Anyone using the Matco WHLBE9 dual piston calipers on an RV-7A/RV-9A?

[bruceh]

I'm helping another RV-9A owner with some braking issues.

First off, I have been in contact with George at Matco and he acknowledges the issue and is looking for a solution. He thinks that other RV's have also been using this dual piston caliper setup, but isn't sure, so I'm asking here.

Here is the situation: The dual piston calipers have a double thickness "brake plate". This is the part of the brake system that bolts on to the Van's U-403 brake flange which then is bolted to the gear leg to hold the brake system. The extra thickness of the brake plate precludes it from sitting on the outboard side of the brake flange, since there isn't enough room between the plate and the bolt that goes through the axle and brake flange. Installing the brake plate on the inboard side biases the calipers too far inboard and the outer pads when bolted onto the caliper (through a spacer) will lock up the brake disk rotor. The brake plate location means that the caliper pins can't "float" around the holes on the brake plate and stay freely over the brake disk rotor. The old pads were horribly worn and cooked on the outboard side and the inboard side pads were barely worn.

A couple of captioned photos are here:
https://www.overthehills.com/Airplanes/N762HV-Annual/n-3H5TWd/i-GG87Gms/A
https://www.overthehills.com/Airplanes/N762HV-Annual/n-3H5TWd/i-6Ld9c2P/A
https://www.overthehills.com/Airplanes/N762HV-Annual/n-3H5TWd/i-ZbZm4Lj/A

On my RV-9A I have the stock PH-1A single piston Matco brake calipers and the brake plate is only a single thickness. I originally had it mounted on the outboard side, per the plans, but later upgraded my Matco disks to their "High Energy" disks which are 1/4" thick instead of the stock 1/8" thickness. I had to move my brake plate over to the inboard side to accommodate this, along with using wider spacers and longer AN bolts. Blog post about my brake disk upgrade is here.

 

[climberrn]

Changing the torque plates out for the single plate thickness will give you a little more spacing. Are you able to move any wheel spacers inboard?

 

[bruceh]

Changing the torque plates out for the single plate thickness will give you a little more spacing. Are you able to move any wheel spacers inboard?

According to Matco, you cannot use the single thickness brake plate on the dual piston calipers. They aren't strong enough.
The options I got back from Matco were to either send in the brake plates to have material milled off of the brake plate lugs, or buy new brake plates that have been similarly modified, or to try and move the double thickness plate back over to the other side of the Van's brake flange and use a close tolerance pin instead of a socket head screw to secure it in place.
The new brake plates (with custom milling) are pretty affordable at $86 each, so that is what we are going to do. This way we will still have the original plates.
Putting in a pin is less expensive, but requires a lot of labor/fabrication/installation time and we'll have to figure out a way to retain the pins on the axle.
Matco did find that some customer out there has an RV6 with these dual piston calipers and apparently they were not customized from the factory.

 

[edhunter]

If you’re just trying to improve the braking on the 9a model, consider swapping in the rv14 brake kit. I did this on my 9a and it significantly helped. I just so happen to have the 14 calipers and rotors available w newish pads. No other changes needed.

 

[PilotjohnS]

I am curious why people are upgrading the stock brakes? Are you all landing too fast. Remember energy is speed squared so touch down speed is really important to be as slow as possible. .

 

[climberrn]

I am curious why people are upgrading the stock brakes? Are you all landing too fast. Remember energy is speed squared so touch down speed is really important to be as slow as possible. .

You are correct, but almost all of us modify our planes some way or another. It’s nice to make the turnoff you want without overheating the brakes. I rarely do that but its nice to have the braking available.

I don’t really *need the IO-390 but I wouldn’t give that up for anything!

 

[Majorpayne317641]

I am curious why people are upgrading the stock brakes? Are you all landing too fast. Remember energy is speed squared so touch down speed is really important to be as slow as possible. .

Have you ever taxied at Charlotte Intl or anywhere else where you have a 2+ mile taxi? The brakes are already at their limit before you take off.

 

[PilotjohnS]

Have you ever taxied at Charlotte Intl or anywhere else where you have a 2+ mile taxi? The brakes are already at their limit before you take off.

I see your point since brakes are used for steering. I do find the really big tail on the 9a alleviates a lot of the need for the brakes for steering if one uses lots of rudder in the prop wash.

 

[bruceh]

Yes, it is fairly easy to over cook the stock brakes. I know. I've done it!

The upgrade that I did on my RV-9A to go for the thicker disks (aka, High Energy, or HE) has effectively doubled the amount of heat that can be absorbed.

I think that going to the dual piston calipers in this builder's attempt to get better braking is misguided overkill. Twice the number of brake pads on the stock 1/8" thick disks!

Anyway, new modified brake plates have been ordered and I'll update this thread on the conclusion.

 

[bruceh]

Following up.
We got the milled down brake plates from Matco. Installation was pretty straightforward, but we did have to ditch the 13/32" spacers for the wheel pant brackets that are called out in the plans. This required us to put in some shorter AN4-7A bolts and used some normal and thin washers to get the correct 1/16" gap between the brake disk on the wheel and the wheel pant bracket. We also had to file off a little bit of the wheel pant bracket to allow the caliper to clear underneath it. We also got new O-rings in the calipers, rebuilt one of the master cylinders and then got the brakes bled with new Royco 782 fluid. No more binding on the brake pads and firm pedals.

New brake plates with milled ends to realign the geometry for the calipers to correctly float around the brake disk.

 

[Majorpayne317641]

Following up.
We got the milled down brake plates from Matco. Installation was pretty straightforward, but we did have to ditch the 13/32" spacers for the wheel pant brackets that are called out in the plans. This required us to put in some shorter AN4-7A bolts and used some normal and thin washers to get the correct 1/16" gap between the brake disk on the wheel and the wheel pant bracket. We also had to file off a little bit of the wheel pant bracket to allow the caliper to clear underneath it. We also got new O-rings in the calipers, rebuilt one of the master cylinders and then got the brakes bled with new Royco 782 fluid. No more binding on the brake pads and firm pedals.

New brake plates with milled ends to realign the geometry for the calipers to correctly float around the brake disk.

Thanks for the update. Did you get pictures of the install? I didn’t realize dual pistons also means double the brake pads. I thought it would just be a longer pad.

 

[bruceh]

I only took a couple of photos as we were putting it back together. My hands were gloved and very messy with brake fluid, so it was not the best time to be playing photographer with my iPhone.
The dual piston calipers have two pucks, two pads on each side and two spacers and four bolts holding them in place. The calipers at the top will interfere with the wheel pant bracket and it looks like the builder trimmed it back and then riveted on a doubler piece. The builder also had to grind a chamfer off a bit of the center of the brake plates to accommodate the weld on the brake mounting plate from Van's. I ended up putting a thin AN-960-416L washer between the powder coated brake mounting flange and the brake plate, then on the other side of the brake plate I put 2 AN-960-416 regular washers to get the spacing correct.

First attempt at reassembly. No thin washers between the mounting flange and brake plate. This caused some misalignment on the caliper guide holes. You can also just see the original spacers in the shadows of the brake plate. This is where we had to use shorter AN4-7A bolts and two regular thickness washers.