As I said before thanks to everyone for all the information. It always helps to know more about what you're working on. When I was speaking of rebuilding the cylinders I meant the Brake master cylinder and the inching pedal master cylinder. I adjusted the clevis to what I believe to be the point indicated by a couple of you in this thread. After putting everything back together I have functional brakes, for now. They worked well the last time too, until they built up enough pressure to lock up. I will keep you posted on their functionality and request further guidance in the event that they lock up again.

Swoop...my information is from doing brake jobs on some of these older C500's, just so you know.
There is bolts on the front side of the frame that are in a half moon arc and on the back side there is nuts, the axle assembly has studs that are quite long that go thru, when you pull the axle assembly off you are pulling the drive shaft along with it, this whole assembly weighs a good 100 lbs or more, the front of the assembly is a planetary gear style drive unit that is why the brake shoes and hardware are on the back side of the drive unit, it is a bear to get to them so when you do get it off is good to replace all parts and hardware while in there so you don't have to "go in" a second time. there is a small brake line on the inside that I would definitely replace as it never comes out and is usually rusted fast and twists when trying to remove it

Well i'm a bit confused, especially after kevin comes in and mentions what type of brake setup is in the axle/wheels from what information he may have. BUT.....

jam did mention earlier in this thread that....

'In addition I removed and rebuild both the inching and break cylinders within the last month.'
so was he referring to the inching cylinder and the master cylinder? or the wheel cylinders...
some clarification might be in order here.

His statement was just a general non-specific one that didnt clarify which other cylinder(s) he meant.

Being that jam has openly admitted his novice status working on these units it seems he would have mentioned how difficult this brake cylinder(s) rebuild would have been. EVERYONE i've ever known that has worked on those 'in-axle' systems has expressed how difficult they are to do and that it takes a minimum of 8hrs to do them being that you have to take the axles apart just to get to them.

Well- since your confident in your abilities- here it goes- exactly what symptoms do you have? The last thing I see on this thread is the locking up issue. I see that you adjusted the brake rod- did the brakes re-lock? Is the inching pedal working correctly? What exactly are you asking?

Thanks for the information. I will take it under consideration. However, I had never used a fork lift 3 months ago when I got here, and the two we have had not been functional for many years. In those three months, I have figured out how to fix every aspect of both of them, ( hydraulics, engines, carbs, radiators, fuel tanks, and almost everything you can imagine that can be wrong with old lifts like these) except for this one's brakes. I fixed the inching pedal on this one and the the brakes ran well for a while. Then for some unknown reason they locked up. When I disassembled the brake master cylinder for the second time I saw nothing that was out of place. Therefore, I am asking for any insight into the working of this particular system. When I say I am new to this, I mean fork lifts only. We disassemble and repair planesm, among other tasks, here in our shop. The inching pedal works great and so does the parking brake. So at no point am I in danger of not being able to stop the lift. I would just like to get all of it running properly to fully complete the task I started. We have jacks that are more than capable of lifting the truck and if I need to get inside the axle, I will do that as well. It's never too late to learn something new, and all obstacles can be overcome with persistence and determination. With helpful tips from you guys I have been able to do so much already. But rest assured, anything I do will be done in a safe and controlled manner. Thanks again

PLUS...the brake system on this old truck is a little different than automotive brakes, yes it has brake shoes but they are internal shoes and if it is a problem with the shoes/wheel cylinders then the whole axle end needs to be removed as the shoes and everything are on the inside/backside of the axle end, NOT a job for a novice to try and undertake in ANY regards

Nothing personal/no disrespect Jam- but if you're unsure of how brake systems works/functions, you will be better off having someone come out & diagnose this for you. A brake system is not a place you want to try things by trial & error. Your lift weighs in exscess of 8000 lbs empty- around 12000 lbs fully loaded. If you service the brakes, the worst time to find out you did something wrong is when you can't stop.

I would STRONGLY suggest you buy a book on automotive brake systems & get familiar with the parts/theories that make the system work before you hurt yourself/others or damage something. I have seen many accidents/injuries from such a undertaking- trying to fix something which you don't understand how it operates.

that little 'one way' valve lets fluid exit the chamber but prevents it from returning. This keeps the fluid from being 'sucked' back into the chamber when the pedal is released and the piston returns to its home position, instead it forces the chamber pressure to pull fluid from the reservoir. It also aids in bleeding the air out and doesn't allow the piston to pull air bubbles back into the chamber. When i replace a master cylinder i request a reseal kit which usually includes this valve (on the cat trucks i've done) not sure about other brands.

This valve was fairly common on older trucks years ago but since then most mfg's have gotten away from this valve and the ports are just open now on newer systems.

As long as that valve is closing properly and not damaged in any way the system should pump up and bleed out correctly and easily.

