(RV-7A) Brake Upgrade

This applies to Parker brakes that were supplied in my RV-7A kit. I think newer kits may have Matco wheels and brakes.

My brake disks were past the wear limits with about 1100 hours on my RV-7A. I use the brakes to make turn-offs rather than coast on a runway to a subsequent turnoff. I taxi a short distance for take off and landing at my home airport, KHIO. My nose wheel break-out force is high. Reading posts from DanH and other's I decided to install thicker disk's to get higher kinetic energy rating (search VAF for "kinetic energy rating" for more discussion).

My worn brake rotor weighed 1.313lbs and were just under 0.15" thick.
A disk from a friend with about 100 hours on his similar plane weighed 1.449lbs and measured 0.178" thick. I've read on VAF that new stock rotors are 0.187". I did not find spec's for the weight of new rotors, I'd guess new weight at 1.5lbs. The new Rapco rotors are about 0.300" thick (I measured 0.294") and weigh just under 2lbs (1.986).



I made spacers for the caliper from 1/8" thick 6061T6.



I replaced the pair of AN4H15A's that hold the caliper's together with AN4H16A's to allow for the spacer and for the thicker rotor. I also had to replace the three bolts that hold my wheel plant mount bracket with longer bolts and added washers so the pant mount bracket would not interfere with the new thicker disk.



Cost comparison, from Aircraft Spruce. The stock RAPCO brake disc (RA164-01700) is $83.75, the thicker RAPCO brake disk that I'm using (RA164-09900) is $96.75. The four bolts for the caliper are about $3, add another $5 for the bolts and washers to adjust the wheel pant mount. Total difference for the upgrade if the disc needs replacing is about $20 and about a pound increase in weight.

I have made a few flights with the upgraded disks. My old disks smelled HOT after most landings. The new disks do not. I'm glad I have Viton O-rings and MIL-H-83282 brake fluid (higher flash point).

Nice job, looks like a real improvement!

~Marc

Interesting upgrade. This is good info to know .... Thanks for posting !

I was just looking at the disc today on my 7. It is pretty close to the bracket - so the question on the extra thickness - it still the same center or on the outboard side?

Excellent post!

One thing you will notice as you use them is there will not be a heat track down on the bell as you see in your photo of the stock disc...... This disc will run cooler and greatly reduce the chance of a brake fire.

I have this disc on mt 6A for three years now and notice a reduction of pad wear also. The change is very worthwhile.

I think think majority of the additional thickness is on the same rotational center as the original disk. This is a picture of the old disc and new disc side by side with the 1/8" thick material I made the spacer from on top of the old disc.



Regards,

Roy Thoma said:

[...] I use the brakes to make turn-offs rather than coast on a runway to a subsequent turnoff [...]

Click to expand...

What, you have to use brakes to make that first turnoff on 31L?? Oh well I suppose I have to do that too on occasion

But seriously, thanks for this Roy! I'm at 1300 hrs and in the middle of a major maintenance marathon, and wheels / tires / brakes are a (relatively small) part of that. I'm pushing the limits on one rotor, getting close on the other but I'll probably put those off till my next annual, since I have enough to do right now just getting the engine mount & engine back on, and the prop, and the landing gear, and and and ... (I'll post about that soon).

Anyway good info, thanks for posting.

Curious about wear limits for the Rapco rotors and your plans. Going to run them down as thin as the Parker lower limit? Or something different?

Are there similar rotors available for Matco brakes?

rzbill said:

Curious about wear limits for the Rapco rotors and your plans. Going to run them down as thin as the Parker lower limit? Or something different?

Click to expand...

Bill -- I don't know the specific minimum thickness and will need to find that later. Wearing the thicker rotors to the original Parker lower limit with the spacer in place seems like a certain way to push the pistons out of their bore, resulting in no brakes, brake fluid everywhere and possibly a fire.

Ron RV8 said:

Are there similar rotors available for Matco brakes?

Click to expand...

Ron -- I don't know of similar rotors for Matco brakes. Do you know what weight plane the Matco brakes are rated for? George at Matcao has been very helpful in the past. Suggest checking with him. (http://www.matcomfg.com/index.html)

Regards,

Roy Thoma said:

This applies to Parker brakes that were supplied in my RV-7A kit. I think newer kits may have Matco wheels and brakes.

My brake disks were past the wear limits with about 1100 hours on my RV-7A. I use the brakes to make turn-offs rather than coast on a runway to a subsequent turnoff. I taxi a short distance for take off and landing at my home airport, KHIO. My nose wheel break-out force is high. Reading posts from DanH and other's I decided to install thicker disk's to get higher kinetic energy rating (search VAF for "kinetic energy rating" for more discussion).

My worn brake rotor weighed 1.313lbs and were just under 0.15" thick.
A disk from a friend with about 100 hours on his similar plane weighed 1.449lbs and measured 0.178" thick. I've read on VAF that new stock rotors are 0.187". I did not find spec's for the weight of new rotors, I'd guess new weight at 1.5lbs. The new Rapco rotors are about 0.300" thick (I measured 0.294") and weigh just under 2lbs (1.986).

