Today's Message Index:
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1. 03:10 AM - Re: Allegro Hydraulic Brakes (Thom Riddle)
2. 08:19 PM - Re: Re: Allegro Hydraulic Brakes (Hugh McKay III)
Message 1
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| Subject: | Re: Allegro Hydraulic Brakes |
Hugh,
I've had one of the older brake units apart and can answer some of your questions.
The newer brakes have a different type of bleed system (probably like yours)
but should not have any affect on what you are doing.
1. What size O ring is used in the unit, and what type material is the O ring
made of? Where can they be obtained?
I did not measure the oring so cannot tell you its size. I don't know the material
but whatever works for brake fluid should be fine.
2. After removal of the finned piston unit from the wheel and disc, and after
removing the 90 brass fitting from the end of the finned piston unit, can the
large hex nut on the end of the finned cylinder casing be removed to extract
the internal cylindrical piston? If so, how is the slave piston extracted and
replaced after a new 0 ring seal is installed (assuming an 0 ring is used to
make the seal)?
The hex "plug" is a standard right hand thread (CCW to remove). The oring is accessible
after removing the hex. The oring seat/groove is in the housing, not
the slave piston. The slave piston floats inside the cylinder and is mounted on
a diaphragm (if my memory does not fail me). If my memory is correct about the
diaphragm, then it may be the source of the leak if the leak is on the disk
side of the cylinder and not the pressure/supply side. The o-ring is the seal
against leaking thru the supply side.
3. Are there any other internal parts that could be damaged that would cause
the fluid to slowly leak?
See #2 above.
4. There are locking retainers used at the points where the disc itself is bolted
on to the wheel. Where can these small retainers be obtained?
We replaced ours with standard external star type locking washers and they work
just fine. We check these periodically because they are not positive locking
devices like the bend over tabs. In over a year and 150+ hours since we did the
brake work, the star washers have not lossened at all.
We ended up replacing the whole expensive slave cylinder unit because of another
unrelated problem and still have the old unit somewhere in the hangar. I will
look for it on next trip to hangar and take a closer look inside to verify my
aging memory on the diaphragm, if there is one. Once you take yours apart to
determine where yours is leaking you can make the measurements you need. I've
had good luck finding all sorts of parts for all things mechanical from McMaster-Carr.com
but you may be able to find the proper oring from a local autoparts
store. Since so many of the cars on the road today are metric you might be
able to find the right size oring locally. Our old oring is still good but we
don't want to part with it in case we need a replacement.
I hope this helps a bit. Let me know how it works out. I'd be curious what the
Evector-Aerotchnik folks charge for parts. The used but servicable unit that Fantasy
Air found for us (in the Bahamas) was outrageously expensive for such a
unit. I don't recall the price but it was high.
On another subject about prices. We had some impact damage to our windshield so
I called Doug Hempstead for a price for replacement. They want $410 for a sheet
of Lexan that is not even cut to size. I found a sheet at McMaster-Carr for
$81. If the Fantasy Air part had been already cut to size with finished edges,
I'd say it would be worth perhaps as much as $200 for the labor savings but
not $410 for a blank sheet!
Thom in Buffalo
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=116601#116601
Message 2
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| Subject: | Re: Allegro Hydraulic Brakes |
Thom:
I received a reply directly from Evektor-Aerotechnik s.r.o. They responded
very quickly and told me they could indeed help me. They are the
manufacturer of the brakes used on the Allegro 2000. In fact they sent me a
pdf file drawing of the brake showing all the internal parts. For your
information I am forwarding you a copy of the drawing in a separate email.
If others would like a copy of this drawing I will be glad to send it to
them. It appears from the drawing that the O-ring material is EPDM 70SH. I'm
not sure what EPDM or 70SH is, maybe you do. The size of the two O-rings
(inner and outer) is given on the drawing. The rubber boot or cup that fits
the internal piston is also specified as CSN 02 9272. Again this is a
mystery to me.
Anyway, from the drawing it appears that maybe only the outer O-ring may be
leaking, but for brake fluid reach the outer O-ring it would have to get by
the rubber boot, so maybe the boot as well as the outer O-ring is leaking.
The inner O-ring is behind the internal piston and keeps fluid from leaking
backwards and coming out around the large Hex nut where the 90 brass
fitting is located. I have no leaks in this area, so this O-ring is OK.
