mk1-forum.net

Following some fluid related issues at Blyton this year that affected both mine and a mates car we have got into a discussion on what's available and if its worth it. I can buy 1lt of standard off the shelf DOT4 for £3 or choose from a selection of "racing" type fluids for anywhere between £20-40 per lt. To complicate matter I have also purchased new masher cylinder that says its not homologated for use with racing fluids only standard DOT4.

The cars are road legal for use all year round, but can also sit idle for a period of a month or two without turning a wheels. Any fluid used cant be to corrosive and leave puddles on the floor each time the cars left alone.


So, any recommendations, experiences or horror stories? There must be some benefits of using a higher grade fluid, but are they worth it?


Thanks
Stephen

ive always just used normal dot4 in all my cars, including my racer

its all well and good buying fancy fluids, but as I always say 'what happens if you need a bottle on a sunday afternoon' - you can get dot4 from just about anywhere.

I use DOT5 (Silicone) in my Sprint as I don't want the paint work shagging by spilt brake fluid. I also put it in the Hoosley Warnit when I re did the brakes before Blyton. But having compared it to a couple of similar set ups, I reckon it does give a slightly "soggier" pedal than DOT 4 or 5.1

I am however happy to continue using it in road cars, track cars may however be a different matter.

The material difference between DOT4 & DOT 5.1 is minimal & the disclaimer in the master cylinder is, I suspect more to do with not wanting to warranty "racing" than the fluid itself.

never had any brake traumas as I like to make sure they are good to go all the time.

M

DOT 4 & DOT 5.1 are compatible, so you can mix them at will. Only DOT 5 isn't & must be used on its own.

A nice speedy response, like it, and saved me money too

I agree with the Sunday afternoon comment, I don't fancy driving around with £40 worth fluid for the just in case scenario.

I've sampled DOT5 in another car and didn't like it, but looking over my nicely peeled baulk head last night I found by self having second thoughts

I've always had DOT5 in my MiniMarcos, and have recently changed
the Mini over to it as well.

1) DOT5 Silicone IS expensive
2) As Mark says, it will not attack paint when it leaks or is spilled
3) Yes, it does have a small amount of compressibility
4) It is hygroscopic, ie it does not absorb water.

It is generally sold on point No. 4 for classic car owners that have
vehicles standing idle for longer periods of time and would not want
to be changing virtually unused fluid every two years... It would not
surprise me if it was not designed with some kind of military use in
mind, for low servicing requirement reasons...

Regarding point No. 3 - The compressibility issue is no worse than
having old/rubber type hoses in a system. When I changed all the
flexible hoses on the Marcos to Goodridge type ones, my "slightly
spongy pedal with DOT5" completely disappeared. After changing
pipes, I could not tell the difference between the pedal on my then
DOT4 car and the DOT5 car.

I have been thinking about the DOT numbering recently and think
that the person that decided that the updated DOT4 would be called
"DOT5.1" deserves a punch in the face...

Surely something as safety critical as brake fluid should have a
very clear numbering system? Maybe I'm too thick for this system,
but when I first saw DOT5.1 I ASSUMED that it was an updated DOT5
and nearly bought some to go in my existing silicone based setup.

THEY DO NOT MIX!

It's not "you should not mix them" - They actually do not mix.
When bleeding the dregs out of my old DOT4 system, I ended up
with a bottle that contained one of those fancy "layered cocktails".

WHY DID THEY NOT CALL THE "IMPROVED DOT4", DOT6 INSTEAD?
...and leave the silicone code of DOT5 alone to avoid confusion?

Ian

ianh1968 wrote: I ended up
with a bottle that contained one of those fancy "layered cocktails".

did you drink it though!

It was tempting, Rich - But then I remembered about those women
being poisoned by their leaking silicone boobies and decided to give
it a miss...

Ian

Over here DOT-4 is not as common as DOT-3. In the old days, none of the rubber used on British braking systems was compatible with DOT-3 and many owners ruined their brakes by topping up with the "wrong" fluid. Sometime in the mid- to late-1970s the rubber formula changed and was compatible with both DOT-3 and DOT-4. All the new brake parts I have bought over the last two decades have been marked as compatible with both fluids.

