Brake Fluid DOT 5.1 Synthetic

[bulldog5046]

my cars booked into the garage for having a wheel bearing changed and told them to do the brake fluid for me in preperation for the MOT.

i asked them to put the above in but they refused saying they recently put it into a Jag and the brakes went awful, but when they changed it to DOT4 it was fine.

anyone have any ideas why? could this be that pedal travels further as i have heard? or somthing more serious?

Cheers,
Ry

 

[cheekycento21]

Ive never held of anything like that.
my boss used it in his supra and he said you noticed the diff when he was on the track.
when he used dot 4 it was bubbling but 5.1 has more of a higher boiling temp.

We sometime use it in a lot of jap car. ie fto's, gto's.

 

[Liam]

They'll put in what's specified where safety is concerned, Punto Gt's are Dot 4, it'll be fine.

Liam

 

[jug]

STOP!!

never mix dot4 and dot5, it creates a silicone gel which means very crap braking a whole load of trouble cleaning the braking system out. dont mix it with any glycol based fluids.

if you really want to use dot5 you will need to fully flush your braking system out with something that is safe to mix with both dot4 and dot5 first.

there is also seal compatability to consider. dot5 can make rubber swell.

some people say you shouldn't use dot5 if you have ABS. i think thats a myth and i've never seen a justifyable reason to support this.

personally i've used dot5 on a few cars that were designed for dot4 only, and never had a problem.

 

[pinin__prestatyn]

Sounds like a crap garage, "recently put it into a Jag and the brakes went awful, but when they changed it to DOT4 it was fine." Well that's a sound reason why I'd go somewhere else.

 

[Ralf S.]

There's a load of cobblars talked about DOT5.x brake fluids and I fear some of it has passed into urban legend.

DOT5 (as distinct to DOT 5.1) is synthetic. It doesn't attack your paint, is non-hydroscopic and has a higher boiling point, even before you factor in problems in DOT3/4 caused by them absorbing water.

It will work in all but the most obscure (older) systems but if you use it you have to be aware of the disadvantages:

1) It's not "oily" so it doesn't lubricate the seals. Some systems need the "oiliness" to lubricate the seals and others don't. Most new cars have seals that don't rely on the fluid to keep them lubricated.

2) As it does not absorb moisture, any water in the system forms "bubbles" of water. These "bubbles", if they are trapped in one point in the brake system may cause pin-hole corrosion of the brake line at that point. DOT3/4 is both oily AND it dissolves water, so it doesn't have that problem. So, if you have DOT5 you must bleed the brakes regularly to expel any trapped water.

3) It doesn't like mixing with DOT3/4 but it doesn't turn to jelly on contact. Pump out as much DOT3/4 as you can and then top up with DOT 5.. Then bleed thoroughly until all the DOT3/4 has been purged.


So, you can see that DOT5 is actually quite high maintenance and unless you run a racing car, probably not worth the trouble.

DOT5.1 is more of an enhanced spec' DOT3/4 rather than having much similarity with DOT5. I'm not sure if it is synthetic or only semi-synthetic. It strips your paint and still absorbs moisture, same as DOT3/4 but in all other respects it is identical to and mixes with those fluids... though obviously to get the full benefit you want to flush out as much old fluid as possible rather than just top up with DOT5.1 (but you could if you wanted).

DOT5.1 is more like DOT3/4 than DOT5, which is unfortunate, given the names.



Ralf S.

 

[bulldog5046]

Thanks for all the info, some of it contradicts other bits but i opted for DOT4 this time anyway, i will get this upgraded to Castrol Super Response DOT4 at a later date

Thanks,
Ry