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Triumph TR6 - Silicone Brake Fluid

Fellow TR6 drivers,
When I put my TR6 on the road in 2003, all brake system components had been rebuilt, or were new. Both master cylinders and the rear wheel cylinders came to me with the car, and were NOS, probably close to 20 years old then. I rebuilt the calipers.
With all new components, I felt comfortable going with silicone brake fluid, as I never planned on auto crossing or hillclimbing the car. (Soft pedal aeration syndrome)
So....last year, the clutch slave started leaking, and examination revealed drastic wear on the piston and the bore. Replaced, bled the system, and back into action. I thought it must have been a faulty cylinder.
Without getting dramatic, I discovered another leak 2 weeks ago, and further examination revealed both the brake and clutch masters leaking. After a quick autopsy, and a bit of reading on the internet, it was apparent the silicone didn't play well with NOS rubber items.
New seal kits, and recently manufactured components should be safe, but the NOS parts will be susceptible to leaking and grief when used with silicone. I would suggest buying newer kits for NOS cylinders if you want the 'absolutely stock' look and the safety net for your paint job that silicone brake fluid offers.
Although many warn about a 'soft pedal' from air in the silicone fluid, I've not had a problem with that, and we put about 30,000 miles on the car since 2003. We do drive it, but not as a daily driver.
BTW, I have only flushed the system one time, last year. This is going to be part of the annual ritual now. Not sure how that may play into things, but I'm pretty confident the black gooey tarlike substance in the cylinders couldn't be solely a result of not flushing at least every 2 years.
I also had a brake master that was salvaged from a 71 parts car, which I had stored in a ziplock when the car was dismantled. When I opened it up (last night) the piston(s) looked really good, seals still intact. It had Castrol LMA in the system.
If anyone wants to see a picture, email me and I'll share...(Warning - images are graphic and may offend) ;)

Rod Nichols


My 75 TR6 came with newly installed silicon fluid in the brake system after some rework by the PO's agent. Even after several rebleed attempts, my brake pedal is definitely soft, no comparison to my previous 73 MGB (which admittedly didn't have a booster). There have been no leaks and no requirement to top-up the reservoir. I am tempted to revert to a good non-silicon fluid but am concerned about what seals have to be changed and the amount of work involved.

Can anyone add to the mystery of changing to a different type of brake fluid. There are many documented warnings about changing from a glycol based fluid to silicon - does this concern apply in reverse? Do all the seals need to be changed?

With thanks in advance,

BJ Quartermaine


I added silicone fluid to my system after installing the new slave cylinder in 2006. I noticed that the fluid was very dark but paid no attention til 2 weeks ago when the clutch failed. I bled the slave and the stuff was black and tarry like Barry describes and all was well til yesterday when the same thing happened; clutch on the floor and grinding gears. Bled it again and drove it and it was fine. Went to go for a drive this morning and the problem was back so it looks like the slave is kaput. I'll be pulling it apart tomorrow to have a look and hope it's the rubber seals and not bore pitting, which it should not be with a 3 year old slave. I'm going back to plain old brake fluid this time. BTW, I hear NAPA carries a good supply of TR6 stuff and you can get the rubber seals for the slave there.

1976 - TR6
Bob Evans

I put my pix in a Picassa album. Check these:
Let me know it there are similarities.
Rod Nichols

Wow, Rod!! That's a mess. I have ALL new brake parts throughout including new SS pipes from Kai Radicke, but my booster is rebuilt on the old and I rebuilt my calipers using TRF parts. I was considering DOT 5, but with your experience am wondering if I should abandon silicone for DOT 4 and watch for leaks. Leaks won't matter too much, the whole tub's first coat is POR-15.
Doug Baker

Your gonna flush every year with the silicon fluid. That's mighty pricey Rod. Might as well use "Synthetic"

Rod-Thanks for giving me something else to worry about. I have always been a believer in silicone fluid and have never experienced any problems. I haven't changed the fluid for about 10 years and the resovoirs shows only a few black particles at the bottom, which I presume is seal material. Nelson Riedel really flogged the subject of seal compatability and mixing different types of fluid (didn't seem to cause any problems). All of the seals were replaced prior to changing to silicone fluid, were purchased from TRF, and were Lucas/Girling or Lockheed brand.
Hope to see you at the ATDI in Redmond.
BTP Price

What an old subject this one is.

