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Triumph TR6 - Silicone Brake Fluid

Switched over to "Cartel" brand silicone brake fluid almost 3 years ago. I had to top off the master cylinder resevoir 2 weeks ago and noticed the fluid was CLEAR - all the blue pigment had settled out. The new fluid was blue, which was the tip-off. Looked today and the fluid in the resevoir is clear again. The pigment or whatever the coloration has settled out. The virgin stuff in the big bottle is still blue.

So what's up? Could it be moisture or residual dot 4 that's coagulating the colorant? I doubt it's a formula stability issue since the sealed bottle is blue.

Brent B

Hi Brent
The Automec fluid I use starts blue and the colour fades to clear after a short period of time, I think it is due to being exposed to light, if it is fading and not settling out I don't think you have a problem
R. Algie

I have used the "fluorescent purple" or maybe one might call it "blue" silicone brake and clutch fluid for 14 summers (over 78,000 miles) in my TR3A with no problem. I never heard of the fluid turning clear. The fluid in my TR turns black, probably because of the black hoses and seals.

When I did my restoration from 1987 to 1990, I put in all new rubber seals in all the brake cylinders and rubber hose lines (black) like everyone recommended, so it was not cross contamination from old seals or old fluid that caused the black to appear.

At one time, I thought I should drain the system because of the black colour and re-fill with new "purple" fluid. When I checked it after about 6 months, the new fluid had turned black.

When I drained it, I let it sit in the clear glass bottle where I had collected it and the black sediment settled to the bottom. When the black was all at the bottom, the fluid appeared clear purple (or blue) again. I actually let it sit for quite a while, like a month, and later when I was sure that all the bubbles were out, I re-used this old clear "purple" fluid in my system with no problems. But it turned black again.

Since then, I have changed the clutch line black rubber hose for a new black hose and have the 3 new black hoses that I plan to install for my brake system. But from experience, the fluid will probably turn black again.

I always bought and used the 1 quart bottle of "purple or blue" fluid from Roadster Factory except I once needed some in a hurry and bought a small bottle at a Harley Davidson supply shop. This silicone fluid was also "blue or purple". It seems that all the bikers use silicone fluid and it is readily available at any bike shop.

Don Elliott, Original Owner, 1958 TR3A
Don Elliott

HI guys,
I use silicone fluid in both brake and clutch M/Cs.
The colour does fade a bit in the brake reservoir
but has never turned back in 5000 miles of driving.
But the clutch fluid turns black within 400 miles after a flush. All parts are brand new and have never
seen Dot 3 or 4. The blackness never changes the
clutch feel in anyway, but I flush it once pre season
just the same.
Christopher Trace

Hi Don
Does your TR 3 have a translucent plastic reservoir like the TR6 or is it metal? I have used the Silicone fluid in both a TR6 & an MGB which both have translucent reservoirs and in both cars the fluid in the reservoir faded to clear quite quickly.
Both cars brake systems were completely renewed before using the silicone fluid, neither of them have ever sown any trace of black, the MG was done about 8 years ago, the TR about 2
On examining fresh Automec fluid again I would say it is purple rather than blue.
R. Algie

Ron - My reservoir is a single combined steel cannister with a center internal resrvoir and serves bothe the brake as well as the clutch systems. It is the original one that came with the car almost 46 years ago. It came galvanised on the inside which is still intact. The outside was painted black and for the first 80,350 miles I ran Dot 3 fluid and the paint came off and got qiute rusty. Since 1987 - 1990 it had been painted a nice shiny Dupont Imron Thusk and Airplane Black 2-pack Paint amd it is still as it was in 1990 with 78.000 more miles on it.

I don't think it's the cannister that caused it to turn black in colour, but rather the black rubber hoses. During that time, I drained and re-filled the system once.

I can see that maybe a translucent plastic reservoir might allow light to cause the fluid to loose its colour.

Don Elliott, 1958 TR3A
Don Elliott

Chris - I have drained my system once in 78,000 miles and re-filled it with silicone purple fluid. When I pour in the fluid, I try to do it carefully, not to entrain any air bubbles as I am pouring it in.

You say you flush yours lines, etc. Can you explain the details how you flush it ?

Do you think it'll keep the purple fluid from changing to black ?

BTW, like you, I have never experienced any problems with the black sediment in the system. But maybe my black rubber hose walls are a bit thinner.

Don Elliott, 1958 TR3A
Don Elliott

Purple, blue...makes no difference if you're color-blind.
Brent B

I use one of those inexpensive one-way brake bleeding valves ,attach it to the bleed valve on the clutch
slave cylinder. Lossen the bleed valve and keep pumping the pedal and topping up the reservoir until
the fluid runs purple into the catch pan.
I've only done that once trying to solve the black
fluid problem, but the new fluid blackend very quickly
so I'll just wait til it is time to flush both brake and clutch fluids.
Christopher Trace

I believe the "turning black" can be due to only one thing--seal and/or hose deterioration. The PO of my TR had done an incomplete DOT5 changeover (actually had both DOT3 & DOT5 layers) so I did the complete ethanol flush and DOT5 purple refill. Granted I also replaced all seals & hoses except for those in the wheel cylinders. That was 2 years ago and the fluid in both reservoirs remains as it did from the Cartel bottle. Go figure.

