DOT 5

[JackIIA]

In thinking about brake and clutch fluid for my truck, I got to thinking about using DOT 5 instead of DOT 3/4. (Did a search on this subject, but didn't come up with a definitive focus on DOT 5 vs. DOT 3/4 in a NEW system.)

My reasoning would be the silicone in DOT 5 would provide a better barrier to water egress and the fact that DOT 3 & 4 actually absorb water and have lower boiling points.

Keeping in mind that this is a complete rebuild of the clutch and brake system, with literally NO reuse of piping, reservoirs, rubber boots, etc., is there any reason why the use of DOT 5 in a virgin system should NOT be pursued?

And also, is my thinking correct that:

1.) I'd get better protection from water resulting in no need to flush the fluid every few years;
2.) a higher boiling point; and
3.) better product access - that is, I'm guessing DOT 5 is the 'modern' brake fluid and DOT 3/4 will eventually go away except for speciality shops like RN. I'd hate to be on the road someday and unable to get some.

All this aside, if there are any basic reasons for not considering the switch, please advise. For instance, does DOT 5 attack rubber? I'd guess no, but I'd hate to mess up on this one.

Thanks

[SafeAirOne]

If I were redoing my complete brake system from stem to stern, I'd use DOT5 in a heartbeat. I can't think of a downside. Though there is plenty of debate on the topic, I don't think it's very likley that you'd get natural rubber seals in any modern replacement parts, but I could be wrong...

[greenmeanie]

I am at the same stage with my hydraulic system. The issue I have come up with from on line research is that which you point out - DOT5 is not hygroscopic. This does not, however, mean that water will not get in the system which is a bad thing. The water works its way down to the lowest part of the system which is usually the cast iron wheel cylinders and wreaks havoc with corrosion. The water bubble also has a lower boiling point leaving you with spongy brakes after repeated use.

It can be made to work but you will have to add a regular bleed of the wheel cylinders to remove water.

You can get the longer version of this from google.

[jgkmmoore]

If you have all new components, you are golden w/ Dot 5. You will NOT be bleeding every 3-6 months any more, not even every year. Prolly want to do it every 2 years, dependent on use. More often with little use.
Win,win situation. The more often you use it, the longer it lasts.:thumb-up:

[yorker]

I have used silicone brake fluid since 1997 it works fine. Go for it.

Gregor, the accumulation of water in a silicone system is apparently due to condensation- if I have never had a problem with it then I think you'll be a-ok in AZ. ;)

[JackIIA]

I had not thought of the water bubble in the wheel cylinders. A great point. That apparently is usually just from condensation though...and if that's the case I'm hearing that the amount of condensation is miniscule (per both Yorker and the web), and often gets reabsorbed into the air (from the sides and cap of the Master Cylinder) when the relative humidity drops (assuming truck isn't running...admittedly a big assumption).

Link below is from a site dealing with military trucks. Interestingly in this case, the original poster wants to go from DOT 5 to DOT 3/4, but same deal in terms of discussion.

The opinion there is that DOT 5 is the way to go. It allows trucks to sit idle for long periods without any negative impact, wheel cylinders do not rust, and water absorption is effectively nil in terms of real impact. One guy claims he's pulled wheel cylinders that are on the order of 16 years old with no apparent wear, rust, etc. Just another data point. On the con side, I guess DOT 5 is harder to get, not more 'modern' solution as I thought in terms of ready access. But as long as you're stateside this seems like a moot point.

Yorker - you are running DOT 5? No foaming or spongy issues I take it?? Anything weird about maintenance or other considerations? JGKMMoore - same deal I'm assuming??

http://www.steelsoldiers.com/deuce/45663-switching-dot-5-dot-4-brake-fluid.html

[JackIIA]

OK, admittedly on a bit of a tear on this one, but located best article I've found to date. Basically singing the praises of DOT 5, noting that it's particularly useful for older cars where some brake/clutch components may be increasingly scarce, and experiments done on older cars including 1970 chevelle (suggesting similar make-up of component materials).

http://71swinger.com/isilconebrakefluid.html

Lastly, Greenmeanie, Yorker, and JGK, here's a printout you can transfer to adhesive backing and put on your Master Cylinder or bulkhead! ;)

[yorker]

You'll find websites that hate DOT5 too. The stuff works though. I usually buy it army surplus a gallon at a time now. It usually costs me $30 for a gallon. The first gallon I bought was retail back in the 1990s and that was $70. I never used that whole gallon but it spilled that was why I had to buy more.

Make sure you have more with you- but that is true of just about any brake fluid, you should have some in your on road tool kit. I once had a flex line ripped off while offroading and had to use DOT3 to get home. If I hadn't left my Silicone brake fluid home I'd have been fine.