That being said, I use DOT-5 in my Mini and the wife's Triumph GT6. Both are weekend cars that can go for a long time between major maintenance. Like Ian, I have replaced the rubber hoses on both cars with braided items and the resulting brake pedal feels about the same as when using DOT-4. DOT-5 is typically colored purple and when it ages turns to a purple/brown making it easy to identify which makes accidental mixing less likely.

Last year Castrol react (minisport alloy 4 pots, Mintex carbon pads) - lost all brakes, hardly any pedal at all, This year Castrol react SRF (back to Std S calipers / mintex carbon pads)- solid hard pedal , no sponginess at all.

But i did flush out last years fluid totally with fresh react first, just incase there was a bit of fluid left in before i refilled with SRF

PAd

Racing fluid does have a higher boiling point.
It is also more hygroscopic -it absorbs more moisture than 'standard' DOT4 fluid. -I would not recommend it for a road car.
In racing, it is 'normal' to change the fluid for each race meeting....
-This can get expensive. -But we are talking about the high-end professional world.

But, if you are not changing it regularly, the increased moisture content will lower the boiling point below DOT4...

While silicone fluid does not absorb moisture, moisture can, and does, get in the system. What happens then is that it tends to collect at the lowest point. -This is often the caliper cylinder....
-It is not unusual to see a corroded corner in the cylinder when you remove the piston.

You can wash off DOT4 with lots of water.
While the risk is there for paint damage, I will continue to use only DOT4

I completely agree about the stupid naming of DOT5.1. -It was probably the same person the started using M10 threads instead of 3/8UNF for brake fittings...
( 3/8UNF will screw into M10, but is loose, so the union can fail under pressure....)

andy1071 wrote:While silicone fluid does not absorb moisture, moisture can, and does, get in the system.
What happens then is that it tends to collect at the lowest point. -This is often the caliper cylinder....
-It is not unusual to see a corroded corner in the cylinder when you remove the piston.

I've heard this said a number of times before and it did worry me a bit...

However, on my MiniMarcos, the car that has had DOT5 for the last 30 years,
I recently changed the 'S' calipers for a set of alloy ones...

There was absolutely no sign whatsoever of any rusting, in fact, when the
pistons were removed for inspection, all that was required was a quick
wipe with some paper to restore the bores to "good as new" conditions.

I would add that much of the time, the car lives in a very dry garage!

The calipers "went north" to another forum member who may well be
reading this. A second opinion as to their condition may be forthcoming.

andy1071 wrote:I completely agree about the stupid naming of DOT5.1.
-It was probably the same person the started using M10 threads instead of 3/8UNF for brake fittings...

... Thinking about it, it was probably a[n overpaid] committee...

Ian

I have just bled my clutch after blyton as during the day it started to go towards the floor. I had a lot of bubbles come out which would suggest to me it boiled during the day from the hot engine beneath it. It's normal dot 4 but is a bit old. Is that my issue with it being a bit old so if I had purged the system beforehand it may not have happened? What are your thoughts?

Old fluid will pick up moisture from the air which will lower its boiling point. If you were doing a lot of high-speed stops and/or using the brakes a lot so they didn't have a chance to cool you may have reached the point where the pedal became spongy and needed more travel to bring the car to a stop. I have heard different recommendations for how often fluid should be changed and I assume it really depends a lot on the humidity where you live. However, I try to change the brake fluid at least once every 3 years in my cars.

davefj: One of the fundamental problems with Mini master cylinder installation, is that they are vertical.

If the slave cylinder is in good condition, then I would suspect the master cylinder: it is possible for the m/cyl to 'gulp' air passed the secondary seal (this is more common as the seals age).
-You don't tend to see this with horizontal installations.

And of course, the clutch is operated over the full stroke of the cylinder.