Rick O.
Rick Orthen

When doing my restore I literally started with 100% new brake parts...front to back. In goes the purple DOT5 and it is now clear to a light brown ( dirty purple:)
Why does it go clear?? I do not know..maybe the dye just disipates over time. I do not think this is a performance problem.
The one thing I do know is, I am glad my systems, both clutch and brake, are synthetically fed.

Brent, I hope you did not just drain the DOT4 and simply refill with DOT5!?!?

Rick C
Rick Crawford

I've spoken about silicone brake fluid to a lot of TR racing guys and none use silicone. Many say they tried it and it wasn't what they had before with earlier fluids. So they switched back.

I believe that when you fill the reservoir with silicone fluid, you entrain a few (or a lot of) air bubbles. And the TR Race drivers have their next practice session in 15 minutes. It's not like us touring TR drivers where we change the fluid in the autumn and the bubbles have all winter to "evaporate".

Don Elliott, 1958 TR3A
Don Elliott


I drained the Dot 4 from the system and then flushed with Dot 5 to all wheels. The flexible brake lines were then changed out, then the system bled.
The calipers were rebuilt in 2002 which got the 30 years of crud out of there the flushing couldn't. The wheel cylinders will be changed in a week or two.

I've not seen any black or brown fluid, just a loss of "purple".

Brent B

if I recall,there is one other thing about silicone brake fluid that racers do not like and I think it is that it does not cool as quickly as DOT 4 under a lot of use as would be the case in racing....more brake fade?? Also Don, I agree they drain and replace stuff in a race car very often so why go to the more expensive DOT 5 that really did not suit their purposes in the first place.
Brent, I think you have been lucky. It has been said: Rubber components in a brake or clutch system that have been use to DOT 4 (or 3) then get DOT5 tend to deteriorate quickly into black gunk in the system and eventually brakes/no clutch. When you do the back cylinders, you might want to look at the master cylinder.....sounds like that is the only thing left from the DOT4 days. A drain and refresh of the system might not be a bad idea also.
Have fun
Rick C
Rick Crawford

I use silicone to eliminate the corrosion that regular fluid - which is hygroscopic- causes when the car is laid up. But the silicone stuff has a lower boiling point and can lead to brake fade. Thats why racers dont use it. I've had it happen in spirited road driving in hilly country. The plus side is I have not had to free of a sticking wheel cylinder or caliper piston for many years.
P H Cobbold

Peter - Your final comment about silicone fluids preventing problems of caliper and wheel piston/cylinders is something I had never considered. It must prevent rusting of steel or iron parts and the production of accumulated corrosive residues on aluminium parts. But now that you have mentioned it, I have to say that in 14 summers of driving more than 78,000 miles plus "TRusty" being kept in warm storage for 13 winters (about 5 months without running each winter), I've never had a problem concerning the brake calipers or wheel pistons or the seals. And that's with "black" silicone fluid that was oiginally "purple".

Last month, my son and his wife from Ottawa spent a week hiking through the trails in the Brecon Beacons of South Wales.

Don Elliott, 1958 TR3A
Don Elliott

Oh yes! The hydroscopic properties captured my attention too a few years ago and put me in the tinkering mood so I changed the fluid. The downside to DOT 5 (apart from the lower boiling point which has been mentioned) is that you do get a slightly softer pedal feel because the fluid compresses more. Perhaps a small tradeoff but I didnt like it and I switched back.

Hi Michael
If you don't like the slightly softer pedal that the silicone fluid gives you try Stainless flexible hoses, they expand less under pressure
R. Algie

What hasn't been mentioned is the frequent misconception that silicone systems don't need to be bled every few years. Moisture eventually gets into the hydraulic system regardless of the fluid; when it's silicone, the moisture simply pools in low (high?) spots instead of being dispersed throughout a glycol system. Depending on the location of the pool, corrosion may set in.

Rick O.
Rick Orthen

Hi Ron
Thanks for the suggestion but I allready have braided hose. Improved hose certainly gives you better pedal feel but it still wont cure the problem with the Dot 5.

Good thread ! I have used both fluids variously over the years. In the MG brakes, I simply switched from Reg to silicone and had years of trouble free driving (though it did turn clear). More recently, with all new components in the clutch hydraulics of my Jeep, was leaking all over in a short time, another of the silicone tendencies I'd heard about, small molecule and very slippery. So the jury is still out and I use DOT 4 in TeResa. Perhaps materials and tolerances vary with manufacturer ?? Peter
Peter Gooch

This thread was discussed between 04/10/2003 and 15/10/2003

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