If you have good pedal pressure but still have no brake actuation in the wheels i doubt your problem is in the master cylinder. I would look at the wheels, backing plates etc. In alot of cases i've seen where brakes have good pedal but no stopping power its usually in the wheels, wet shoes, worn backing plates or some type of hardware issue 'in the wheels'.

ok now for a dumb question, does this lift have any type of brake assist valve like a lock valve? 'mico brake lock' ???
just curious and off the wall but i had to ask ;o)

Ok, I have the entire Master Cylinder off and apart. I do not see any residual pressure relief valve. The only spring I have found is the main piston return spring. This spring has a little valve on the end of it with a rubber diaphragm inside of it's housing. It appears that it only allows fluid to go through it one way. Therefore I am unsure of how any pressure could ever be released off the breaks. As I said before I am very new to fork lifts and motor components. I am mechanically inclined but don't see any other way of putting this back together. I have looked at images online of similar products and i feel I have the orientation correct. However, A diagram or walk through would be much appreciated. Thanks again for all the help.

I was unaware of what you meant when you were speaking of it earlier. Thanks for the info. I don't remember seeing any spring on the master cylinder at all when I cleaned and rebuilt it recently. I will have to take another look. Thanks again!

The "pressure relief valve" is actually the "residual pressure check valve" I cited earlier in this thread.
If the master cylinder has one, it will require disassembly of the brake master cylinder to see it.
These valves generally are the very last component to come out of the master cylinder during disassembly and may in fact be be an integral part of the piston group of parts.
The residual pressure check valve has some type of spring to push the valve face down against the fluid outlet/return passage of the cylinder.
It is this spring which sets the amount of the residual pressure which will be held in the plumbing between the brake master cylinder and the wheel cylinder rubber cups.

I have noticed that the parking brake has it's own system on a cable and is not connected to the brake fluid system. i adjusted it just in case i overlooked something. I was unaware of the pressure relief valve on the brake cylinder. I will look for it and try to determine if it is functioning properly. Thanks for the heads up. I will give this a try.

You are correct that the 2 systems are connected, but working with the inching system shouldn't affect the brake side if everything is working/adjusted properly.

You say you've rebuilt the both master cyl's- perhaps the maladjustment occured at that point. The brake system is exactly the same as any light duty truck/car without anti-lock brakes.If you do research on automotive brake systems, it'll get you in the ballpark with your lift

As far as the inching system- it's also very simple in theory & operation. As you depress the inching pedal- 2 distinct operations are in play. 1rst- pressure from the master cylinder applies to a valve in the trans which dumps the pressure which was going to the clutch plates. 2nd- pressure from the master cylinder applies to a piston ( the long cylinder with all the brake lines going to it behind the upright, on the front of the diff)- this cylinder in turn applies pressure to the brakes.

There is a difference in the master cyl's which is important- the brake master cyl ( right side) has a pressure releif valve which holds pressure in the brake system at about 6 lbs. This is to keep all wheel cyl's slightly pressurized to eliminate air seepage into the system. The inching master cyl (left side) has no such provision- no pressure is held in that system.

If the clevis is improperly adjusted (no freeplay) on the brake side, the brakes will slowly but surely hold more & more residual pressure until the brakes become locked. If the clevis on the inching side has no freeplay, the system will also hold more & more resicual pressure, eventually causing the trans to slip.

Also- on this model lift- the parking brake is not in the wheels, but has it's own drum & brake shoes under the trans. Adjust the p.brake to hold the lift still while idling (or just slightly higher than idle). Any looser than that is useless, tighter than that will stretch the cable &/or wear/break the handle assy.

Okay, so I have adjusted the clevis on the Brake and also adjusted the parking break just in case. there appears to be free play in both. However, i have to note that the inching pedal didn't work until i recently replaced the inching valve. The next week was when I suddenly had the break locking problem. I find this a little more than coincidental since the inching pedal and breaks are related. Perhaps the inching clevis needs adjusting? In addition I removed and rebuild both the inching and break cylinders within the last month. Any insight involving this new information and how to pinpoint my problem would be helpful. I am handy but my knowledge of this system is minimal and I find out most of what I learn from you guys or trial and error....mostly the latter. LOL

jam,
just relieving the pressure off the master cylinder will not fix the problem bbforks was pointing out. All brake systems require a certain amount of 'freeplay' in the pedal linkage/mastercylinder.
the way to check this is to lightly depress the pedal and see how far it moves before you feel the rod start pushing the piston in the mastercylinder. There is a very distinct difference, so you can tell when the adjusting rod hits the piston. That travel should be about 1/4 inch and no more than 1/2 inch movement "BEFORE" the adjusting rod touches the master cylinder piston. This is called "freeplay". If there is no freeplay the system will just keep pumping itself back up again because the piston inside the master cylinder is not returning completely as bbforks explained earlier.

I would definatly say this is causing the rockhard pedal and brake lockup.

Now as for this 'checkvalve' lift1mech is talking about? i have seen those in older lifts, they were commonly used to help the operation of the system but in todays master cylinders they did away with this valve. So unless this unit has the origional master cylinder or if it has been rebuilt and the kit had this check valve in it i wouldnt count on this being the issue. Worst case scenario if this valve went bad is just a mushy pedal from air or something. I suppose if it became stuck it may lockup the system but i have yet to see this happen in any of the ones i have dealt with, generally they deteriorate and just become ineffective.