Is synthetic brake fluid EVIL.......?

Buckle · #1 PostAuthor: **Buckle** » Fri Aug 01, 2008 8:18 pm

I'm having trouble with my brakes and I suspect it may be the synthetic brake fluid....... :?:

Riding home from work today on the trusty old Z550 I noticed that the front brakes didn't seem to be performing as usual, and by the time I got home I could pull the lever all the way to the bars with one finger :shock:

The bike has only been on the road for about 3 months with fresh synthetic fluid in it.

On closer inspection I noticed the master cylinder wasn't fully returning either. After ruling out air in the system or either of the calipers messing around I decided it must be a problem with the master cylinder. Took it off and took it apart - no real fault found, bit of rust on the piston outside the dust seal. Anyway reassembled with rubber grease etc. and re-fitted. Bled it and okay for about five minutes and started sticking again :?:

Took off, cleaned, had another even closer look, lubed, back together, work it loads of times on the bench, put back on bike, bled, 5 minutes and it's sticking again :evil:

Is synthetic brake fluid EVIL :?:

Pigford · #2 PostAuthor: **Pigford** » Fri Aug 01, 2008 9:39 pm

Should only use DOT 4 as synthetic is not very robust... can damage seals :!:

Think it absorbs water even more than normal stuff :evil:

Buckle · #3 PostAuthor: **Buckle** » Fri Aug 01, 2008 10:17 pm

That'll be me off to the garage for some "normal" brake fluid tomorrow then :!:

Garn 1 · #4 PostAuthor: **Garn 1** » Sat Aug 02, 2008 8:07 am

Does anyone know whether they use dot 5 synthetic oil in new bikes (ie.2008 models)?
I've never tried it as I don't know, that if I suddenly need some to top-up, that it will be available. However, if as Pigford says, it absorbs more H2O than dot 3 or 4, why would any one use it?
RegardZ.

Pigford · #5 PostAuthor: **Pigford** » Sat Aug 02, 2008 8:48 am

Garn,

http://www.shoptalkforums.com/viewtopic ... 952f98bfe2

http://www.stoptech.com/tech_info/wp_br ... d_1a.shtml

If i recall correctly, it has a higher boil rate for racing applications... :?:

or sumink... :??

But as racers cahnge it regularly, its not a problem with hydro-thingy :wink:

RALPHARAMA · #6 PostAuthor: **RALPHARAMA** » Sat Aug 02, 2008 9:37 am

I used to ride right on the limits, never braking 'til the last possible moment and so putting the absolute maximum grief on the braking systems of the bikes and I can honestly say I've never boiled the brakes on a bike.

I used to have a Range Rover years ago and I regularly boiled the brakes on that and was left whit the foot to the floor syndrome on a two ton vehicle with only a rather iffy transmission brake to help stop it.

I have never used anything any more flash than dot 4 in bikes.

As dot 4 works a treat why use anything else?

Very interesting threads though Piglet!

Rich · #7 PostAuthor: **Rich** » Sat Aug 02, 2008 11:03 am

What do you mean by synthetic? If you mean silicone it is less hygroscopic than mineral brake fluid which is why it has a different boil point, but you will probably have trouble with the seals if you have previously used mineral.

RALPHARAMA · #8 PostAuthor: **RALPHARAMA** » Sat Aug 02, 2008 3:04 pm

Rich wrote:What do you mean by synthetic? If you mean silicone it is less hygroscopic than mineral brake fluid which is why it has a different boil point, but you will probably have trouble with the seals if you have previously used mineral.

Silicon is more compressible than traditional glycol ether fluids, so apart from buggering the seals it gives you a more spongy feel. DOT 5.1 however is not a silicon fluid and is therefore more likely not to attack your seals.

But when did anyone last boil the fluids on a Zed :?:

Stick to DOT 3 or 4 is what the brakes were designed to use

Rich · #9 PostAuthor: **Rich** » Sat Aug 02, 2008 4:53 pm

Ah but I use dot 4 which is synthetic with no problems, and it is sold to mix with 5.1, 3 and is probably what 99% of people on the road use.

Dot 5 however is silicone and if he has put that in........................

Pasc · #10 PostAuthor: **Pasc** » Sat Aug 02, 2008 6:21 pm

Rich wrote:Dot 5 however is silicone and if he has put that in........................

I totally agree Rich, using dot 5 in a system that has previously held dot 4 is not a good idea.

Buckle · #11 PostAuthor: **Buckle** » Sat Aug 02, 2008 8:34 pm

I have now completely stripped both front calipers, the master cylinder and flushed through the brake lines. Thoroughly cleaned master cylinder and calipers. I couldn't say any of the seals looked obviously damaged or puffed up.

Reassembled and tried to bleed with traditional Dot 4 fluid. Didn't even manage to get any resistance at the lever before the master cylinder started sticking again. Unless I physically grasp the end of the piston with pliers and pull it back, it will not return fully. But when tried on the bench with no fluid in it it works fine, repeatedly. :??

The fluid I had in it before was labelled as Synthetic 5.5 but on reading the small print it said it was synthetic Dot 4 :?:

It was made in France though

Not sure what to try next, any ideas?

Rich · #12 PostAuthor: **Rich** » Sun Aug 03, 2008 3:38 pm

another master cylinder.

Buckle · #13 PostAuthor: **Buckle** » Sun Aug 03, 2008 4:42 pm

Rich wrote:another master cylinder.

Didn't have one of those, but did find a rebuild kit that came in a pile of other bits with the bike - Doh! :shock:

So rebuilt the master cylinder with new seals ect - and it now works! Hurrah

!

But seem to have a problem with the calipers now

! The pistons seem to be sticking on the seals and retract quite a way after pressure is released at the lever. If I clamp the hoses near the calipers the brake lever is rock solid. Clamping one hose at a time produces approximately halve the movement at the lever. So seal kits on order. :roll:

Synthetic brake fluid IS EVIL :!:

Is synthetic brake fluid EVIL.......?

Is synthetic brake fluid EVIL.......?

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