Master Cylinder Confusion

[cliff.b]

Hi, after a gap of 40 years since I last owned a Spitfire (MkIV) I have just bough a mostly restored 1500 as a non runner.

Having managed to get it running, I have now discovered that the brakes really don't work very well and amongst other things, I intend to change the master cylinder. However, the one fitted doesn't look like any I can see being sold for a Spit 1500.

I have attached a picture. The ones on sale are GMC224 (I think) which looks more like the Clutch cylinder.

Any clarification would be greatly appreciated.

 

Brake master cylinder.jfif

[Nigel Clark]

Hi Cliff,

Don't know of its just me but I can't open your file and don't recognise the file extension.

Would you be able to upload a .jpg image?

Nigel

[Mathew]

Sorry the picture does not work for me. The original was just like the clutch, but bigger! A clutch one would work, it all depends how much fluid you want to push for the bore size. Generally the bigger the bore the harder the pedal but the more pressure could be put to 🐻. With a servo alot of pressure , without could be a pain. 

[cliff.b]

I have tried posting the pic again. Hopefully will work this time.

[johny]

Looks like a GMC150 master cylinder for MGB. These are 3/4" bore so bigger than the 5/8" GMC224 that was probably originally fitted. As said this will make the pedal harder but require more pedal pressure especially if you dont have a servo. Also the type of brake pads used on our cars seems to have quite an effect on brake performance....

[cliff.b]

Well the pedal certainly isn't hard at the moment (lol), despite copious bleeding which is why I'm considering replacing the cylinder.

So I can fit the GMC224 instead?

If I do that I am also thinking of fitting a servo at the same time, which may raise more questions.

 

 

[dougbgt6]

Cliff,

I would replace the pads first, an easier job than a new M/C. Mintex 11/44s are widely regarded here, not just a bit better they make an astonishing difference.

I have a servo, it doesn't make the braking better, but it makes it easier and more like a modern, which is a relief when you swap between the two. 

Incidentally that is stunning paint work, be careful not to spill brake fluid! 

Doug

[cliff.b]

I am replacing the pads as well but there are more serious problems. After getting the engine running I took it out for a road test and was shocked to find almost no braking.

First push the pedal went to the floor, several more quick pumps resulted in "gentle retardation" rather than actual braking.

So cautiously back home and now working on improving matters.

 

[dougbgt6]

Cliff

Ah, well, you've got a leak or air in the system. Is the M/C fluid reducing? Have a look at the rear slave cylinders, are they weeping? There are repair kits, but whole new units aren't much more expensive. M/C rubber could also be shot, repair kits for that to. 

Doug

[cliff.b]

Many thanks for all the advice. I will investigate further this weekend. 

[Colin Lindsay]

1 hour ago, johny said:

Looks like a GMC150 master cylinder for MGB. 

Had to look those up and it's the same... very unusual!

Is that Java Green?

[cliff.b]

Hi Johny, thanks for your thoughts that this master cylinder looks like a  GMC150 from an MGB.

I was just wondering, if I do change the cylinder and go back to the original GMC224, would the push rod from the pedal be the same?

Just noticed that the replacement ones say the push rod is not supplied and must re-use the old one, which is OK if it's the same but obviously a problem if it's not.

 

[Mathew]

Definitely check the rear brake adjusters. You could be making the cylinders travel too far

[cliff.b]

18 minutes ago, Colin Lindsay said:

Had to look those up and it's the same... very unusual!

Is that Java Green?

I don't think it's an original colour. During the restoration work it had a "body off" respray so the entire car, inside and out is that colour.

I don't think I would have chosen to spray it that colour myself LOL

[johny]

14 minutes ago, cliff.b said:

Hi Johny, thanks for your thoughts that this master cylinder looks like a  GMC150 from an MGB.

I was just wondering, if I do change the cylinder and go back to the original GMC224, would the push rod from the pedal be the same?

Just noticed that the replacement ones say the push rod is not supplied and must re-use the old one, which is OK if it's the same but obviously a problem if it's not.

 

Think theres a good chance the push rods are the same but cant guarantee it.

That MC looks pretty new but it could be faulty: if theres no fluid leaking under the rubber gaiter then the only other possible problem is that the feed from the reservoir isnt closing off properly when you press the pedal. You can check this by seeing if the level in the reservoir increases slightly as the pedal goes to the floor. If you dont find either of these issues then, as stated previously, the problem must lie elsewhere....  

[cliff.b]

As this car is new to me and I am finding various issues I have just taken the N/S brake caliper off and one of the pistons is seized. Obviously this won't have been helping the braking but can't see why it would affect the pedal travel.

Happy to be enlightened, though.

[johny]

No, cant see that would do it but might be an indicator to the general state of the brakes so Im sure there will be more findings....

[cliff.b]

1 hour ago, johny said:

No, cant see that would do it but might be an indicator to the general state of the brakes so Im sure there will be more findings....

Yes indeed, will need to go through everything I think. Thanks again for your help.

[johny]

Let us know how you get on👍

[cliff.b]

Right, parts have arrived and I plan to look at the car again later but before fitting anything I want to investigate further. I have read about "clamping off" flexible pipes but have never done that myself so wondered what the best way of doing this is/what to use? 

[johny]

There is a specific pipe clamp tool available that can be used on rubber hoses (its not recommended to clamp the ones with braided metal covering due to risk of damaging them). Otherwise various other tools can be used like G clamps or mole grips etc as long as only smooth non cutting surfaces are applied to the hose so in some cases packers have to be inserted. The clamping force also has to be set to do the job without being excessive...

Its a way of identifying a part of the brake system that is causing pedal softness as you could clamp all 4 brakes and if the pedal still isnt solid theres a problem with the servo/MC. Otherwise you can release a brake at a time to find the dodgy one☺️ 

[Mathew]

I tried that on my spitfire, did not find anything. Turned out one of the rear hubs was bent. Probably from a PO pulling the hub without the correct tool. As the hub rotates it had tight spot due to the hub. Thus lots of travel as the piston pushed back. Replaced and adjusted all ok.

[johny]

Blimey Im surprised there wasnt vibration to be felt when driving plus smoke coming out of the rubbing brake!

[cliff.b]

22 minutes ago, johny said:

There is a specific pipe clamp tool available that can be used on rubber hoses (its not recommended to clamp the ones with braided metal covering due to risk of damaging them). Otherwise various other tools can be used like G clamps or mole grips etc as long as only smooth non cutting surfaces are applied to the hose so in some cases packers have to be inserted. The clamping force also has to be set to do the job without being excessive...

Its a way of identifying a part of the brake system that is causing pedal softness as you could clamp all 4 brakes and if the pedal still isnt solid theres a problem with the servo/MC. Otherwise you can release a brake at a time to find the dodgy one☺️ 

That's what I was planning to do. I have some very small G clamps so if they are likely to be appropriate I think I will try those, maybe with a bit of packing

. 

[johny]

The official tools use round rod of fairly small diameter as the clamping surfaces to spread the load and ensure good close off but its not critical...