DOT4 to DOT 5 Silicon

[Lobo]

I’ve my old Kombi on axle stands, replacing the rear drum slave cylinders with new ones; and all brake lines drained down.

Q. What would be required to switch over to DOT 5 Silicon - eg is there a simple flushing product I can use - eg DOT 5 (S) itself? (I have no plans to change out the existing Master Cylinder, or indeed the front disc / caliper seals.)

Ta muchly in anticipation…

[Trigger]

Link >>> http://www.sohc.co.uk/index.php/topic,18973.msg167267.html#msg167267

[McCabe-Thiele (Ted)]

I'm guessing your vehicle has no ABS so draining down old fluid & then flushing with 5.0 should be fine.
Start bleeding from the furthest  point to the nearest to the master cylinder. If you have a bleeding tool even better. Iirc the old fluid will be heavier than the 5.0.
Personally after using the vehicle for several journeys I would re-bleed a drop and check it for quality. Places like the master cylinder reservoir & brake balancer valves tend to retain some of the old fluid.

[Lobo]

Thanks Trig / Ted… interesting. Tbh, I have been t’internetting the subject in the past couple of hours with the general advice being to not bother due the possibility of incompatible seals, or causing issues due the two fluids ‘clumping’ (my word) and promoting blockages.

So more confused than ever, and given that the Master + front brake seals won’t be renewed I pondering whether to just play safe and stick with DOT 4; carefully topping the Master Cylinder through the access hole in the cab floor under the carpet. Wot could go wrong 😂.
Still happy to hear comments, my mind not fully made up; in case you’re wondering ‘why’ it’s just that 3/5 of the vehicles are now DOT 5 Silicon - ie it’d be nice to standardise.

(Interestingly, due Silicon not being hydroscopic, any included water apparently pools more easily, and towards the bottom of the system - causing worse corrosion issues. So I read.)

[Johnny4428]

Maybe the dot 5 will require more frequent changes. Interesting to drain it out into jar after a couple of years and see if there’s any water present.

[McCabe-Thiele (Ted)]

There can't be pooling as there is no emulsified water if you use 5.0 so where can the water come from? No water to boil off with 5.0. You can  use Dot 5.1 as an alternative - I'm guessing it's not humid where you live so if you're worried stick with 5.1.

You can mix 5.1 with anything except 5.0.

[Lobo]

I guess Ted, said water comes from the same place as it does with DOT 4 - ie it just sneaks in there one way or another, accepting of course that DOT 4 is ‘actively’ hydroscopic. And we live right on water, so it is indeed humid at times.

Interestingly Johnny, that ‘precaution’ of more frequent changes with Silicon is indeed mentioned in what I’ve been reading.

[Trigger]

I have DOT 5 silicon in all my old bikes, some have had it in for the past 7 years and have read somewhere that it never needs changing .
DOT 5 is mainly used for classic cars and classic motorcycles. Since they do not run ABS and it is a really good application for these types of vehicles. In addition to this, this type of fluid prevents corrosion and this makes it perfect for bikes intended for long-term storage. So, if you have a classic car or bike, this is the right fluid for you. Though i did disassemble the whole system and cleaned and renewed everything before reassemble. You should always treat brakes as a whole system and after years any rubber parts are on there way out and passed there best 

[McCabe-Thiele (Ted)]

I guess Ted, said water comes from the same place as it does with DOT 4 - ie it just sneaks in there one way or another, accepting of course that DOT 4 is ‘actively’ hydroscopic. And we live right on water, so it is indeed humid at times.

Interestingly Johnny, that ‘precaution’ of more frequent changes with Silicon is indeed mentioned in what I’ve been reading.

Trying to work out how water might pool with Dot 5.0 fluid.

As you will know with hygroscopic brake fluids the water is absorbed from the atmosphere via the master cylinder venting system - this absorbed water then leads over time to corrosion and under extreme braking can boil in the brake caliper leading to loss of braking performance.

With Dot 5.0 not being hygroscopic the only way I can envisage that water might get into the brake system would be by condensation within the master cylinder top area - a very slow process I would imagine. If water is denser than the Dot 5.0 fluid I guess it could sink over time down the brake lines to the caliper - next time I'm bleeding my brakes I'll check if water sinks or floats in the  fluid.

