Brake Pedal feel?

[67 evil eleanor]

I've been working on the brakes for a couple of days now and seem not to be getting nowhere. When I push the pedal it goes about half the way down before I feel any resistance and the brakes work. I have read several threads on the subject but am still confused. Should the pedal be firm from when you first push on it? Like I said, it goes about half the way down before it seems to work. Also I have bled the lines and air pack several times starting with the air pack first with the same results. Am I looking at a master cylinder problem or is it the air pack?

 

[Barrman]

You are supposed to have about 2" of pedal travel before you get any pressure build up. If you are getting more, then you probably need to adjust your brake shoes.

The -20 manual calls it a "minor adjustment and it is real easy. Jack up an axle, spin a tire and using an 11/16" wrench on the adjust at either the 11 or 1 o'clock position of the backing plate. Turn it until you hear rubbing, but can't really feel any drag. Do both adjusters on each backing plate. Do both sides of each axle and move onto the next axle. This will raise your pedal up a lot.

You mention you had a solid but low pedal. If you have a spongy, low pedal then you still have air in there somewhere.

 

[G-Force]

Disconnect the brake pedal return spring and see how far the pedal drops. It might just be an adjustment on the push rod for the master cylinder. If it isn't like Barrman said above, adjust your brake shoes.

 

[67 evil eleanor]

I must add it seems there is no help from the air pack and it would take both feet to stop the truck.

 

[rlwm211]

I would do a brake shoe adjustment on all wheels. If the brakes are way out the pedal has to push 6x2=12 pistons so far that it runs out of travel before you get to the build up oint. You can pump the pedal andf see if the pressure point rises but even if it does you are not going to get a useful pedal.

You have to remember that the single circuit system has a very limited about of fluid displacement when you operate it. Even the air pack is limited.

You see, the displacement of the airpack piston is the same as the master so the airpack is also at the end of its travel when it finally reaches pressure build up.

If the pedal does not build up, there has to be a problem somewhere that prevents the movement of BFS to the pressure side of the pistons in both the master and airpack. Bad seals in the airpack could be a problem or the airpack may not be moving (or moving very little) internally at all

Hope this helps
RL

 

[67 evil eleanor]

Thanks for the reply. I agree and think it's a combo of problems mostly due to lack of service. I think, like you said, the brakes need to be adjusted. I also removed the air pack today and found fluid in the air space so it must be leaking in the piston area. Upon removal of the piston I noticed there are "crustrations" on the walls and thus leaking fluid. Also, I'm not sure but there may have been some DOT3 fluid added on top of the silicon fluid. When holding it up to the light in a glass jar, there is a red tinge to the color. My plan is to hone the piston wall and if the piston seals are not too scratched up, put it back together and see if it works.

 

[rlwm211]

It is not unusual for fluid to accumulate in the piston area. Once moisture gets in there it cannot get out very easily.

Be sure to check the compensator piston assembly as if this sticks the entire airpack will not work correctly.

The comepnsator is located very close to where the hydraulic line comes in from the master. In order to remove it you need to pull the air valve assembly.

One note, while rebuilding or otherwise, if you take the compensator assembly apart, do not remove the seals as the manual says when you take it out. This is how so many folks get messed up on these units. Wait until you are installing the new ones to remove the old ones. It is very easy to reverse a seal and the unit will not work properly if that happens.

CRANETRUCK a.k.a. Bjourn has wrtten extensively about the deuce as a vehicle and longer than most anyone else has been dealing with these and if you do a search for his name and also brakes or some other key word you will find a wealth of information based directly on experience.

Hope this helps
RL

 

[67 evil eleanor]

After a clean up with the air pack everything looks pretty good. The valve was free and seems to work. After reinstalling the air pack and bleeding it I'm still in the same boat. The first push on the brake pedal and its like no or very little brakes (maybe no air pack assist). When I "pump" the brakes the air pack seems to start working a little and the truck will stop quicker but is far from locking up the wheels. I bled the system again with the same results. I have read and searched for hints as to what is wrong but am still in the dark. The one thing that I haven't done is adjust the brake shoes. I'm not sure if this will help with the air pack working but it needs to be done anyway. OH, I also noticed when using the power bleeder with about 10 lbs pressure there was a slow drip from the master cylinder. I have a rebuild kit on the way and will repair it when it arrives. The funny thing is, there is no leak when not using the pressure bleeder even after pumping the brakes up and standing on them with both feet. I am a little confused on what to do next.

