Paul H Posted April 19, 2023 Report Share Posted April 19, 2023 When refitting the gearbox in my M2 Vitesse I must have strained the slave piping as there is a minor leak . Using the opportunity to move to DOT5 . Once I’ve cured the leak Is it simply remove the brake fluid from the master cylinder and replace with DOT5 and bleed as normal . I have already added a bleed extension so can bleed from the engine bay . The brake fluid is a few years old so looking to replace this with DOT5 as well . I’ve purchased 1/2 litre , will this be enough to do both jobs ? Any tips appreciated Paul Link to comment Share on other sites More sharing options...
Pete Lewis Posted April 19, 2023 Report Share Posted April 19, 2023 from Buckeye triumphs have a lot of conclusive testing and reviews on the swap takes a bit of a read but sums up most worries as irrelevant Selecting+Brake+Fluid.pdf (squarespace.com) 1 Link to comment Share on other sites More sharing options...
dougbgt6 Posted April 19, 2023 Report Share Posted April 19, 2023 Sadly I needed a litre to do my brakes and clutch. Yes, read the Buckeye stuff, very comprehensive. Doug Link to comment Share on other sites More sharing options...
johny Posted April 19, 2023 Report Share Posted April 19, 2023 Been a lot of discussion on here Paul on changing over with different opinions, methods and outcomes. I would have a read through some of the threads as theres various issues to consider.... Link to comment Share on other sites More sharing options...
Mjit Posted April 20, 2023 Report Share Posted April 20, 2023 (edited) The short version is there what you CAN do and what it's WORTH doing. As you say you can just drain the old DOT3/4 fluid, fill up with DOT5 and bleed through as normal - but you'll always have some degree of a 'blend', and any remaining DOT3/4 fluid will still absorb moisture. Provided you do a good drain that tiny percentage of 'wet' DOT3/4 is unlikely to make any difference/be noticable. DOT5 is expensive though so I'd always recommend replacing your master and slave cylinder seals while you're at it, unless the parts are new/recently resealed. Seals are service items that do wear out and the cost/extra time and effort of doing them while you're changing the fluid is nothing compared to the annoyance of finding you need to buy another bottle of DOT5 in 12 months time as one of the seals have reached the end of its life and you need to drain all that DOT5 you only put in last year in order to replace a seal! The DOT5 specification was created for the US millitary who wanted to be able to just park up their spare vehicles and leave them when they didn't need them, without having to worry about having people go around them all changing the brake fluid every couple of years. Of course the US millitary also didn't want to find themselves trying to fix one of their vehicles at the side or the road in some random war zone and be stuck trying to find some relativly rare DOT5 fluid while surrounded by sources of DOT3/4 (for example the nearest civilian vehicle) so part of the spec. is that it has to be 'compatible' with DOT3/4. Edited April 20, 2023 by Mjit 1 Link to comment Share on other sites More sharing options...
dougbgt6 Posted April 20, 2023 Report Share Posted April 20, 2023 (edited) From a resent thread 1 litre of dot 4 £7.40 ! litre of dot5 £36.75 So silicone costs 5 times the price of dot4, but you should change dot4 every 2 years. Which means in 12 years silicone is saving you money! The only question to ask is will you still be driving in 12 years time? One of our guys at East Berk topped up with Dot4, ignoring the labels attached to his master cylinders that said !!DOT5 SILICONE ONLY!!! He drove around fine for 6 months before noticing. Doug Edited April 20, 2023 by dougbgt6 Link to comment Share on other sites More sharing options...
AndyTV8 Posted April 20, 2023 Report Share Posted April 20, 2023 Dynolite dot 5 is current selling at Moss for under £25 for 946ml, so a little less than mentioned above - it does often fall under their seasonal offers which gets it closer to £20. Perhaps there are cheaper sources. Personally, I think the major benefit is no paintwork damage from any spillage - much more wallet-friendly. ……… Andy Link to comment Share on other sites More sharing options...
dougbgt6 Posted April 20, 2023 Report Share Posted April 20, 2023 Silicone does damage paint work, it doesn't eat it like dot 4, but paint looses it's shine and goes dull. But who cares, it's under the bonnet?!! Doug 1 Link to comment Share on other sites More sharing options...
