DOT 5 Brake Fluid

[gary442]

Am planning on flushing my brake system this weekend ( 93 K100RS w/ABS) and plan on converting over to DOT 5....any folks here done this ? I assume it is compatable.....

[gary442]

May have answered my own question....just found this analysis on the AAA web site...




DOT 3 and DOT 4 fluids are called polyglycol fluids for the principal compounds used in their manufacture. DOT 5 fluids are all silicone based because only silicone fluid can meet the DOT 5 specs. No vehicle manufacturer, however, recommends DOT 5 fluid for use in its brake systems. Although all three fluid grades are compatible, they don't really combine if mixed together in a system. Therefore, the best general rule is to use the fluid type recommended by the carmaker, and not to mix fluid types in a system.

CAUTION: Do not use silicone DOT 5 fluid in an antilock brake system. Operating efficiency will be reduced.


Silicone DOT 5 fluid has some other characteristics that you should beware of. Silicone fluid compresses slightly under pressure, which can cause a slightly spongy brake pedal feel. Silicone fluid also attracts air more than polyglycol fluid does, which makes brake bleeding harder. It also tends to vaporize slightly just below its boiling point; and it will aerate from prolonged vibration. All of these factors mean that DOT 5 silicone fluid should never be used in an antilock brake system

[Jeff]

Don't do it! Stay with the DOT 4 fluid and do the recomended changes. DOT 5 will produce a different some what spongy feel at the lever when compared to a fresh change of DOT 4 fluid. Also the BMW brake system ( Brembo) does not recomend using DOT 5.

[deilenberger]

Originally posted by Jeff
Don't do it! Stay with the DOT 4 fluid and do the recomended changes. DOT 5 will produce a different some what spongy feel at the lever when compared to a fresh change of DOT 4 fluid. Also the BMW brake system ( Brembo) does not recomend using DOT 5.

I'd also suggest staying with a 'standard' brake fluid. Besides the problem with bleeding DOT5 (air doesn't flow in it like it does in standard fluid) - you'll never get the remaining DOT 4 completely out of the system.

I'm sure you'll hear from a few people who have done it and love the DOT5 - but I tend to be conservative on things like brakes - I want them to work as designed.

There is another standard 5.1 fluid - which is an organic fluid that is compatible with DOT4 - and has a higher boiling point (which is a factor of how much water can be absorbed) - but I've had good luck with ATE fluid - changed at least yearly. If you do regular fluid 'flushes' (where you're flushing the fluid through the system without ever introducing air) - your brake components will last a very long time without giving any trouble.

Best,

[dlearl476]

Am planning on flushing my brake system this weekend ( 93 K100RS w/ABS) and plan on converting over to DOT 5....any folks here done this ? I assume it is compatable.....


DOT-5 brake fluid in Brembo brake systems: TSW Vehicle Concepts - submitted by Mark Kaczmarczyk

IMPORTANT: All brembo braking products use natural-rubber base seals, and therefore are INCOMPATIBLE with DOT-5 SILICONE-based brake fluids.

DOT-5 SILICONE-based fluids react with natural-rubber seals to swell them WHICH CAN CAUSE SEVERE PISTON RETRACTION PROBLEMS. There is no cure for problems caused by DOT- 5 use other than complete seals replacement - USE ONLY DOT-3/4 NON-SILICONE TYPE FLUIDS in your brembo components.

(Yes, we know the cap on the rectangular master cylinders says DOT 3 - 5 Fluids - BUT PLEASE NOTE: Silicone DOT- 5 fluids are NOT generally in use in Europe, but Glycol-based DOT-5.1 fluids ARE. Hence, the DOT-5 cap designation)

For best braking performance, they recommend changing brake fluid twice a year. If the machine is to be stored in a damp environment (over the winter, say), they recommend installing fresh fluid before and after the storage period. At minimum service levels, glycol brake fluids MUST be completely changed at intervals not to exceed a period of 18 months.

There's a reason BMW gives you an owner's manual. I'd suggest reading it.

[Kayseventyfive]

I've had good luck with ATE fluid - changed at least yearly. If you do regular fluid 'flushes' (where you're flushing the fluid through the system without ever introducing air) - your brake components will last a very long time without giving any trouble.



