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Brake upgrade.

S2D

S2D

MEMBER
Montana
I'm just getting tired of spongy brakes on this old pig. It's a constant battle each year to try to get the brakes to even give some semblance of braking action . Years ago I could stick this thing on it's nose if I wasn't careful and could land on a narrow road. Now I wonder if I'll still be going the same direction before I get stopped.
Original master cylinders are straight out of a 40s Studebaker. Originally the system used automotive brake fluid. But when it was changed over to Cleveland's, it went to 5606. Hoses from the cylinder to the brakes are pretty new.
Looking for ideas of getting more pressure to the brakes. Different master cylinders. Solid lines instead of flexible lines ??;


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Do you mean spongy or just can't seem to push hard enough?
Your flexible lines are already the high pressure type. They should not be the issue.
Have you blown out the entire system with air and refilled from the bottom?

When you changed to Clevelands were the brakes good for a while?

What type of wheel brakes were on it originally? Expander tube or shoe brakes?

It's important that the output pressure of the master cylinder matches the requirements of the wheel cylinders. Your wheel cylinders will require high pressure.
 
Did you break in the new brake shoes?? (Run them with brakes on to get them hot) when they went from asbestos to the new materials this became a needed step.


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Oh as you add MORE volume of brakes on disks the math don't work same. Can't think how to explain that right.... ratio of master cubic inches to cubic inches of brakes(fluid)


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If you head down to Olney, Tx, they'll sell you a set of brakes with a brand new 602 or 401 if your dead set on radials attached to them:wink:. If you need a master cylender, dad has a few old studebaker cars and pickups sitting around.
 
That looks like a lot of caliper. What are you trying to stop? Maybe you need vacuum assist - disc brakes have no "servo" effect.

I converted my ancient '66 Mustang convertible to front disc brakes, and have never really been happy. The 64 1/2 convert still has drum brakes, and stopping is much easier.
 
They orinially came with shoe brakes. I bought this one this way years ago. I know they can be made to set up hard cause I've done it before.
By spongy I mean once you start feeling pressure on the pedals, you can still push them half way to the firewall.
These brakes originally came with a snap ring on the pucks. They are no longer on the pucks. I don't know their purpose but maybe they are to hold the brakes close to the disk. All thiose pads springing back just a little displaces a lot of fluid.
I think I broke the pads in right. If I push on the brakes, then set the parking brakes, then grab another load of brake fluid, I can lock the brakes up. But that's kinda hard to do on landing without a couple extra hands.


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That kind of spongy is probably air. With your setup it is going to be difficult to get it all out.

Here is what I would do - I would put bleeder screws on the bottom of both calipers, and tie the lines together with a "Y" fitting, keeping in mind that you want no places in any brake lines where a point closer to the master is lower than any portion of the vertical line. No "dips" in the line.

I have seen Cubs that are impossible to bleed. I bet, when the gear legs are uncovered we will find an expansion loop. You cannot bleed a vertical expansion loop.
 
Cub Special Ed said:
If you head down to Olney, Tx, they'll sell you a set of brakes with a brand new 602 or 401 if your dead set on radials attached to them:wink:. If you need a master cylender, dad has a few old studebaker cars and pickups sitting around.
Click to expand...

The brakes probably cost more than my Snow.
 
bob turner said:
Here is what I would do - I would put bleeder screws on the bottom of both calipers, and tie the lines together with a "Y" fitting, keeping in mind that you want no places in any brake lines where a point closer to the master is lower than any portion of the vertical line. No "dips" in the line.

I have seen Cubs that are impossible to bleed. I bet, when the gear legs are uncovered we will find an expansion loop. You cannot bleed a vertical expansion loop.
Click to expand...

That would be an interesting project. Probably why it works better to bleed them when the are not attached.
should work the same if I just took the end caliper off and had it lower when bleeding.
 
mike mcs repair said:
Oh as you add MORE volume of brakes on disks the math don't work same. Can't think how to explain that right.... ratio of master cubic inches to cubic inches of brakes(fluid)


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Click to expand...

