Brake Fluid Issues

[BarryG]

16 hours ago, Peter Cobbold said:

Hi Barry. Glad you're still here. I wonder if the previous owner used silicone and failed to mark the reservoir. If you still have the fluids in the bottle you photgraphed, take some of the clear upper layer and see if it mixes with water. If it doesnt its not glycol and is probably de-dyed dot 5. Brake system rubber may swell differently in glycol and dot5. and switching fluids may well shorten its life and reliability There was along thread a few years back when PaulAA dicovered his mechanic had topped up his dot5 with the "new version 5.1". He decided to replace all rubber components throughout.

Peter

Hi Peter

Just tried carrying out your suggestion of separating the clear fluid floating on top of the crud and mixing with water. The answer is that it does'nt, two layers clear water and misty liquid.

So i am not totally sure how what i think is a silicone based fluid is still in the system after several changes of fluid using DOT 4.

I said previously that my rear slave cylinders looked like new from previous owner. Have just gone through my receipts of work recently done on rear suspension rebuild and found that the rear cylinders have both been replaced. So now the only old rubber in the system must be the four flexible pipes.

So I think now my only option would be to carry out yet another flush and replace all 4 rubber pipes.

 

[stillp]

If it's had a mixture of silicone and DOT4 in the system, I'm sorry to say you'll need to change all the rubber seals as well as the flexible hoses. Rather than trying to flush the system with fresh fluid, you'll need to drain all the old fluid out - I'd then blow through with compressed air. If you try to just flush it, the new fluid will just take the easiest route to the bleed nipples, by-passing much of the existing fluid. 

Pete

[RogerH]

1 hour ago, stillp said:

If it's had a mixture of silicone and DOT4 in the system, I'm sorry to say you'll need to change all the rubber seals as well as the flexible hoses. Rather than trying to flush the system with fresh fluid, you'll need to drain all the old fluid out - I'd then blow through with compressed air. If you try to just flush it, the new fluid will just take the easiest route to the bleed nipples, by-passing much of the existing fluid. 

Pete

if you go tp this trouble then also flush through with methylated spirits.

 

Roger

[stillp]

I'm not sure Roger, since you'd then have to get rid of the meths. Does SBF mix with meths? I know it mixes with isopropanol but not sure about meths.

Pete

[RogerH]

the meths would evaporate away when you bow the airline through

 

 

[stillp]

Hopefully, yes. I've only tried it once, and failed (on an MGB...) so perhaps I didn't blow hard enough or long enough!

Pete

[RogerH]

................not with your lungs - use a compressor.   

 

Roger

[stillp]

It wasn't much of a compressor, but it was good enough to spray the car!

[Waldi]

Hi Barry,

I had the same issue, but not by incident: I was told dot 4 and dot5 could be mixed, so when I converted to dot 5 I simply flushed with dot 5 until only clear purple liquid came out. Some time later, a front bake seized, which was caused by small particles blocking the tiny “vent hole” in the MC (the car was a freshly restored XK140). I opened the entire brake system, and the rubber cups felt strange, very soft. I suspect they were chemically attacked by the mixture but unlike Peter, am not a chemist. I replaced every rubber bit, including the hoses, and all was fine since.

So this is what I would do with your car too, brakes are too important and if you do it all in one go, it is more rewarding as a job and less aggravating should you have to do it again when only a part of the system is changed.

Regards,

Waldi

[Spit_2.5PI]

On 8/26/2019 at 11:39 AM, RogerH said:

the silicone fluid is very very inert and would cause no damage to anything but the most delicate materials.

Roger, I was amazed to find that silicone oil is not compatible with silicon rubber. I have sometimes wondered if some of these very supple seals you come across might be made of silicon rubber, and if this is why some brake manufacturers do not recommend Dot-5.

Cheers, Richard

PS: One comes across these surprising incompatibilities from time to time. I learnt a few weeks ago that Viton is attacked by acetic acid - or lemon juice to you and me!

[RogerH]

48 minutes ago, Spit_2.5PI said:

Roger, I was amazed to find that silicone oil is not compatible with silicon rubber. I have sometimes wondered if some of these very supple seals you come across might be made of silicon rubber, and if this is why some brake manufacturers do not recommend Dot-5.

Cheers, Richard

PS: One comes across these surprising incompatibilities from time to time. I learnt a few weeks ago that Viton is attacked by acetic acid - or lemon juice to you and me!

Hi Richard,

                    not heard that before - as you say, amazing.  Could it be that it acts like a solvent.

I wonder what DOT5 does to silcone gasket goo - I feel and experiment coming one.

 

Acetic acid - vinegar

Citric acid - lemons

The Viton thing rings a bell.  Also do NOT burn Viton seals and allow the goo to hit your skin. It contains Hydrofluric acid and will eat you away till there is only your shoes left - I think.

 

Roger

[Spit_2.5PI]

2 hours ago, RogerH said:

Acetic acid - vinegar

Citric acid - lemons

D'oh! Stop trying to be clever Richard. You know you're not very good at it.

Thank you Roger.

[Andy Moltu]

You seem to have a mixture of silicon and standard brake fluids which gives you the downsides of both and the benefits of neither. Drain the brakes, replace the seals in the master cylinder (This would be the likely source of the black debris) and refill with the fluid of your preference.

If you know the rear wheel cylinders are old consider replacing the seals too.