Air in front calipers...

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Eccles
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Air in front calipers...

I have got this recurring problem of air getting into my front calipers (standard Triumph brakes) after a couple of weeks whether I use the car or not. I only ever need to bleed 1ft of fluid out of each caliper each time for the pedal to become firm again but two weeks later the air is back again and the pedal goes soft.

There are no (fluid) leaks in the system and have just replaced the piston seals and copper washers on the banjo bolt with no change.

Anyone else had this/got any ideas where it is getting in from?

TIA

Ivan

Wrightpayne
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How old is the master cylinder? They are usually dual circuit split front and rear so could be an issue with one set of seals within.

I had a problem 2 years running where after the winter lay up pedal went to the floor. 1st time I bled the brakes and monitored and it was fine for the summer. 2nd time I'd lost faith in it so swaped for the uprated AP MC.

Wrightpayne
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PS mine had no visible signs of leaks even when I stripped it down.

SM25T
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That sounds bizarre. For air to get in, you would expect to see a leak under pressure.
Eccles
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Thanks for the reply, everything is original so about 14 years old. I was thinking it wouldn't be the master cylinder by how little fluid I would bleed before it was ok, the air comes out within the first couple of seconds of opening the nipple (using Easybleed) so was thinking it was already in the caliper.

2007 S3 Sigma 150

21jigsaw
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Where fluid gets out air gets in,  check for the slightest signs of damp on the system  also look at the secondary seal on the master cylinder ,the one behind the boot and check for fluid.

 

ScottR400D
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Hard to understand how air can repeatedly get in if fluid isn't coming out.  presumably you're adding fluid each time? 
 

L7C
JonT
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How do you know there are no leaks? If it's a tiny airlock, then it's probably an unnoticable amount of fluid from a simple visual check.

Try going around all the joins with some clean, dry towel/paper - it will quickly wick any fluid and show you the tell tale of a damp spot on the paper - check joins through the side skins, 3-way joint, and into the master cylinder.

I had a similar nightmare with mine - it was fine on road, but any track use and I'd have a problem. Eventually cured with new calipers (not that expensive from rimmerbros). I think the bleed nipples themselves weren't actually sealing properly although I also had an issue after replacing the master cylinder where the old pipe flare didn't seal properly to the new cylinder. I made up a new section of pipe with a join into the old pipe that solved that.

OldAndrewE
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Were you getting this problem before you replaced the piston seals?

Andrew

1985 S3 1700 XFlow.  Undergoing full restoration

JonT
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Oh, if you've got an easybleed, try the paper thing I mentioned with the easibleed attached and creating some pressure in the system (or with an assistant pushing the brakes). The leak might not be very apparent until there's some pressure.

Eccles
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It is a bit strange and I don't understand, yes I would have thought that there would be fluid coming out somewhere - must be but I just can't find it. 

I top up the system when I bleed the air out but no need at any other time.

It was happening before I changed the seals, after reading about someone who had the same problem and air was getting passed the seals but then fluid wouldn't leak out. I was a bit skeptical but figured it was only £20 and a few hours in the garage so tried it.

Think I'll try trying your idea 21jigsaw/JonT and clean all the joints and test for leaks with paper towel. I can put something on the TV in the garage and sit there with my foot on the pedal as I'm not sure I'll get the wife out there to help. Laugh

Thanks all

2007 S3 Sigma 150