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Triumph TR6 - Brake Fluid Conversion DOT 3 to DOT 5

I have searched the archives and found some topics on the conversion of brake fluid to DOT 5 and noted the cautions and suggested procedures. But I am asking if there is anyone who has switched to DOT 5 without replacing the hoses and rubber compnents and if so what procedure did they use and would they do it again?

I am in the process of replacing a leaking master cylinder since my rebuild job failed to prevent leaking out the back end. (I guess the master cylinder was too corroded having sat for years and my honing to clean the cylinder surface was not sufficient or there are still imperfections on the surface) Since I am doing this , I would like to switch to DOT 5 but I am not keen on having to replace all the rubber components of the wheel clinders and calipers and hoses since the ones I have are essentially brand new. Nor I am too keen on having to take them apart and clean them individually and then reinstall them (I should have switched before when I rebuilt the car last year but for some reason which fails to be remembered by me I went with DOT 3- probably wanted to keep it as original as possible)



Mike Petryschuk
69 TR6
Michael S. Petryschuk


I converted 2 different cars (my 6 and my Fiat Spider) from DOT3 to DOT5 two years ago without changing a thing. The only noticeable difference is that I still have all of the paint left in my engine compartments.

Jim Vandenberg

I've gone through the same thought process your'e going through today.
The one big benifit to dot 5 is that my new paint job is still intact. I'm also using it for my clutch slave cyl.
I'm sure you are aware not to mix dot 3 with dot 5.
From a SAFETY stand point, don't short cut! Do it the right way the first time. Replace accordingly and blow out the dot 3 from your components with a air compressor.
Good luck

I can appreciate you not wanting to replace all rubber bits in the brake system. I was fortunate when doing my restore in that I was talked into going DOT 5 right at the beginning of replacing everything.

OK so the big question is: is there some product/cleaner that will remove/flush all the dot 3 from the system? There probably is but I do not know its' name. The bigger problem is that the dot 3 has had years to penetrate the pours of all the rubber components. How do you deal with this?

Maybe that since you are only about a one year old system, the components will not have had the time to absorb dot 3 and a good cleaning/flushing might do.

Sorry Mike but I metion this but I do not suggest you do this. The braking system is just too important to ones health.

Rick C
Rick Crawford

My TR6 was changed to the silicon fluid last year just before I took ownership. I have had difficulty getting a really hard pedal and on checking the archives found some threads that indicated similar problems - suggestion was that the higher viscosity fluid had some impact on performance. Some posters had/planned to change back to the dot3 fluid. One of my respected car friends said to just bleed the brakes at each wheel and keep topping up the reservoir with the alternate fluid until it came out at each nipple. Sounds simple but ignores some of the warnings about mixing fluids posted above.


75 TR6
B.J. Quartermaine

Michael - I don't think there is an easy way out here.
There is a lot of info if you search the net, not TR specific, but the TR is just another standard braking system. the following is taken from the site listed below, but there are many that confirm this....

"The viscosity of silicone brake fluid is different than DOT 3 and DOT 4 fluids, so most manufacturers don't recommend it for use in systems with ABS brakes. The biggest disadvantage of silicone fluid has to be that it is more difficult to seal. DOT 5 fluids will seep past seals and gaskets that would normally contain DOT 3 and DOT 4 fluids...... Silicone brake fluid and Glycol-based fluids should not be mixed. The complete system needs to be disassembled and cleaned before filling it with silicone fluid." (

I am guessing that you don't use your car that which case, silicone fluid (DOT 5) is an answer. I too have had a pain in the bulkhead, but prefer to maintain the car with Dot 4.

I suspect that this is not what you want to hear, but you know is right.


Roger H

Michael-In my humble opinion and experience,it is not a problem to change to silicone fluid. It would be better to start with rebuilding all of the cylinders, mainly to get rid of the residue and moisture laden fluid that lurks in bottom of the cylinders. Any remaining moisture negates one of the reasons for converting to silicone, but minor mixing of the different fluids will not cause catastropic diaster. I know, heresy to some people. Nelson Riedel really beat the subject of brake fluids to death in his excellent article on the Buckeye site and it might still be available through the "Wayback machine". I have used silcone fluid since about 1983,not changing it for at least 10 years, and have not had a problem with leaking or bleeding issues. If a car with silicone fluid is stored over the winter in a damp climate, you will will not be greeted with a corroded or rusty hydraulic system in the spring. I see the town folks approaching with pitchforks and torches, time to sign off.
Berry Price
BTP Price

Brake pedal is a little softer with DOT 5. (and when I say a little softer, it's not very different) Doesn't bother still stops very well for it's vintage.
I don't have any leaks because I replaced most of the parts and never put Glycol-based fluids after rebuild.
The only reason I would recommend for you to use DOT 5, is if you are concerned about your paint job. If this is not a concern, I'd just stay with what you've got now and fix your present leak.
Good luck in what ever you decide to do.


Roger and Mike,
The next paragraph in your LINK Roger states the following and I quote:
" What's new in brake fluids? Non-silicone based synthetic brake fluids. Sometimes referred to as DOT 5.1, it is compatible with DOT 3 and DOT 4 brake fluids. This fluid is advertised as "synthetic" but has much the same characteristics as DOT 3 and DOT 4 fluids."
Maybe this is the answer. I know it is difficult to find and it is expensive. Be clear that it is DOT 5.1 NOT DOT 5. I do not know if it is hydroscopic like DOT 3and 4 and do not know how it reacts with paint. A google of DOT 5.1 might answer these questions.
Rick C
Rick Crawford

I went to Dot 5 without changing hoses - those should be the least of the worries as they are cleared relatively easy when bleeding. Over the next 3 years or so everywhere else that could trap a pocket of the Dot 3 (and gunk) developed problems and had to be fixed - new seals in calipers, new rear wheel cylinders (went ahead & changed the old hoses), MC, and finally the long ignored PDWA. So if I did it again I'd start completely fresh on those components.
Brent B

Thank you for all your suggestions.

I switched the master cylinder today and went with the DOT 3 material. I felt it was safest since the new master cylinder shouldn't leak and cause lifting of the paint and I then didn't have to worry about incompatibility of the silicon material. I also don't have to worry about any potential failure of my braking system which for some reason seemed to be a good idea :-)

Maybe when I get a few free hours I will dismantle everything and make the switch or maybe I will do it when I flush the system out in the next couple of years or so.

Happy motoring and I hope to see all the Ontario guys this summer.

Mike Petryschuk
Michael S. Petryschuk

This thread was discussed between 02/06/2006 and 03/06/2006

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