Soft brake pedal in spite of much bleeding

[Dave McHattie]

Hi Folks

 

Got around to start checking and wasn't to sure about clamping the steel braided hoses, so tried the back one then released, it did distort the steel but it was easy to correct without damage. So one at a time clamped each brake hose and tried the pedal and was still soft with all clamped thus indicating a master cylinder problem, checked the piston rod length and was correct and well clear of the piston at rest....Then I noticed the cylinder had the reservoir at right angle to the main body, whereas I remember it should be leaning back about 15 deg, so I'm beginning to suspect it may not be the correct type as there's no markings to indicate type, I need to go back to the (well known triumph) supplier.  Another friend has suggested it could be an air lock in the cylinder which is very difficult to remove as it has no bleed point, he said a lot of mechanics in the day would prime the cylinder before installation. Anyone had this experience?

[johny]

I'm not sure on your model but many have the clutch MC reservoir angled back as it's quite small but the brake one is at 90 as it's larger and doesn't need to be filled to the top. I've never had problems with air locks as any air in the MC should naturally float out into the pipe exit as this is the highest point. Then once in the pipe it should be easy to flush out through a wheel bleed nipple.

If you repeatedly and rapidly pump the pedal does it harden up or continue to be spongy?

[mark powell]

I had this issue when I put my Herald pick-up back in action.   Cured by pumping the pedal until hard, then leaving it wedged down hard overnight. (suitable length of timber between seat base and pedal...)  No problem since.  

[Pete Lewis]

whilst the angle of the reservoir may be wrong the cyl itself is as should be ,you cant change that,   it wont affect the cyl operation only the volume you can top up the reservoir 

had these on many cars with no problems , the ones witha full clear  resv are best as you can see the levels.

you really should not clamp metal braided hoses you as found crush the braid and theres no way of seeing what you have done to the thin walled tube liner 

if you have bledd with the foot and done a fast down nip nipple and slower return open nipple fast down slow return should easitly bleed any air from the system, 

if its not giving a well defined squirt on each down stroke its going to point to a M cyl seal is not working , most likely the small one that  seals the reservoir off on the start of the initial press

if this little seal is not working all you do is push fluid in and out of the reservoir , 

you dont need any pressure ,ezebleed or any other solutions  , when bleeding have a long tube and keep the catch bottle well above the wheel height , 

hopefully you can get a mate to pump,and you can  nip on each down stroke , keep bleed bottle up high , watch for a good squirt,not a dribble  and if that all fails change the seals in the cylinder

pete

 

 

 

[Dave McHattie]

Yep, have tried rapid pumping but it's still the same. The pedal goes down freely until almost at the bottom of travel then feels spongy. The cylinder has the large white plastic reservoir, whereas the original was integral casting and leaning back so the when it was installed the reservoir was upright.

There are variations in cylinders particularly in bore size, but your right Pete, no matter all that it should work. I have bled the system conventional as you describe to no avail and also used a one man vacuum system that I've used over the years on all my various triumph TR and E Type rebuilds with excellent results....The cylinder is brand new, so like your thoughts, I now suspect it is faulty and will drain the system and remove for checking. Unfortunately I will have no recourse to the supplier as I purchased it in 2014, so i'll dismantle and check so "watch this space".  As a professional metallurgist I really should know better regarding clamping the braided hoses, but I'm fed up with this problem and could not think of any other option to isolate the master cylinder.

 

 

 

 

 

 

 

 

[johny]

were you able to see the reservoir level go up as the pedal goes down?

[Pete Lewis]

good now you have got to the culprit, they are a simple bit of kit with just two seals

it may be the main seal has a fault but if failing they will let fluid into the pushrod boot 

the small recuperation seal that blocks the reservoir entry is often where snags lurk  it has a the spring that keeps the seal against the port ,not an issue but the small thin wavy washer that 

seats the seal on the lightest of pedals can be displaced and this causes your sort of havoc as the fluid will continually return to the resv.  

which is why jonny is asking 

let us know whats going on inside 

Pete

[Dave McHattie]

Yes, I did check the fluid level both with pedal depressed/released, but with no discernible difference in level. Thanks for the very helpful info' on the internals. I'll let you know what I find when I get back from my Easter holiday in the Bahamas (in my dreams!!)

[Pete Lewis]

you have to press the pedal and look in the reservoir all at the same time or you miss the telltale shift in level   its only small   blink and its gone 

anyway if you of to the BAAAharmus  you can get some drift on this   

so just enjoy the deck chair in the back garden or else !!!!!

so there 

Pete