As Peter said. Fitted with Laycock de Normanville overdrive

 

I think its highly likely my carbs need a clean and service. I'll have her running right in no time.

 

Mysteriously missing brake fluid with no external leaks, is a sure sign that you have an internal leak on your remote brake servo.
The piston has a seal that leaks into the large vacuum chamber, if left long enough, it will fill up to the point where the brake fluid will get sucked into the engine.
Guys running silicon brake fluid have to be especially careful not to let this happen.
Once the silicon fluid hits the engine, the temperatures in the combustion chamber get hot enough to turn the brake fluid into sand that will ruin the engine.

 

As an oilco man I don't recommend silicone brake fluid because seal manufacturers seldom run seal swell tests on the stuff so compatibility with elastomers in the system is seldom known or published. Silicone brake fluid can do awful damage to some elastomers. (when last did you see a brake rubber stating suitable for silicone fluid)? So I recommend DOT 4 or DOT 4+ and changing every 2 to 3 years as glycol based brake fluids are hygroscopic. (absorb water). No OEM I know of uses silicone brake fluid in their braking systems. On top of that a very small quantity of silicone ingested by your engine will kill/poison your Lambda/O2 sensors. Don't even use silicone spray under the bonnet of your modern cars.

Regarding forming sand if silicone brake fluid is combusted in your engine. This is somewhat misunderstood. What combusting it forms is silica fume, a very small (1micron or smaller) particle of SiO2. SiO2 is quartz. Your airfilter is unlikely to capture particles this size but we don't want silicon dioxide in our engines. If you are losing brake fluid with no visible leaks it's likely going out the exhaust & some smoke should be visible. Replace or refurbish your brake Servo/booster soonest.

BTW we sell both (The whole DOT range of fluids in fact) so it's no skin off of our noses & I am retired now so don't punt any specific oilco products.

 

Well, I've had the new seals on my brake servo soaking in silicon brake fluid for many months, so long so I forgot it _ they're still OK.
I had Introcar, the only ones, come right out and say that all their seals are compatible with anything, including silicon brake fluid, an that's what is in my Bentley now.
I'll never go back to hygroscopic brake fluid.

 

You must do as you wish. It's your car. I'm just giving a valid warning. Alan Wiedie gave his experience with "dissolved" seals in his master cylinder IIRC. Rubbers/elastomers are a bit of a black art. We provide the aromatic extract that makes up a large proportion of the finished product. Tests are crude & batch variation large.

There is a reason OEMs don't use silicone brake fluid & it's not to drive your service bill up every 3 years.

 

I can second what Glyn wrote about rubber being a black art. I had some indirect involvement in the development by the old Dunlop company of hose for a difficult oil company application. Considering what they achieved, I think those people were brilliant. Still, it appeared to me to be very much accidental engineering (or chemistry). Unfortunately, being British industry, there were takeovers, re-organizations and optimization of shareholder value in the process of which everything was lost and no one was ever able to re-produce the material. Following all that, my view on rubber that is in contact with anything with possibly demanding fluids, especially if subject to high pressure, is go totally conservative, use well established and tested products and don't take any risks.

 

I've just had a glance at another current thread on the S-type where there's discussion of the brake servo. It reminded me that the seal around the piston in the air/vacuum cylinder cylinder should be lubricated with brake fluid and a few drops should be poured into the remote type of filter as a service job. In fact, the seal in my servo dried out once and was easily repaired by a few drops of fluid. That fluid will certainly end up going through the engine.

 

Yes Peter ~ it comes as no surprise that you were unable to replicate that rubber "blend". It is an imprecise process/science. What you term "accidental engineering (or chemistry)". A black art.

In a braking system the fluid is required to lubricate the seals & provide a very small & controlled degree of swell. With Glycol based fluids we have a clear & precise, repeatable degree of swell that we fully understand & control. With Silicone fluids it's all over the place & unpredictable.

 

I managed to investigate the vacuum leak today, under the wing I found a hose hanging loose, blocked the end with my finger, the hissing stops and the car runs very sweet! So a temp job blocking off that hose and I'll be able to attempt a drive home. Then I'll be able to get it in the workshop.

One step at a time.

 

I think "new-old-stock" seals are the biggest problem with silicon fluid.
I can easily find the stuff all over, somebody must be using it, don't know if the military still is _ that was quite a while ago when I heard that, and now I hear that they're not so much anymore.

Apparently there is some new alcohol base fluid that's available that will not be so sensitive to absorbing water, I may consider that.

Peter said:
"few drops should be poured into the remote type of filter as a service job"

Is that the air breather filter in the engine bay that leads to the air valve on the brake booster, if it is, how is pouring a few drops of fluid in there going to do anything ?

And who is Alan Wiedie, do you have a link to that, nothing comes up on any search ?
If he had some seals sitting on a shelf for 40 years, then yes, they are probably a natural rubber based product that will only survive with an alcohol base brake fluid, they would have been easily turned to mush with a silicon based product.
If they were that old, they should have been chucked in the garbage.
Any manufacturer still using rubber in their seals today is highly unlikely, it's too expensive and it doesn't last.

Glyn, as knowledgeable as you are at many things, I some times get the impression that you may not be, at least when it comes to brake seals and their relation to silicon brake fluid.
I'm not saying that I do, so I find out, with lots of reading, and if I still can't get an answer, I find out for myself with my own tests, I don't pretend to know what the seals are made off, but I didn't fall of a vegetable truck yesterday.