[JezzaPeach]

When starting work on mine the front brake was useless, and after realising fluid had been leaking onto the disc, I replaced seals etc, which didn’t work. I then realised there was slight corrosion in the channel the piston seal sits in, and in the master cylinder bore. Barely noticeable, but I’m guessing minute traces of Dot 4 in those interfaces with the outside air attract water and then slight corrosion takes place over many years. As I couldn’t machine these I bought replacements and all now working very well, with the SBS501HF pads. They squeaked a bit, but I’ve slightly chamfered the leading edges, but also cleaned the disc with Wonder Wheels cleaner which may have helped, and if it has will use it periodically.
I just bought 250ml of ECB Dot 5 which I will not use, as I don’t want to do the full clean/rebuild (if the above is correct re the ‘interfaces’) which would need all old fluid cleaning off seals etc. (I got it for a good price £15.75 inc postage if anyone wants it for that!)

[Lobo]

Thanks all… very informative.

Trig, all brake seals (Master, front callipers, rear slaves) are <3 yo and not on their way out (I assume). Honestly, I’ve had enough monkey’ing around under her; I finish each day grimy and aching - getting too old for this malarkey. = don’t wanna dismantle the braking system. So… do ya reckon I could comprehensively flush the system with DOT 5 Silicon, and perhaps repeat in a month - would that do the trick?

I can’t afford ‘fails’ - the car has zero useful engine braking, and regularly comes down the local ‘mountain’ with engine @ max revs and brakes being ridden fairly hard (when she had 4x drums it was even more exciting with the burning smells). I’m awfully aware there’s no plan B at such times - fairly nail biting 😂.

[K2-K6]

To answer the otiginal question, no I wouldn't change over as noted with original system still in place.

The risk is small, but you don't know the outcome, and none can state that clearly. That's for using the pre-used front end system and flushing the dot 4 out.

Don't know if there's enough upside in going to dot 5 to make it worthwhile, but each case is going to be different for each owner.

It's really just the corrosion potential as far as I understand it, none of the other properties seem to be large enough to hold sway really.

Current popular projection would have it that dot4 is so unstable as to be useless, that's just not the case and proven over so many years.

The bicycle world is absolutely stark staring nuts over this stuff, with plenty of opinions seeming to spill out of that sphere.
They have mineral oil as well in the equation, the exponents of which suggest anyone using dot 4 will die  its amplified out of all proportion, and with many transferring that thinking to other vehicles. Those two are definitely, absolutely incompatible for interest.

Reading about one recently on mtb forum, Aus based car truck technician, got a test kit for checking water ingress and boiling point in brake fluuds, banging on to his father about having 9 year old dot 4 in his Toyota truck, thought he maybe at risk of dying  partly a joke in his writing, tested that fluid and surprised to find water inclusion very low, with boiling point well above minimum threshold.

As Ted notes, it's the arrangement around mastercylinder and how that is vented that gives the only scope for water ingress in practical terms. Decent system design will help with long term performance.

Converted systems dot 4 to dot 5 can scavenge any existing moisture of systrm if not going from dry assembly. Ending up at tge calioer ultimately. Specific gravity of most oils is lower than water.

Also the mtb crowd routinely seem to jet wash their calipers etc at about 50 trillion psi and may risk getting water past the piston seals that way. It wont ordinarily get through there in systems well maintained and not subject to external pressure.

[JezzaPeach]

Lobo is the system servo assisted just out of interest?

[McCabe-Thiele (Ted)]

Lobo is the system servo assisted just out of interest?

With that disc front brake upgrade it should have some sort of pedal booster set up I would have thought.

[K2-K6]

Lobo is the system servo assisted just out of interest?

With that disc front brake upgrade it should have some sort of pedal booster set up I would have thought.

Thats more dependent on mc and caliper bore sizes that should have bought more pure brake power in absolute terms.

The downhill scenario demands more cooling capacity than shear brake torque, that's normally through vented disc route. Can't see what's there in photo.