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Old 06-18-2020, 12:30 AM
hughfi hughfi is offline
Join Date: May 2007
Location: Seattle
Posts: 151
Default Help... Cannot get brake lines to stop adding air to the lines.

Hi there,

I am just about finished my RV12is E-LSA but the brakes master cylinders keep adding air into the lines right from the first compression. Any ideas what I am doing wrong. Anyone know of an instruction guide on how to make the lines just right? I talked to Matco and they pretty much told me they should be fine if they extend fully open to allow fluid in from the top. Well, they are not and they are extending fully.

I am inclined to believe it has to do with the way I constructed the lines. Also, there appears to be different fittings to go over the lines on the top 45 degree fittings compared to the bottom 90 degree fittings.

Seems simple, and I have bled a bunch of brakes before on my RV6 with no problems, but I cannot stop these cylinders adding air to the lines.

Any advice or instruction greatly appreciated.

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Old 06-18-2020, 06:09 AM
Red Mtn flyer Red Mtn flyer is offline
Join Date: Jul 2017
Location: Carson City, NV
Posts: 128

You've probably self- diagnosed the issue.... Best option is to get some hand-on from a local who has done the deed, or a tech counselor, or an A&P [tho last doesn't mean they've actually worked on these - Nylo is not common in Part 23].
If you're using Nylo -- not specified. If Aeroquip or Stratoflex, or teflon - there are some construction details/ techniques unique to each that can cause problems. Again, getting an experienced somebody hands-on is your best bet.
Ben K.
A&P; RLSA - A,G,W/S Falco F-8L
50 yrs of flight and counting
Dues paid 2017 thru 2020
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Old 06-18-2020, 09:17 AM
lr172 lr172 is offline
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,735

Is the air upstream or downstream from the cylinder? I struggled with getting air upstream of the MC's and it required rebuilding the MC's, as the rubber seals dried out from age.

N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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Old 06-18-2020, 01:22 PM
Robertc's Avatar
Robertc Robertc is offline
Join Date: Jul 2015
Location: Omaha, NE
Posts: 69

Lr172 is right on. Be sure to check the piston rods for scoring and use plenty of petroleum jelly on the o-rings per Matco?s instructions. I got in trouble by getting fiberglass dust on the pistons during the build.Vans has replacement MC?s for about $100 and rebuild kits for a lot less, but it doesn?t include the rod. YMMV. BOB
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Old 06-18-2020, 01:52 PM
PilotjohnS PilotjohnS is offline
Join Date: Jan 2016
Location: Southwest
Posts: 1,839
Default Thanks for Post

Thanks for posting.
I will put blue painters tape on my master cylinders to prevent stuff from contaminating the rod and getting in the seals. Would never have thought of this without your post.
John S

WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

Dues paid 2021, worth every penny

RV9A- Status:
95% done, 5% left to go
Electrical/Panel done
Firewall Forward 95% done (waiting on fiberglass to be done)
Fiberglass 5%
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