I am about to refurbish my brakes for the first time since 1997 I'll let you know how the brake cylinders look. I don't anticipate any corrosion in the aluminum brake cylinders though.

Silicone brake fluid and Automec or Fed Hill brake lines are the way to go.

That printout is funny! Godzilla....

[TedW]

What, if any, special steps need to be taken when switching from Castrol GTLMA to DOT 5?

I am considering the switch, as I need to change my clutch & brake fluids anyway.

[SafeAirOne]

I don't know exactly what compatibility issues there are between DOT4 and DOT5 fluids, but my PERSONAL OPINION is that the switch between fluids should only be made with a complete virgin system (exclusive of the lines themselves).

Your rubber seals in the MC and wheel cylinders and the rubber hoses have been soaking up the old brake fluid for years/decades.

[crankin]

I have a virgin system...and the new MC had in big black blocked letters "Use DOT 3 only!!!" I decided that if they felt the need to use three exclamation points, I should honor their request and use DOT3.

[yorker]

What, if any, special steps need to be taken when switching from Castrol GTLMA to DOT 5?


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

:thumb-up:

[jgkmmoore]

Thanks for that printout sticker 'JackIIa'.
Ted W- If your current brake components are in good to excellent condition, you simply flush and replace with Dot 5. That's all, but the two are definitely NOT compatible like syn oils. Once I went to Dot 5, I carry a small can of it in each car(under the hood). Dot 5 does not eat rubber. Just got a bad name from people that switched using worn out components (that failed from repositioning) instead of doing it right. Those same components would have failed if you flushed and changed the Dot 3/4 fluids as well.:nono:
Synthetic Dot 5 has worked impeccably for 3 of my 4 vehicles. Only one (the 109) had new components, the other two I flushed once (with Dot 5) and then replaced with Dot 5. Nary a problem. Closest to 'maintenance free' you can get with brake stuff.:thumb-up:
In telling you this, I still insist that you take responsibility for whatever you decide to do. READ the directions on the can. If you can't comply with ANY part of those directions, don't do it. Your safety is at stake.

Best Regards-Jeff

[jgkmmoore]

Further- I agree with Mark (SafeAirOne) to a degree, in that a virgin system is the best way to go if you need to replace everything anyway.
If, given the same opportunity, and the same trucks again, I would have changed only the 109 to synyhetic because of it's extended periods of non use. The other vehicles I change off more often, and the Dot 3 and 4 stuff works fine for long periods of time with daily drivers. In retrospect, Dot 5 was overkill for both the other trucks, but I often overkill anyway.
If it ain't broke, I fix it 'till it IS broke.:D
Jeff

[bobzinak]

Early land rover braking system rubber is/was natural rubber. and as such needed a vegtable oil base fliud, re castrol. most american makes used synthetic rubber and could withstand the petroleum based "american" brake fluid, the problem with the petroleum fluid was that it would soften the real rubber to the point it would be like bubble gum. if you see small pieces of black stuff in your fluid you might suspect at one time it has had the wrong fluid in it. this also applies to the fkexible brake lines. I have seen cases where the insde if the brake lines sluff off pieces of rubber that are to big to get through the hard lines, and end up acting like a one way valve. you step on the brakes and hold them for a long period of time and when you release the brakes the pieces will have floted to the top of the hose and stop the fluid from from flowing back to the master cyl. this is a rare occurance but you should be aware of. I cannot speak for the more modern replacement rubber parts, if from rover or other aftermarket seals. but if it says castrol use castrol use castrol. I live in a place where it gets very cold(65 below zero) the castrol would be so thick that the clutch and brakes acted as if I had STP for fluid. you had to wait four or five seconds for the clutch to re-engauge. bad news going up a hill and shifting. I switched to a silicone fluid so the rover would be drivable in extreme cold. one thing I have noticed with silicone fluid is that it holds air for along time if bubbles are introduced though the pouring of fluid into the master cyl. or if the fluid was agitated in any way in the can. I think thats why some say that the brakes felt "spongy or soft" with it. liquid does not compress...I have driven my series 111 sice 1972, it has been my only vehicle. I have learned alot about it in that time. and I have seen every part, inside and out. some parts more times than I would like. I have always fixed it myself. these are just my two cents, but just be aware of different types of rubber are used. I have bled my brakes lots of times and it is not a big deal on 88's, harder on 109's. Hope this helps bobzinak

[JackIIA]

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

:thumb-up:


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/

:thumb-up:


looks like they are up to b suffix now.

[JackIIA]

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

[109 Pretender]

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. :thumb-up:

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.