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alan c
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Bleeding Brakes

I am struggling to get my brakes bled properly. Car has the up rated  AP  calipers front and rear, and front ones are just back from a refurb. I have pushed 1.5L through and fluid is running clear with no bubbles but the pedal is still soft

I have the rear ones unbolted so I can have them vertical with the bleed nipple at the top.

Any others tricks I can try?

Alan

Pendennis
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Have you got the rears up high with bleed nipple highest point in caliper

alan c
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Hi

The fronts are vertical with two bleed nipples at top so fairly sure problem is with the rears. They are on flexible hoses so have them unbolted and I am holding them vertical with the bleed nipple at the top. I will have another go in the morning and focus on the rears holding them higher and perhaps tapping them a little.

I am using the Sealy pressure system which helps a lot and if I leave the system pressurised it hold the pressure so no leaks and there are also non visible .

Just got a little frustrated, tried traditional method last week and had hoped the Sealy system and taking th rears of and holding them would solve the issue. Will let frustration subside with some red and try again in the morning.

Pendennis
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Get them as high as possible, I tend to cable tie them up nearly top of damper. Presume you've got something in damper between Pistons?

7 wonders of th...
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When you say 'soft' are you meaning springy or does it pump up with repeated applications of the pedal?

Is the fluid your using from a new sealed bottle thats been stood for a while - seen sooo many people get a new bottle of fluid and shake it before opening it as if it were ketchup! - which naturally fills it full of tiny air bubbles... Nono

Whilst under pressure gently tap the calipers, use the hammer shaft, to dislodge and tiny bubbles still clinging to the inside of the caliper

Ivaan
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Have you installed new pads? In which case it could just be that they need bedding in.

Does the brake peddle hold up firm with constant foot pressure on it, or does is continue to sink down? If so, then you have a problem with the master cylinder seals.

Having the calipers re-furbished means that the system has been drained for some time, so the seals could suffer.

 

BECs Rule !
alan c
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Thanks for the various comments, I have had another go today and not really made any progress. In answer to the various questions:-

1 Fluid I am using is new and purchased in last couple of weeks so that should be ok.

2 I had a brake judder issue and have already replaced front discs etc so calipers were away for a refurb to try and solve that so I have not yet got as far as trying the car on the road so newish pads not the issue. At least if so I have not got that far yet.

3 if I pump the pedal and keep my foot on it there is no further movement and pedal feels firmer but not right, it does not go down even with foot on brake for some time. Take foot off and leave for a few seconds and it's soft again. So I don't think its an issue with the master cylinder.

4 I had rear calipers as high as I could get them and ran about 0.5 L through them whilst tapping them. Fluid runs clear with no bubbles. (Block of wood is wedged between the pistons)

Unless I am missing something it still feels like there is air in the system somewhere. 

Any other ideas?

 

 

Pendennis
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Have you tried bleeding the brakes the old fashion way with someone in car and you on calipers?

If I remember correctly on your other thread I thought It would probably be the master cylinder. I be interested to know like you what the problem is, but as I said on your other thread I had a similar situation and was convinced it was moisture then after flushing it was still there so thought it must be air, after I checked for air again and any leaks which there were none I had no choice but to change the master cylinder as it couldn't be calipers, my evidence did not justify them at fault. That was my problem, abnormal pedal travel with pressure differential feed back via pedal.

Before you go and buy one have you checked for any leaks? Do you have a brake bias valve in the rear line? If yes, I presume you have it fully open at this stage?

alan c
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Hi

Fairly convinced the original problem was not the mater cylinder. We were able test the car at an MOT station on their rolling road and vibration/judder was only evident on the front wheels. So I assumed if it had been the cylinder it would have been evident on all wheels. Having said that I guess I cannot rule out that there is now a problem there given car was sat for about a months with no brakes.

I did start with the traditional method of foot on pedal but purchased the Sealey kit so I could try and make progress on my own. I might go back to traditional approach tomorrow evening. 

There are no visible leaks anywhere and if I leave the system connected to the Sealy brake bleeder with 20psi of pressure it holds that.

I am not aware if I have a brake bias valve and I have certainly not adjusted one. If had one where would it be and what does it look like.

Pendennis
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Last seen: 1 year 7 months ago
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There are many types of bias valve, but here is the CC version: https://caterhamparts.co.uk/other/2459-valve-brake-reducing-csr.html

They could be installed anywhere on the rear brake line, normally it's located either drivers or passenger footwell compartment near seating position. To be honest you'd know if you have one

Pendennis
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I only bleed the brakes the old fashioned way, never trust the new devices! Starting left rear, then right rear, left front then right front, always bleeding furthest away nipple from MC first, so last nipple is front right nearest to MC