 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
hgmckay
Joined: 23 May 2006
Posts: 397
|
 Posted: Mon Jun 04, 2007 5:24 am Post subject: Allegro Hydraulic Brakes |
 |
|
Gentlemen:
<![if !supportEmptyParas]> <![endif]>
I have determined that the right hydraulic brake unit on my Allegro 2000 is slowly leaking brake fluid from the clearance between the slave cylinder (piston) and the cylindrical bore in the finned housing. This fluid is ending up on the brake pads and the disc itself. Eventually over time I loose braking. I need to repair this unit. Not having seen this unit disassembled, I don’t know if the internal “0” ring seal (I assume it is an “0” ring) is mounted in a groove on the slave cylinder (piston) i.e. the “0” ring moves with the slave cylinder, or if the “0” ring seal is mounted in a groove in the cylindrical wall of the finned housing i.e. the “0” ring does not move when the slave cylinder moves.
<![if !supportEmptyParas]> <![endif]>
Have any of you serviced, or do you know of some one who has serviced the Allegro 2000 hydraulic brake units? If you have, can any one answer the following questions for me:
<![if !supportEmptyParas]> <![endif]> - What size “O” ring is used in the unit, and what type material is the “O” ring made of? Where can they be obtained?
- 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)?
- Are there any other internal parts that could be damaged that would cause the fluid to slowly leak?
- 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?
<![if !supportEmptyParas]> <![endif]>
I have asked the US Distributor (Fantasy Air USA) these same questions, but have received no clear answer to either question. I have contacted Evektor-Aerotechnik a.s. (the brake manufacturer) in the Czech Republic and they can supply parts to me. But before I order any parts from Evektor-Aerotechnik I want to be sure I can indeed fix the brake unit. I would appreciate anyone’s help in this matter.
<![if !supportEmptyParas]> <![endif]>
Hugh McKay
Allegro 2000
N661WW
<![if !supportEmptyParas]> <![endif]>
[quote][b]
| | - The Matronics Allegro-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Allegro-List |
|
|
|
| Back to top |
|
 |
Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
|
| Posted: Tue Jun 05, 2007 2:09 am Post 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
| | - The Matronics Allegro-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Allegro-List |
|
|
|
| Back to top |
|
|
hgmckay
Joined: 23 May 2006
Posts: 397
|
| Posted: Tue Jun 05, 2007 7:19 pm Post subject: 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
--
| | - The Matronics Allegro-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Allegro-List |
|
|
|
| Back to top |
|
|
Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
|
| Posted: Wed Jun 06, 2007 3:28 am Post subject: Re: Allegro Hydraulic Brakes |
|
|
Hugh,
The CSN 02 9272, I assume is merely a part number and means nothing to me. EPDM is the type of material (ethylene propylene diene monomer) and is in common use for many applications. The 70 is probably the inside diameter of the o-ring in mm. I have no idea what the SH specificies but do know that o-rings go by material, inside diameter, and thickness. I GOOGLED "epdm 70sh" and found lots of references to it in parts lists for all kinds of things, including expresso machines, mostly from manufacturers in eastern Europe. You may be able to find this part from an American distributor of some of these manufacturers. You may also want to try the Evektor Aircraft (SLSA) importer. They may have them in stock and could be cheaper. I think this brake system is used on several of the eastern European manufacturered LSA, so if Evektor America http://www.evektoramerica.com/ does not stock them you might want to try some of the others listed at http://sportpilot.org/learn/slsa/
For future reference here are standard o-ring size charts
metric o-ring sizes:
http://www.lutzsales.com/metric_o-ring_sizes.pdf
American Standard o-ring sizes:
http://www.lutzsales.com/standard_o-ring_sizes.pdf
Please keep us posted on what you learn as we may all need this information in time.
Thom in Buffalo
| | - The Matronics Allegro-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Allegro-List |
|
|
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
