Siezed bleed nipple

Following from this thread:

http://www.diynot.com/forums/automotive-repairs/dealing-with-corrosion.351321/

I have started to strip the brakes down to replace the discs and pads. The Honda manual states that when pushing back the piston the hose should be clamped and the bleed nipple opened to avoid flipping the seals in the master cylinder. Nice idea, except for the fact the bleed nipple is seized solid. I have tried some Plus Gas but no joy. My usual method for seized nuts is the MAPP torch but with brake fluid being highly flammable and all this probably isn't a good idea.

Any other suggestions? I can't a socket and breaker bar on it either, could try a small bar I suppose.

Once I get it off is it ok to put some copper slip on the threads or is that likely to contaminate the fluid?

 

If your brake fluid is "highly flammable" then surely that's only when exposed to both heat and air (the combustion triangle). On the basis that the nipple is seized and hence the fluid totally sealed in, I'd have thought a bit of heat should be OK, since the fluid is not being exposed to air. But I might just be wrong on that one

 

First off Ian, worry ye not - just press the piston back slowly and all will be well. I appreciate you will want to change the brake fluid, but I see many vehicles with snapped off nipples and all still works well - despite recommendations to change it regularly.
Regarding the nipple, try a little heat, (not excessively) use a hexagonal socket, then try moving the thing each way. Penetrating oil can't do any harm either.
If all else fails, replacement calipers are aroud £100 exchange.
John

 

There's a good few controversial opinions on this, Jack....and who are we to argue
Brake fluid is hygroscopic, fair enough. Manufacturers claim that moisture can be absorbed through the flexible rubber brake hoses - can't comment on that one......I believe the synthetic DOT5 is less prone.
Excess heating of the brake caliper can cause the fluid to boil - naturally - and if there's any water present then the boiling point is lowered. Obviously that means air in the system which we don't want.
That fact is, I've worked on braking systems where the disc was nearly red hot (35 tonne MAN truck) and the caliper was much, much cooler. Cars suffer much less from caliper heating.
Personally I've had bleed nipples bloody hot and have rarely been beat. If the bleed nipples are 10 or 11mm size then so much the better. The 8mm ones are a pain though.
I reckon the flipping over of master cylinder brake seals is a myth, started many years ago from Vauxhall. Certainly I've never experienced this, and hopefully there won't be a first time
John

 

Thanks chaps. I thought the flipping of seals was odd too. Other manuals (including the Audi workshop manual I acquired for my old car) all say take the cap of the reservoir and check the level as you push back. First time I have ever seen it specifically state not to do that.

I have heard one mechanic say he opens the bleed nipple, his reasons were because it helps to stop the nipples form seizing if they are occasionally undone and prevents crud being forced back up the pipe - with the system being sealed I couldn't understand how crud would be in there in the first place.

I shall try some heat and more Plus Gas.

 

Your mechanic is talking sense Ian - it does keep the nipples mobile, and does go some way to replacing some of the brake fluid.
The gunge he's referring to is actually rubber debris from the piston seals.....they do degrade over a good few years and turn the fluid brown.
John

 

I have overcome a number of siezed bleed nipple problems by slackening off the pipe connection on the caliper - not ideal but it works. If you can get that undone of course.

Peter

 

You could try repeatedly tapping it (down into the caliper) with a little hammer to see if that "shocks" the rust into submission and allows it to turn.

I wouldn't use DOT 5 brake fluid if the car has ABS. It can "foam" in the ABS pump.

 

I usually tap a spanner round with a hammer, as mentioned it helps loosen the rust.

You're right to use Plus Gas - a very good ointment. However it can take a few days to soak through properly.

My main concern would however be corrosion and pitting of the slave cylinders if you say the calipers are that rusty. If this is the case then the piston will seize every time you apply the brakes, and will hit your fuel economy and pad wear rate in equal measure. Make sure they're running freely.

I have in the past refurbished calipers, but by the time you've bought the seals, dust covers, pistons etc it's never worth it.

Furthermore, I doubt the brake seals will be wearing enough to cause the darkness in the fluid, that will just be the result of moisture getting in. Slave piston seals perform two tasks in the braking system: to prevent fluid leaking out, and to slightly retract the piston at the end of the brake application (the seals are usually square-edged for this purpose, like the profile of an elastic band). If anything prevents this from happening then you will get the seizure outlined above, therefore its imperative to keep the brake components in good working order and replace fluid regularly at the stated 2 year interval.

 

Generalising, if the piston dust seal is ok, then the piston within will be mobile. If the dust seal is split, then guaranteed the piston will sieze - if it isn't already.
I think you'll find the brown colour is due to rubber....on motor bike stuff you can often see the particles.
John

 

Update - tried everything it wouldn't budge.

In the end I pushed the piston back without it and all is fine. I will replace the calipers at some point when the fluid needs doing.

Did a service and brakes on my Accord today. Whoever designed the engine must have been drunk. Oil filter in the least accessible place and a splash guard that is almost impossible to remove without breaking all the crappy clips. Want my Audi back - you may have needed a special tool for everything but at least it was accessible.

 

have been thinking about this brake fluid thing where all the main dealers advise on changeing it every 2 years because it absorbs moisture
then why not just vacuum the system like the air con system
i was told once that refrigerant pag oil was a higher grade of brake fluid
not that i would try swaping

 

To vacuum the system would introduce air into areas which would be notoriously hard to evacuate....ABS pumps and valves in particular.
Regarding the bleed nipple - I've sheared a few off in my time, and none caused a fluid leak....because the nipple remains shut. I guess what I'm saying is that you can heave away until the inevitable happens however, your caliper may not be exchangable if its inspected on exchange!
John

 

Try giving a good clean around the nipple (could also seal the hole), fashion a plasticine dam/bowl such that it can be filled with plus-gas immersing the nipple, left overnight this can be surprisingly effective.
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