that a straight swap? I've read things about different rod lenghts causing problems?

Another option is using a master cylinder body i have had lying here. I think it's a brake master cylinder, but it's also a 0.75" bore.



Are the brake and clutch master cylinders internally the same?
I know they are differently angeled, I tried it on and it looks a bit odd, but could work for now...



So, any advice appreciated: did i fit the repair kit OK? Is the cylinder too long? should I stop hassling and buy a new one?

[InimiaD]

I'm not 100% sure, but i think the clutch repair kit is only suitable for later master cylinders. I'll have to check.
I re-built one recently using a later cylinder and don't have any issues.

edit. your repair kit is the correct type for the pre 85 minis.

Check the cylinder bore for any signs of rust.

[NicholasUpton]

Look like you are using a Brake master for your clutch

[NLcoopermk1]

Thanks for your advise guys, the cylinder bore looked OK to me, but I could feel one tiny scratch and saw some debris. Just to be sure I ordered a new master cylinder today. Since I'm tired of bleeding the clutch I also treated myself to an eesibleed
I just hope it's a straightforward swap and there are no differences in pushrod lenghs or something like that.

[tsumini]

I'm surprised that the MC worked at all. The longer piston probably extended the front seal lip past the fluid supply(reservoir) hole an didn't allow piston to refill. Your old piston will work but you should use Minispares repair kit GRK1026 for 3/4 bore. Use your old spring also along with the plastic gizmo at the small end of the spring. The new spring won't fit into cup seal at the front of the piston. Also make sure that the ring seal at the back of the piston is installed correctly. The groove on the inside must fit correctly over the ridge on the piston. It should look like the ring seal on the long piston. I've repaired at least two MC this way. As far as I can tell Brake and Clutch MC's are the same except clocking of the clutch base. A brake MC will work fine as shown except the cap will be on the opposite side as the other. Again don't use any part of the kit shown on your photos.

MC generally corrode where the seal lips spend most of it's time and will leak there. I test mine by assembling and filling the reservoir with brake fluid and prop it up in a corner for a few days with something under that will show seepage under the bore so you can see immediately if seals are seeping. This method was used to identify a leak at the solder on the bean can which had been dented. Actually this was the result of the clutch and brake MC's being installed backwards. Interference caused a dent in the can at the solder. Re-solder repaired the hole and leak checked again OK.
I should qualify this as 1960 vintage Austin 850 LHD.
BTW: GRK3007 is the wrong kit for the 3/4 bore MC.

[NLcoopermk1]

Thanks very much! I checked the kit I used: it's GRK3007, listed on the MS site as the pre 85 repair kit. The kit you mention simply doesn't show unless the part number is entered. When I entered GRK1026, it showed, and I see what you mean! This is what I should have ordered (but how do you know?) it's listed for old mk1's.
Unfortunately the new MC is already on it's way so I have to decide on what to do. (fit the new one anyway and repair the old one later?) I'll get in touch with MS first.
Again: thanks for the advice or else I wouldn't have known this.

[andy1071]

Brake and clutch m/cyls are the same except for the little piece of spring steel in the plastic part at the bottom of the cylinder (this acts as a non - return valve for the brakes. -Remove the spring steel piece if you use it for the clutch)

Although the piston is longer, if you lay the seal in position the length from the back of the piston to the seal lip should be the same on both types. They should be interchangeable.

The most common problem with clutch master cylinders is wear in the fork - end / clevis pin / pedal hole.

[tsumini]

Brake and clutch m/cyls are the same except for the little piece of spring steel in the plastic part at the bottom of the cylinder (this acts as a non - return valve for the brakes. -Remove the spring steel piece if you use it for the clutch)

Although the piston is longer, if you lay the seal in position the length from the back of the piston to the seal lip should be the same on both types. They should be interchangeable.

The most common problem with clutch master cylinders is wear in the fork - end / clevis pin / pedal hole.

Yeah so it is. Should be interchangeable. As you point out, wear in the fork area may be a problem. I may try one of these.