RV4 brake line routing and bleeding?

[Kooshball]

I will be rebuilding my right master cylinder soon and want to be prepared for bleeding the system.

My RV4 has a bleed fitting at the high point in the line, located in the cheek cowl, aft of the firewall. Is this the normal location for a bleed valve (I always thought they were down on the caliper)?

With a bleed valve at the top, and the caliper undisturbed, will I be able to get all the air out by bleeding between that top valve and the master cylinder or do I still need to bleed at the caliper?

Thx!

 

[Snowflake]

You should always bleed from the bottom up. Pump brake fluid into the bleed fitting on the caliper, bubbles rise out the top. Have someone flick the lines in the cockpit with their finger while you're pumping it in so the air bubbles move and coalesce before exiting into the reservoir on the firewall.

 

[RVFan671]

On the rv-4 specifically you need to pull the moubt bolt on the rudder pedal for the master cylender and flip it upside down to get them to bleed. I spent a couple hours trying to bleed until finally figuring it out. The rv-4s mount those cylenders "upside down" for clearance.

 

[Kooshball]

On the rv-4 specifically you need to pull the moubt bolt on the rudder pedal for the master cylender and flip it upside down to get them to bleed. I spent a couple hours trying to bleed until finally figuring it out. The rv-4s mount those cylenders "upside down" for clearance.

Won’t that also end up putting my reservoir upside down?

 

[RVFan671]

Oh, my reservoir is on the firewall... you might need to spin the reservoir so it is upright?

 

[Roadjunkie1]

Won’t that also end up putting my reservoir upside down?

Ummmmmm.........ummmmmmmmmmmmmmmm........ That's inventive........not sure I've seen that before. Huh. There is a whole lot going on in that picture..... Back out and take a wider view of that area. Just curious as to what all IS going on there......... What is the reservoir attached to? Is that the starter solenoid next to it...?

 

[Kooshball]

Ummmmmm.........ummmmmmmmmmmmmmmm........ That's inventive........not sure I've seen that before. Huh. There is a whole lot going on in that picture..... Back out and take a wider view of that area. Just curious as to what all IS going on there......... What is the reservoir attached to? Is that the starter solenoid next to it...?

I’m not at the plane but below is the best pics of the brake setup. The reservoir is mounted right into the master cylinder. And yes, I think that is the starter solenoid.

 

[Roadjunkie1]

OK; that clarifies some things. Yes, that is the starter solenoid. Interesting placement. Are there reservoirs on both master cylinders?

 

[Kooshball]

OK; that clarifies some things. Yes, that is the starter solenoid. Interesting placement. Are there reservoirs on both master cylinders?

Yes, they each have their own reservoir.

 

[Roadjunkie1]

My RV4 has a bleed fitting at the high point in the line, located in the cheek cowl, aft of the firewall. Is this the normal location for a bleed valve (I always thought they were down on the caliper)?

To answer this question: no; that is not normal placement for the reservoirs nor the bleeding valve. Not sure I've seen a bleeding valve in the brake line. But, be that as it may, that is what you have.

SO, Maybe this: you will need to empty the reservoir and that can be done when you take the master off. You will get some brake fluid out of your high pressure (to the brake) line so be prepared for that. Rebuild the master and put it back in place as it was removed. Fill the reservoir and slowly pump the brake with the upper/line bleed valve open until there is no air coming out, monitoring the fluid level in the reservoir. THEN go to the slave cylinder (caliper) and pump fluid UP from there with the upper/line bleed valve open until there is no air coming out. Do both (pump the brake and pump fluid from the slave) again to make sure there is no air. I would pre-pressure the system from the slave....I think...... Then test the brake (BEFORE you fire up the engine!!!) to make sure you have brake power. This MAY be the working solution. YMMV. No guarantees here.... Others might have other ideas. This is not a typical break line configuration. But that's OK; obviously it's been working........

 

[gasman]

With a bleed valve at the top, and the caliper undisturbed, will I be able to get all the air out by bleeding between that top valve and the master cylinder or do I still need to bleed at the caliper?

Thx!

With a bleeder valve at the highest point, you will need to pressure bleed from the slave (at the wheel) to the high bleeder.
And then pressure bleed from the master to the highest point.
Place a clear tube at the high point into a bottle. Pressure through the fill port in the reservoir. Make sure the pedal is pulled fully released and you to confirm the cylinder port is open.

 

[Kooshball]

With a bleeder valve at the highest point, you will need to pressure bleed from the slave (at the wheel) to the high bleeder.
And then pressure bleed from the master to the highest point.
Place a clear tube at the high point into a bottle. Pressure through the fill port in the reservoir. Make sure the pedal is pulled fully released and you to confirm the cylinder port is open.

Any idea what size / type fitting I will need to install at the top of the reservoir to pressure bleed it from there?