Here is the "kicker". Evektor wants $75.00US for the two O-rings and the
rubber boot, plus the cost of shipping from the Czech Republic!! Absolutely
ludicrous!!! I am first going to try to find the outer O-ring here, and
replace it first. Since it is a metric size, I should be able to find it. I
just need to know what EPDM 70SH stands for. I won't know if I have to
replace the internal rubber boot until I replace the outer O-ring and
assemble the unit so I can test it without putting it back on the plane. I
will have to figure out how to do this. If the unit leaks after replacing
the outer O-ring, I will have to "pay the price" and purchase the two
O-rings and boot and replace all of them. I just hope the plunger (the part
that is pushed out to contact the brake pad) is not scored. If it is, then I
have another problem.
Anyway, that is what I KNOW AT THE MOMENT. I'LL KEEP EVERYONE INFORMED AS TO
WHAT HAPPENS. I have never overhauled a hydraulic disc brake unit so I am in
unknown territory.
Hugh McKay in NC
-----Original Message-----
From: owner-allegro-list-server@matronics.com
[mailto:owner-allegro-list-server@matronics.com]On Behalf Of Thom Riddle
Sent: Tuesday, June 05, 2007 6:10 AM
Subject: Allegro-List: Re: Allegro Hydraulic Brakes
Hugh,
I've had one of the older brake units apart and can answer some of your
questions. The newer brakes have a different type of bleed system (probably
like yours) but should not have any affect on what you are doing.
1. What size O ring is used in the unit, and what type material is
the O ring made of? Where can they be obtained?
I did not measure the oring so cannot tell you its size. I don't know the
material but whatever works for brake fluid should be fine.
2. After removal of the finned piston unit from the wheel and disc, and
after removing the 90 1/2 brass fitting from the end of the finned piston
unit, can the large hex nut on the end of the finned cylinder casing be
removed to extract the internal cylindrical piston? If so, how is the slave
piston extracted and replaced after a new 0 ring seal is installed
(assuming an 0 ring is used to make the seal)?
The hex "plug" is a standard right hand thread (CCW to remove). The oring is
accessible after removing the hex. The oring seat/groove is in the housing,
not the slave piston. The slave piston floats inside the cylinder and is
mounted on a diaphragm (if my memory does not fail me). If my memory is
correct about the diaphragm, then it may be the source of the leak if the
leak is on the disk side of the cylinder and not the pressure/supply side.
The o-ring is the seal against leaking thru the supply side.
3. Are there any other internal parts that could be damaged that would
cause the fluid to slowly leak?
See #2 above.
4. There are locking retainers used at the points where the disc itself is
bolted on to the wheel. Where can these small retainers be obtained?
We replaced ours with standard external star type locking washers and they
work just fine. We check these periodically because they are not positive
locking devices like the bend over tabs. In over a year and 150+ hours since
we did the brake work, the star washers have not lossened at all.
We ended up replacing the whole expensive slave cylinder unit because of
another unrelated problem and still have the old unit somewhere in the
hangar. I will look for it on next trip to hangar and take a closer look
inside to verify my aging memory on the diaphragm, if there is one. Once you
take yours apart to determine where yours is leaking you can make the
measurements you need. I've had good luck finding all sorts of parts for all
things mechanical from McMaster-Carr.com but you may be able to find the
proper oring from a local autoparts store. Since so many of the cars on the
road today are metric you might be able to find the right size oring
locally. Our old oring is still good but we don't want to part with it in
case we need a replacement.
I hope this helps a bit. Let me know how it works out. I'd be curious what
the Evector-Aerotchnik folks charge for parts. The used but servicable unit
that Fantasy Air found for us (in the Bahamas) was outrageously expensive
for such a unit. I don't recall the price but it was high.
On another subject about prices. We had some impact damage to our windshield
so I called Doug Hempstead for a price for replacement. They want $410 for
a sheet of Lexan that is not even cut to size. I found a sheet at
McMaster-Carr for $81. If the Fantasy Air part had been already cut to size
with finished edges, I'd say it would be worth perhaps as much as $200 for
the labor savings but not $410 for a blank sheet!
Thom in Buffalo
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=116601#116601
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