Strange Brake Failure

[Ed Price]

_____

From: Midwest Amphicar [mailto:]
Sent: Friday, September 12, 2008 2:41 PM
To: edprice@cox.net
Subject: RE: [General Amphicar Discussion-t-20133] Re: Strange Brake Failure


I asked our Club editor to get permission to run a column that was in Old
Cars Weekly. The US Army tested some equipment that was in water. Then they
cut in half the parts. Dot 3 looked like rusted crap. All out Dot % looked
perfect. Then they mixed with no changing or cleaning and it looked very
good. Later Dave the Wave




If the original US Army story / report was referenced, then that would be in
the public domain, and available from some Army site for our use.

Ed Price
El Cajon, CA USA
61 Rust Guppy

 

[gzink]

David/John,
Reason I asked the question is, I was aware of Dot 3 non-synthetic and Dot 5 synthetic which I have used successfully for over 5 years, but went to store the other day and saw Dot 3 synthetic. So I get that mixing Dot 3 non-synthetic with Dot 5 synthetic is either bad or at least negates the benefit of synthetic, but what about the two different synthetics? What is really the difference between Dot 3 and Dot 5 synthetic and which is better?


--- On Fri, 9/12/08, DavidC <> wrote:

> From: DavidC <>
> Subject: RE: [General Amphicar Discussion-t-20133] Re: Strange Brake Failure
> To: g_zink_us@yahoo.com
> Date: Friday, September 12, 2008, 4:07 PM
> Quote:
>
>
>
>
> > You can use either one, but you CAN NOT mix them.
> If you change over the
> > entire system must be flushed out (denatured alcohol
> works well) and all
> > seals replaced. The can not be any traces of > DOT3
> left because DOT5 and
> > DOT3 do not mix.
>
>
>
>
> John, actually you can mix them (ie have them in the same
> system) they work
> together fine but you don't want to do that as you
> loose all the benefits of
> silicon if there is any of the old DOT3 stuff in there.
>
> I don't like flushing fluids, you are adding something
> foreign, what I
> always do is dismantle and clean the wheel cylinders and
> master cylinders
> and then assemble them using silicon fluid to lubricate.
>
> Either replace the brake lines or clean then with air.
> Always replace the
> flexibles front and back - cheap and easy and you can be
> sure it's only
> silicone in there.
>
> Main silicone supplier in the UK is Automec but I think the
> product actually
> comes from the States. More info here:
>
> http://www.automec.co.uk/pdf_files/b...uid_answer.pdf
>
> Click on the "press page" bit.
>
>
> David C
>
>
>

 

[Jon March]

Hi John B - awhile back, i read these comments and im at the point where i just got the dual chamber master and getting ready to remove the original. i have all new wheel cylinders and rubber lines as well. Are you still recommending denatured alcohol to flush the lines before i use Amsoil DOT5?

Also - I dont have a drill press - so do you think Larry Solheims idea makes sense: putting the custom shaped piston from the original master into the new dual master?

jon

 

[LSolheim]

Hi John B - awhile back, i read these comments and im at the point where i just got the dual chamber master and getting ready to remove the original. i have all new wheel cylinders and rubber lines as well. Are you still recommending denatured alcohol to flush the lines before i use Amsoil DOT5?

Also - I dont have a drill press - so do you think Larry Solheims idea makes sense: putting the custom shaped piston from the original master into the new dual master?

jon

You misread something, Jon --- You CANNOT put the OEM piston into a dual housing! They work differently. I swapped compatible parts between single system units to compensate for the stock 'throw'. Brakes are not something to screw with haphazardly!

 

[Ken Chambers]

You'll need a tapered push rod for the dual master cylinder. I machined a new one out of a 10mm bolt so I wouldn't have to use an original one.

My take on brake fluid is this; glycol based fluid (DOT 3 and 4) is hydroscopic, meaning it can absorb water over time. That's not a problem until the moisture becomes excessive and the corrosion inhibitor additives can no longer perform their function. That's why it is recommended to exchange new brake fluid every few years.

