DOT 5

[JackIIA]

Read this:

http://www.tpub.com/content/automotiveaccessories/TB-43-0002-87/

Yorker, just to be sure I'm on the same page, it seems that the military DOT 5 you buy is marked "MIL-B-46176" or "MIL-B-46176A" as that in the attached photo. (What does the A stand for?) And that this is identical to the commercial DOT 5 stuff branded under names like North American DOT 5 brake fluid.

See below for image of what I'm talking about. And yup, you're right, 1 gal for $30! Assuming the fact that it was tinned when Clinton was President is OK.

As for air bubbles, I've read suggestions to pour it down a screw driver blade to avoid such problems. But I'd think it would work equally well with a transmission fluid funnel and a very slow pour.


Jack

[yorker]

The stuff I had was bottled in the early 80s and was fine, I still have a gallon somewhere. I swapped my RRC over to it too, more or less following the method outlined in TB-43-0002-87. I bought mine from Fred at Adirondack Dodge Parts http://www.adirondackdodgeparts.com/ but I think he told me I bought his last 2 gallons.


I am not sure what the A stands for, the contract data is probably on the net somewhere though.

[yorker]

And that this is identical to the commercial DOT 5 stuff branded under names like North American DOT 5 brake fluid.

6.1 Intended use. The brake fluid covered by this specification is military unique due to
the requirement that it perform at a minimum ambient temperature of –55°C, whereas commercial
silicone-based brake fluids are rated at a minimum ambient temperature of –40°C. It is intended
for use as an operational fluid and preservative fluid in automotive hydraulic brake systems at
ambient temperatures ranging from 55°C to

-55°C and fluid temperatures ranging from 205°C

to -55°C.

http://www.everyspec.com/MIL-PRF/MIL-PRF+(030000+-+79999)/MIL-PRF-46176B_6492/

looks like they are up to b suffix now.

[JackIIA]

Thank you Yorker. You clearly have excellent eyesight. Sorry for the font.

[109 Pretender]

DOT 5

Folks,
I encourage everyone to try DOT 5 silicone fluid at least once... when you get tired of the spongy pedal, you'll go back to Castrol LMA - I hope!

The silicone fluid is great in a race car where you change the fluid every 2 races or so - unless you're top tier then your mechs do it between heats.

Silicone brake fluid doesn't attract water true enough - BUT it absorbs AIR like nobodys business and your brake fluid cap has a HOLE in it to equalize to ambient baro. Otherwise a vacuum would be imparted in the collection well everytime you applied the brakes. You cannot prevent the silicone fluid from absorbing air and over time your pedal will get progresively spongier. It's also difficult to bleed all the air bubbles out.

Read up on the Internet before you try this...

Cheers!

[JackIIA]

Folks,
I encourage everyone to try DOT 5 silicone fluid at least once... when you get tired of the spongy pedal, you'll go back to Castrol LMA - I hope!
.......Read up on the Internet before you try this...

Cheers!

I agree with your points. Just an important disclaimer that it's not as easy as just switching back and forth between the two. I get the sense you're kidding about it in such a casual way. But wouldn't want anyone to think they'd give it a try by just draining and refilling. That's not a good idea based on my research.

If you're going to make the switch, it's a major undertaking to be sure it's done right. The U.S. Army hasn't been so thorough (more of the drain and refill approach from what Yorker posted), but I wouldn't recommend it.

[109 Pretender]

Point well taken Jack!!
Yes, you should only use the DOT 5 silicone fluid after a complete rebuild - I mean a complete breakdown with ALL seals replaced and ALL lines purged with air and/or pumping replacement fluid as a flushing agent first. DOT 5 Silicone is incompatable with all other types of brake fluid.

It just isn't worth the headache, expense and ultimately the poor performance for a street vehicle. Much better to use Castrol GTX LMA, Lockheed, or Duckham's brake fluid which is compatable with the natural rubber content of British seals. (I really think that modern British stuff today uses the syn. neoprene/whatever type synthetic that all the rest of the world has been using for years).
Interestingly, the Brit's used more natural rubber in the old days owing to their long association with a "former colony" - India. When WW2 broke out,we (USA) developed synthetics (ie neoprene and others) because of the instability and worry about supply shortages.
If folks would use the correct fluid, their British rubber seals will last as long as any other brake seal - at least that's been my experience.

I believe that there is some new DOT 5 brake fluid available today that isn't silicone based because the racers hate the stuff too! Among other parameters, DOT 5 has to do with the fluids ability to not breakdown under specific high temps and it's ability to resist absorbing moisture. Silicone was just the industries 1st attempt at making a better product, but as mentioned, it brings it's own set of problems.

Don't forget we're talking series Rovers here - drum brakes, top speed about 55mph on ave. etc. Spend your money on having a 100% correct brake system by replacing worn parts with new and using a quality fluid that gets changed every 2 or 3 years.

Cheers!

[yorker]

Silicone brake fluid doesn't attract water true enough - BUT it absorbs AIR like nobodys business and your brake fluid cap has a HOLE in it to equalize to ambient baro. Otherwise a vacuum would be imparted in the collection well everytime you applied the brakes. You cannot prevent the silicone fluid from absorbing air and over time your pedal will get progresively spongier. It's also difficult to bleed all the air bubbles out.

Silicone brake fluid does not "absorb" air- it can hold air in suspension when you pour it. If you properly fill and bleed the brakes in a Land Rover silicone brake fluid you won't have any issues with spongy brakes. The inherent compressibility of silicone is less than 2% at the temps that our brake systems operate.

Silicone brake fluid isn't compatible with other brake fluids- but by that it means that they are different densities and will settle separate, even a system contaminated with one or the other will still function as designed- that is why the process the military uses for changing types of fluid is simple flushing.

Another popular misconception is that silicone brake fluid is not compatible with natural rubber seals. The PDF attached earlier in this thread dispels that. It has been formulated to be compatible with all brake seals since the 1970's.

[109 Pretender]

Yes, silicone has an affinity to hold air bubbles -(google is your friend here - ck it out) and personal experience backs that up 100%. Maybe absorb was a poor word choice...

Silicone will never make a homogenous mixture with any other type brake fluid - EVER.

Silicone has zero problems with ANY type rubber seal - only US spec or non-British spec fluids affect the seals adversly.

*It does have a very high tolerance to temps. - but then we are talking about one of the slowest vehicles legal to drive on the road aren't we?

The military does it wrong. Shame on them... I wouldn't recommend their method at all.