johny Posted June 22, 2022 Report Share Posted June 22, 2022 4 minutes ago, Pete Lewis said: Many would be amazed the test of whats in the reservoir is upto 60% water in 2 years Surely you would see a substantial increase in reservoir level if that amount of moisture has entered the system😁 Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 22, 2022 Report Share Posted June 22, 2022 if it was that obvious we would all know somethings going on i guess there is some change in volume but its off set by levels dropping as friction wears down we had to test all our stock trucks in storeage as they can sit around for ages and the results were alarming the reservoir has to vent so any temperature changes allows moist air in thro' the cap vent holes as the resv breathes probably you can reduce the breathing if the resv. is filled so less air volume to breathe Pete Link to comment Share on other sites More sharing options...
johny Posted June 22, 2022 Report Share Posted June 22, 2022 I like the motorcycle idea of having a flexible rubber diaphragm cover under the reservoir cap which seals it completely but still allows for changes in fluid level.... Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 22, 2022 Report Share Posted June 22, 2022 yes something that never seemed to be used on vehicles you need to patent one made from some old Marigolds !!!! Pete Link to comment Share on other sites More sharing options...
Josef Posted June 22, 2022 Report Share Posted June 22, 2022 50 minutes ago, johny said: Surely you would see a substantial increase in reservoir level if that amount of moisture has entered the system😁 I don’t know the exact behaviour of brake fluid and water in this scenario, but mixing two liquids of volumes A and B ml does not necessarily result in a volume of A+B ml. Especially when one liquid is water as the hydrogen bonding results in all sorts of interesting behaviour! Link to comment Share on other sites More sharing options...
johny Posted June 22, 2022 Report Share Posted June 22, 2022 Im no expert but common sense says that if 60% of your reservoir is water, either by weight or volume, its level will have gone up noticeably👍 Be interesting to find the maximum DOT4 brake fluid can absorb.... Link to comment Share on other sites More sharing options...
NonMember Posted June 22, 2022 Report Share Posted June 22, 2022 1 hour ago, johny said: Im no expert but common sense says Common sense is often highly misleading 1 hour ago, Josef said: mixing two liquids of volumes A and B ml does not necessarily result in a volume of A+B ml Exactly this! Especially if liquid B is soluble in liquid A, you can get almost no expansion at all from adding liquid B up to saturation point. 1 Link to comment Share on other sites More sharing options...
johny Posted June 22, 2022 Report Share Posted June 22, 2022 Interesting, right I think a bit of experimentation is required. Ive got some old brake fluid so I'll add 60% by volume of water to it, mix and see what volume I end up with and report back... Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 22, 2022 Report Share Posted June 22, 2022 that wont be right its moisture content not straight water you need to measure the moisture content with a meter and add small droplets its not a % of tapoline and most diy test meters only go to 4% and then blow a alarm to get you worried Pete Link to comment Share on other sites More sharing options...
johny Posted June 22, 2022 Report Share Posted June 22, 2022 ok think I have a bit more from the wonderful internet: brake fluid becomes saturated with water at around 3.7% by volume which is why this is the recommended limit for its use. After this point the water is free and so can boil to produce steam which of course is compressible and so potentially dangerous in a hydraulic pressure system. It follows that once the fluid is saturated any additional water entering the system will increase the total fluid volume but that additional amount so I think we can safely say that 60% there will be a substantial increase in reservoir fluid level👍 What Im not sure about is whether brake fluid remains hydroscopic and continues to attract more moisture even once its fully saturated.... Link to comment Share on other sites More sharing options...
Badwolf Posted June 22, 2022 Report Share Posted June 22, 2022 2 hours ago, johny said: Interesting, right I think a bit of experimentation is required. Ive got some old brake fluid so I'll add 60% by volume of water to it, mix and see what volume I end up with and report back... Am I understand g this correctly? If you add 60% water by volume, the total volume will increase by the amount added, whether the original liquid absorbs the water or not? Link to comment Share on other sites More sharing options...
Colin Lindsay Posted June 22, 2022 Report Share Posted June 22, 2022 43 minutes ago, johny said: What Im not sure about is whether brake fluid remains hydroscopic and continues to attract more moisture even once its fully saturated.... I'm no chemist but I reckon the term 'fully saturated' means it can't take any more? Link to comment Share on other sites More sharing options...
Josef Posted June 22, 2022 Report Share Posted June 22, 2022 Johny you’re right, the best way is experimentation! For a proper test though you would need fresh brake fluid from a sealed bottle. Otherwise it will have absorbed some water from the atmosphere. Though that’ll be a few % and whatever you have to measure with with at home is not likely to be accurate enough for you to have a small enough measurement error for it to matter. Properly, saturation is the point when no more of a substance will dissolve in another. If you make a cup of tea and keep putting sugar in and stirring till you can still see the sugar sitting at the bottom, you’ve saturated your tea with sugar. For brake fluid this term must be being used to describe the point at which it needs replacing (my chemistry knowledge tells me you must be able to mix more than 4% water with brake fluid, but here’s some evidence - a paper describing boiling point vs water content for DOT3 here - they test up to 10% water content). BW the point I was making is that chemistry of materials is complicated, if you have 60ml of one liquid and add 60ml of another, it’s unlikely you’ll end up with 120ml of liquid in the end (same applies to mixing liquids and solids, and even sometimes solids and solids). Link to comment Share on other sites More sharing options...
