Are there any benefits to using DOT 5.1 brake fluid instead of DOT 4. Any help would be useful


Regards,

Arnie

Interesting article:

http://www.vtr.org/maintain/brake-fluids.html

I use silicone (DOT 5) because it does not absorb moisture but DOT 5.1 has the best performance

HTH Mark

Mark,

Thanks for the info. Good article.

Regards,

Arnie

Warning here - don't assume you can use dot5 as a replacement. Volvo's in particular will lose firm pedal and braking becomes poor - not sure of the exact reasons but Volvo do highlight this in their documentation and was born out when I rebuild a brake system on one and thought it opportune to use dot5.
Could not get the brakes to work effectively and ended up going back to dot4.
Check with your manufacturer first!

[Edited on 17/9/04 by Terrapin_racing]

I tried DOT5, mostly due to the benign nature of silicone brake fluid - it doesn't react with anything, it's non-poisonous and non-flammable.

Trouble is, the brake pedal felt very spongy no matter how many times I bled the system - the ability of this stuff to hold air in microscopic bubbles is well documented.

Could never get happy with it, and ended up going to conventional DOT4 - and changing over is a real bar-steward as DOT4 and DOT5 combined can form a goo that gets into the works. It took a LOT of DOT4 to flush the DOT5 out.

I now have a good firm brake pedal.

Also, never use DOT5 with ABS systems - the sponginess stops the system working properly.

Finally, according to some US websites, it may get difficult to get hold of DOT5 fluid soon as the only major customer is the US military and the US Post, and they're abandoning it.

Shame, as it has some good features and conventional fluids have a lot of bad ones.

rgds,

David

With regard to silicone fluid, I have used this in several cars - Spitfires, a Herald, 2 Scimitars and my Indy.

I had a host of Minis MGs and Triumphs years ago and they all had a large rusty patch around the brake M/C mounting due to leaking/spilt fluid. Silicone fluid was the answer!

When changing over, I have always used new or reconditioned parts throughout - there is no point in using it if there is already old brake fluid in the system and I have read that seals that thave been exposed to regular brake fluid don't like changing to silicone.

I now have a pretty firm pedal in my Indy, but it required bleeding twice, the second time after the fluid had settled for a day.
I figure that as my car is not used every day, and stands in a garage which cannot be guaranteed to be totally dry then for me the silicone fluid gives a better chance of the system lasting longer.

I am now worried that I won't be able to get hold of it any more

[Edited on 17/9/04 by mookaloid]

None of you have mentioned DOT5.1. Anyone used it? Would seem to be the best option??

Cheers,
James

so you didnt read the first post in the thread james

quote:

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Originally posted by James
None of you have mentioned DOT5.1. Anyone used it? Would seem to be the best option??

Cheers,
James

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I think I read somewhere that 5.1 is no better than DOT 4 ultra and isn't a true DOT standard or something.

Note, Volvo brake system was fully replaced and repetitively bled sover a week. Still not happy with a pedal like a springboard so went back to dot4. Been OK for last 2 years now.

DOT 5 is silicone-based and really not used that much in modern braking systems. It was introduced as it had higher wet and dry boiling points than DOT 4 (synthetic) and also it didn't eat paint, and as it wasn't hygroscopic it would last longer than DOT 4.

However, due to it's nature, the fluid is more compressible than the synthetic DOT 4 and to make it worse, it is also very difficult to bleed all the air out of the system as you tend to get entrained air quite easily in the fluid. Also, as it doesn't mix at all with water, any moisture in the system tends to pool together and collect, which can cause rust. Also, it is totally incompatible with synthetic fluid as stated above and so ideally the brake lines should be very thoroughly cleaned and seals renewed.

Two products exceed the requirements of DOT 4.

Super DOT 4 meets exactly the same minimum specifications with regard to wet and dry boiling points as DOT 5 but as it is synthetic (and by synthetic i mean Glycol Ether & Borate Ester based) it is fuly compatible with all DOT 3, 4 and 5.1 products.

DOT 5.1 meets the same minimum boiling point specifications again, only has a different viscosity measurement at low temperature in line with some manufacturers requirements for their ABS system. In reality, Super DOT 4 is suitable for pretty much all ABS systems though.

So...

In answer to your question, either DOT 5.1 or Super DOT 4 offer advantages over standard DOT 4 in terms of wet and dry boiling point and they are all compatible.

Having said that, I would think that most manufacturers actually exceed the minimum standard by a fair bit with the DOT 4 fluid which would reduce the advantage a Super DOT 4 / DOT5.1 gives.

Edit - DOT 5 will be fairly difficult to find. Very few manufacturers use a silicone-based fluid now, in fact i can only think of Harley Davidson off the top of my head.


[Edited on 17/9/04 by skinny]

Don't know about anyone else, but this has given me a headache

keep it simple, you won't get anything better than Super DOT 4.

(unless you want to go for a racing brake fluid)