33 replies to this topic

[bikenutmart]

Have totally renewed complete braking system, including pipes, about to refill and bleed, am thinking of using automec silicon fluid, its not cheap, £30 a litre, but it apparently doesn't ever need changing and wont damage paint, are there any negatives to using it? thanks Mart.

[cal844]

Yes

Get any on paint and if you need to repaint it will react!

Better using standard brake fluid but give thepaint time to fully harden

[robminibcy]

I've heard that it can sometimes cause premature failure of seals in master cylinder and calipers. I personally would go for a quality dot5.1

[59 Speed]

I was going to go for silicon when doing mine but opted for Halfords 5.1 after reading the cons:

"This type of fluid is more compressible and can give the driver a feeling of a spongy pedal.
Silicone based brake fluid has not been developed for, or intended for, use in race applications."

https://www.merlinmo...e-explained-272

[nicklouse]

The only major user of it is looking to dump it.

That being the US forces.

Cons
holds bubbles.
Does not mix with water.

Pros
Does not mix with water.
Does not eat paint.




Real life issues.

A ******* to bleed.
Water pools at the lowest points and rusts your parts.



Would I use it? Only if I had the car in a museum and just about never drove it.

[dklawson]

My British cars are collector cars so I use DOT-5 in all of them.  

 

As mentioned, DOT-5 holds bubbles.  Therefore you have to be careful when pouring the fluid but otherwise the system bleeds like "normal".  It does not create bubbles or suck air into itself to make bubbles.

 

No, DOT-5 does not damage new seals.  Period.  Modern brake system rubber is made of EPDM which is only affected by oil and petroleum products.  DOT-3, -4, and -5 fluids are not oils.  You DO have to have all new rubber in the brake system to switch to DOT-5 (brake seals, brake hoses, servo internal seals, proportioning valve guts, hydraulic brake switch when fitted, and PDWA seals when fitted).  If any of the seals or hoses have ever seen DOT-3 or -4 the seals will sluff off black rubber goo and fail prematurely.  

 

Some brake cylinder makers will not warrant their product if used with DOT-5.  I had a vendor contact the maker to ask why.  The answer from TRW was that they felt DOT-5 does not lubricate the seals as well as DOT-3 or -4.  I have used DOT-5 for more than 20 years in our Triumph GT6, 15 years in the Mini, and 7 years in our Spitfire.  I have not seen any seal failures.  I am not alone.  When you press people who have had bad results with DOT-5 you always find that they either didn't flush the old steel lines with alcohol or they didn't change all the brake rubber.  These are mandatory steps when switching.

 

As far as "you don't have to change the fluid"... that is simply not true.  With any brake fluid you need to flush the system every few years.  DOT-3 and -4 should probably be flushed every 3 years or so.  WIth DOT-5 you can push that to 5 to 7 years but it is not infinite.

 

It WILL complicate repainting if spilled on the paint.  Therefore, if you have any cosmetic issues to address under the bonnet, do them and apply fresh paint before making the switch to DOT-5.  The flip side of that is if you DO spill DOT-5 on paint, the paint is not damaged like it will be with DOT-3 or -4.  This is one of the reasons DOT-5 is sometimes used in restored collector cars.

 

As for the spongy pedal, I cannot comment.  While I have heard the comment many times, my car's brake pedal is firm.  However, the car also has stainless steel braided brake hoses in place of the standard rubber hoses.

 

WIth all that said, I would not use DOT-5 on a daily driver late model car.  It is not worth the expense or extra caution required to make the change.  If you consider your car a collector car or fun car that will see little use, DOT-5 is ideal... just make sure you go through all the necessary steps when making the change.

 

EDIT:  I forgot to respond to the pooling water issue.  DOT-5 fluid does not pull moisture out of the air like other brake fluids do.  Therefore, the amount of "moisture" in DOT-5 is lower throughout its service life.  Yes, there is the possibility of condensation inside the air volume in the master cylinder reservoir but when the reservoir is kept full the amount of condensation is insignificant.  (See comment above about flushing intervals).  If the presumption is that moisture will get in by some other means... address those problems as you don't want water getting in your brake system regardless of what fluid type you use.

Edited by dklawson, 23 December 2015 - 01:53 AM.

[Spider]

I'd agree with Doug's post. I have it in some of the cars. It's non-hygroscopic nature is what drew me to it.

 

In regards to what TRW have said in regards to wear and it being non-lubricating, to a point, that maybe the case, though I haven't seen any problems from wear with the brakes, however in a non auto application, I have seen Silicon Fluid chew out pumps in fairly short time.

[jaydee]

I'd never use a silicone based fluid:

It reacts with any residue of dot4

Painting the car again is gonna be a huge problem

 

Use quality fluid and renew it on regular basis, at least each two years, no more really.

[stevede]

I put the Automec Silicon in mine when I renewed the brake system. The lack of damage to paint and non water absorbing (infrequently used car) drew me to it. Been in 4 years and have had no issues whatsoever.

 

Regards

 

Steve

[carbon]

I've been using Automec Silicone brake fluid in one of my cars for the past 5 years (7.5 inch discs, no servo). This one gets use most weeks during summer but less frequent in winter, particularly if there has been salt on roads.

 

No difference in pedal feel between this and normal brake fluid, and no problems with seals. As an added bonus I have not had any issues with rear brake cylinders rusting up solid since using silicone.

[bikenutmart]

Wow!! Thanks for all the replys, Im going with it, as my mini will be a toy really, and only used on nice days. Thanks Mart.

[nicklouse]

I hope you don't really use it.

[bikenutmart]

Ok, so whats the difference between dot 4 and dot 5.1 fluid, they are both a similar price. Thanks Martin.

[59 Speed]

http://www.advancepe...tbrakefluid.htm

[tiger99]

I agree with Doug. I have used DOT5 in several cars in which I rebuilt the brake system, including 2 Minis, 1 fwd Cavalier, 1 Avenger and 1 Maestro. They were all rebuilt, with all seals replaced, because that is necessary after a few years anyway. Changing odd bits and pieces is no way to maintain a vital hydraulic system, if it needs a rebuild, it needs a full rebuild. I knew nothing about the effect on seals which had been exposed to DOT4. I used Kunifer pipe every time, copper being manifestly unsafe,  and so even if water was lying at the low points, which I do not necessarily agree with, it would not have done any harm. I also used Goodridge flexibles. I also cleaned the red grease, which is basically water-absorbing, corrosive trash, out of any new wheel cylinders and replaced it with a generous dose of high temperature silicone grease.

 

I thrashed all of these cars hard for a few years each, and did no maintenance at all on the hydraulics. One or two stood unused for a couple of years, and the wheel cylinders did not seize. The only "problem" I ever saw was that master cylinder reservoirs were stained purple. I poured it carefully and allowed it to sit for a while before bleeding, and using an Easybleed never had any problems, even on the Minis.

 

I would suggest that people who complain about DOT5 have never used it properly, most likely by not putting it in a fully overhauled and clean system, or they have listened to the likes of Halfords, who don't like it