simonjrwinter Posted May 20, 2015 Report Share Posted May 20, 2015 Many year ago I used to own a GT40 replica. After advice from so called experts, I drained the brake system and replaced the normal fluid with silicone. MAJOR MISTAKE! There's no problem with changing from one to another but you MUST change all the rubber seals at the same time as they can swell after a while causing lots of interesting (and maybe dangerous) problems. There will always be people who have changed over with no issues, but this is probably because the system has enough tolerance to cope with any swelling of seals. Whatever fluid is used, as Stuart says, new rubbers are essential Simon Quote Link to post Share on other sites
RogerH Posted May 20, 2015 Report Share Posted May 20, 2015 DOT5.1 is designed for ABS systems. It does have a higher spec to standard DOT4 but it is designed for the heavy use in the ABS valves where they open and shut rapidly. There are some high spec DOT 4 fluid and some very high spec DOT 4. If you like EG fluids stick with DOT 4. Roger Quote Link to post Share on other sites
graeme Posted May 20, 2015 Report Share Posted May 20, 2015 I've used silicone** for twenty years, no issues. Brakes - all standard, no idea what pads are in there - will lock 205 section tyres even under cadence braking. I am extremely sceptical that Alastair's brakes are suffering from Dot5. And I certainly would not change two things at once ! Peter **It was put into brand new system - new seals, pipes, hoses etc +1, no problems with 15 years use. Graeme Quote Link to post Share on other sites
mike3739 Posted May 20, 2015 Report Share Posted May 20, 2015 +1, no problems with 15 years use. Graeme +2 no issues with 13 years & 40,000 miles. Cheers Mike Quote Link to post Share on other sites
Jersey Royal Posted May 20, 2015 Report Share Posted May 20, 2015 +2 no issues with 13 years & 40,000 miles. Cheers Mike As this is turning into a Love sillycon -1 from me It was put into my brake system by a Tr specialist when I did a brake upgrade many moons ago,in the days when I didnt work on the car myself. Never opened the bonnet. Shock horror Was never really happy with the pedal feel, and having to carry a bottle of the stuff in the boot, as you cant pop into any garage to buy it.So I removed the stuff, new Mc seals and new uprated calipers and discs last year. Now my car stops. Cheers Guy Quote Link to post Share on other sites
Guest ntc Posted May 20, 2015 Report Share Posted May 20, 2015 - 2 clad you can stop Guy Quote Link to post Share on other sites
Peter Cobbold Posted May 20, 2015 Report Share Posted May 20, 2015 A soft pedal after first filling with Dot5 will decline with time. Tiny air bubbles inevitably entrapped during filling ( or dropping the bottle!) take time to dissolve in the fluid. Stuart's trick of using a stick to wedge the pedal down against the seat will speed up bubbles dissolving. If you have a vacuum pump try 'boiling' the air out of the bottle first. Peter Quote Link to post Share on other sites
thealastair34 Posted May 20, 2015 Author Report Share Posted May 20, 2015 my dad driven it today with the new pads on 10 miles or so not not bedded in but says that they feel better, ill be using it this weekend to get it down to my garage to replace front crank oil seal so i will bed them in properly Quote Link to post Share on other sites
Tom Fremont Posted May 20, 2015 Report Share Posted May 20, 2015 +2 no issues with 13 years & 40,000 miles. Cheers Mike +3 twenty-five years and well over 100K miles - but not track use. Cheers, Tom Quote Link to post Share on other sites
Tim D. Posted May 21, 2015 Report Share Posted May 21, 2015 +1 have had silicone in a number of cars and seems to work well. Mind you have normal in the tr as would only change to silicone if I changes all rubbery bits. Tim Quote Link to post Share on other sites
John L Posted May 21, 2015 Report Share Posted May 21, 2015 This may be a silly question, (I know no questions are silly) but I'm a bit confused, could somebody put me straight please. Most of the DOT 4 I've seen in car shops lately is all marked as synthetic, does this mean that it has silicone in it, or am I getting confused with DOT 5 that is a silicone fluid. What was wrong with the old DOT 4 fluid? (I know this fluid attracts water) why does it need synthetics in it now? Can you still get the original DOT 4 fluid without synthetic additives? John Quote Link to post Share on other sites
thealastair34 Posted May 21, 2015 Author Report Share Posted May 21, 2015 driven the car tonight brakes with the new pads are 100% better so it will be staying like it is Quote Link to post Share on other sites
RogerH Posted May 22, 2015 Report Share Posted May 22, 2015 (edited) I had the same problem the other month in Halfords - lots of bottles with synthetic DOT4 on them. I ended up with a bottle of DOT4 that didn;t state synthetic. Synthetic is NOT silicone and does not have any silicone in it. However I have since found out that they are much the same and completely mixable. Halfords own brand was conspicuous by its absence !! Roger Edited May 22, 2015 by RogerH Quote Link to post Share on other sites
stuart Posted May 22, 2015 Report Share Posted May 22, 2015 Synthetic is NOT silicone and does not have any silicone in it. However I have since found out that they are much the same and completely mixable. No they arent, on no account mix the two. Stuart. Quote Link to post Share on other sites
