chris666
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| posted on 23/10/10 at 10:04 AM |
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leaking union
Just tried bleeding my front brakes and got good pressure. the problem is the union that goes into the caliper is weeping.
The caliper is a hi spec 4 pot.and the pipe was pre made with the calipers.could i use ptfe to help it seal?by wrapping it around the threads that go
into the caliper?
Chris
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Strontium Dog
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| posted on 23/10/10 at 10:46 AM |
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NO!
You need to find out why it is leaking. Assuming the seat and threads are good in the calliper then a re flare of the pipe is probably in order and a
new fitting for the end of the pipe if it is not in good order too.
I'm not sure what would happen to PTFE that is in contact with brake fluid but it could well degrade. Very bad practise and a "get you
home fix" only in my book!
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mistergrumpy
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| posted on 23/10/10 at 11:48 AM |
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YES 
PTFE doesn't degrade with brake fluid. I've got it on some of my joints and there's been no issues with them. There was even an
article in CKC a couple of months ago where John Dickens discussed this and the whole possibility of of a stray piece entering the caliper and the
fact that it will do no harm.
Ideally as Strontium says find out the cause but I'd say don't be afraid to use a bit of PTFE.
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Strontium Dog
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| posted on 23/10/10 at 12:05 PM |
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The concern over the degradation of the PTFE (and there is more than one type, which have you used?) is secondary to the concern over why it is
leaking in the first place! A correctly fitted union will not leak.It is NOT the threads of the union that seal but the compression of the soft metal
tube flare against the hard metal seat in the calliper. Now consider that if the leak is due to a small fracture in the pipe at the point at which it
flares. PTFE may well seal it up for a while but sooner or later the pipe will let go and probably suddenly. Now I appreciate the benefits of dual
circuit brakes and all that but would you like to lose all braking force ( or at best have totally unbalanced braking) to the front as you try an
emergency stop? The most likely time the pipe will let go according to the law of Murphy!
Get it checked and repaired properly by someone that knows what they are doing. Brakes and steering should be right, no exceptions to that! IMHO!
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chris666
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| posted on 23/10/10 at 12:05 PM |
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fluid must be leaking through the threads,the front joints ARE NOT compression joints .if the pipe is wound to the stop like a compression joint the
lower piston pushes out.
[Edited on 23/10/10 by chris666]
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Strontium Dog
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| posted on 23/10/10 at 12:20 PM |
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quote:
Originally posted by chris666
fluid must be leaking through the threads,the front joints ARE NOT compression joints .if the pipe is wound to the stop like a compression joint the
lower piston pushes out.
[Edited on 23/10/10 by chris666]
?
Are they a taper fitting then? How does the fitting seal to the pipe if it is not under compression? Is there a further fault in your brake system?
The master should allow fluid back into it when at it's rest state. If it didn't you would never go anywhere as the brakes would never
release. You should NOT be able to force a piston out by doing up the union!
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adithorp
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| posted on 23/10/10 at 12:21 PM |
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Chris, you must have something wrong going on there. I've never seen a brake fitting that relied on the threads to seal unless it's a
taper thread. If it is a taper then PTFE is of with brake fluid but ideally should be avoided.
Do you have a picture of the pipe end and caliper.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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Strontium Dog
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| posted on 23/10/10 at 12:28 PM |
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Chris, where are you. If you are near Plymouth I'd be happy to have a look for you. If not then PLEASE get another engineer to take a look. You
can't afford for a fail here.
As Adithorp has just said, post a pic up at least!
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mistergrumpy
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| posted on 23/10/10 at 01:41 PM |
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Chris. Out of interest, you say the pipe was made with the caliper. Is there any way that you're placing the wrong end in the caliper?
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chris666
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| posted on 23/10/10 at 03:03 PM |
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just spoke to hi spec apparantly there should be a banjo union fitted to one end of the goodridge hose,also two copper washers.Will have to get hold
of some banjo fittings to go on my goodridge hoses.
thanks again.
life saving information.
p.s camera is not working.in the middle of buying a new one.
Chris
Chris
[Edited on 23/10/10 by chris666]
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rusty nuts
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| posted on 23/10/10 at 03:42 PM |
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In over 43 years as a motor vehicle technician I have never had to use PTFE or any other sealant on a brake pipe fitting and IIRC it may be an MOT
failure . When you think of the very high pressures generated in a braking system do you really want to rely on a piece of PTFE in an emergency stop?
PTFE is fine in it's place but not on braking systems
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Strontium Dog
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| posted on 23/10/10 at 03:54 PM |
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The picture is clearing! Good job you posted up and sussed what is going on or that could have ended in tears!
The next question is what type of end is on the hose/pipe. When you called it a pipe is it in fact a flexible hose? Is it a taper and what thread is
it. I would take the hose to a brake specialist to make sure you get a banjo and bolt that is correct. A picture would tell a thousand words even if
taken with a phone.
Having said all that the calliper firm should be able to supply exactly what you need if the calliper came with the pipe from them in the first
place!
[Edited on 23/10/10 by Strontium Dog]
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Strontium Dog
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| posted on 23/10/10 at 03:59 PM |
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quote:
Originally posted by rusty nuts
In over 43 years as a motor vehicle technician I have never had to use PTFE or any other sealant on a brake pipe fitting and IIRC it may be an MOT
failure . When you think of the very high pressures generated in a braking system do you really want to rely on a piece of PTFE in an emergency stop?
PTFE is fine in it's place but not on braking systems
Exactly what I think and yes it could be a MOT fail as it is NOT an original part and if the tester wants to be funny he is within rights to fail ANY
non standard parts. This is because he is only qualified to test and inspect OEM parts according to my local examiner!
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mistergrumpy
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| posted on 24/10/10 at 03:19 AM |
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If he's only qualified to inspect OEM parts then I suspect that he is breaking the rules daily. Could he really fail it or just refuse to test?
If it were true then even a non OEM standard tyre or even winscreen wiper should be refused and if I were him I wouldn't want to put my neck on
the line. I suspect that there's a little more to the interpretation though.
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chris666
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| posted on 24/10/10 at 12:33 PM |
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Bajos on the way for the braided hoses.And banjo bolts with two sealing washers.will try to post pic to show finished article.
Chris
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Strontium Dog
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| posted on 25/10/10 at 12:10 AM |
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quote:
Originally posted by mistergrumpy
If he's only qualified to inspect OEM parts then I suspect that he is breaking the rules daily. Could he really fail it or just refuse to test?
If it were true then even a non OEM standard tyre or even winscreen wiper should be refused and if I were him I wouldn't want to put my neck on
the line. I suspect that there's a little more to the interpretation though.
I suspect it is part of his discretionary powers. The conversation came about when he MOT'd my Mini which hardly has a standard part left on the
front suspension and brakes As to whether he would fail it or refuse to continue to test the result would be the same. No MOT and a bill to pay
anyway!
I have been taking very modified cars and specials there for many years and he takes an interest. He gets to MOT a local Ultima as well as an AMG Merc
and several other interesting local beasties! He was just commenting on the way the rules are going and how it is all getting a bit too much!
Chris,
that's brilliant news. I'm glad you got that one sorted out
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mistergrumpy
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| posted on 25/10/10 at 10:02 AM |
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quote:
He was just commenting on the way the rules are going and how it is all getting a bit too much!
I suspect he's right there
As for getting the Ultima in, how envious am I right now. I'd almost have to fail it just to get it back in again
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