Air in front calipers...

[Eccles]

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]

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]

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

[SM25T]

That sounds bizarre. For air to get in, you would expect to see a leak under pressure.

[Eccles]

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.

[21jigsaw]

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]

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

[JonT]

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]

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

[JonT]

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]

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. 

Thanks all

[john g]

I purchased new callipers from a Triumph/MG 'shop', no idea who the manufacturer was, it was certainly not Girling. When fitted I had a similar problem, air in the system and no leaks. With much force you could actually press the break pedal down to the floor. I contacted the 'shop' who told me I had been supplied with the incorrect nipples, they sent me some more nipples, a little longer, I wasn't convinced and still the issue remained. I contacted them to complain questioning the build quality of the callipers (castings) and they basically told me to 'go away'. I eventually rebuilt my old Girling callipers and pleased I did. This tale doesn't really help you, however it's just to let you know I had air in the system and no leaks.

[ScottR400D]

I guess the only way it could happen is with air being drawn back in around the calliper seals when the brakes are released. There'd be a slight lift in fluid level at the MC but then you'd be bleeding the air out  and back to square one  

It's still hard to fathom though, there's no vacuum created behind the piston, just a release of pressure so why would air be drawn in? Seems the only explanation though?

[SLR No.77]

Check for unevenness or corrosion in the calliper bore around the piston, yes it means dismantling everything. 

Stu.

[O.G.]

How old are the flex lines?

If not, as it's both sides, sounds Master cylinderish.

O.G.

[Eccles]

Hi john g, it does help me, I now know this can happen so I'm not going mad and doubting everything I do so thanks.

That was the way I was trying to think of it ScottR400D, I know leaks through molecule size is a thing through talking to people at work but it's hard to relate that to a car brake system.

The bores and pistons looked good when I did the seals but that doesn't mean I didn't miss something so yeah, as messy as it will be, taking things apart again is on the horizon. The flex lines are 14 years old, I have found someone on eBay selling seal kits for the Seven master cylinder that I have so have bought one as they don't seem that readily available.

I'm almost tempted to bite the bullet and just do the M/C, get new flexibles, and new calipers (or new pistons, bleed nipples and checking where the nipple seats) rather than one thing at a time to minimise the amount of mess taking apart/brake fluid used.

Cheers

Ivan

[Eccles]

I know a while has passed but what with winter and breaking my leg I have now got it all sorted.

Turns out it was getting air in through the bleed nipples, after replacing all the seals the problem was still there so I bought a pair of new calipers from Rimmerbros and fitted and the problem went away.

The one thing I noticed with the new calipers was that the pistons retracted too far after releasing the pedal meaning there was an inch or two of nothing before the brakes came on. Reading on another forum it was mentioned that the seals can sometimes cause this and to push out the pistons a bit further (against some bits of wood/plastic so they don't pop out) and then push them back in and refit the pads. Tried this and now all fixed, brakes now bite at the top of the travel.

Thought I'd update the thread so that it may provide an answer to anyone who has similar in the future.

Cheers

Ivan

[Beagler]

May not be air it maybe the the recuperating valve seal and not getting enough fluid charge. After 14 years change it anyway.