I put DOT 5 in my fully rebuilt brake and clutch systems....100% all new seals and new or rebuilt cylinders. I did this in May 2001 and I have changed it once in those 8 years. I have topped up a little over the years but that is all. Absolutely zero leaks in either system. This is, I guess, another experience with DOT 5. Sorry to hear your bad experience Rod with DOT5. I do not think that DOT 5 should be condemned though.
IMHO DOT 5 is the only way to go. The Archives I think will have lots of threads on this subject back in 2000 to 2002. If you search the internet, try to find articles relevant to our era of car.
PS do not be fooled by thinking DOT 5.1 is the latest and greatest silicone fluid.
Why on earth some idiot would do this is beyond me. DOT 5.1 is glycol base used in certain ABS systems. 5.1 it appears can be used in our cars IF it is going to be used in a system that is already a glycol system.

It has been said many times by many people not to mix glycol and silicone in either system. Barry, If you go over to DOT4 you will need to change every seal on every component. Otherwise, you will end up with "gummy bears". (not my name for seals after a swap of fluid type).


Rick Crawford

Actually some manuf. are telling you NOT to use Silicon in their units.

I talked to Layton at BPNW yesterday. Couple of things came out, one being that a lot of guys have opted out of silicone on the clutch system because of the aeration giving a shorter throw on the clutch. Nuff said about that.
Since I am putting in a new clutch master and the slave is getting a reseal, I'm seriously contemplating going to a Valvoline synthetic. Local Napa guy claims it not be be nearly as aggressive on paint as LMA and other DOT 3 & 4 fluids.
The brake system, however, will remain charged with silicone. I am going to take a look at the rear brakes, that's my next concern. New brake master is already in place.
My friend Pete Rolfe, here in Boise, has quite a few cars that are using silicone, and he has no problems. Most of the cars got a flush and refilled with silicone, no seal replacement. Where did I go wrong???? (looking up at the sky to the TR Gods)
Well, guys....keep on moToRin'!

Hey the TR7.8 running??? Are you coming to Redmond? I'll hang around with you! ;)
Rod Nichols

You did not go wrong. We both where in the same era of rebuild. We both went for the more expensive repair kit and you had failure. But then you have put on a LOT more miles than I have.

I have noticed one thing about the rubber parts that I bought new to go every where in my car. From the round grommets to the little pieces of rubber that go behind the door handles...they are ALL falling apart! The stuff is crap! It all lasted only 8 years. But then I would bet my last dollar it ALL came from China or some place over there....OK don't get me started on THAT subject.

It sounds like I am not up to date. Synthetic brake fluid??? Did I miss a class?

Rick Crawford

Rod- This just posted on BCF. It is what I was posting about that some suppliers are nixing the silicon

"I just received a new brake master cylinder for our project '72 Spitfire. It arrived in a TRW box with a statement/decal on the outside warning that the use of Silicone brake fluid would void the warranty.

I discussed this with the supplier and they told me that there have been issues with the compatibility of the fluid with the seals due to surface finishes and the DOT-5 fluid not providing enough lubrication. They suggested several problems that might arise from this.

I'm still considering using DOT-5 as I've used it with success (and no problems at all) in both my Mini and our GT6. Has anyone out there experienced seal problem with master cylinders when using DOT-5?"

Hi Rod/Guys:

Definite similarities in the black goop in my clutch slave cylinder and the reservoir of the clutch master but I have not yet pulled the old master apart for a look at the guts. You mentioned aeration and that is what I had on the first bleed; a LOT of air and tarry bubbles. They were even noticeable just looking in the MC reservoir. There is no scoring or pitting in the relatively new clutch slave but all of a sudden, NAPA can't find the rubber seal so I'm ordering a kit. It just appears the seal has worn because with the new .75 bore clutch master, trying to bleed it just blows air and fluid past the rubber seal on the piston and actually blows off the rubber end cap. Sure appears to be nice pressure in the .75 bore clutch MC so a slave kit should result in a better clutch.
P.S. Thankfully, I did not use silicone in my new brake MC a couple of years ago. Had a can of regular Dot 3 and used it.

Bob Evans

This thread was discussed between 11/07/2009 and 21/07/2009

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