NonMember Posted June 22, 2022 Report Share Posted June 22, 2022 1 hour ago, Badwolf said: If you add 60% water by volume, the total volume will increase by the amount added, whether the original liquid absorbs the water or not? No. You can only take that simple "add the volumes" approach with liquids that don't mix or interact. If they mix by dilution then the molecules of the two liquids bind closer than the pure molecules of each separately, and so the density increases and volume decreases. In an extreme case, the second set of molecules may bind so closely to the first that they perform a chemical reaction, and the volume after adding can be the same as the volume of one part. Link to comment Share on other sites More sharing options...
johny Posted June 22, 2022 Report Share Posted June 22, 2022 Yes I can see that up to saturation the water actively combines with the brake fluid but after that point its free water which is what makes it a greater risk in brake systems. Also, as you say, up to saturation its difficult to calculate how the total volume will be affected by the entry of moisture however when the water is free its not chemically part of the brake fluid so any volume change should be as normal. As in Josef's paper theres nothing to stop more free water being added (because water is miscible with mineral brake fluid) giving a corresponding volume increase and further detrimental effect on boiling point. Link to comment Share on other sites More sharing options...
Badwolf Posted June 22, 2022 Report Share Posted June 22, 2022 N/M - Now I see why I failed my O level chemistry. Thanks. Link to comment Share on other sites More sharing options...
johny Posted June 22, 2022 Report Share Posted June 22, 2022 Really as its so dangerous and many people never change their brake fluid Im surprised we dont get more accidents where the moisture has boiled and brakes gone to zero😲 Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 22, 2022 Report Share Posted June 22, 2022 i passed my chemistry but me bike only had cables !! Pete Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 22, 2022 Report Share Posted June 22, 2022 many dont use the brakes hard enough and just pottle about its only found when more extremes have to happen going to the super market wont do it but a holiday and a dash down countisbury or porlock hills would cause a wake up pete Link to comment Share on other sites More sharing options...
johny Posted June 22, 2022 Report Share Posted June 22, 2022 Moisture testing should be in the MOT test! Well I see Spain (and rest of EU?) is now insisting that the tyres on an axle must be identical so why not? Its got to be same make, model, size and pattern so you damage a tyre and cant find exactly the same one you chuck both - great for the environment and of course the tyre manufacturers... Link to comment Share on other sites More sharing options...
Colin Lindsay Posted June 22, 2022 Report Share Posted June 22, 2022 Wonder what the reasoning is behind that? If a tyre is correct for the make and model, plus presumably the speed and road conditions, then minimal variations in tread pattern wouldn't make much if any difference. Different tyre pressures on the same axle would probably have more impact, will they test pressure next? Link to comment Share on other sites More sharing options...
johny Posted June 22, 2022 Report Share Posted June 22, 2022 yes makes you a bit suspicious and fearful other countries will follow. Dont know about the effect of different tyre pressures but better drivers would give the biggest improvement.... 1 Link to comment Share on other sites More sharing options...
cliff.b Posted June 23, 2022 Author Report Share Posted June 23, 2022 Ok, to get back to the original thread, I have now inspected the RHS rear assembly and all looks good. Also, it is correctly assembled with the seal housing on the inside of the back plate and the grease trap on the outside. I greased it and eventually, old grease came out of the hole in the lower back plate, as expected. Thinking back to last year, the LHS, which had the grease trap fitted incorrectly, dumped the grease I was pumping into the brake hub. So now I understand why. There was nowhere else for it to go. Also, having seen that happen I was careful not to put too much in the RHS which is possibly why it needed quite a lot now 🤔 Hopefully, both sides now happy, for a while at least 🤞 Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 23, 2022 Report Share Posted June 23, 2022 the oil seal behind the back plate should containt the grease until it starts to fail so if it exuded grease via the drain hole the main seal could be looking for replacement soon it should ooze out the drive shaft seal on service it recomends 4 pumps to re lube it ( 4 pumps from what is not given) but for now happy motoring for a while Pete Link to comment Share on other sites More sharing options...
cliff.b Posted June 23, 2022 Author Report Share Posted June 23, 2022 2 minutes ago, Pete Lewis said: the oil seal behind the back plate should containt the grease until it starts to fail so if it exuded grease via the drain hole the main seal could be looking for replacement soon it should ooze out the drive shaft seal on service it recomends 4 pumps to re lube it ( 4 pumps from what is not given) but for now happy motoring for a while Pete 😒 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now