Mark B Posted April 21, 2023 Report Share Posted April 21, 2023 After replacing my gt6 brake master cylinder seals I decided to use some Dot5 i had left from the Vitesse. Bled until no air bubbles present and clear purple stream of fluid. The car was not used much and sat for a couple of years with the odd short run. Noticed the front pads binding, and knock back on the pedal. Stripped the calipers, found a little surface corrosion on the pistons that I polished out. I was surprised to see a small pool of Dot 4 brake fluid still in the inside of the caliper, along with the purple Dot5. So despite bleeding I hadn't removed all of the old brake fluid. Maybe if I had kept bleeding I would have eventually flushed all the old fluid out, but I didn't know it was still there, and because of the cost of silicone fluid, once I saw purple fluid coming out of the pipe I assumed all the old fluid was gone, but I was wrong. 1 Link to comment Share on other sites More sharing options...
GrahamB Posted April 21, 2023 Report Share Posted April 21, 2023 Typical DOT 5 fluid will have a relative density of 0.97 compared with DOT 4 fluids which have a typical relative density of 1.05 so DOT 5 will float on top of the DOT 4 and will therefore be expelled first from the bleed valve. It would very difficult, if not impossible, to flush all the DOT 4 fluid from the system by just bleeding without using copious quantities of DOT 5. Link to comment Share on other sites More sharing options...
johny Posted April 21, 2023 Report Share Posted April 21, 2023 I believe thats why its recommended to do the change over to DOT 5 on new systems or at least flush existing ones with alcohol and then blow through... Link to comment Share on other sites More sharing options...
Paul H Posted April 21, 2023 Author Report Share Posted April 21, 2023 20 minutes ago, johny said: I believe thats why its recommended to do the change over to DOT 5 on new systems or at least flush existing ones with alcohol and then blow through... Buckeye doesn’t recommend Alcohol as it leaves a residue and Buckeye used a compressor to blow out the Dot 4 Paul Link to comment Share on other sites More sharing options...
dougbgt6 Posted April 21, 2023 Report Share Posted April 21, 2023 (edited) I've just been on the Telecaster guitar forum, they're a bit like us talking about all sorts of unrelated forum stuff. So a 3 page thread about changing dot3/4/5.1 A guy got told his fluid needs changing and it should be done every 2-3 years. OUTRAGE he's never had it done in 50 years! Is it a con?!! . However dozens of replies from "Good Ole Boys" saying yes, SCAM! Strange as silicone fluid is thanks to USA military, who have vehicles standing for years and needed brakes that work. Other guitar related things on the Telecaster forum Hot car. Hot Babe Hot Parrot Doug Edited April 21, 2023 by dougbgt6 Link to comment Share on other sites More sharing options...
johny Posted April 21, 2023 Report Share Posted April 21, 2023 3 hours ago, Paul H said: Buckeye doesn’t recommend Alcohol as it leaves a residue and Buckeye used a compressor to blow out the Dot 4 Paul Yes of course best if you can blow it all out but difficult to guarantee that without stripping everything so although alcohol might leave a residue (idea is it all evaporates off) it should still help to ensure all DOT4 is removed... Link to comment Share on other sites More sharing options...
JohnD Posted April 21, 2023 Report Share Posted April 21, 2023 DOT 5 requires a complete strip down and flush out. Silicone based fluid not compatible with the old stuff. But use DOT 5.2 which is NOT silicone based and all you need to do is to do a complete bleed, using about a reservoir-ful of fluid. Two if you're anxious. John 1 Link to comment Share on other sites More sharing options...
johny Posted April 21, 2023 Report Share Posted April 21, 2023 Cant find the spec sheets on DOT 5.2, is it a new one that doesnt attack paint work? Link to comment Share on other sites More sharing options...
JohnD Posted April 21, 2023 Report Share Posted April 21, 2023 No, just don't spill it. It's higher spec. than earlier. Sorry "DOT 5.1" spec is the same as "DOT 5" but isn't silicone. Link to comment Share on other sites More sharing options...
Unkel Kunkel Posted April 21, 2023 Report Share Posted April 21, 2023 (edited) I discovered only one problem changing to silicone brake fluid. One not seen reported elsewhere. Sudden and unexpected - a tiny amount spilt on the floor is very slippery … Edited April 21, 2023 by Unkel Kunkel Link to comment Share on other sites More sharing options...
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