Another advantage of ATE is it comes in two colors. I alternate colors every year, and the color change tells me the bleeding is complete. This is more of a big deal on a car or motor home, but is handy for bikes, too.

Yet another advantage is ATE comes in metal cans, which do not allow moisture to penetrate and be absorbed during storage. I dump marbles into a partial can to exclude air before storing. My stored fluid always tests dry that way.

[dlearl476]

Another advantage of ATE is it comes in two colors. I alternate colors every year, and the color change tells me the bleeding is complete. This is more of a big deal on a car or motor home, but is handy for bikes, too.


Yes, that's a pretty cool feature, and Porsche recommends that, but the Castrol I use turns brown as it absorbs water, so I have the same feature as well as an indicator when to change fluid (when it gets dark in the resevoir). I know when clear/light yellow fluid comes out, all the old (brown) fluid is gone.

[rinty]

Gary:

There were a number of lengthy technical articles on this topic published in the MOA News a number of years ago. The last one, which was written by a hydraulic fluid engineer, warned against combining DOT 5 with anything else, and raised other serious technical concerns.

I've had good luck with DOT 3 in my vehicles, and I like it's hydrophilic properties. I confess that I ran a BMW 320i for 10 years without a flush, with absolutely no ill effects (my home city is 3,500 above sea level, and is pretty dry). The fluid looked pretty grungy when I eventually changed it. :doh

Rinty

[Kayseventyfive]

the Castrol I use turns brown as it absorbs water, so I have the same feature as well as an indicator when to change fluid (when it gets dark in the resevoir). I know when clear/light yellow fluid comes out, all the old (brown) fluid is gone.

I wonder if there is a color chart out there.

[PGlaves]

May have answered my own question....just found this analysis on the AAA web site...




DOT 3 and DOT 4 fluids are called polyglycol fluids for the principal compounds used in their manufacture. DOT 5 fluids are all silicone based because only silicone fluid can meet the DOT 5 specs. No vehicle manufacturer, however, recommends DOT 5 fluid for use in its brake systems. Although all three fluid grades are compatible, they don't really combine if mixed together in a system. Therefore, the best general rule is to use the fluid type recommended by the carmaker, and not to mix fluid types in a system.

CAUTION: Do not use silicone DOT 5 fluid in an antilock brake system. Operating efficiency will be reduced.


Silicone DOT 5 fluid has some other characteristics that you should beware of. Silicone fluid compresses slightly under pressure, which can cause a slightly spongy brake pedal feel. Silicone fluid also attracts air more than polyglycol fluid does, which makes brake bleeding harder. It also tends to vaporize slightly just below its boiling point; and it will aerate from prolonged vibration. All of these factors mean that DOT 5 silicone fluid should never be used in an antilock brake system

This one is so simple it is a total "no brainer." BMW and the manufacturers of BMW brake components say do not use DOT 5 brake fluid. They say that the rubber seals and other rubber components (including the lines on many models) are not compatible with DOT 5. They say that the rubber parts will swell. They say that the brake system can fail to operate properly. They say that the system will be ruined or at least will require a total rebuild and replacement of all the rubber parts.

I know a rider who has fought a spongy brake system, stuck calipers, dragging pads, overheated calipers and scored disks for years - but who insists DOT 5 is just fine.

[vanzen]

OK you've got about everyone here saying DON'T USE DOT 5.

BMW says DON'T USE IT.

and just to add to that mix, BREMBO says: DON'T USE IT – incompatible with / will deteriorate seals used by them.

dot 3-4 brake systems whose materials ARE compatible with dot 5 CAN be flushed and the switch made to dot5. not a big deal. thorough and complete are the operative terms when flushing to make the change.

NEVER add dot 5 to a system with glycol based fluid – the mix creates a nasty "gel" that WON'T even OPERATE the brakes

[HANSRUYS]

The only reason DOT 5 emerged on the motorcycle market is in the early 70's
when Harley Davidson started installing disk brakes on the FLH and their Superglide models
they "brilliantly" placed the rear master cylinder between the engine and transmission
(right next to the exhaust pipe)
the police motors were the first to complain of brake fading under extreme temperature conditions,
seems the brake fluid was absorbing too much heat and boiling,
rather than redesigning this obvious "flaw" they opted for DOT 5
because it has a higher "boiling point" and that is the only advantage it has,
just because it has a higher "number" does not make it a better product.