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front seat brakes versus rear seat brakesa

K

kevind

Registered User
Alaska
When flying w/instructor in my cub, he was constantly telling me " on the brakes". Thing is I already was. I thought it was maybe because I am short and was not getting full extension on my legs. I rigged my seat so my position was closer. I had plenty of muscle on them. Finally the instructor was in the front one day, he had the same problem and actually asked me to help him from the back. From the back seat I noticed the brakes responded like they should. Any ideas? Fluid levels are all maxed. I have not pulled the floorboards to check for obstructions (dirt) yet..I will, but thought I would throw this out there. Brakes and wheels are fairly new.
Thanks
 
the front pedals are bent probably too... the face of a front pedal should line up with the outbrd hole in other arm of it that wire goes in that heads back to rear master cylinders...

if bent they use up some of the front pedal's travel just sitting there... hence you might only get 1/3 of full working travel they originaly had before they(pedal part heal rest on) hits the front edge/floor board.....
 
What airplane
What master pedal
what wheel brakes

Super Cub?
Clevelands double puc?
BF's?
Bled lately?

Flew a super cub with 31's, boosters ,double puc's and still couldn't get on the brakes like the rear passenger.
 
This sounds like a problem that long legged pilots have. With one foot on the rudder pedal you can not bend the ankle far enough to fully depress the brake pedal. This is because, with long legs, your knees are too far forward thereby making it more difficult to push your heal fully as far as the pedal requires to be effective. Try attaching small blocks to the forward brake pedals.
 
Simple thing to check would be that the front brake pedals aren't bottoming out against the floor board at the front. If the wires that connect the front to the back are too long this will happen.
John
 
skywagon8a said:
This sounds like a problem that long legged pilots have. With one foot on the rudder pedal you can not bend the ankle far enough to fully depress the brake pedal. This is because, with long legs, your knees are too far forward thereby making it more difficult to push your heal fully as far as the pedal requires to be effective. Try attaching small blocks to the forward brake pedals.
Click to expand...

Actually if the rudder cables are too short this will impede the correct or should I say optimum heal to pedal angle. I set mine up so that the rudder pedal stops just short of the firewall when deflected left or right. Using this as a standard maximizes the forward position of the rudder pedals when parallel while still having full rudder deflection left and right. If you don't own boosters, there an affordable must. The original Scott diaphragms don't allow you take full advantage of the Cleveland's as well as allow to much travel before engaging. Easy fixes.
 
Front vs. Back brakes

Fortysix12 said:
Actually if the rudder cables are too short this will impede the correct or should I say optimum heal to pedal angle. I set mine up so that the rudder pedal stops just short of the firewall when deflected left or right. Using this as a standard maximizes the forward position of the rudder pedals when parallel while still having full rudder deflection left and right. If you don't own boosters, there an affordable must. The original Scott diaphragms don't allow you take full advantage of the Cleveland's as well as allow to much travel before engaging. Easy fixes.
Click to expand...


I am having the same problem with my 72' supercub brakes. The system has the Scott diaphragms and Cleveland double puck brakes. We were landing on a 900 foot strip in western colorado and I was on the brakes with everything I had in the front seat. The cliff edge was coming up so I yelled out to my passenger " Help me with the brakes" and he was able to lock them up from the back seat. I was just curious to hear what corrections were made to alleviate the problem from the original posting. I am looking into the floorboard issue, lengthening the rudder cables and Steve's booster setup. Thanks for your help!
 
btracy said:
flexing floorboards.
Click to expand...

i have the boosters, HD double puck brakes, still thought the brakes were weak...At tear down for rebuild, found the brake pedal doubler under the floor cracked in numerous places. The whole thing was flexing instead of applying pressure to the boosters
 
Brakes

bob turner said:
I have the opposite problem - cannot get a few of my older students off the brakes.
Click to expand...

I will investigate the pedals but without removing the floor I assume that an inspection and repair would be difficult. Is it possible to see the "doubler" without removing the floor? Since the rear brake pedals are working well I suspect some damage has occurred somewhere on it's way to the front brake pedals. I will let you know what I find. I guess I could always bring a passenger to brake for me! Thanks
 
I have 31" wheels with boosters and if there is one thing that has helped me is removing pads and cleaning pads and rotors with brake clean. Everytime we handle brake parts we have oil and or grease on our hands and it takes very little to adversly affect brakes. This may not be directly related to your issue but has made a big difference to my braking performance.
 
Moabpilot said:
I am having the same problem with my 72' supercub brakes. The system has the Scott diaphragms and Cleveland double puck brakes. We were landing on a 900 foot strip in western colorado and I was on the brakes with everything I had in the front seat. The cliff edge was coming up so I yelled out to my passenger " Help me with the brakes" and he was able to lock them up from the back seat. I was just curious to hear what corrections were made to alleviate the problem from the original posting. I am looking into the floorboard issue, lengthening the rudder cables and Steve's booster setup. Thanks for your help!
Click to expand...