I made spacers for the caliper from 1/8" thick 6061T6.

I replaced the pair of AN4H15A's that hold the caliper's together with AN4H16A's to allow for the spacer and for the thicker rotor. I also had to replace the three bolts that hold my wheel plant mount bracket with longer bolts and added washers so the pant mount bracket would not interfere with the new thicker disk.

Cost comparison, from Aircraft Spruce. The stock RAPCO brake disc (RA164-01700) is $83.75, the thicker RAPCO brake disk that I'm using (RA164-09900) is $96.75. The four bolts for the caliper are about $3, add another $5 for the bolts and washers to adjust the wheel pant mount. Total difference for the upgrade if the disc needs replacing is about $20 and about a pound increase in weight.

I have made a few flights with the upgraded disks. My old disks smelled HOT after most landings. The new disks do not. I'm glad I have Viton O-rings and MIL-H-83282 brake fluid (higher flash point).

Click to expand...

The Cleveland bolts are almost $11 a piece from ACS - is there a suitable replacement / substitution?

EDIT: Never mind - The standard AN4H bolts are like .74 if you eliminate the Cleveland name

Brake disk wear update

It's been almost 5 years and 800 (hobbs) hours since I installed thicker brake rotors. I measured the thicker rotors at 0.294" when new. Current measurement for the right rotor is 0.284" and 0.281" for the left rotor.

I'm a Happy Camper.

Regards,

June 2023 Thicker brake disk wear update

I just replaced my brake discs again. I got about 1000 hours on the thicker rotors. That's somewhat meaningless as the number of landings and the time steering while taxiing would be more useful. The thicker Rapco brake disc, (RA164-09900) that was $96.75 at the end of 2016 are now $207.95.

rzbill (Bill Pendergrass) asked about the wear limits for the thicker rotor. I found the answer is minimum thickness 0.275". Mine were 0.279 left and 0.281 right. See https://www.aircraftspruce.com/catalog/pdf/Brake-Cross-Reference-Web-2014.pdf

Regards,

Roy Thoma said:

This applies to Parker brakes that were supplied in my RV-7A kit. I think newer kits may have Matco wheels and brakes.

snipped

Reading posts from DanH and other's I decided to install thicker disk's to get higher kinetic energy rating (search VAF for "kinetic energy rating" for more discussion).

snipped

Click to expand...

Here is the link to the thread mentioned above. I've added a few photos to that thread.

https://vansairforce.net/community/showthread.php?t=10366

Excellent question by Bill

rzbill said:

Curious about wear limits for the Rapco rotors and your plans. Going to run them down as thin as the Parker lower limit? Or something different?

Click to expand...

My apologies for not responding sooner. Somehow, I never spotted this thread until today.

When using the .300" thick rotors, you will need to do one of three things to prevent the pistons from coming out to far when the brakes are worn out. FYI, the rotor and pad thickness limits are designed to prevent the piston from coming out to the 50% point. At that point it can **** [aka tilt sideways] and lock up the brakes Note: Not every meaning of that word is anatomical

1 Increase the minimum rotor thickness by .012"

2 Increase the brake pad minimum thickness by .012"

3 Remove .012" from your 1/8" [.3125"] shims

I didn't have this problem, as the rotors I bought off the Canard list were 3/8" [.375"] thick. The cardboard box they were in [unopened] must have been left on a damp floor, as the bottom surface was badly rusted. Not a problem for me, as I simply put them in the lathe and turned them down to 5/16" [.3215"]

Charlie

FYI, seen the below multiple times:

https://vansairforce.net/community/showthread.php?t=206981&highlight=brake

Ron RV8 said:

Are there similar rotors available for Matco brakes?

Click to expand...

No idea. That said, why not investigate how your Matco rotors compare to the Cleveland units? Does anyone at your airport or in your EAA chapter have the Cleveland brakes? FYI, the Cleveland wheels and brakes originally supplied with the earlier kits, are also used on Cessna 150s.

If the offset is reasonably close, perhaps you could buy the 3/8" [.370"] thick rotors and machine them down to 5/16" [.312"] on whichever side will [hopefully] bring the offset the same as the Matcos.

The .370" rotor is Cleveland P/N 164-08500. I'm sure Rapco makes a less expensive replacement.

Cleveland Model 164-01700 .187" Rotors (rotors included w/ 40-78B wheels) These were the stock parts supplied by Vans "back in the day".
Rotor minimum thickness .167"

Charlie

Running the RA164-0990 .300 discs using a 1/8" shim, you could wear the disc down to .270 and then replace the 1/8" shim with a 3/32" shim. At that point, you could wear the disc down to .240" and replace the 3/32" shim with a 1/16" shim. And replace the disc at .210.

At any time during this process, the piston will not travel beyond maximum limits.

If the rotor needs to be turned to remove grooves, just reduce the shim by the same amount.