Also, the clutch hydraulic system is more 'vertical' (with the slave cylinder close, under, the m/cyl).
-It's difficult to bleed the system properly if you don't have 'pressure-bleed' type kit.

What's worth doing is after bleeding the system, wedge the pedal down and leave it over-night.
-This will do 2 things: any air bubbles in the system will be compressed which will make them less likely to 'stick' to the wall of the pipes; and the air bubbles will float to the highest point in the system.
Then the next morning, release the pedal, the back-flow of the fluid will push the air back into the cylinder, and hopefully ( ) into the reservoir.

-You can use this principal for the brakes as well, but then the thing to do is remove the pads from one caliper (placing a thin spacer in to prevent the pistons popping out). Then wedge the pedal again, and next day push the pistons back into their bores.

-Both these methods are basically 'back-bleeding' the system. (-Some bleed kits do this anyway).

-I've always done this with motorcycle brake hydraulics. It can be quite amazing how much firmer the pedal/lever is after...

andy1071 wrote:One of the fundamental problems with Mini master cylinder installation, is that they are vertical.

... and with the argument about water settling at the bottom of the cylinder
in a DOT5 system with a vertical cylinder, this could be a "Good Thing"... ?

Instead of getting a rust line running from end-to-end, any formation would
start at the bottom, right by the seal. A vehicle which is either used regularly,
or otherwise has the pedal pressed down occasionally - will clean the
entire "tide-mark" off.

In a horizontal system, the seal will suffer all of its rust-wear at a single location
around its circumference, ie, at the bottom..

Would this be more of a problem, or less? Who knows? ...

I don't think that there is a right or a wrong answer here, these are just my thoughts...

andy1071 wrote:<SNIP>it is possible for the m/cyl to 'gulp' air passed the
secondary seal (this is more common as the seals age).

I had wondered about 'gulp' on my Mini - I've fitted a master cylinder
extender to hopefully remove the volume of spare air in the cylinder which
sits at the top of the reservoir.

Ian

andy1071 wrote:davefj: One of the fundamental problems with Mini master cylinder installation, is that they are vertical.

If the slave cylinder is in good condition, then I would suspect the master cylinder: it is possible for the m/cyl to 'gulp' air passed the secondary seal (this is more common as the seals age).
-You don't tend to see this with horizontal installations.

And of course, the clutch is operated over the full stroke of the cylinder.

Also, the clutch hydraulic system is more 'vertical' (with the slave cylinder close, under, the m/cyl).
-It's difficult to bleed the system properly if you don't have 'pressure-bleed' type kit.

What's worth doing is after bleeding the system, wedge the pedal down and leave it over-night.
-This will do 2 things: any air bubbles in the system will be compressed which will make them less likely to 'stick' to the wall of the pipes; and the air bubbles will float to the highest point in the system.
Then the next morning, release the pedal, the back-flow of the fluid will push the air back into the cylinder, and hopefully ( ) into the reservoir.

-You can use this principal for the brakes as well, but then the thing to do is remove the pads from one caliper (placing a thin spacer in to prevent the pistons popping out). Then wedge the pedal again, and next day push the pistons back into their bores.

-Both these methods are basically 'back-bleeding' the system. (-Some bleed kits do this anyway).

-I've always done this with motorcycle brake hydraulics. It can be quite amazing how much firmer the pedal/lever is after...

Seems like a lot of faffing around, why not use a vacuum pump and suck the fluid into the calipers/cylinders?

These days there are inexpensive kits for hydraulic bleeding. After using one I wouldn't do it any other way now.

smithyrc30: I do use an Eezi-bleed these days for bleeding the brakes and clutch.
I know some people like them, and other loathe them!
I've never had a problem with the 'normal' method of bleeding, but find that the 'faf' method works for difficult cases....

-Why is that 2 cars that are the same can have completely different characteristics/problems? ...magic?

rich@minispares.com wrote:

ianh1968 wrote: I ended up
with a bottle that contained one of those fancy "layered cocktails".

did you drink it though!

I like a little tipple of brake fluid but I do not have a drink problem, as I tell all my friends I can stop anytime I want..