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TR2/3/3A Intermix of Silicone and Dot 3 brake fluid

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mastaphixa

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The '60 TR3 that I am working on has a very mangled tag on the Brake/Clutch Master reservoir that says "Silicone Oil Only". Just prior to my friend purchasing the car, the PO's mechanic replaced a leaking Clutch Slave. I was able to speak to him and asked what kind of brake fluid was used in the car and he stated that he put DOT 3 in when he changed the clutch slave. Looking in the reservoir the fluid looks very cloudy with a very gray look to it. The other thing that has me wondering what is going on is the fact the clutch master just up and failed yesterday. I have to pump it up and the shaft is leaking out into the pan under the windshield wiper motor.

I have done a lot of searching here and can't really seem to find a thread addressing this issue, but I am sure it has been beat to death. Where do I need to go with this, completely bleed the entire system with either dot 3 or silicone fluid (I assume dot 5) or does it need to be rinsed out with alcohol, or what?

Thanks in advance,
Steve
 
Opinions and methods will vary - but all 3 times I 'converted' a British car to DOT5 I simply removed whatever old fluid I could get out of the reservoir, filled with DOT5 and then bled until I was clearly (purplely) getting the new stuff coming out.

A couple of those cars have more than 15 years on them since I did this with no brake issues I would attribute to the change of fluid.

If you do work with DOT5 it is useful to be familiar with its characteristics - in particular the need to not disturb it in such a way as to introduce bubbles and they (including bubbles too small to see) can remain in suspension for quite awhile.
 
mastaphixa said:
The '60 TR3 that I am working on has a very mangled tag on the Brake/Clutch Master reservoir that says "Silicone Oil Only". Just prior to my friend purchasing the car, the PO's mechanic replaced a leaking Clutch Slave. I was able to speak to him and asked what kind of brake fluid was used in the car and he stated that he put DOT 3 in when he changed the clutch slave. Looking in the reservoir the fluid looks very cloudy with a very gray look to it. The other thing that has me wondering what is going on is the fact the clutch master just up and failed yesterday. I have to pump it up and the shaft is leaking out into the pan under the windshield wiper motor.

I have done a lot of searching here and can't really seem to find a thread addressing this issue, but I am sure it has been beat to death. Where do I need to go with this, completely bleed the entire system with either dot 3 or silicone fluid (I assume dot 5) or does it need to be rinsed out with alcohol, or what?

Thanks in advance,
Steve
Click to expand...

My advise would be to pull the master,dissasemble and inspect,rebuild,have rebuilt or just replace.
I have gotten very poor life,last one failed after 2k miles or so with dot 5,on reproduction clutch masters.Moss replaced last one,number three in about 7k miles and 4 years.If you have the time and extra money I would have it rebuilt by someone like Apple hydraulics.
Then I would flush all the brake lines,pull apart brake Mc , the calipers and wheel cylinders and clutch slave to clean and inspect,and then put it all back with dot 5.
Maybe more than you want to do but with only one brake circuit,and it sounds like it is already contaminated, I wouldn't take any chances.
Merry Christmas everybody,
Tom
 
This is another of those topics that has been discussed and recussed with no clear consensus.

Obviously the clutch MC has to either have new seals or be replaced. After that, I would do as Geo suggested, bleed as much old fluid out as possible then fill with DOT 5 and bleed at all locations until you get only clean purple fluid.
 
What I don't get is that several parts I have both bought and had rebuilt have tags that say warranty is void if you use silicone fluid. I love silicone and ignore the tags...but anyone know what the deal is with that?
 
My uneducated understanding is that silicone fluid could cause some types of rubber seals to swell, and that the molecules or whatever are smaller and there is more likelihood of leaking. I'm like John, I use DOT5 on everything and would not use glycol again.

Dan
 
Dan, the DOT-5 fluid will only affect silicone seals and/or seals that have previously been used with DOT-3 or DOT-4. Silicone fluid will NOT attack new, standard EPDM brake seals in any way.

I noticed the same warning about voided warranties (on TRW/Girling) brake parts when used with DOT-5. I inquired of TRW (through BPNorthwest) and was told that TRW has decided that DOT-5 fluid provides less lubricity for the seals in their products which can reduce seal life. That is TRW's position and I have no reason to doubt their findings. That said, our GT6 (including its TRW brake parts) had DOT-5 fluid in it for over 20 years.

Last year I replaced the GT6 hydraulics again, not because there were problems but because I wanted to change to braided brake hoses and figured at 20 years the seals must be nearing the end of their lives. The seals were still intact without swelling and there were zero signs of cylinder corrosion.

DOT-5 is not for everyone. However, based on my experiences to date I would not hesitate to use DOT-5 again. I would never switch to DOT-5 fluid without replacing all the rubber bits in the brake system and flushing the lines to remove all residual DOT-3/4. My advice is never change fluid type without replacing all the seals at the same time.
 
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