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Old 08-14-2009, 09:48 AM
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dhall_polo dhall_polo is offline
Join Date: Nov 2006
Location: Cumming, GA
Posts: 610
Default RV-7 brake mods summary

Brakes are on my mind lately. My left brake went soft, and I discovered that the pads were toast after only 85 hours, with the right pads being virtually new. For this and a few other reasons, I spent a few days overhauling the brakes and re-bleeding them.

There are a lot of threads talking about some very simple mods that can be done to the brake system. I thought I'd summarize things to look at when working on your brakes, especially for the guys with rudder assemblies that are still easily accessible. I did most of these mods on a finished airplane, thus getting a nice dose of cockpit-diving.

1) The long bolt mod. Use (4) AN3-56 bolts as the axle of rotation for the rudder pedal instead of using 2 smaller bolts per pedal. Obviously having a single axle of rotation is better than (2) almost the same axles of rotation.

2) Return springs. These help the brakes return to the non-braking position. The mod calls for a spring, stop, and collar on the shaft of each master cylinder. I suspect the left brake was dragging, and I'm hoping this will help improve pad life. It's an easy mod. See pic here. Part list required is here.

3) DOT4 conversion. There are a lot of threads on what fluid to use, including Mil-5606, Mil-83283, Synthetics, Dot4, Dot5, etc. I chose dot4 fluid due to its availability and resistance to fire. If you use dot4, the o-ring mod is required. You also need to use brake lines that are dot4 compatible. The lines that come from Van's are not. Stainless Steel Aeroquip 666 will work. If you're sticking with the MIL stuff, this is not required. I'm not necessarily pushing the dot4 mod. Please go do some research. There are a half-dozen good threads on VAF about brake fluid options. Thanks to Charlie Kuss for being THE source of O-rings to adapt all the brake components to support Dot4. He sent me a complete kit of O-rings with pictures. Replacing the O-rings is very easy.

4) Parking brake valve. I added a parking brake during the build. Frankly, I don't use it much yet. If you think you want a parking brake, do it during the build. Much harder to add later. I used a matco parking brake valve like the ones pictured in this thread. I'm not sure if this is still available. There are similar looking valves at ACS from Matco and Grove. If you use dot-4, you need o-rings for this too.

5) I also was recommended not to use the default plastic brake lines between the pilot and pax, and that I'd be rewarded with brakes that aren't as susceptible to becoming mushy. The line from the pax to the reservoir would still be the default plastic lines. I haven't done this yet, but maybe next time I service the brakes I'll remember to measure the lines and have the new fittings and hoses at the ready...
Don Hall
N517DG - RV7 - Flying!
Ticked Van's Hobbes meter at #6110, 3/7/09
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Old 08-14-2009, 11:41 AM
gasman gasman is offline
Join Date: Mar 2007
Location: Sonoma County
Posts: 3,412

Don, check your left brake pedal to confirm that it is in line with the right pedal. The right pedal should be leaned back so that the face of the pedal is just about in line with the back of the rudder pedal frame. The left pedal will be further back due to the fact that the weldment for the left pedal is fwd (closer to pilot) of the right weldment.

I have noticed that some builders set up the pedals on the work bench with the master cyls, and line the pedals up with the weldment. Looks OK, ...... but won't work after it is installed in the A/C.
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Old 08-14-2009, 05:43 PM
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frankh frankh is offline
Join Date: Jul 2006
Location: Corvallis Oregon
Posts: 3,547
Default Stop using the brakes

If you can..My first set lasted about 100 i stopped using them on the rollout..I've got 300 hours on the new pads and I will check them when i change the tires this weekend but i wouldn't be surprised if the pads DON'T need changing.

Frank 7a
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Old 08-15-2009, 09:23 AM
Steve Steve is offline
Join Date: Jan 2005
Location: Roy, Utah
Posts: 1,069
Default older kits

I'm helping a friend finish an 80% complete RV6 kit he recently purchased. The kit includes 4 brake cylinders from Cleveland not Matco. Those cylinders already have the external return springs factory installed! However, they did require the builder to mill the shoulder on the bottom end for the pedal attachment bolt.
One or two steps forward and.....
Five Sierra Fox
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Old 08-15-2009, 09:47 AM
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Mike S Mike S is offline
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 14,083

Originally Posted by Steve View Post
I'm helping a friend finish an 80% complete RV6 kit he recently purchased. The kit includes 4 brake cylinders from Cleveland not Matco. Those cylinders already have the external return springs factory installed!
The Cleveland cylinders, and the Matco ones, both have a single return spring--it is internal in the Matco, and external in the Cleveland units.

The mod discussed in this thread is to add a second spring to the Matco units, which is the external spring.

There are a couple of minor internal differences, piston and relief porting, that make the Cleveland unit really nice.

Your friend is lucky to have the Clevelands.
Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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Old 08-19-2009, 10:37 AM
Bavafa Bavafa is offline
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 2,302

I just completed my 100 hour inspection (in four months since started flying) and thought I would need new break pads. After ordering the break pads and taking the wheel pants off, I discovered that I still have about 90 to 95% life left on them. Not bad for the first 100 hours, I break only when is needed.
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Old 09-02-2009, 07:39 PM
BillSchlatterer BillSchlatterer is offline
Join Date: Jan 2005
Location: Arkansas
Posts: 485
Question What about the Master Cyls and Matco Valve ?

If you do the conversion on the calipers and replace the o-rings to use the higher flash point fluid,... do you also have to replace anything in the Master Cyl and Matco Valve?

I can't seem to find part numbers in the Spruce book, sure would appreciate it if anyone has them close at hand!

All help appreciated ;-)

Bill S
7a finishing
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Old 04-12-2017, 04:19 PM
PG13 PG13 is offline
Join Date: Apr 2017
Location: Fresno
Posts: 12

Would you mind re-posting that pic or emailing it to me on the spring mod?
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Old 04-12-2017, 06:10 PM
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DanH DanH is offline
Join Date: Oct 2005
Location: 08A
Posts: 7,602

Originally Posted by BillSchlatterer View Post
If you do the conversion on the calipers and replace the o-rings to use the higher flash point fluid,... do you also have to replace anything in the Master Cyl and Matco Valve?
Bill, are you talking about DOT4, or MIL-H-83282 (higher flash point upgrade for Mil-H-5606)?

The automotive fluid requires a system flush, and changing all the seals.

83282 mixes with standard 5606, and requires changing nothing, although many install Viton o-rings in the calipers for high temperature resistance.
Dan Horton
Barrett IO-390
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Old 04-13-2017, 03:21 PM
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MikeyDale MikeyDale is offline
Join Date: Aug 2012
Location: Garden City Texas
Posts: 795

I installed Grove wheels and brakes. I have 208 hours and 276 landings on my plane. My home grass runway is slightly downhill and 1700' long coming over 200' displaced electric lines so I have to get on the brakes sometimes landing when the wind is light. I am beginning my second condition inspection and after hearing all the brake wear stories, I ordered new pads and the brake rivet tool from ACS so I would be ready when I inspected my brakes. All four pads looked very similar to the pic below comparing the new pad with the old so I'm good for now on the pads.

I installed the spring mod but can still hear the brakes dragging a little at times when on an asphalt taxiway.
Mike Hillger
Garden City, Texas
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