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Hello, I am going to attempt upgrading the front discs on my 1981 TR7 V8 this week, and wondered about also going to Dot 5 brake fluid, to avoid the hygroscopic tendencies of Dot 4.  I have read that the system has to be flushed to purge the old Dot 4 fluid but otherwise are there likely to be any problems?  Anyone had any experience of this?

Thanks,

David

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Hi David,

the hygroscopic "tendency" is not a problem, this is wanted!

It's only hearsay in good believe since ages (sorry this honest words).

The real problem indeed is the difference of moisture concentration.

It is high in the surrounding air and must be zero in the brake fluid and is absolute zero in DOT5.

But you cannot avoid the moisture to go in the brake fluid because of the differenc of concentration, the moisture moves through all rubber parts, seals and the ventilation drill in hhe container cap.

This is why DOT brakefluid was created the way it is: to catch the moisture in the fluid and get it out of the system by changing it.

If you use DOT 5 it goes there anyway ("next" to the fluid) because of the difference of moisture concentaration - but you don't get ist out.

Often is pointed out the US army uses it in their air planes and tanks, but I don't know what they else do to keep the moisture out.

But our TRs are much more simple than this war wappons. And perhaps they only don't know what they are doing - I would not wonder about that.

And often it is pointed out it's uses in TRs since decades from some of our mates. Yes - but this is no reason why it is correct to do this.

Perhaps our cars are simply much more tolerant and the problem is overrated?

But I think you should know and you can decide how ever you want.

But please simply don't glorify DOT5 by telling about what you have been told.

Ciao, Marco

Edited by Z320
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From decades of anectotal evidence, both DOT3/4 and DOT5 will give perfectly fine service in these cars. The decider for many of us is that DOT5 will not attack paint when (not if) it leaks.

Most sources say that DOT3/4 should be thoroughly flushed before going to DOT5. 

Ed

Edited by ed_h
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Many use Dot5 quite happily and enjoy the anti-corrosive properties. Others have mixed experiences and prefer to stick with Dot 4 or 5.1.

I'm on the Dot5.1 side of the fence.

Jerry

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DOT 5, every time. Some say that moisture will condense in the master cylinder and find its way to the lowest point in the system, but no-one seems to have any evidence of that happening. Even if it did, the quantity of water would be minute, unlike DOT 4 which will actually attract atmospheric moisture, to the extent that an open container of DOT 4 will eventually overflow.

DOT3 or 4 does have its uses - it's a very good paint stripper!

Pete

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I use DOT 5.1 because it is clear, this is another (some kind of better) DOT 4.

To protect the car from loosing paint is very easy on the TR4-4A!

I made myself a container to catch a leak from the master cylinders.

see my post here

That allowed me to finish the season 2018 - even when I realizes a minimum leak during October.

Edited by Z320
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From experience the DOT4 or DOT5 question never gets a clear answer. I have run both with know issues in Triumphs and MGs and moderns. In terms of actually fact-based differences the only real difference is the lack of paint removal upon spillage.

Tim

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Just now, Tim D. said:

From experience the DOT4 or DOT5 question never gets a clear answer. I have run both with know issues in Triumphs and MGs and moderns. In terms of actually fact-based differences the only real difference is the lack of paint removal upon spillage.

Tim

I think that's right, though DOT5 is not recommended for most modern ABS systems.  I believe the rapid cycling of the ABS can cause bubbles to form in the DOT5.

Ed

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Many thanks everyone, great international response, and it seems a split verdict. Albeit non paint stripping does have its appeal! However, I think I will be sticking to Dot 4 if only to save changing all the other rubber components in the system!

David

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11 hours ago, stillp said:

, unlike DOT 4 which will actually attract atmospheric moisture, to the extent that an open container of DOT 4 will eventually overflow.

Pete

So, they have created a water magnet !!!!:rolleyes:

I think you will find that it does not attract from afar but any moisture laden air (nearly all air has moisture) will sit on top of the Dot3/4/5.1 and the water will combine with the BF.

This will also happen with DOT5 but possibly on  a slower scale. And, the water molecules, do not combine with the BF. - But, it is still there.

For DOT3/4/5.1 you must be careful how you handle it so as not to damage the paint.

 

Roger

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My TR4 was re-built in the early 1990s with all new rubber components in the brake and clutch systems, and I have been running with Silicone DOT5 since the car returned to the road in 1993.

Whenever I have had to bleed the brakes (I have had to remove the rear axle twice!), the fluid has run clear.

Ian Cornish

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My 4A had all new brake components in the late 80s and has been running with DOT 5 since. Like Ian, I've not found anything other than SBF in the brakes. The clutch fluid went dark soon after the car went on the road, but then cleared, and the clutch functions fine. I assume there was some rubber dust on the new seals.

2 hours ago, RogerH said:

So, they have created a water magnet !!!!:rolleyes:

I think you will find that it does not attract from afar but any moisture laden air (nearly all air has moisture) will sit on top of the Dot3/4/5.1 and the water will combine with the BF.