 

[Barrman]

Brake theory time.

Fluid pushed by the master cylinder piston moves pistons in each wheel cylinder. The master can only push so much fluid per push of the pedal. The pistons in each wheel cylinder are pushed back by the brake shoe springs. If you have a large gap between the shoes and the drum. All of the travel is used up just getting the shoes out to the drums. A fast pump doesn't let the springs pull the shoes all the way back in and they will now travel out further.

Adjust your shoes.

You should have a nice hard and high pedal with no air pressure in the tanks. The truck should lock up the tires without the air pack helping if you have the leg muscles for it.

 

[rlwm211]

From what the 67 evil eleanor mentioned, the master is leaking at the rear seal when the pressure bleeder is connected. That should not happen. Regardless of how much pressure the bleeder applies the rear master cylinder seal should not leak.

When you rebuild the master be sure to check and make sure the return port in the master is clear after honing. This is a tiny port from the resevoir to the front side of the piston in the main bore. If you need an explanation there is a great manual on JATONKA's site from Lockheed Wagner dating back to the post WWII days that has great cutaway drawings of the master cylinders typically used in military vehicles.

Without question, the brakes should be adjusted and depending on how long your truck sat before you bought it the wheel cylinder pistons may be rusted in place in their bores. On my deuce I found 5 out of 6 wheel cylinders had either one or both pistons and seals frozen in their bores.

The major problem in the deuce brake system is that moisure collects at the lowest points in the system. This includes the air pack and the wheel cylinders. If the brake system was left empty for any period of time there will be corrosion inside.

Let us know how things work out as you continue to troubleshoot and repair your brakes.

RL

 

[DeucesWild11]

I had all kinds of issues with my brakes, I rebuilt the airpack first. Did you do a complete rebuild or did you just clean it up a little? Here is a thread I put out with Photos that may help you. http://www.steelsoldiers.com/deuce/82753-my-airpack-rebuild-photos.html After I did the rebuild I was still losing some pressure in the pedal so I then rebuilt the M/C. Problem then solved. It's not that hard to rebuild both. Sounds like you may be loosing some air pressure in the airpack by a bad seal possibly internally. You should be able to stop the truck with one foot.

If I were you I would rebuild both for peace of mind.

 

[67 evil eleanor]

On the air pack I just cleaned it up a bit and honed the walls. I didn't see any damage to the cups and I feel they are OK. It also appeared the large piston was moving but I agree with the brakes not being adjusted there is too little fluid being moved to push the shoes firmly into the drums. This PM I was able to adjust three of the wheels on the back but ran into an issue with the fourth. The three I done were way out of adjustment and it required about a half a turn each on the cam to close shoe to where it felt right. On the fourth, I was unable to adjust it with the top cams period and even tried to use the bottom ones also. The wheel remained free with both the top and bottom cam adjustments all the way out. I ran into darkness and had to stop at removing the tires, but I plan to get back on it in the morning. I am "guessing" that there will be something broke or out of place when I get the drum off and see what's going on inside. Also today, I received the kit to rebuild the master cylinder and hope to knock that out too. I haven't made it to the front brakes period but suspect there may be adjustment problems there also. One things for sure, the more I learn and work on these vehicles, the more I love about them. I've had nothing but fun talking and learning from you guys and hope some day I can pass it on to others. And as a fellow Elvis fan I've been dying to use this........

love the avatar!

 

[67 evil eleanor]

OK, I've set all the brakes up and the pedal is firm from the top. I still can't stop the truck without standing on the brake with both feet. Crap! Not sure what to do now.

 

[G-Force]

Rebuild your air pack.

 

[67 evil eleanor]

Sounds right. Can you get parts to only rebuild the hydraulic piston part? The large piston and seal look new and appear to be in perfect condition. Also, I have read on some of the search material that there is a valve within the AP that controls it. When I took it apart, I noticed evidence that the large piston was moving but "I'm guessing" the problem is with it bypassing (maybe with the control part) and not helping the hydraulic assist.

I'm the horse.

 

[Barrman]

The kits available are for an entire rebuild. The -20 walks you through the entire process and it is pretty easy to do. I would suggest doing everything so you know for sure you didn't miss something.

You do have the long style older one, right? That is the version the kits are for. I haven't seen kits for the newer shorter air pack.

 

[67 evil eleanor]

I have the short one.....crap!