Synthetic / non-synthetic brake fluid

RobTwin · Post by **RobTwin** » Wed Jan 09, 13 1:33 pm

Can you just flush out DOT4 and replace with synthetic?

I've read that synthetic is compatible with the DOT4 but also heard that some have had problems with their seals after the change-over.

The main reason for wanting to change is to eliminate the chance of damaging paint etc with the old DOT4 (we have a slightly leaky m/cyl cover and/or seal, but are in the process of sorting that) - so if synthetic doesnt affect paint, thought we may as well make the change.

Anyone had any experience - good or bad - in swapping over to synthetic? Should we expect any problems with seals, rubbers etc? Some of our seals are new but there are still some older bits on there

Any advice on what type/spec is best?

Grateful for any advice

R&S

Dave-R · Post by **Dave-R** » Wed Jan 09, 13 1:56 pm

I use DOT 5.1 in my Corvette.

I really really really would not try to use DOT 5 Silicone.

Good article here;

http://www.corvetteclub.org.uk/viewtopic.php?t=10237

Dave999 · Post by **Dave999** » Wed Jan 09, 13 2:12 pm

belive the seal issues are thus

old style brake fluid is hydroscopic i.e sucks in water vapour

water and rubber seals don't mix
and the rubber seals in brake components are submerged in the brake fluid

so old nasty water contaminated brake fluid can result in a some degredation of the seals

they get contaminated with water.

eventually the seals perish and swell creating a locked on brake situation

when you swap to a silicone based fluid

the vast majority of the water comes out with the old fluid
and would only be in there if the system was left with the lid off, had a major leak or the fluid was ancient

however water and new fluid doesn't mix

water either floats of sinks (can't remeber which)

so any trapped in the seals under pressure vapourises floats about as tiny bubbles causing spongy peddle and then condences back elswhere in the system and causes problems from then on
i.e just boils and causes major peddle spongyness or peddle hitting the floor

i'd suggest you look after your car well enough for this not to be a problem you will encounter.

there may be other issues

i'm not up on what makes dot 4 and later different

there is about 3 or 4 types now

Dave

Dave999 · Post by **Dave999** » Wed Jan 09, 13 2:14 pm

ah dave got there first

Dave

Dave-R · Post by **Dave-R** » Wed Jan 09, 13 2:35 pm

Dave999 wrote:ah dave got there first

Dave

I even took my time about it.

R&S Twins, you could always fit a nice stainless drip tray under the M/C.

RobTwin · Post by **RobTwin** » Wed Jan 09, 13 3:10 pm

Thanks Dave, that'll look nice

Stu's been looking into the problem and it looks like the cover and spring/clamp thingy we got with the new/remanufactured m/cyl leave a bit to be desired on the sealing front, so we're going to swap them for the old ones which give a bit more clamping and sealing, to see if that cures it.

So far, the fluid that has leaked from around the cover/seal area has only messed up the clear lacquer on the m/cyl - dont think it's damaged any paint below that. Yet.

Hopefully we can cure the leak, so we dont need a drip tray, but thanks for the suggestion

Dave-R · Post by **Dave-R** » Wed Jan 09, 13 3:16 pm

The Plumb Crazy Hemi Cuda that used to live somewhere in Wales years ago had a drip tray under the master cylinder. Nicely made. It didn't look as bad as you might think. But I did wonder why anyone would go to those lengths rather than just fix the bloody leak.

I seem to remember Mopar Kev using a childs nappy or something to "cure" an oil leak once.

AllKiller · Post by **AllKiller** » Wed Jan 09, 13 4:02 pm

OH well thats Great!! I have Dot 5. never had a problem with it.
but now im questioning my choice.....Cheers

RobTwin · Post by **RobTwin** » Wed Jan 09, 13 4:40 pm

We've got a heat shield on the Polara, cos the MW manifold comes up quite close to the m/cyl - perhaps that cuda had a heat shield too, that you thought was a drip tray?

Dave-R · Post by **Dave-R** » Wed Jan 09, 13 4:42 pm

Maybe. But I talked to the owner and he was using it as a drip tray.

Guy · Post by **Guy** » Wed Jan 09, 13 7:36 pm

Dave wrote:
I seem to remember Mopar Kev using a childs nappy or something to "cure" an oil leak once.

That was a trans leak Dave I seem to remember the converter had split, and having driven all the way to shakey, Kev was going to race so out came the pampers

MrNorm · Post by **MrNorm** » Wed Jan 09, 13 11:24 pm

AllKiller wrote:OH well thats Great!! I have Dot 5. never had a problem with it.
but now im questioning my choice.....Cheers

I wouldn't sweat it Steve. Richard Ehrenberg in the US swears by DOT 5 synthetic, he is very vocal in his support and makes his case well.
Silicone is expensive and can be difficult to bleed, but neither of those really affect the braking performance (once bled). Because the water won't mix it can allegedly pool near cylinders etc & cause rust, which for me means you need to change it out just like the regular stuff. The only (big) advantage for me would be that it would not eat paint, but for the expense and a possibly slightly spongy pedal it was not worth it, I went with 5.1 but would not be sweating if I had gone with silicone

steveo · Post by **steveo** » Thu Jan 10, 13 12:11 am

i would never use it ,

stick with dot 4 , & change it ever year or two , read / heard about running silicone fluid causing no end of problems , one of the other problem was with our type of brake proportioning /pressure valves , like the ones for the rear , when have discs up front , causing it to lock up the rear wheels ,

also fitted a dorman manufacture , new/ rebuilt master cylinder last year or was it the year before !! sure it said in instructions , warranty void , if using silicone , anyway
if your determined to use the stuff , flush / clean all old fluid out , all rubber seals etc with metalated sprit etc

Roger · Post by **Roger** » Thu Jan 10, 13 7:33 pm

steveo wrote:i would never use it ,

stick with dot 4 , & change it ever year or two , read / heard about running silicone fluid causing no end of problems , one of the other problem was with our type of brake proportioning /pressure valves , like the ones for the rear , when have discs up front , causing it to lock up the rear wheels ,

also fitted a dorman manufacture , new/ rebuilt master cylinder last year or was it the year before !! sure it said in instructions , warranty void , if using silicone , anyway
if your determined to use the stuff , flush / clean all old fluid out , all rubber seals etc with metalated sprit etc

Another no from me. Used it for afew years in several cars. They all suffered cylinder failures. Maybe becuase of the water? Anyway, went back to normal fluid, never had a problem since.

Jim · Post by **Jim** » Tue Jan 15, 13 11:16 am

Dave wrote:The Plumb Crazy Hemi Cuda that used to live somewhere in Wales years ago had a drip tray under the master cylinder. Nicely made. It didn't look as bad as you might think. But I did wonder why anyone would go to those lengths rather than just fix the bloody leak.

I seem to remember Mopar Kev using a childs nappy or something to "cure" an oil leak once.

That was my Cuda while it belonged to the previous owner. I bought it from him in 1999 complete with brake leaking and servo problems.

There was loads of work needed doing to the car when I got it, and I think he used the money to buy a new Harley.