Jump to content

Brake system Airleak


Recommended Posts

I have bled the brakes many times and after a while they are soft again. Could I have an airleak at one of the unions. If yes how do I check it and find out where.

I have no signs of fluid. Washing up liquid did nothing. Master cylinder never seems to change. Locking the pedal down over night has no effect. I cannot think of an easy way to pressurise the system to see if there is a pressure change.  Or am I missing something?

Link to post
Share on other sites

Hi, 

are the rear brakes correctly adjusted?

If they have too much play the pistons have to move much way out and are pulled back by the return springs.

This is needless way of travel.

And it is interesting to know the seals of the pistons of the front calipers are elastic to pull the pistons a minimum way of travel back.

They rest in a position to the seal and only slide in a different (and more fortune) position after the brake pads wear out.

So the pistons slide through the seal is steps,

each time the elastic movement gets too far the slide.

Hope this helps,

Marco

Edited by Z320
Link to post
Share on other sites

Hi Peter,

on my smartphone I did not see you are located at Munich!

We better chat here visible for all, perhaps I'm wrong or others have more ideas.

What is your question to my explanation above?

Tschüss, Marco

 

Edited by Z320
Link to post
Share on other sites

Ok but I cannot write german correctly. Reading perfect. Speaking very good but German grammer beats me. I never learnt German as I always worked with English or French. (long time ago). PM me a tel number and we can Whats app.

Link to post
Share on other sites

Peter - I think this depends on whether the pedal actually feels soft or whether it just has a longer travel the first time you use it.

 I think Marco was describing the second case where the pistons get retracted so that some of the pedal travel is used in closing them up again. That can also happen if the front wheel-bearings have excessive play, allowing the disc to wobble a bit,  which also pushes the pistons back. 

If the pedal really is soft then other than air in the system there is the possibility of a weak flexible hose which is 'ballooning' under pressure. 

Edited by RobH
Link to post
Share on other sites

The hoses are new/good. Have not noticed wheel wobble but will check. I like very hard brakes and tight handbrake. So I do notice small changes. The brakes piping has been renewed. I checked every union. I am just wondering if a union is not seating poperly. Hence the original question.

Link to post
Share on other sites

It is difficult to imagine a problem with a union which would let air in but not let any fluid out. I don't think you can pressurise the system to any degree with everything connected,  as that would just force fluid back into the reservoir.  Locking the pedal down through a strong spring would seem the only easy-ish way to achieve that.  

Link to post
Share on other sites

Keeping the pedal locked down over night was a trick used by the motorbike community in the days when there were Britsh bikes racing. It got rid of any unwanted air from the system. I have tried it and it does work. In this case, it was of no help. Hence I started to look elsewhere for a leak or whatever.

 

Link to post
Share on other sites
2 hours ago, Peter Douglas Winn said:

Keeping the pedal locked down over night was a trick used by the motorbike community in the days when there were Britsh bikes racing. It got rid of any unwanted air from the system. I have tried it and it does work. In this case, it was of no help. Hence I started to look elsewhere for a leak or whatever.

 

I suppose the issue was not air, it is "Lüftspiel" (German), translated in English something  about "ventilation play / gap"

Link to post
Share on other sites

What about a reply in French, dear Peter ?

Salut Peter, tu devrais quand même regarder sous les cache-poussières (dust cover) des cylindres de freins arrière (rear brake cylinders) : tu pourrais avoir une petit fuite de liquide (fluid leak), mais que le liquide ne sorte pas encore du cache poussière.

Pour ça, il faut déposer les tambours (remove the brake drums), et soulever le bas du cache-poussière avec un petit tournevis.

Sorry, Il learned German at school for 5 years, but it was a long time ago !

Link to post
Share on other sites

Hi, Peter and I had a lovely telephone call,

but want to explain what I mean also here at the forum with 2 photos and in other words.

 

We know the brake calipers are self adjusting and the pistons slide out of the calipers with the wear out of the brake pads.

Next you see a sketch (not perfect, sorry) of a brake caliper (black lined), the brake fluid (blue), the piston, seal (red), brake pad and brake disc.

There is no pressure on the system, the piston is "in" the brake caliper and there is a gap between brake pad and disc, about 0.10 - 0.15 mm (red line).