The Scott diaphragms eventually take a set, you end up with less travel. The rubber gets hardened in a pushed forward position and won't displace the same amount of fluid. You can eliminate that problem with boosters....
 
Pretty common problem is the brake reinforcement cracking, causing the floorboards to flex and eventually crack. When I got my cub, with boosters and double pick Cleveland's and the brakes pumped way up, I wondered how people put them on there noses. The brakes sucked. Then I fixed the floor and brake channel. Woah now I know how they go on there noses. Night and day difference. I cut some inspection panels in my boot cowl under the brakes and was able to fix them. Pita, working through two small holes but it worked.
 
I agree with raisedbywolves etheir two inspection holes or one larger rectangular inspection hole in bottom of boot cowl.
 
We were able to cut an inspection hole in the boot cowl to investigate the floor and the metal brake channel. Everything looks to be in original 1972 working order with no cracks in the channel or the floor. However, The floorboard is flexing when pressure is applied to the front brakes. Is it an issue to double the floorboard in that area with a thin sheet of aluminum bolted to the wood? The wood is just to thin to stay put under heavy braking pressure. (I really have to stand on them HARD to get positive braking) I am also curious if by installing boosters it takes less pressure on the brake pedals, eliminating the floorboard flex?
On a good note, topped off both the right and left master cylinder with 5606 which improved braking 20%
Thanks for your input.
 
Well, that blows my theory! I just looked over a J3 with very poor braking from the front seat, but good from the rear. Turned out to be a home-made swedged 1/8" cable connection between the pedals that was too long. Just couldn't pull the rear pedals hard enough.

John Scott
 
If thisis a Super Cub with stock masters and double- puck brakes that could be a problem - but we have a J-3 that has Seneca wheels and brakes and stock masters, and absolutely no problem in the front. We just caress the pedals and the thing stops.

I am with John - get the adjustable rods with clevises. The rear clevis is special, so probably just as cheap to buy them as to make them.
 
bob turner said:
If thisis a Super Cub with stock masters and double- puck brakes that could be a problem - but we have a J-3 that has Seneca wheels and brakes and stock masters, and absolutely no problem in the front. We just caress the pedals and the thing stops.

I am with John - get the adjustable rods with clevises. The rear clevis is special, so probably just as cheap to buy them as to make them.
Click to expand...


It is a supercub with stock masters and double puck brakes. 26" ABW's. After looking through all the post I'm guessing to have a combination of small issues. Flexing floorboards, a little slop in the brake linkage and no booster. Where do you recommend finding the adjustable steel rods with clevises?

I like the idea of having boosters, but I do want to perfect the system I currently have before band-aiding the other problems. The north river units are 1/2 the price of steve's but I wonder if that is even worth the trouble. Everyone seems to love Steve!

Thanks
 
Last edited:
If you have one insp hole cut I'd go ahead and put in the other so you can replace that reinforcing piece because if its stock yoooooull be back...
 
Moabpilot said:
It is a supercub with stock masters and double puck brakes. 26" ABW's.

I like the idea of having boosters, but I do want to perfect the system I currently have before band-aiding the other problems. The north river units are 1/2 the price of steve's but I wonder if that is even worth the trouble. Everyone seems to love Steve!

Thanks
Click to expand...

Your problem appears to be the wrong master cylinder for the tire/brake combination.

The original stock masters can only put out 350 pounds of pressure which is suitable for expander tube wheel brakes. The double puck Clevelands require a higher pressure with a smaller amount of fluid volume. Thereby the development of the North Rivers and Steves. The stock masters work fine if you are running small stock tires. Once you install a larger diameter tire, the extra tire radius has a larger mechanical advantage against the available braking power. Thus the need for more powerful brakes. Installing large tires and Clevelands is only a partial installation. The master cylinder needs to match.

The Steves unit is vented with a internal reservoir. The North River is a closed system which was designed to be simple and inexpensive. A simple bleeding system with reservoir can be added and has been shown elsewhere on this site. Plug: The North River kit can be accomplished without removing the original masters. The Steves replaces the entire master.
 
Here is an old picture of my brake cylinder mounted to a stock SCOTT frame with an original parking brake valve...

5641665762938895b8a64919be568d4a.jpg


Newer picture... Note the plugs on the side of the cylinder on the front of the cylinder... Those were added for clearance of the brake line when installing in a PA-12 with stock gear and bungee cords... Also works well for floor mounted PA-22 cylinders...

91e526d8944ed12cd5d80c4628c21f28.jpg


Last picture.... Pressure gauge testing.... This is with about 750 pounds or so of foot pressure on the peddle.... 1100 PSI...

b3cd33a7a3da57d687e2048bce708805.jpg


Brian
 
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