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Air bubbles in brake master cylinder


Barry Kemp
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Ok so I've probably bled a cars  brakes a dozen or so times in my life but I have a question that I am now surprised I have to ask. I hope this is not  dementia coming on as I feel I should know the answer!

Having pumped the brake pedal 3 or 4 times air bubbles come up from the bottom of the master cylinder when I release the pedal. Is this normal or a sign of a leaky seal in the M/c?

 

 

 

 

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Barry.

As you say, air is getting somewhere and it probably is the M/C as John has identified; you will have to check it out on the bench so an overhaul  is the next step.

What's the history of the unit ??

Regards.

Richard.

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Reckon so Barry.

I'm probably going to get shot down in flames here, but I'm not a big fan of rebuild kits for brake components and would rather purchase a new unit.

Just depends on your stance with such things.

Regards.

Richard.

 

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And if you do, time to consider if you want to modify the system, or else just bring it uop to spec.

The integral reservoir is a pain, IMHO, the old metal caps never fit.    Modern M/cylinders come without and you can choose a plastic reservoir to screw in,in a vaiety of sizes or even remotely, if that were necessary (it's not, for a Triumph).  And, you can consider a different bore to the M/c.    Larger means less travel but more foot pressure needed, smaller the reverse.   Available in a range from 0.625" - 1".

All the other tweaks too.   Best, again IMHO, are Aeroquip flexible hoses (nylon, braided metal sheath).   No better than rubber, but fit and forget, though they do look spiffing at first!   And vented discs, and MIntex 1155 pads, if you plan pass storming or similar.    Otherwise Triumph brakes are as good as your tyres!

John

 

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Barry,

I'm guessing as you only bleed your brakes infrequently you're not racing your Triumph? If so you don't need vented disks, but Mintex 1144s will make a big difference.

My master cylinder is 45 years old and the bore is still in good condition, but after 9 years certainly try a rebuild kit, dead easy to install and cheaper than a new master cylinder.

Brake fluid absorbs water and should be replaced every two years. Now might be the time to consider silicone fluid which lasts almost indefinitely and doesn't eat your bulk head.

Doug

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22 hours ago, classiclife said:

Reckon so Barry.

I'm probably going to get shot down in flames here, but I'm not a big fan of rebuild kits for brake components and would rather purchase a new unit.

Just depends on your stance with such things.

Regards.

Richard.

 

I agree....i always find rebuild kits to be a bit short-lived.

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There must be a small air bleed hole in the pushrod seal otherwise when you press and release the pedal you can get air past the 

End cup seal which will apear in the reservoir  

Should have a small 2mm hole in the end covering boot  to allow the inards to breathe

Pete

 

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