Yea, thats why I'm wondering if a different master cyl would help.
Small piston but larger displacement.

Might just have to spend a day rebleeding the whole thing, and put the snap rings in.
 
S2D said:
View attachment 37807
Click to expand...
Did you ever have a hard brake after the clips were removed?
I had a retractable geared plane where the lines went up from the wheel, across the wing, down, then under the floor boards and up to the masters. You could start out with a hard brake, retract the gear, come back and land with spongy or no brake. When pressure bleeding the brakes the fluid would bypass any air bubble leaving you with the false impression that all was good. When the gear retracted the bubble would shift it's location.

Try blowing out the entire system with air so that there is no fluid at all remaining. Then reverse pressure bleed through that top right bleeder until the reservoir is clear and full. Then using the brake pedal push out any air bubble which is trapped in the top of that right caliper.

Another thing, that disk is rusty which leads me to think that the pins which hold the calipers in place are also rusty. If the caliper pins are rusty or the plate in which they ride is not aligned with them, the caliper will bind. In this case even with a proper bleed job with no air in the system they will feel spongy. This is because when you step on the pedal, the pistons move but the caliper doesn't slide on it's pins. It twists so that the brake pad is only pushing on one side of the disc instead of clamping it. The pins must slide so that the brake pads can clamp both sides of the disc with equal effort.

With the 6 caliper bolts removed you should be able to very easily move the brake housing on it's pins in their bushings. If there is any resistance it is likely that you've found the problem. The pin to bushing clearances should feel sloppy. Sometimes the plate with the two bushings may be warped so that the bushings are not perfectly parallel.
 
S2D said:
The brakes probably cost more than my Snow.
Click to expand...

Oh, no doubt! They are outrageous. What i would try brian if you havnt already is use a clear tube on bleeder or go to parts store and get a brake bleed kit. You can have someone help you bleed and see if theres air bubbles in the fluid. If so your getting air somewhere.
 
Good thing about airplanes is that they are easier to diagnose than a car becouse of individual brakes. If both brakes are spongy id be looking more towards master cylender area. But you can do the method i described to see if you have air intrusion.
 
Since you mention a desire to try a different master cylinder, consider the Tilton 74 series masters, these are available in many different bore sizes allowing you to easily swap cylinders to tune the ratio of master to calipers.
These masters also can be side mounted as your original masters are. The side mount holes are 3" spacing and the drawings are available on the Tilton site.

Hoses, I would consider changing the hoses to a Teflon hose, there are many options here but commonly these are used with the stainless braid with proper AN fittings. The hoses are also available with a synthetic braid which has it's merits as well.
I would recommend working with graystonesystems, Bill Graystone will make the hoses to your specs and ship them out, sometimes within hours of your order. His website only touches on what he offers. He knows his stuff.

Seems I am forbidden to make a post with any links so I had to remove allot of useful info.
 
skywagon8a said:
Did you ever have a hard brake after the clips were removed?
I had a retractable geared plane where the lines went up from the wheel, across the wing, down, then under the floor boards and up to the masters. You could start out with a hard brake, retract the gear, come back and land with spongy or no brake. When pressure bleeding the brakes the fluid would bypass any air bubble leaving you with the false impression that all was good. When the gear retracted the bubble would shift it's location.

Try blowing out the entire system with air so that there is no fluid at all remaining. Then reverse pressure bleed through that top right bleeder until the reservoir is clear and full. Then using the brake pedal push out any air bubble which is trapped in the top of that right caliper.

Another thing, that disk is rusty which leads me to think that the pins which hold the calipers in place are also rusty. If the caliper pins are rusty or the plate in which they ride is not aligned with them, the caliper will bind. In this case even with a proper bleed job with no air in the system they will feel spongy. This is because when you step on the pedal, the pistons move but the caliper doesn't slide on it's pins. It twists so that the brake pad is only pushing on one side of the disc instead of clamping it. The pins must slide so that the brake pads can clamp both sides of the disc with equal effort.

