A couple of months ago I maintained the brakes on my Lomax. I replaced discs, calliper pistons and seals and master cylinder rubbers. The rear brake is good, shoes and slave cylinder replaced not long ago. I was unable to obtain a decent hard pedal, always needing one additional pump to obtain good braking. The master cylinder seal replacement was tricky (turned out there are two seal bores and I was sent the wrong one) so I replaced the master cylinder. The pedal remains exactly the same.
I have bled the system countless times and am absolutely certain there is no air in there. The condition persists - it feels as though the pistons withdraw some distance at rest, requiring two pumps to move them back into contact. The rear brake is adjusted perfectly but does not come on until the first pedal application is right down. I see no sign that the pads move away from the discs but of course cannot see the pistons.
Having today tried once again with no success I am now out of ideas. Does anyone have any suggestions please?
Soft brake pedal - baffling
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howardjs
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Re: Soft brake pedal - baffling
Hi Viv,
I too suffered from impossible to bleed brakes a few years ago (article in Flat Out Sept-Oct 2017 p25).
Eventually I concluded that the trapped air was somewhere in the front calliper circuit.
My fix was to re plumb the callipers using a tee piece and fitting both callipers with bleed nipples.
It worked first bleed attempt.
Howard
I too suffered from impossible to bleed brakes a few years ago (article in Flat Out Sept-Oct 2017 p25).
Eventually I concluded that the trapped air was somewhere in the front calliper circuit.
My fix was to re plumb the callipers using a tee piece and fitting both callipers with bleed nipples.
It worked first bleed attempt.
Howard
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Davidm
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Re: Soft brake pedal - baffling
Viv
Sometimes new dust covers on the rear cylinder can be stiff enough to push the pistons away from the brakes shoes. A cure is to fit a light spring (like the spring in the 2cv rear light cluster) between the pistons to push the pistons apart.
For bleeding the brakes when no assistant is available I gently pressurise the system as follows -
-Cut an old bicycle inner tube about a foot each side of the valve.
_Tie a knot in one length of tube to seal it
- stretch the other end of the tube over the master cylinder filling opening
-gently pump with bike pump on tube valve to pressurise the system to enable bleeding
Davidm
Sometimes new dust covers on the rear cylinder can be stiff enough to push the pistons away from the brakes shoes. A cure is to fit a light spring (like the spring in the 2cv rear light cluster) between the pistons to push the pistons apart.
For bleeding the brakes when no assistant is available I gently pressurise the system as follows -
-Cut an old bicycle inner tube about a foot each side of the valve.
_Tie a knot in one length of tube to seal it
- stretch the other end of the tube over the master cylinder filling opening
-gently pump with bike pump on tube valve to pressurise the system to enable bleeding
Davidm
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Boggy
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Re: Soft brake pedal - baffling
Vyv,
Spoke to Owen about this when he delivered the Lomax, have you got the right pushrod for the master cylinder you fitted? There are two lengths
, 105.5 and 88 mil
Boggy
Spoke to Owen about this when he delivered the Lomax, have you got the right pushrod for the master cylinder you fitted? There are two lengths
, 105.5 and 88 mil
Boggy
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Vyv Cox
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Re: Soft brake pedal - baffling
Thanks for the suggestions.
Howard - not quite sure why fitting a T to the supply pipework would make a difference but it may be worth a try. I'll keep that in reserve for now.
Davidm - The rear brakes are definitely not the problem. I thought the dust seals in the front disc pistons might be causing problems, particularly since the old pistons, that worked perfectly for the last 10,000 miles, had none fitted. The grooves were filled with grease instead. So I took them out but this had no effect. I have a glamorous assistant who has been pressing brake pedals for me for the past 50 years!
Boggy - The rod is the correct one for the master cylinder. I thought I might have adjusted it wrongly and checked it yesterday. There is definite clearance between it and the piston when the latter is fully back.
My next move is to empty the reservoir and fully push the pistons back into the cylinders, hopefully to expel any air that is trapped inside. Then refill and bleed again. After that I don't know.
Howard - not quite sure why fitting a T to the supply pipework would make a difference but it may be worth a try. I'll keep that in reserve for now.
Davidm - The rear brakes are definitely not the problem. I thought the dust seals in the front disc pistons might be causing problems, particularly since the old pistons, that worked perfectly for the last 10,000 miles, had none fitted. The grooves were filled with grease instead. So I took them out but this had no effect. I have a glamorous assistant who has been pressing brake pedals for me for the past 50 years!
Boggy - The rod is the correct one for the master cylinder. I thought I might have adjusted it wrongly and checked it yesterday. There is definite clearance between it and the piston when the latter is fully back.
My next move is to empty the reservoir and fully push the pistons back into the cylinders, hopefully to expel any air that is trapped inside. Then refill and bleed again. After that I don't know.