RogerH Posted May 22, 2015 Report Share Posted May 22, 2015 Hi Stuart, I knew when I posted that it was dodgy. This is where I got my info http://www.commaoil.com/productsguide/view/6/197 Here is a Moss blurb http://www.mossmotors.com/SiteGraphics/Pages/brake_fluid/page1.html Confuse - me, very. Roger Quote Link to post Share on other sites
peejay4A Posted May 22, 2015 Report Share Posted May 22, 2015 Is it not the case that all non silicones can be mixed? Quote Link to post Share on other sites
RogerH Posted May 22, 2015 Report Share Posted May 22, 2015 Hi Pete, No. you shouldn't put mineral oil i(Citroen etc) in a EG or SBF system (synthetic or not). Roger Quote Link to post Share on other sites
stuart Posted May 22, 2015 Report Share Posted May 22, 2015 Hi Stuart, I knew when I posted that it was dodgy. This is where I got my info http://www.commaoil.com/productsguide/view/6/197 Here is a Moss blurb http://www.mossmotors.com/SiteGraphics/Pages/brake_fluid/page1.html Confuse - me, very. Roger Well it doesnt say anywhere in all that blurb that you can mix DOT3/4/5.1 with Silicon DOT5 so Im not sure at all where you got that idea from as you cant end of. You can mix DOT3/4/5.1 but its spec will then be degraded to the lowest spec in the mix. Stuart. Quote Link to post Share on other sites
Peter Cobbold Posted May 22, 2015 Report Share Posted May 22, 2015 I had the same problem the other month in Halfords - lots of bottles with synthetic DOT4 on them. I ended up with a bottle of DOT4 that didn;t state synthetic. - - - - - - - - - - - - - However I have since found out that they are much the same and completely mixable. Roger I think the above is what Roger meant, but the intervening sentence about silicone confused the reading. Peter Quote Link to post Share on other sites
Alec Pringle Posted May 22, 2015 Report Share Posted May 22, 2015 There is a compatibility requirement within the DOT classifications, such that for example any DOT 4 fluid should be compatible with any other DOT 4 fluid to an acceptable degree, and in the case of DOT 4 it should also be retro compatible with DOT 3 installations. That compatibility within category applies to all four categories, but neither DOT 5 nor DOT 5.1 are necessarily retro compatible with older installations designed for DOT 3 or DOT 4 fluids. In an ideal world, you don't mix different brands of brake fluid even of the same category, as the whole can be less than the sum of the parts in operating performance. DOT 5 and DOT 5.1 will function when mixed with the earlier spec fluids, but not very well - and it's a damn stupid idea to mix unless in dire emergency as a stop gap measure. All brake fluids are synthetic, the more recent addition of 'synthetic' to the title of some brands is marketing, originally tied to improved formulations offering higher boiling points. All hydraulic system seals will swell to some degree when soaked in brake fluids, that's a necessary function, the degree of swelling will vary depending on the particular fluid employed. There is at least a possibility that seals will over time swell to a greater extent, or even deteriorate, after immersion in more than one variety of fluid. That is unusual, but it can and does happen, and I suspect it is more likely to occur with 'new old stock' seals from way back when or with old seals which have been installed for many years. As a generalisation, brake component seals are designed for use with a specific category of fluid - utilising any other fluid is, as they say, at your own risk . . . . . Common sense rules here - if you are going to use anything other than DOT 3 or 4 then check with the supplier if the specific component is suitable for use with your preferred DOT 5 or 5.1 Cheers Alec Quote Link to post Share on other sites
RogerH Posted May 22, 2015 Report Share Posted May 22, 2015 Hi Stuart, sorry for any confusion - I was trying say (as Alec has done quite well) that any synthetic DOT3 or DOT4 can be mixed to any other synthetic DOT3 or DOT4. And also when mixing you end up with the lower denominator. Obviously DOT5 is in its own world. Roger Quote Link to post Share on other sites
TR6GAZ Posted May 22, 2015 Report Share Posted May 22, 2015 My tr6 has the same set up as yourself simonjrwinter from racetorations. About town there pretty good but yeah when it comes to seriously having to stop quick they are fantastic, money well spent! Hope you get yours sorted! Quote Link to post Share on other sites
stuart Posted May 23, 2015 Report Share Posted May 23, 2015 I will only say this once more DO NOT MIX DOT5 SILICON WITH ANY OTHER FLUID. Stuart. Quote Link to post Share on other sites
RogerH Posted May 23, 2015 Report Share Posted May 23, 2015 (edited) Hi Stuart, we are talking about synthetic EG DOT 3 or DOT4 (and DOT 5.1). They all seem to be labelled synthetic these days. Whereas a year or so ago they were simply DOT3 or DOT4 or DOT5.1 From the labeling you can add Synthetic DOT 4 to systems with original DOT4 in with no adverse effects. DOT 5 stands alone in the corner. Roger Edited May 24, 2015 by RogerH Quote Link to post Share on other sites
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