But then Roger the air adjacent to the surface of the fluid will be drier than the ambient air, and the moisture from the ambient air will diffuse into the air adjacent to the fluid, so yes, it will work like a water magnet. Leave the top off your bottle of DOT 4 and see what happens!

Water does not combine with silicone fluid. There's a few articles on this subject in that excellent Triumph documentation at https://drive.google.com/drive/folders/0B2H2NJt34OffdnhWS19scjlNUU0

Edited by stillp
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1 hour ago, stillp said:

Water does not combine with silicone fluid. There's a few articles on this subject in that excellent Triumph documentation a

Hi Pete,

quite right - water does not combine with SBF but there is nothing to stop it being in the system sitting next to the SBF.

 

Roger

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Think it largely is a personal choice and there is no common “best option”.

Anyway if you convert from normal BF to SBF, I recommend to dismantle all components and replace all rubber parts. 
I’m on SBF by the way.
Waldi

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Water has the higher density than DOT5 and sinks down to the lowest point, you cannot "bleed" it out with the DOT 5.

A very interesting issue would be to dismantle 20-30 years old DOT5 calipers,

catch all the fluid and examine it and have a very close look on all metal surfaces.

Believe me, I would do that, but I have no such DOT5 calipers.

Perhaps someone already did that with the focus on that?

Edited by Z320
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6 hours ago, RogerH said:

quite right - water does not combine with SBF but there is nothing to stop it being in the system sitting next to the SBF.

There isn't Roger, but how would it get in there? Unless the car is parked in the rain, with the bonnet up, it can only arrive from condensation, and the quantity that can condense will be very very small. I'm sure someone cleverer than me could calculate how much air can enter the space at the top of the reservoir due to pressure/temperature changes, and how much water could condense out of that volume of air, but it ain't gonna be much. Any water that did enter the master cylinder is very unlikely to reach the small hole that leads to the 'works', which is quite a distance above the lowest point of the reservoir. If it can't enter the workings of the m/c then it can't go any further into the braking system.

I've just had a really close look at the inside of my master cylinder reservoir, and there's a bit of sediment in there, but no sign of any water. I can't remember exactly when I installed the braking system, 1988 or '89, but the fluid has been in there since then. This was after a full rebuild, with new seals in original cylinders and new Automec pipes. I did bleed a little fluid out from a caliper a couple of years ago, and it was as clear as when I first filled the system.

Another thought just struck me (no wonder I've got a headache) - if water did enter a steel vessel previously filled with SBF, would the water actually be able to wet the steel, or would there be a film of silicone preventing the water contacting the steel? Presumably the SBF would act as a surfactant? Must see if I can find something made of unprotected steel and set up an experiment.

Pete

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Hi Pete,

the water gets into a MC with DOT 5 the same way as it does with DOT4 - there are no other 'doorways'.

I acept that your system does not have water and never has had.  Have  you actually seen water in  a DOT 4 system. 

I change my DOT 4 on an ad hoc basis but it would probably be every 3 or 3 years on aggregate and i have never seen evidence of water.

 

Roger

 

 

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We've all obviously got too much time on our hands!!, I've just taken a fresh un-opened bottle of DOT5.1 and mixed a little of it with water, small amounts of H2O will completly dissolve to give a clear liquid, not until you get towards a 50:50 mix does it begin to go cloudy, so small amounts absorbed by the braking system would not be noticed visually, but get those brakes hot enough (coming down a mountain pass is a good test) and you'll get that un-nerving spongy feeling that tells you it's time to change the brake fluid.

Cheers Rob 

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36 minutes ago, RogerH said:

Have  you actually seen water in  a DOT 4 system. 

 

Never actually seen it Roger, because water will be absorbed by the DOT 4 so won't be visible. I've seen the evidence though - rust, and poor braking when hot.

Pete

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21 minutes ago, stillp said:

Never actually seen it Roger, because water will be absorbed by the DOT 4 so won't be visible. I've seen the evidence though - rust, and poor braking when hot.

Pete

hi Pete,

 your winning 40-15.  

 

Roger

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Pete, you are welcome

P1170936-b.JPG.c3c6d3543f26a31665113837fbd33f17.JPG

DOT5 is swimming up, is clear, gave all its pigment to the DOT4, keeps no dust or mud.

DOT4 is below, aged brown - honey, with some mud on the ground.

I'm convinced - between is water with all the mud and rubber, because I did too much of it in there on purpose.

I did mixing experimets some time ago (some of you might remember).

 

Edited by Z320
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The uninitiated need to know Dot5 is silicone fluid and Dot 5.1 is glycol based. They are NOT compatible despite the stupid nomenclature.

I've been using Dot 5 for at least 25 years with no issues and no siezed cylinders, in an all-new system. There are doubts about rubber components' resistance to changing from glycol to silicone.

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