Changing Brake/Clutch Fluid

[dusz]

Just wondered if anyone has experience of changing from the usual DOT4 hygroscopic brake fluid to the DOT5 non-hygroscopic silicone brake fluid. On a car that will not be used often is it beneficial changing to DOT5?

I will be changing the flexible hoses, rear cylinders and rebuilding the front callipers maybe even rebuilding the master cylinder, likewise the clutch system. However the brake lines are cunifer so will not be changed. What is the best way to avoid contamination?

Thanks for any advice.

[Nick Jones]

Personally, I wouldn't do it. 

As the silicone fluid doesn't absorb the water, any water that gets into the system eventually settles in the low points, causing corrosion.

Also many of the brake cylinder rebuild specialists will not warranty cylinders used with DOT5.

If you do convert, flush through with more DOT 5 or meths.

Nick

[Hogie]

Hi Jeremy,

             I would stick with a good quality DOT4 or even DOT3.

If you insist on DOT 5 then flush with plenty of Meths.

 

If there is a very small amount of DOT4 mixed in with the DOT5 then don;t panic. It will not stop it working.

 

Roger

              

[Beans]

Quoted from Nick Jones-

Personally, I wouldn't do it. 

As the silicone fluid doesn't absorb the water, any water that gets into the system eventually settles in the low points, causing corrosion.

Also many of the brake cylinder rebuild specialists will not warranty cylinders used with DOT5.

If you do convert, flush through with more DOT 5 or meths.

Nick

I fully agree with Nick's remarks.

Another thing to bear in mind is that silicon "fluid", contrary to normal fluids, can be compressed slightly.

This will show itself in a slightly spongy pedal. 

[Dannyb]

Yes I agree with the spongy bit. I changed over to DOT5 12  years ago when I renewed all the braking system. But changed back to DOT4 because it felt spongy.

[ODIN]

Been using  silicone  fluid  for years .No issues at all.

[Mañana2]

Jeremy, now is the perfect time to change it out.  That's exactly when I did mine yeeeeears ago and it's worked out great.

Flushing with alcohol - many say to do this, but I just blew my lines out with compressed air.  I think the whole flush thing is over-stated, but if you really wanted to be keen I'm sure it doesn't hurt.

Warranty - The manufacturers don't warranty it for only one reason, and I got this directly from them, they just haven't spent the money to test with DOT 5.  They see no reason it should cause any issues, but they just haven't tested it.

Spongy Pedal - I run Autocross about once a month in the summer and any increased sponginess was not noticed by this foot.  Well, except when I did my engine swap and the header ended up a little closer to the brake line than I hoped.  That did a great job of softening the pedal. :)  Interestingly though, once it cooled it was back to normal without even a bleeding.

Bench Bleeding - I bench my MC while on the car and invariably fluid gets spilled.  Nice that it doesn't peal the paint.

Good luck whichever way you go.

 

 

 

[thescrapman]

Change theseals, blow the pipes through with an airline. 

Every few years bleed the whole system, take the calipers off and turn upside down.

the water will settle out in the jam jar if there is any and you can decant the good fluid off, put it through a micro filter and reuse it.

 

[Guppy916]

Hi Guys, I have used this since the rebuild from Rimmer's 

Automec Silicone Brake or Clutch Fluid - DOT 5

Ive not had any spongy brake issues, the mot guy commented that the brakes were very good for a completely new system, the car had only done 5 miles to the mot bay, so nothing was bedded in, and now there are as good any modern car, I did fit a servo when it all went back together 1973 Mk3 GT6,

I would post pics but I haven't sussed that out yet, I have no "click to attach" button

[Dogsbody47uk]

I,ve been using Automec silicone fluid for about 3 years without any problems.

[Guppy916]

Evening Daniel, do tell how did you get your avatar sort ?

Did anybody notice the change of thread (arnt I naughty )

[Brit car fan]

I had aged DOT4 fluid in the system and it corroded it solid. I replaced the master cylinder, calipers, rear cylinders, flexibles front & rear, and replaced the rear pipes with Kunifer. As the system was just about all new it was the ideal time to change to silicone fluid (Automec DOT5) and have had no issues since. The fluid will change colour from blue to yellow in time but this is normal.

When I was pressure bleeding the brakes the reservoir on the after-market master cylinder split at just 14 psi (I used to bleed the old Girling one at 25!) - not only did the contents of the reservoir flow out but before I could release the pressure the pressure bleeder had also discharged most of its contents all over the car and the driveway. Fortunately it just made a mess - Just imagine what it would have been like with DOT4 !!

[Tim Bancroft]

Not a fan of DOT5 silicon brake fluid since a friend driving my Saloon down an alpine pass managed to boil the brakes, the fluid had the consistency of Cresta (a 70s soft drink, that was sold under the catchphrase 'Its frothy, man'), it was, extremely frothy. The big issue was that I could not get any more fluid (Sunday in Switzerland) so had to use DOT4, therefore contaminating the DOT5. Since then have always used DOT4, simply down to supply issues when out and about...

 

Nothing wrong with DOT 4 on a car that is regularly used, maybe if a car is not used much, then DOT5 might be an idea.

[Jason]

I've always been a fan of DOT5 simply because I've never been able to bleed the brakes without making a mess! (and I prefer that mess to be non-destructive of my paintwork!)

I've resurrected a few cars from long term storage and usually change the fluid, the one time I didn't I eventually found that whilst the master cylinder was full of DOT5 the system was full of something else! It had been like that for a couple of years before it started to cause issues and I eventually sorted it with a fluid change and a master cylinder refurb. I'll be putting DOT 5 in the TR when I replace the master cylinder (this weekend).

 

[Jason]

UPDATE - fluid changed and used a vacuum bleeder for the first time, far easier and gentler than the usual pressure bleeder (aka the Easibleed) and still a one man job.

[RobPearce]

Vacuum bleeder sounds a good idea.

I've used DOT5 in all my cars since I had a total brake failure while driving enthusiastically in my first Vitesse. Exactly the "turned completely to compressible froth" symptom that Tim mentioned, but in my case caused entirely by the state of the DOT4 fluid. No Alpine passes required - I was in Berkshire!

[Hogie]

All brake/clutch fluids can go 'bad' given enough time.

DOT5 SBF was designed as a storage medium that would work when require (US army trucks in long term storage).  One of its big failings is the time taken to remove air bubbles once introduced - this could be caused by excessively bad road surface.

 

DOT4 is more forgiving of air bubbles as they dissipate quickly.

However the fluid does age with bad results  - change every two/three years

 

Roger

[ODIN]

 

Only disadvantages I have encountered with silicone:

1paintwork contamination.

A  quite difficult problem with ‘fish eyes” when attempting to re-paint because of  merest traces of silicone.(not insurmountable but careful prep needed)

2 From painful experience - it is very slippery  stuff  underfoot if  you spill just a little bit!

 

 

 

 

[Brit car fan]

For the clutch I'm flogging these on eBay if anyone's interested:

https://www.ebay.co.uk/itm/273663005728

They make clutch bleeding a LOT easier!

[Bitumen Boy]

On the Herald at least I find I can just bleed the clutch on my own once the tunnel is removed. For my purposes that's probably easier than trying to round up an assistant.