With the 6 caliper bolts removed you should be able to very easily move the brake housing on it's pins in their bushings. If there is any resistance it is likely that you've found the problem. The pin to bushing clearances should feel sloppy. Sometimes the plate with the two bushings may be warped so that the bushings are not perfectly parallel.
Click to expand...


Yes, it has been hard without the clips.
Thanks for the ideas.
Haven't even used this plane this year. everything's getting rusty cause of all the rain we had.
Think I will just start by blowing everything out, overhauling the master cylinders ( all the seals are 5606 compatible except the check valve. so they go bad after a few years) then set up a good bleeder with clear lines and pull the end brake off to get it below the rest and see if that works.
Maybe this winter I will look into the different masters.
 
I switched from solid brake lines to all flexible on my Ag Cat, and the brakes are much more spongy than before. I’ve gotten used to it now so it’s not a big deal, just not the feel it used to be. I also bleed from the bottom up, makes a mess in the belly but it’s the only way to get the air out for sure.
 
CenterHillAg said:
I switched from solid brake lines to all flexible on my Ag Cat, and the brakes are much more spongy than before. I’ve gotten used to it now so it’s not a big deal, just not the feel it used to be. I also bleed from the bottom up, makes a mess in the belly but it’s the only way to get the air out for sure.
Click to expand...

I'm going to pick up a cap and cap the fitting coming out of the master cylinder to make sure its not that.
This might have gotten worse when I replaced the lines a few years ago. the old lines were probably so hard they had no give.
I've always bled for the bottom up too. I'll make a cap with a fitting to return the fluid to a container and pump and bang on everything for a while to see if I can eliminate any air.


Went out and removed one brake and polished the pins and bushings and checked op. No improvement. The torque "plate" is a huge cast block and doesn't appear to be warped.
 
You will also get spongy feeling if the pins on calipers are stuck in tourqe plates as it must flex caliper & torque plate instead of floating. I see you mentioned rust....


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I had a Cessna 210 I maintained years ago that would never bleed completely. Figured out to get it as good as I could and then put it in the customer's hanger, pump them up with the pedals and then lock the parking brake, next day good as new.
 
S2D said:
..
These brakes originally came with a snap ring on the pucks. They are no longer on the pucks. I don't know their purpose but maybe they are to hold the brakes close to the disk. All thiose pads springing back just a little displaces a lot of fluid. .
Click to expand...

could be.... makes sense.... all those leftover parts...
 
Lowering the last caliper is a great idea. I did 310 brakes on a Waco, and a buddy had a vacuum bottle, which we set up on the master cylinder. Pump from bottom, suck at top. Perfect.

For the Cubs, I just have a fitting for the master with a clear hose into a bottle. Somebody watches while I pump from the bottom. I also put extra bleeder screws at high points, and I can always get a teeny bit of air out even after careful bleeding.

The Cub with the expansion loops? We drained, and then slammed fluid in there at 35 psi - no improvement. We went back to a closed system.
 
Steve Pierce said:
I had a Cessna 210 I maintained years ago that would never bleed completely. Figured out to get it as good as I could and then put it in the customer's hanger, pump them up with the pedals and then lock the parking brake, next day good as new.
Click to expand...

Model 35 Bonanza was spongy after master cylinder overhauls. Last resort, owner went up to 12,000 and pushed the pedals a few times. No more spongy.
 
Used to run a small fleet of Piper Aztecs with the same configuration of calipers. We had to take them off, c-clamp the piston-side plate down snug to minimize the fluid volume, lay them out on a board to incline everything uphill and pressure bleed. Assuming it is air, all was good. The snap-rings are said to hold the pistons in place so as not to over-retract with seal roll, it gives you a bunch of pedal travel when they retract too far. I have not idea how they decide which ones get the rings.
Pressure bleeder is a god send, the one from ATS is great for the price.
I think brakes are responsible for a good part of my hair status (missing).
Ken
 
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