 

[Roadjunkie1]

With a bleeder valve at the highest point, you will need to pressure bleed from the slave (at the wheel) to the high bleeder.
And then pressure bleed from the master to the highest point.
Place a clear tube at the high point into a bottle. Pressure through the fill port in the reservoir. Make sure the pedal is pulled fully released and you to confirm the cylinder port is open.

Hm....but the reservoir is a passive flow 'device' that would work no different from a reservoir on the firewall. Would not the pressure in the brake line come from the master cylinder? I'm trying to visualize what putting pressure in the reservoir would accomplish? Splain, please!

 

[Kooshball]

I think we are all clear on the geometry of my setup but here is a pick of the high-point bleeder inside the cheek cowl.

 

[Roadjunkie1]

Well, that's entertaining!! About what I visualized but a bit more complicated. Looks like the cheek cowl is hinged.... What is the other line going back on the left? And it looks like the fuel tank vent line is just hanging out in space on the right side? Is that what that is? What is the fire sleeve covering? Curious.........

 

[gasman]

Hm....but the reservoir is a passive flow 'device' that would work no different from a reservoir on the firewall. Would not the pressure in the brake line come from the master cylinder? I'm trying to visualize what putting pressure in the reservoir would accomplish? Splain, please!

In this situation, the master is mounted with the inlet at the bottom with the res attached. If the cap of the res is such that a fitting can replace the cap, then the easiest and cleanest way is to pressure at the start of the fluid supply (the res cap) so when finished, just siphon off a small amount from the res and cap it off. Everything stays connected and stays in place.

 

[Kooshball]

Well, that's entertaining!! About what I visualized but a bit more complicated. Looks like the cheek cowl is hinged.... What is the other line going back on the left? And it looks like the fuel tank vent line is just hanging out in space on the right side? Is that what that is? What is the fire sleeve covering? Curious.........

I’m not sure I see a fuel vent…but the line on the left is the sleeve that the piano wire goes through to secure the top and bottom cowl. The fire sleeve is on one of the oil lines connected to my remote oil tank since I have a dry sump inverted system.

 

[gasman]

Any idea what size / type fitting I will need to install at the top of the reservoir to pressure bleed it from there?

Looks like you have a bleeder valve already attached in the picture. Just connect a clear tube to it and place the other end in a jar and leave it there till done. Pressure up from each side, one at a time until there is no air discharged. Shut off the bleeder at the wheel, then at the top and remove the tube. Last, remove the tube to the reservoir. Remove the fitting and suck out a small amount for an air space and replace the cap.

Read the post 16 also.....

 

[Roadjunkie1]

Post #10 says about the same thing.....if I am reading this correctly.....

 

[Pat Falley]

Seems like it might work this way...
(Do one side at a time) Start by filling the reservoir and bleed the brake old school, that is top to bottom. You will need an assistant to open and close the caliper bleeder valve after you pump up and hold pressure on the pedal. Once all the air is out of the line, fill up the reservoir. You will probably find, however, that the brake is spongy. New RV4 guys usually get to this point !!%%$#!, there is a bubble inside the caliper you can't get out. Since you have a high point bleeder, you can now open it and pump fluid uphill from the caliper bleeder valve. The bubble should emerge and go out the high point bleeder, and you are done.

This avoids flipping the master cylinder trick, but you need an assistant.

 

[sf3543]

I will be rebuilding my right master cylinder soon and want to be prepared for bleeding the system.

My RV4 has a bleed fitting at the high point in the line, located in the cheek cowl, aft of the firewall. Is this the normal location for a bleed valve (I always thought they were down on the caliper)?

With a bleed valve at the top, and the caliper undisturbed, will I be able to get all the air out by bleeding between that top valve and the master cylinder or do I still need to bleed at the caliper?

Thx!

You might consider rearranging your master cylinder set up. My RV4 plans show them mounted right side up and there is plenty of clearance assuming you have the correct
ones. There are at least two types, one fatter than the other. As shown in the picture the part called out in the newer RV4 plans fit just fine and wouldn’t require unbolting from the pedal for bottom up bleeding. You could still use your existing reservoirs. YMMV:

 

[HFS]

EZ-FILL Brake Reservoir Fitting

This is a little fitting I make to automatically retain the necessary "head space" (air gap) in your brake fluid reservoir when bleeding the brakes. Especially handy in those situations where "mini" reservoirs are mounted on the brake master cylinders, deep down in the "well" of the fuselage.

When installed, the tube inside the reservoir limits the level of fluid rise when bleeding, before overflowing the excess to a catch basin - with the air "gap" above being maintained for future use when operating the brake system.

Most reservoirs have a 1/8-27 NPT thread, but there are a few out there that use 1/4-18 NPT - and I make both sizes.

This is just an idea that I DIYed because I could, but anyone can do the same ...

If anyone has any interest, I'll be glad to send one for your toolbox ...

HFS

The "attached" op instructions are for a FW mounted reservoir, but works just the same on reservoirs on master cylinders ...