QMEhZz-jN2P5NdH35PzB_Ok0YBSPuStzh_BSzdpU

The seal is special, it is tight on the piston and has some adhesion on the pistons surface, it is not made to slide perfectly.

When you now give pressure on the brake caliper the pistons moves out the brake caliper and presses the pads on the disc.

But the pistons are pressed out against the adhesion of the seal and the seal reacts elastic deformed, the piston mainly does not slide through the seal.

uqHEvyiLSJdQEAy5_JREJaoC8I6Khcfa8SJLqYwB

When you give the brake pedal / brake lever (motor cycles) free this elastic deformation pulls the piston back (like a spring),

gives the gap free again the wheels spins free the next moment! Hey, that's genious, isn't it!?

With the wear out of the pads the elastic deformation is increasing, also the gap between disc and pad and the way of travel of the brake pedal.

Until the way of travel of the piston moving out causes the seal to slide on the piston! Next  moment the elastic deformation is reduced, also the gap and the way of pedal travel.

This is what Peter wanted to get with the brake pressed down over night:

hoping for the seal starts to slide on the piston  to get the air (play, elsatic deformation) out, not at all "real air".

And sometimes this works! Perhaps new / other seals and cleaning the piston works in Peter's case?

I feel the growing and reducing of the gap / way of travel slightly on my TR4A and in a fare future I have to look for the seal and the piston surfaces.

But as long as it is sealed I keep it untouched.

Ciao, Marco

 

edit:

there are "ground valves" aviable to hold the he pressure on drum brakes more or less and 

"special ground valves" (with reducing hole) for disc brakes to reduce the pressure slowly,

very informative is the "Bremsen-Handbuch" from ATE (German badge), 368 pages, 21x30 cm paperback, countless number of illustrations,

I only know a German edition 

Edited by Z320
Link to post
Share on other sites

I am wondering how old were the new cailpers from Rimmers. Had they been stored on the back of the shelf, for many years and the rubbers were already out of date. As I have a complee new set of rubbers for the pistons I will take them apart and renew the rubbers. Thanks everybody for the help. I will let you all know what has happened.

Link to post
Share on other sites

I have just had a phone call from my Triumph supplier. He said as there is no  manufacturing date control of spare parts. So nobody knows how old they are. Even firms like Moss and Rimmers have this problem. Manufacturers have a habit to make things in batches. So after the batch has been finished perhaps 80% are sold and 20% wait for future sales and sit on their shelf for ages..

Link to post
Share on other sites

Hi Peter,

I remember this question about "air" in system was one of the "workshop questions" of the German classic vehicle magazin "Oldtimer Markt" - some years ago.

I went through all issues down to 2018 but did not find it.....

Link to post
Share on other sites
On 9/14/2021 at 1:40 PM, Peter Douglas Winn said:

I have bled the brakes many times and after a while they are soft again. Could I have an airleak at one of the unions. If yes how do I check it and find out where.

I have no signs of fluid. Washing up liquid did nothing. Master cylinder never seems to change. Locking the pedal down over night has no effect. I cannot think of an easy way to pressurise the system to see if there is a pressure change.  Or am I missing something?

How old is your master?

If one of the piston seals are worn, fluid is being transferred back into the reservoir.

 

Link to post
Share on other sites

Hi Jochem,

sadly this thred is already fixed on my suggestion

and this is why I'm very pleased about your post in this thread and another possible failture.

If the return valve to the reservoir does not seal the brake fluid level must raise in the reservoire when Peter steps on the brake pedal.

This is lovely easy to check.

I'm pleased about any other sugestions.

Ciao, Marco

Link to post
Share on other sites
  • 2 weeks later...

Master cylinder is brand new. From TRW/Moss where by the 1st one did not work as the piston was stuck in and the servo did not touch anything.

Something else. Many years ago I had a problem with the saloon brakes sticking. It was the master cylinder. When taking the foot off the pedal the fluid did not go back into the resevoir so the brake pads were slightly on. The caused heat everything expanded until the front end just locked up. I was only with brut force that I got to a layby and then everything cooled down. These new pads in the short distance were worn down to the metal. So beware.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.