Silicone based fluid (DOT 5) does not absorb water. Sounds good at first but that means when moisture enters the system small puddles of water sit in the low spots doing what water does with steel - rust.

Be aware that DOT 5.1 fluid exists and it is glycol based, not silicone, despite the number nomenclature.

 

[Jon March]

Larry - thanks - Ok, got it! What I did was lay out both brake master cylinders on a towel, removed retainer clips, and removed the pistons.

Happened to chat with John Bevins, who suggested something that works well for his projects, that i like the sound of, namely:
find a drill bit that fits the diameter of the entry-hole in the original master, measure how deep to the end of the hole, and carefully drill the piston of the new dual-circuit master cylinder to the same depth. The original pushrod should touch exactly the same as the original cylinder. Im just unclear as to what the "taper" is exactly for - but John says that theres never been a problem - countering opinions? I would like to not have to fabricate a new pushrod.

Also - what is the difference or benefit of 5.1 vs DOT3?

 

[Ken Chambers]

When the brake pedal is depressed the geometry of the pushrod movement is not perfectly straight into the master cylinder. The ball end allows for a bit of side to side movement generated at the pedal connection.

The hole in the original piston is tapered. The blunt rounded end of the pushrod seats at the bottom of the hole and the taper of the hole allows the rod room to pivot.

The original rod diameter is too large to seat at the bottom of the hole in the dual circuit piston. Tapering the pushrod allows it to seat properly in the piston and room to pivot side to side.

In my opinion, drilling out the piston presents some problems:
- It should be a tapered hole to allow the pushrod room to pivot. Problematic, however, to drill a tapered hole.
- Bottom of the hole would not be rounded but a v-shaped drill point.
- An oversize hole to allow for pivoting might result in the pushrod falling away from the center of the piston each time the pedal is released.
- And then there's a question of drilling into and modifying a critical component of the braking system.

 

[jfriese]

Jon,

The taper is there to allow for slight wobble of the shaft when the brake is pressed since the pedal is on a swivel mount. It might not seem like much but one of my cars came with the wrong style piston and I noticed it by the fact that the adjustment was way different from a car with the correct master cylinder. I had the cylinder brass sleeved and rebuilt by White Post before using the car.. I thought the difference might not matter but it damaged the master cylinder after a couple of years of use. Of course the leakage ruined the epoxy paint under the master cylinder. I sent the cylinder back to White Post for repair and told them about why I thought it failed. They rebuild the cylinder again and replaced the piston with the correct one for the Amphicar that they had in their stock. And did all this under warranty. Talk about great customer service. It's been fine ever since and that's about 12 years now. Oh, and I switched to silicon brake fluid so that my interior paint will tolerate any brake leakage that might occur in the future. P.S. A leaking wheel cylinder can do a good job of ruining your wheel paint if your using DOT 3 or 4.

John Friese
67 White
67 Red

 

[Jon March]

ooo kay.... well, so im looking at the 10mm bolt thing that you ground down - it sure looks like more than just a bolt to me (the nuts in the middle, etc)
Looks complex - and even maybe welded or machined on a lathe? and i dont own either.

? why not just grind down the stock Amphicar pushrod to fit the pushrod-inlet on the Cardonne/reman VW bus master i have?

 

[Ken Chambers]

That's a 5 degree taper done on a lathe. The collar in the middle slips over the bolt and is pinned in place. I machined the new collar to better fit the new boot.

 

[LSolheim]

And all of the above is why I used the OEM piston (w/ new rubber bits) in a new VW MC housing. It solved the rod/cylinder interface. But I did not "upgrade" to the dual-mode MC.

 

[Jon March]

So Ken, if im careful, is there a reason i coudnt manually taper the stock Amphicar pushrod?

 

[Ken Chambers]

Sure, I think the important points to consider are rod length, ball end diameter to fully seat in the piston hole, and enough taper to allow for some side movement of the rod during pedal movement. Should work.