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Re: [GMCnet] Brakes and brake fluid [message #64299 is a reply to message #64282] Sat, 14 November 2009 21:35 Go to previous messageGo to previous message
GMC_LES is currently offline  GMC_LES   United States
Messages: 569
Registered: October 2009
Location: Montreal
Karma:
Senior Member
I've always disconnected the lines and blown them out with air only. I've
had the belief that any solvent not designed specifically for brake system
flushing might potentially affect the boiling point of the new fluid should
any of the solvent remain in the system. Alcohol has a fairly low boiling
point, and in a closed system, would not be able to evaporate unless long
periods of air flow were provided through the system prior to adding brake
fluid. There is apparently a proper solvent made specifically for flushing
brake systems but I haven't looked for it.

Another point of interest:
All commercially rebuilt and new brake hydraulic components are lubricated
with a water soluble grease and/or brake fluid. Unless you are willing to
fully clean and appropriately re-lubricate these parts before using DOT 5,
you will always have a small qty of a hygroscopic product in the system.
Unless you are a purist to the Nth degree, this isn't really an issue.

I always recommend that any DOT 5 conversions begin with all the hydraulic
components being dis-assembled, cleaned with alcohol and dried, then
re-assembled with a light smear of Dow Corning #4 silicone die-electric
grease on the moving parts. The Cartel DOT 5 that I use dissolves & blends
with this grease over a short period of time, so it has no negative effect
on the system function. Doing this much work assures you of having the best
possible chances of not having trouble later.

Les Burt
Montreal




-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Rob Mueller
Sent: November 14, 2009 8:27 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Brakes and brake fluid

Les,

Since you didn't disassemble brake system in the Audi and it worked OK then
the old adage of "you can't argue with success" is apropos.

I wonder if it would be a better to blow all the Dot 4 out; flush the system
with denatured alcohol, blow it out again, and then fill it with clean Dot
5.

HOWEVER, I think the "best practice" would be to take the whole thing to
bits and clean everything then change over to Dot 5!

Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426


-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Les Burt
Sent: Sunday, 15 November 2009 11:30 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Brakes and brake fluid

Rob,
The very first car in my fleet to receive the DOT 5 was my father's Audi
5000. We did a 5 minute flush using the DOT 5 and the pedal pump bleeding
procedure, unaware of the fact that DOT 5 is bad for creating & holding air
bubbles. We got a mediocre pedal initially but it got better after a few
days. We eventually did a second bleeding procedure several weeks later with
a pressure bleeder and the car ran for many years like that without any
problems. The brake system was not dismantled and cleaned, The lines were
not flushed, and the hydraulic components had been in service since the car
was new. I certainly would not do that now with the knowledge I have gained,
but the car didn't suffer any from the way in which we did the conversion.
This was the car in which we noticed the improvement in rear brake
sensitivity during severe cold operation (-20 and colder) We had done the
conversion over Xmas so we had a good feel of the before and after with no
other changes to the braking system.

During a lengthy discussion with the engineer at Cartel many years ago, I
asked about what happens to the two fluids when mixed together. The engineer
said that the old fluid would just puddle in the lowest points of the system
and be somewhat harmless other than to hold moisture and potentially cause
corrosion at those points. The two fluids would not intermix. He said that
the best method was always to do a thorough cleaning and refurbish of the
hydraulic system prior to using DOT 5 silicone fluid.

If you wanted to just dump the old fluid and add DOT 5 without dis-assembly
& cleaning, the engineer recommended a thorough flush of the system first
using fresh, clean DOT 4. This ensured that whatever DOT 4 fluid remaining
in the system after a DOT 5 conversion would contain a very low moisture
content and be relatively harmless.

Les Burt
Montreal



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Les Burt Montreal 1975 Eleganza 26ft A work in Progress

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