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Leaking Matco master cylinders

alcladrv

Well Known Member
My pilot side Matco master cylinders just started seriously leaking this week after 9 yrs. and about 1000 hrs. My cylinders didn't have part numbers on them so I emailed Matco tech support about which rebuild kit is appropriate and got the following in return:

It should be an MCMC-4F. It has a half lug at the bottom making it either the MCMC-4F(R) or MCMC-4F(L). The rebuild kit is the same for both and it is the MCMCRBD4. You will find it on our website at:

http://www.matcomfg.com/MC4REBUILDKIT-idv-3130-46.html

The cylinder is at:

http://www.matcomfg.com/MASTERCYLINDERHalfLugLeft62-idv-3228-5.html

with the drawing at:

http://www.matcomfg.com/InstallationMC4FRLS-idv-2666-21.html

The standard VANS installation uses a bolt from the pedal to the shaft that is not restrained to the pedal. Since the load is offset from the pedal, there is a bending moment when force is applied to the shaft. Since the bolt is not restrained to the pedal, the bending moment is carried in the shaft and causes it to wear against the end gland. Some have changed to an all thread bolt so the bolt can be secured to the pedal with a nut. Some also reinforce the area of the pedal to better support the bending load. A better solution is to use a bolt that goes across both side of the pedal so the cantilever portion attached to the shaft is very rigidly supported for bending.

Please let me know if more is needed.

George R Happ
MATCO mfg

I ordered 2 rebuild kits for the pilot side cylinders. The right side cylinders have hardly ever been used and don't leak.

My installation was made per Vans plans. Another tech suggested that the service life I got out of these cylinders was pretty good and close to what can be expected.

I haven't had brake dragging issues and am only on my second set of brake pads since new. The current pads still haven't gotten down to the wear indicators.

I can see how the long bolts give better pedal response. But, I'm still unclear on how an all thread bolt attached to the pedal provides a more rigid installation to reduce the bending moments.

I'd appreciate any thoughts or pictures you might add.

Mike
 
My pilot side right master cylinder developed a small leak (drops on the floor) at 1,480 hrs. I replaced all three o-rings (like 90 cents). Unfortunately, during the process I damaged the Stat-0-seal (metal washer with rubber insert). Replaced it too. No leak afterwards. No other parts need replacement. I used Van's original hardware. No modification made.
 
Ditto

Hi Mike,

I had the same issue with my units on the pilots side only. Mine were actually leaking around the top where the center shaft exits the housing--and then running down the back side of the housing to deposit a small amount of fluid on the end of the housing along with a couple of drops on the carpet. You are right that the current install creates a side load on the masters----on mine you could actually see the burnish marks along one side of the center shaft where it exits the housing. I polished the center shafts, rebuilt all four masters, switched them from co-pilot side to pilot side, and modified the attach to reduce the side loads--so far after another 50 hrs no leaks. Don't like standing on my head in the footwell working on those masters.

Cheers,

db
 
Thanks for the response db.

What did you use to polish the center shafts?

How did you modify the master cylinder attachment to reduce side loads?

Thanks,

Mike
 
Repairs

While I had the masters apart, I put the center shaft in a drill press--clamping in the press at the top end which is never in contact with an o ring inside the cylinder and then used 600-1200-2000 grit sandpaper on the shaft. Be careful not to remove too much material---just enough to smooth the side burnish from the center shaft.

For the removal/reduction in side load, prior to removal of the master from the plane, I watched the movement of the shaft as pressure was placed on the brake pedal. You can see the upper inside (upper left on right pedal) of the pedal move more than the upper outside edge. This puts a twisting motion to the cylinder/shaft assembly. I tried to reduce this motion by using various spacers on the pedal bolts to get a better alignment, but the best way to do it is to use a single long bolt for the pedal pivot. I simply did not have access at the time and wanted to get the plane back together. Go to ACS and order four long bolts for this application.

I also switched the masters from co-pilot to pilot side since the co-pilot masters never leaked and the center shafts had no sign of side load--although I rebuilt all four while I was at it!!!!!

Hope this helps.

Cheers,

db
 
Thanks, Dave

The Matco tech talked about using an "all thread" bolt to attach the pedal to to the bottom mount of the cylinder. The plans installation just has a stack of washers between the pedal and the cylinder. I understood the tech to say that the looseness of that bolt creates some of the side loads. Did you use an "all thread" bolt and nut to secure the bolt to the pedal, then use whatever washers were needed to align the cylinder?

