Matco installation recommendations
Part List
- Viton o-ring for the RV-10 Matco brake kit:
- AS568-218: https://www.theoringstore.com/store/index.php?main_page=product_info&products_id=6821
- Specifically for main gear wheel kits with order number WHLWI600XLT-2 (and variations): verify the o-ring size as your setup may differ.
- Be sure you are getting the o-ring with temp ranges of at least -40F - 350F.
- AS568-218: https://www.theoringstore.com/store/index.php?main_page=product_info&products_id=6821
- Flex gear leg brake lines:
- Aircraft Specialty: https://www.aircraftspecialty.com/rv10products.html (gear-leg only hoses are available by special order)
- High-temp brake fluid:
Summary recommendations
To ensure the longevity and safe operation of the Matco installation, Matco has provided a set of recommendations.
A builder experienced brake failure after just 175hrs as a result of leaking brake fluid at the caliper. Due to the airport layout, the builder frequently had very long taxis and the opportunity for heat buildup was significant. The follow was sent in reply to the builder via email after inquiring about stock o-ring deformation ("squaring") likely due to high heat.
Viton O-rings can be used but must have the same -40 deg F dynamic low temperature rating as Buna Nitrile. They will be expensive as there are only a few specific variations of Viton material that have the low temperature properties required.. Since the o-ring application is for a dynamic seal, be sure to pay attention to the dynamic temperature rating and not the static temperature rating.
When changing break fluid between 5606 and 83282, you must take care to thoroughly flush the 5606 out of the system. A very small amount of contamination from 5606 in the 83282 dramatically alters the higher flashpoint of 83282. Drain the system and flush with 83282 and drain again. Then refill with fresh 83282.
You may also want to consider using MobilOne Synthetic ATF. It has slightly higher flashpoint than 83282 and you may find it easier to find (at most auto parts stores). I would use the same flushing technique changing to it as for 83282.
The caliper is designed to be free floating. There is a document on our website that provides more detail at:
https://matcoals.com/wp-content/uploads/2023/04/skids_hydraulics.pdf
The free-floating caliper is central to the self-adjusting hydraulic system. When pressure is applied, the caliper slides into position, centered on the disc. When pressure is relieved, the caliper should ‘relax’ in place. When your feet are off the toe brake master cylinders (MC’s), there is a bypass valve inside that open the hydraulic system to atmosphere. The bypass valve and vent to atmosphere allows the caliper to adjust for disc wear, pad wear, and fluid temperature changes. The running clearance between the disc and the pads will be very small and should be the same though out the wear life. That way the toe brake feels the same each time it is used regardless of the wear state of the brake.
- Verify the vent in your hydraulic reservoir is open. The hydraulic system won’t self-adjust if the vent is clogged or closed.
- The bypass valve on the MC’s opens in the last 1/16 inch or so of shaft extension. You need to verify that there isn’t any excessive drag in the pedal preventing the extension. There is excess sporing force in the cylinder to assure the full extension as long as there is not drag in the pedal mechanism. When you stroke the cylinder and remove your foot pressure, use your hand to reverse travel the toe brake while holding your fingers on the shaft of the MC at the face of the MC end gland. You should not feel any further extension. If you do, the cylinder is not fully extending.
The VANS pedals do not properly load the master cylinders. The master cylinder needs the load down the centerline of the cylinder. When done so, there are no bending loads on the shaft that can cause the piston shaft to rub against the end gland. The VANS installation does not put the load down the center of the cylinder as desired. The connection at the shaft end uses a loosely connected bolt that imposes an offset load. The offset load results in a moment that must be reacted by the shaft. This typically results in the piston in the bore and the shaft at the end gland reacting the moment. This will cause wear on the shaft at the cylinder end gland and in the bore at the piston. This can restrict the free stroke of the cylinder. The shafts must be able to fully extend when at rest for the hydraulic system to work properly and self-adjust as explained in the linked document at:
https://matcoals.com/wp-content/uploads/2023/04/skids_hydraulics.pdf
For the VANS installation, there is an AN bolt on the toe brake that is loosely attached to a lug. Then a series of washers are installed to space the shaft in position. Since the bolt is not able to carry any moment, the shaft must carry it. It results in the shaft rubbing on the end gland which leads to scratches on the shaft which eventually damage the seal in the ID of the end gland. Some of the VANS pedals have a flange on both sides of the pedal that allow a long bolt to pass through both flanges and then attach to the shaft. This type mounting will allow the bolt to carry the moment and will eliminate the problem.
Others have stiffened the lug and used an all-thread bolt so that the bolt can be tightened against the lug with a nut. The now cantilevered bolt will carry some of the bending moment and relieve the shaft. Some simply use the all-thread bolt and nut which helps but the stiffness is likely not enough to eliminate the problem completely although it is helpful.
We had a customer recently who rectified his RV-6A pedal to eliminate the problem. He fabricated an extra lug half and welded it to his pedal. Elegant fix. I have attached a photo.
There was also a modification done on an RV-8 by a customer that I included as well.
- The caliper has to be free floating. The VANS plans call for a coiled aluminum line acts as a big spring. Rather than allow the caliper to relax in the last position and be centered on the disc, it is biased to the last position of the deformed tubing ‘spring’ Instead of running clearance between the pads and the disc, either the moveable or the stationary shoe is held in contact with the brake disc. When the moveable shoe is the one in contact, heat is conducted from the hot disc to the caliper pistons and housing. You will likely find the O-rings have been made square. They will have to be replaced. The last 12-18 inches of brake line needs to be flex line. If you have the coiled line, you may want to check in with Vic Syracuse at BaseLeg Aviation in Georgia regarding adapting flex lines to the solid tubing on the gear leg. It is a common change he performs on the RV line.
- The RV’s steer with differential brakes. It is important to not drag the brakes continuously when taxiing. If taxiing in a cross wind, you should use proper stick and rudder position relative to the wind and over steer with the brakes so as to allow periods of full release of the brakes. This will minimize heat flow into the caliper.
Thank you.
George R Happ
Matco Aircraft Landing Systems, LLC
801-335-0582 801-335-0581 (F)
www.matcoals.com
Technical Support Disclaimer: While we strive to ensure that the advice/information provided through our support is correct, Matco Aircraft Landing Systems, LLC does not accept any responsibility for errors or omissions. Any advice or information that Matco Aircraft Landing Systems, LLC gives you via any form of communication is not a guarantee that it will correct your problem. It is only offered as assistance to you. Matco Aircraft Landing Systems, LLC will not be held responsible for any loss or damage as a result of our advice or information supplied.