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Changing TR4A Brake and Clutch fluid to Silicone DOT 5


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I am about to get my car back from the paint shop. One of the previous issues on purchasing the car last year was a leaking brake system that had destroyed the area all around the pedal box, so I have decided to change to a silicone DOT5 fluid.

 

I believe that I have read all that the internet and the TR forum can offer on the subject, boiling points, wet absorption, the supposed danger of loss of pressure due air-bubbles, servo failure etc etc. BUT on balance the general dampness of the English climate that results in a recommendation for 24/36 month fluid changes of standard Dot 3/4 Fluid, together with its corrosive nature has me decided.

 

I understand that the pipes and cylinders must be thoroughly cleaned and the best way is with methylated spirits and then blown through with airline to dry. I understand that the rubber seals are not affected by DOT5 however I am also renewing the Master cylinders and brake calipers and will do the seals as well as a precaution.

 

If anyone is interested in this change over or has done it themselves and has any comment I would like to hear from you. Here is a very knowledgeable and reliable linked report from an engineer that debunks a lot of the scare stories and myths about swapping over and has supported the report with factual comparisons and actual test results. Do read this and the various links if you are considering doing this as its very helpful.

 

http://www.buckeyetriumphs.org/technical/Brakes/Fluid/Fluid.htm

 

Cheers

Charles

 

 

 

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Hi Charles,

 

the many buckeye technical articles can be interesting, and often useful, but they didn't come down with the tablets . . . . as the author of the SBF modestly explains, his notes " are provided here for entertainment ".

 

The internet is full of apparently learned articles written by well meaning chaps who, having decided on a personal project, undertake a whole lot of reading around the subject . . . . and in some instances undertake a degree of experimentation to boot. Good on them, worthy efforts, and often jolly helpful stuff - but the authors tend not to be specialists, let alone experts, in the field . . . . and hands-on experience tends to be limited to the one exercise.

 

Over the past 40+ years there have been a number of oft-quoted reports, commentaries, technical observations emanating from automotive, braking and chemical manufacturers . . . . . unfortunately too many of these seem to display a lack of objectivity and a degree of vested interest, one way or another . . . . .at least in my opinion.

 

I first used SBF back in 1975, and I've maintained an interest in the topic over the years . . . . as an amateur enthusiast, and in the past as a member of the motor trade. I'm not against SBF, and I do use it for some applications, both brake and clutch - whether I prefer SBF or glycol or borate based fluids depends on the priorities of the individual application.

 

One thing I have learned, from first hand experience, is that exposing some hydraulic seals to more than one variety of fluid can be a mistake - a mistake which can lead to dire consequences, if the result of exposure to more than one type of fluid results in seals swelling beyond their designed parameters. I'd suggest that the likelihood of problem has been much reduced in terms of current seals compared to those of half a century ago, but nevertheless aftermarket brake system components tend, as a generalisation, to be designed for the particular variety of brake fluid originally specified by the vehicle manufacturer. Relatively few vehicles have ever been specified for DOT5 hydraulic fluid as original equipment.

 

As a purely personal opinion, I wouldn't now consider switching from one type of fluid to another without completely replacing the hydraulics - lock, stock and barrel. That may indeed be over-cautious, but having experienced various brake problems over the years, I've no great wish to repeat the problems resulting from boiling fluid, nor yet those resulting from malfunctioning seals. All a bit too much like the proverbial brown trouser moments, and the reflexes required to correct sudden brake failure tend not to improve with the passing years !

 

The cost of fitting new component, and selling off the old component as decent used parts previously utilised with whichever fluid, is not great in comparison with the costs of even a minor shunt.

 

Cheers

 

Alec

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Hi Charles, I have done the Change on my TR6 while overhauling the Brake and Clutch System in 2010. Cleaned the System and replaced all Seals. In the meantime made about 25'000 miles and checked the Seals in the Master Cylinders, Calipers and Brake Cylinders. No difference, no swelling or Deterioration but one important Thing, no corrosion anywhere. For me is even the High Cost per Litre Ok. I have done a few more TR's in our Club, no negative Results yet.

 

Robert

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Being in the trade and having declared an interest I will never use nor recommend Silicon fluid Im afraid, and as far as I know no car manufacturers in the world fit it as OE. Yes I know people who do use it without problems but its company policy and that is an end to it.

Stuart.

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I've got Silcone in my Herald and GT6. The TR4a will be converted soon. Never had any problems with braking, except in the 4a.

 

Dave

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Thanks all,

Interesting to hear your opinions and especially Alec for your considered advice. I have time to chew over the issue before my car comes back from painting and in the meantime I am amassing the various parts (this all started with a leaking MC and rusty Discs). :(

 

Charles

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Skewing the subject slightly but is that upper steering coupling standard Charles?

It was like that when I bought it last year so I don't know. The car had been renovated some 14 years previously then garaged and off the road till last year, I am fairly sure someone on the site will tell us?

Charles

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