Brake / clutch fluid

[oily66]

With a freshly worked engine ready to be installed and knowing how troublesome the bleeding of the clutch can be. What would be your recommendations for the type of fluid to be installed in a completely new and empty system? Oh and it’s trackerjack on the front if that makes any difference.

[dollyman]

Personally i would use silicon fluid in a new system.

Tony.

[xvivalve]

The seals used in the club recon cylinders are original equipment material; if you use silicon fluid with them, there is a chance the seals will expand and the cylinders seize.

If using silicon fluid, you ideally need to change every seal in the system for compatible material.

[matt of the vivas]

Id use Silicone. Have run it in various cars for years, never had an issue. If you have all new seals its an ideal time.

[Carledo]

I'm probably a lone voice crying in the wilderness here, but I neither like nor trust silicone fluid. Sure it doesn't remove paint for a hobby, but that's the only real advantage. Oh and it's not hygroscopic so fit and forget. IMO, there are some things that shouldn't be fit and forget and I think brake fluid is one of them. Better to check every now and again and if not using silicone, change it every couple of years or so. It gives you an excuse to thoroughly check your braking system!

As Alun has said, unless you have a perfectly clean (ie NEW) entire hydraulic system you can run into problems. Get a leak and don't have any in the car to top up? Hard luck, garages don't sell it! And putting ordinary in as an emergency measure is not on, see 1st comment! I also know people who've had problems with silicone fluid boiling at an unconscionably low temperature. Other cars seem fine, so it may have been a duff or counterfeit batch. But it makes me think.

As you all know, I take my brakes very seriously, the way I drive, I HAVE to! So my cars all get DOT 5.1, high boiling point, synthetic race fluid. It's not that much more expensive than DOT 4, which is the modern "standard" issue either. But I don't regard it as necessary on a strictly road car, for one of those, DOT 4 is perfectly adequate, available anywhere and anyones product will mix in OK. If it ain't broke, don't fix it!

My 2 pennorth, Steve

[new to this]

Im starting to repipe my brakes,i was planning to use silicon fluid,but now im going to use 5.1 fluid has a higher boiling point than silicon just

Dave

[xvivalve]

I’ve had two cylinders returned where silicon fluid has reacted with the seals, from the several dozen I’ve sent out: that’s a measure of the risk.

[matt of the vivas]

Silicone fluid does not react with seals. Its DOT rated and as such is perfectly ok to use, and it will mix with ordinary glycol based fluid - although by doing that you lose the point of it!
Silicone is not hygroscopic - it wont absorb water and contaminants - which is great in a perfectly clean system but less good in a system thats just had piecemeal part replacement and then filled with silicone. What happens then is anything nasty in the system gets pushed to the lowest point, usually the rear wheel cylinders, and sits in there, rotting the bores and wrecking the seals. I would suggest thats the trouble Alun has seen with Silicone?
In a new, or freshly overhauled system Silicone is great. It wont give you a spongy pedal - if it does you have not bled it enough - and if you get a leak it wont strip your paint. It also wont rot your system out like normal fluid will once it gets water in it.
Silicone is NOT fit and forget - this is very important, and its where people come unstuck. Although the fluid does not absorb water you can still get water in the system from condensation - and as stated above it ends up in the lowest parts of the system. Every 3 - 5 years you need to bleed the brakes to get rid of it - no need to replace the fluid, just drain a little off from each nipple and top the reservoir up.
Ive run silicone in my Dolomite for 9 years. Every year, in the spring, it comes out of hibernation. I never have trouble with seized brakes and its very comforting to know that if i do get a leak, its not sitting inside my chassis or floor rotting it away....

[xvivalve]

Nope, master cylinder seals swollen to point of seizure. Rare, but it happens.

[James467]

All of my restos get silicone fluid, specifically Automec. Never had a problem so far!

My brake systems are completely new though, pipes rubber bits etc...