When I read statements like this:

"it comes as no surprise that you were unable to replicate that rubber "blend". It is an imprecise process/science"
and
"Rubbers/elastomers are a bit of a black art"

Seals that were made from natural organic rubber, I can see that as a very imprecise coming from a tree, but I can't see man-made seals as being black magic and this whole guessing game going on to what will work and what won't.
I watched this special on TV about how they made tires, there was no guessing going on, no black magic; there were complex formulas where they could manipulate them to get exactly what a manufacturer wanted, I would assume that brake seals would receive the same attention.

 

I forgot earlier, when tinkering with the car today I noticed a vertical rod next to the radiator that seems to operate a drain tap at the bottom of the rad. Nice little feature.

 

Yes, that is very useful, all that was missing was a proper end to attach a hose to the drain tap so sticky messy coolant doesn't get all over the under-carriage.
The British come up with some very good ideas and don't follow through with others.

 

If you look on the side of the block at the back under the exhaust manifold you will find a second little tap for emptying the block of water.

 

Let me assure you that the tyre companies know full well what a black art it is. It's exactly them that we provide the majority of our aromatic extracts to. Michelin, that spends more than any other tyre company on research would & have agreed with me. I'm repeating their top technical peoples comments that I've learned from. Same comments from, Bridgestone, Good Year etc. etc. I've watched plenty of rubber being compounded & tested in my job over the years.

You can't manipulate them to get exactly what you want. That is the very point. Your TV show was misleading if it implied that. Suggest you go and talk to the head technical honcho of a Tyre company that is prepared to be honest with you.

The military with redundancy on most vehicles had endless issues. We obviously can't discuss much about the military. I don't feel like getting locked up next time I step into the US or disgracing my heritage company.

Observe Peter's wise counsel. And there is a reason that none of the car companies/OEMs use silicone fluid. Care to explain that?

Regarding Alan Wiedie. He is a member on many forums. Sorry I got them muddled. He passed the comment on the Register.

quote " Thanks, Nigel, I am definitely going to look into this possibility. As part of my engine compartment rebuild a few years ago, I had the master cylinder re-sleeved with brass and of course put in new seals. Doesn't mean they might not be defective. On a related note, similar to Glyn's comment, I had a problem with clutch operation on my 66 E type in that I had no pedal and then I did. The system was filled with silicone. When I dismantled the master cylinder, I discovered that the seals had just about dissolved," unquote.

BTW ~ what percentage swell are you getting on the seals in your home experiment with silicone fluid.

 

OEM doesn't use it because it's too expensive _ bean counters are always busy; with that said, if I was going to spend upwards of 8,000,000.00 on a new Bugatti, I would want them to design the system for silicon fluid.
I would never buy one of those of course, it's just not practical, I think there are like 15 oil drain plugs in the thing, and for all that money, it has the crappy plastic cartridge type oil filter.

I've never had bad luck with silicon, I even had put it in my Mazda B2200 in the clutch, it's still in there many years later and nice and clean _ the old fluid always got black after a while with new master and slave cylinder.
The truck is a garden truck and sits outside in the weather all year round.

None of my seals have expanded with silicon (so little so, I don't notice), and in all cases, they didn't have too, the seals were nice and snug, they didn't have to swell.
That has been my experience with it.

On the other side, I have had nothing but bad luck with hygroscopic fluid making a huge mess of aluminum cylinders; this white pasty oxide plugs everything up and it starts to snow-ball.
It leaks and destroys everything because it attracts water and everything rusts.
I have a tiny bit of seepage lets say on a healthy master cylinder on my Bentley, the film of fluid attracts water inside the cylinder, then a very small amount of rust starts _ and then it's off to the races and pretty soon it turns into a huge mess where it's gone way beyond just changing the fluid.
This all happens with in two years.
The same with the Jag, only it's worse because the cylinders are pointing down, I don't get leakage with silicon fluid.

I refuse to put something in that requires it to be changed every two years, and even if I decide too, I'm sick and tired of cleaning up after it and being careful of getting on freshly painted surfaces.
I think it may be where I live on the South West Canadian Coast, there is so much moisture in the air, it's a death sentence with old cars and alcohol based fluids.

I have no idea why everyone else seems to have problems with silicon fluid.

I still have no idea what Pete is talking about and where is putting these few drops of fluid.
Putting a bit of fluid down the air purge hose where the filter is, makes no sense to me.
That's not going to lubricate anything, it's going to sit on the diaphragm on the air valve isn't it ?

 

Let me give you some typical seal swell results from our labs of known, compatible & same batch reference seals. This done in a properly controlled environment.

Swell percentage:

1. DOT 4+ brake fluid A ~ 0.25%
2. DOT 4+ brake fluid B ~ 0.38%
3. DOT 4+ brake fluid containing a synthetic component ~ 0.75%
4. Silicone brake fluid ~ 2.5%

As I said you must do as you wish. Lack of OEM use has nothing to do with price. They can have silicone fluid from any of us suppliers at the same price as DOT 4+. You only get ripped off by retailers. Silicone is cheap.

Use glycol fluid & change every 3 years & you will have zero issues even with the sensitive ABS unit & pump. Million Km Benz Taxis have no brake issues on DOT4+

 

Just think of all that brake fluid they're selling having to change it every 2 or 3 years.

You'll never convince me otherwise.

 

That's fine. Some are set in their ways. I'm just offering prudent advice as is Peter who seems a fine engineer with a long oilco background. Albeit today in the upstream.

 

The 'few drops of fluid' go into the remote filter. It has (or is supposed to have) two effects. One is to help the filter to capture dust. The other is to be slowly sucked down into the servo and lubricate the rubber seal of the vacuum/air piston. For the latter function, I can guarantee that it works. If the brakes on all wheels stay locked on after releasing the pedal, it's pretty certain the piston is sticking and needs those few drops of fluid (or even a teaspoonful poured straight down the pipe).