Dot-4 or Silicone.

[RogerH]

Hi Ed,

that is interesting reading.

Most manufacturers specify DOT 3 as that is the base material.  DOT 4 has other additives (Borate for one) but is essentially the same.

DO NOT go near mineral oil brake fluid - it will kill oyur seals very quickly.  They have their own spec rubber.

Silicone fluid DOT5 is quite inert and gets on well with the DOT3/4 seals.  There are no specific seals for DOT5

 

Roger

 

R

[Tim D.]

Yes and one of the active ingredients for silicone fluid is related to the major lubricant on condoms :-)

not sure DOT4 would be good in this context. Would strip yer paint:-)

Tim

Edited August 25, 2021 by Tim D.

[Chris59]

Well, guys, just let a standard, modern brake seal in DOT5 for a couple of minutes, and you might be surprised by the result 

[Chris59]

2 hours ago, ed_h said:

The DOT specifications list the rubber compounds that brake fluids must be compatible with.  No reputable maker of rubber brake parts would use anything not on that list.

Many of the brake parts for these cars were designed at a time when the choices for brake fluid were mainly limited to glycol types and mineral oil types.  The DOT3 and later DOT4 specifications refered to glycol fluids.  Parts from this era designed for glycol fluid often came with markings like "Use only DOT3 brake fluid" (as opposed to mineral fluid). 

The design documents, tooling, and the rights to make and sell these parts have been bought and sold over the years, with most owners  not really interested in or capable of fiddling with the designs, so the markings remain. The outdated message also gets transferred to product packaging and literature.

Ed

 

Mmmmmh, you might be right about fluid reservoir caps, but I'm talking about paper documents who are include in hydraulic brake or clutch elements cardboard box.

I've rebuilt hundreds of brake and clutch hydraulics parts other the last 40 years, and won't, by experience, use silicone fluid on any of my cars without testing each rubber seal in silicone prior to fitment.

 

[ed_h]

2 hours ago, Chris59 said:

Well, guys, just let a standard, modern brake seal in DOT5 for a couple of minutes, and you might be surprised by the result 

I've seen this done several places.  A rubber brake seal from a reputable source will swell slightly in either silicone or glycol brake fluid by design.  The more interesting effect that I've read about, but not verified, is to remove the seal after a few hours in the glycol fluid, wipe it clean, and put it in silicone fluid (or vice versa).  Reportedly, the seal will swell further.  The offered explanation is that the swelling agents in the two fluids are different, and their effects compound.

Ed

[ed_h]

2 hours ago, Chris59 said:

 

Mmmmmh, you might be right about fluid reservoir caps, but I'm talking about paper documents who are include in hydraulic brake or clutch elements cardboard box.

 

Yes, use restrictions and recommendations would be part of the documentation package that passes to new owners, and likely dates back to the original design. Subsequent owners of the design are not necessarily technically savvy, so they just go with a proven design, along with the documentation it comes with.  Besides that, the outdated warnings may actually reduce their warranty risk.

Ed

[Tim D.]

8 minutes ago, ed_h said:

I've seen this done several places.  A rubber brake seal from a reputable source will swell slightly in either silicone or glycol brake fluid by design.  The more interesting effect that I've read about, but not verified, is to remove the seal after a few hours in the glycol fluid, wipe it clean, and put it in silicone fluid (or vice versa).  Reportedly, the seal will swell further.  The offered explanation is that the swelling agents in the two fluids are different, and their effects compound.

Ed

All thus makes sense. Not done the switch in a system without first rebuilding. 

[Z320]

Hi and sorry, it's me again with my story.

Indeed I don't use DOT4, it's DOT5.1 by accident, what happened?

I bought my TR4A 12 years ago with DOT5 in brake and clutch, sadly the DOT5 clutch master was leak very soon.

All the DOT5 of the master was on the carpet during winter, very annoying.

 I changed the seal and further used DOT5.

The brake master was leak next season, sorry for my trousers….

In my case no good reputation for DOT5?

I don't know when I used DOT5.1 by accident for this or another repair - I was a young little rabbit (German saying).

This was without any special cleaning, when I noticed the “mistake” I changed both systems to DOT5.1 - again without any special cleaning.

No DOT5 anymore, because I noticed the DOT5-problem of not fixing moisture.

During the time I changed the rear slaves from 0.70" (TR4A) to 0.75", the clutch is anyway completely different now, so all seals are new and have never seen DOT5.

Only the front calipers are still the same, have seen DOT?, DOT5 and DOT5.1 without any special attention and I don't touch them.

Advantage is: DOT5 is lighter than the others and swims on top of them, so most of it should be "bleeded" out meanwhile.

Ciao, Marco

[DaveR]

I have used Silicone fluid DOT5 for over 25 years with not problems with spongy brakes or bleeding or seals. It works well for me.

Dave

[Z320]

BTW above is DOT5 swimming on DOT4,

next is DOT5 on top of DOT 5.1 WITH water between

shaked....

abracadabra, after some hours, ups.....

Edited August 26, 2021 by Z320

[mhossack]

Thank you all, I was warned this could end up being a real can of worms.

But with this great forum and cross referencing old and new posts, I now know so much more, and what to check for like push rod length etc etc.