Mike
 
Hi Mike,

No, I did not have an "all thread" bolt and I used solid mild steel tubing spacers (vs stacks of washers), cut to the appropriate size. This reduces the "play" in the attach point. You do have to insure the tubing/spacer is snug around the bolt shaft and the ends of the spacer are cut square or you are back in the same situation.

I believe the main issue is the non-symetrical movement of the pedal due to seperate bolts attaching the pedal to the rudder tube, the use of stacks of washers for spacers, and the natural position of your foot when applying pressure to the brake pedal. The use of one long bolt all the way from one side of the pedal to the other would fix most of this issue. The next time I am up to standing on my head in the footwell I will replace my bolts with sinlge long bolts.

Cheers,

db
 
Followup

FWIW. Here's a followup to my Matco brake cylinder leaking issues.

I rebuilt both pilot side brake cylinders. The right side cylinders were untouched as they weren't leaking because they had hardly ever been used. I replaced the individual hinge pivot bolts on all 4 rudder pedals with a 6" length of 3/16" diameter music wire with a washer and 3/16" wheel collar with set screw on each end. Then I added external return springs to the pilot side brake cylinders.

This is the 3rd time I've tried to bleed the brakes from the bottom. I haven't been able to get that method to work. Filling and bleeding them from the top finally rewarded me with nice firm brake pedals.

I followed the building plans closely to get into the air as soon as possible when I built 9 yrs. ago. This appears to be a case where the original design lacks long-term durability. I think my total cost for a 36" length of music wire and 8 wheel collars was about $6.50 at the local R/C airplane hobby store. The 2 rebuild kits totaled about $27 from Matco, including shipping.

Mike
 
Hey Mike,

Glad to hear you "got er dun"!!

Not familiar with piano wire---do you have any pics of your installation.

I still need to fix the pivot point attach like you did---before I wear the center shafts again.

Cheers,

db
 
Resurrecting....

I just rebuilt both master cylinders in my -8A, due to a leak on the top of the left master cylinder discovered during my current condition inspection. The cylinder apparently has been intermittently leaking for a while since there was evidence of dried fluid on the cockpit floor when I bought the plane from the previous owner. Anyway, the leak seems to occur after heavy braking (I had been ground testing / conditioning new pads.) Later that day, I discovered fresh fluid on the floor, and when I pulled the front baggage floor, I discovered the source of the leak. When the master was removed from the pedal, you could feel the shaft binding a bit. I ordered Matco rebuild kits from Vans, which includes in addition to o-rings: springs, a stat-o-seal, and a new piston. When I disassembled the master, I discovered wear on the shaft - you could see "burnishing," but I could also feel the worn area was out-of-round. I disassembled the right master, and saw the same type of wear, but it did not feel out-of-round like the other shaft, so I ended up ordering two shafts from Matco. I had already modified the pedals with long bolts and return springs, but the rebuilt cylinders don't seem to require the the extra spring, so I decided to remove them. I added an extra washer next to the mounting tang on the rudder pedal frame to restrict the twisting of the master cylinder, and repositioned the tang slightly to help align the cylinder with the action of the brake pedal. Hopefully that will reduce the side loading / bending moment of the shaft during braking. Bottom line: when rebuilding the master cylinders, consider spending $10 more and get the complete kit, and be sure to inspect the shafts for abnormal wear - I'm pretty sure the out-of-round shaft caused the leak.
 
MATCO Support Solution - Clarified

After 1100 hours I'm tackling leaking brake master cylinders on my -8A. Have studied the responses to this thread but couldn't figure out how the 6 inch all-thread bolt or piano wire solution would work with my pedals. MATCO support quickly clarified the issue.

The best solution is a 6 inch bolt/piano wire connection across the pedal into the top lug of the master cylinder. Since my pedals don't have a hole drilled in the outer pedal flange to accomplish that, I figured the bolt was to connect the bottom lugs. Wrong - the bolt goes across the back side of the pedal to a newly drilled hole in the pedal flange.

Plan B - effective but not as effective - is an all thread shorter bolt between the existing hole on the inner flange through the master cylinder lug.
 
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