I will take my time and take care and hopefully end up with it working as it should again. 

Mick.

[ed_h]

7 hours ago, Z320 said:

abracadabra, after some hours, ups.....

Ive seen that odd effect demonstrated somewhere--Buckeye, maybe?

It appears that the purple dye migrates to the glycol fluid.

Nice pictures of the effect!

Ed

[Z320]

Hi Ed,

you have seen this here at one of my posts a few years ago.

YES, DOT5 can fix nothing, so all the purple pigments move to the DOT2, 3, 4, 5.1.

And this is why you have serious problems to paint a surface that ever was in contact with DOT5.

Annother advantage of silicone brake fluid...

[Andy Moltu]

17 hours ago, Z320 said:

Hi Ed,

you have seen this here at one of my posts a few years ago.

YES, DOT5 can fix nothing, so all the purple pigments move to the DOT2, 3, 4, 5.1.

And this is why you have serious problems to paint a surface that ever was in contact with DOT5.

Annother advantage of silicone brake fluid...

However you are somewhat less likely to end up repainting your engine bay because the DOT5 won't have stripped the paint in the first place.

The issue with silicones and painting is not just applicable to brake fluid. Many of the lubricant sprays contain slilicones as do the electrical sprays and so on.  Nothing new there - just requires appropriate preparation before painting unless the fish eye look is your wish!

[stuart]

12 minutes ago, Andy Moltu said:

However you are somewhat less likely to end up repainting your engine bay because the DOT5 won't have stripped the paint in the first place.

The issue with silicones and painting is not just applicable to brake fluid. Many of the lubricant sprays contain slilicones as do the electrical sprays and so on.  Nothing new there - just requires appropriate preparation before painting unless the fish eye look is your wish!

Well I for one do get concerned about spilt sillycon fluid, its not funny trying to repaint a car and chassis where its been used, its not that easy to get rid of. FWIW if it gets into your servo and gets ingested into the engine via the vacuum port it turns to sand under heat.

Stuart.

 

[Andy Moltu]

You cn always add it to the labour charges Stuart!

Neither of the brake fluid is perfect, they have pro's and con's.

Silicone fluid may turn to sand under heat but DOT4 burns and is the accellerant in many under bonnet fires.  A failsafe servo that doesn't allow the brake fluid to enter the vacuum side if the cylinder leaks might be good!

 

 

[Tim D.]

The silicone/sand in the engine issue is really interesting. Has anyone got any pictures of this sort of damage. My suspicion is that the amount that could leak before you noticed it is pretty small. More worry is that both types of fluid ruin sensors. More of a problem for modern cars than ours. 

Tim

[ed_h]

Remember the government program a few years ago where they would pay you to turn in your older car to have the engine destroyed? It was  to help get more polluting cars off the road.

The method they used was to pour sodium silicate into the oil sump.  Engine heat decomposed the silicate to silicon dioxide, same compound as sand.

Whether siloxanes similarly decompose to sand, I don't know, but it sounds reasonable.  I'm less sure about how likely it is to have leaked brake fluid actually sucked into the intake.

Ed

[Tim D.]

2 hours ago, ed_h said:

Remember the government program a few years ago where they would pay you to turn in your older car to have the engine destroyed? It was  to help get more polluting cars off the road.

The method they used was to pour sodium silicate into the oil sump.  Engine heat decomposed the silicate to silicon dioxide, same compound as sand.

Whether siloxanes similarly decompose to sand, I don't know, but it sounds reasonable.  I'm less sure about how likely it is to have leaked brake fluid actually sucked into the intake.

Ed

Interesting. Looking at the literature siloxanes don't decompose in the same way. Hence why they are used as high temperature sealants. Looks like they have to get pretty hot to decompose. 

[ed_h]

4 hours ago, Tim D. said:

Interesting. Looking at the literature siloxanes don't decompose in the same way. Hence why they are used as high temperature sealants. Looks like they have to get pretty hot to decompose. 

Looking at a cutaway of a TR6 brake booster, it also doesn't look like fluid ingestion into the intake would be very likely.  Vacuum is pulled from the fitting on top of the vacuum chamber.  It seems that the chamber would have to be nearly full of fluid for any of it to be sucked into the vacuum port.  As far as I know, the connection between the master cylinder and the booster is not fluid tight, so most of any leaked fluid should end up outside the assembly.

Ed

Edited August 27, 2021 by ed_h

[ntc]

It can get sucked in fact.

[ed_h]

4 hours ago, ntc said:

It can get sucked in fact.

You could be right.  Can you outline the mechanism by which that happens?

Ed

[stuart]

Sheer vacuum alone can suck it up and into the manifold pipe. Many years ago I had a Consul 375 and if you remember them they had vacuum wipers as well as servo for the brakes and a failed master cylinder provided an interesting stream of white smoke out the exhaust and screwed up the wipers.

Stuart.

[ed_h]

Interesting.  So is the servo chamber full of fluid when that happens?

Ed

Edited August 28, 2021 by ed_h

[Mike C]

From memory those early English Fords had the booster vacuum connection mounted below the master cylinder on the booster drum, TR6's have the vacuum connection mounted near the top- maybe one of the reasons for this was to prevent  brake fluid being sucked into the intake in the event of  gross leakage from the MC?