Tannewitz Brake Job

nektai · Post by **nektai** » Tue Nov 29, 2005 1:44 pm

Hello fellow Junkies,

I am struggling with the hydraulic brake system on my 30" Tannewitz bandsaw. This project had been looming as the performance of the brakes on the saw have been slowly deteriorating for a number of months. The project was forced on me the last time I used the saw as I noticed that the saw was not making max RPM. I started by trying to back off the brake pads on the upper wheel. I was not seeing movement in one of the bake pads so I figured it was time to remove the top wheel. Thus began the endless cycle of taking off and putting on the wheels.

I started by removing the brake pads and thoroughly cleaned all pivot points. I made the assumption that the sticky goop was preventing the pads from moving freely. The pads now moved freely and reflected every little adjustment perfectly. On goes the wheel. I adjust the pads to the recommended tolerance and test the brakes. It works so I move on to the lower wheel. I follow the same procedure and put the wheel back on. The lower wheel has a different pad adjusting mechanism than the top wheel and I am not seeing any movement in the pads nor am I getting any consistent braking power. I do not recall exactly what follows but wheels are coming on and off and I am now at my wits end.

Here is what I know;

One of the pistons on the top and one of the pistons on the bottom were frozen

All four pistons needed to be cleaned

While replacing one of the pistons I squirted a bit of fluid out of the cylinder as I poked at the cup to compress the spring. After completing this phase of the brake job I lost just about all braking action. Now I start to bleed the brakes as I figure that I have gotten air into the system. I start with the upper wheel as the bleeder valve is much more accessible. After no improvement I went in on the bottom wheel. This was the only way I could reach the valve.

It turns out that the bleeder valve is clogged and now i dismantle the cylinder and clean out the passageways (I drain all brake fluid at this point). Later I discovered that I did not follow the correct procedures for re assembling the slave cylinder so I took both of them apart again and this time made sure that the piston was in contact with the cup from the beginning so that there would not be any air trapped between them. I have bled the system but I get no movement from the pads when I fire the brakes. I should say that the wheels are off (the drum is part of the wheel) as I refuse to put them back. The rest of the brake assembly is in place. Here are my immediate questions;

Am I testing the system correctly or do i have to put the wheels back on?

Is there a procedure that I have missed when one completely drains a brake system?

Thanks fof the help

mr douglas t · Post by **mr douglas t** » Wed Nov 30, 2005 9:31 am

hello Nico,
I certainly see how a simple prodject turns out to be a very large one. I have many questions for you in order for me to understand what you have going on. You are on the right track, in that air in the system will prevent it from working. You do not need to put the wheels on the test the system. Your procedure for repair and bleeding is correct, but there are a lot of issues to watch carefully. What is the "Slave cylinder" that you mention. Is that the master cylinder with the small resevoir and selenoid that activates the brakes? The wheel cylinder must not only be clean, it must be smooth and not scored or scratched. I have a small "Hone" to clean and smooth the bore propoerly. The bleeder valves must function smoothly.
My procedure would be the same as yours. With all parts clean and back on the machine, check for leakes in the lines and on all connections. First, the slave cylinder must be bleed of all the air or you will pump air into the system. To do this you remove the lines that exit the slave cylinder and affix short temporary lines that go right back into the resevoir. than pumping the slave will circulate the fluid until the air is out. Than you can start by bleeding the wheel cylinders. The method of pumping the slave and opening the bleeder valve sucks. It takes a long time and doesn't always work. I have a small hand held vacume pump that you place on the open bleeder valve and it draws the fluid thru the system.

In order to test the system with out the wheels, I would put on the brake shoes and place a clamp across them. once the system has presure, and the slave cylinder does not bottem out and the clamp is "tightened" you could put the wheels on. You must however keep the pistons from extending out of the the wheel cylinders. The clamp is essential. Send me you address and I will UPS you my vacume pump. I would not attempt any brake job with out it. I also have short temp lines for bleeding the slave. Good luck.

nektai · Post by **nektai** » Wed Nov 30, 2005 11:48 am

Mr Douglas T,

I now believe that i will saw again someday soon- I had almost lost hope. I want to make sure that we are on the same page so I will ask you to confirm the names the following parts. I believe this first picture to be the Master Cylinder do you agree?

I referred to the next picture as the slave cylinder I think you called it the Wheel cylinder tell me which name you prefer and I will adopt it for consistency.

I will try to describe the process that I used for bleeding after the system had been drained and rebuilt-

First I pumped the master cylinder like crazy and did not manage to get any fluid to come out of the bleeder valve on the lower wheel. The Tannewitz manual suggests to always bleed the bottom wheel first.

I got frustrated and was about to start sucking on the bleeder tube but i thought better of it and went online to see if there was a pump that i could buy. I found a pump but I also came across a technique that used the spray mechanism from a Windex bottle connected directly to a bleeder hose. The fluid is sprayed into a clean bucket. It worked like a charm and after a fair amount of pumping fluid ran through without bubbles.

Next I used the Windex method on the top wheel. I tested the system and got no movement so I went back and bled the bottom and then top wheels with the bleeder bottle while hand pumping the master cylinder.

That is where I am.

Should i start again with the bleeding process?
Should I clamp the pads and try to build pressure?
Is this the correct way to clamp the brake pads and if I understood you correctly the clamp should be loose and the pressure from the master cylinder should tighten it?

Thanks for the help Mr Douglas T

mr douglas t · Post by **mr douglas t** » Wed Nov 30, 2005 9:50 pm

It sounds like you are making good progress. As for referance, the master cylinder is the top one that you had pictured. The wheel cylinders, or slave, are the ones in the drum. Are you getting fluid from the bleeder valve of both cylinders now, or just the bottem? Could you, when sucking on the upper wheel, draw fluid out of the lower wheel cylinder? I see a "Tee" where the lines divide right after the master cylinder. If needbee, you could separate the lines and isolate each wheel so when you suck from the bleeder valve, it pulls only from the master cylinder. You would of course have to plug the removed half of the tee to do this. It also looks like a very small resevoir on the master cylinder. Keep it full when sucking or you dont pull air into the system. the clamp position is correct. I think the clamp may have to be touching the shoes due to such a short stroke of the cylinder. Maybe a ratchet strap around the shoes. The clamp or wratchet strap would be my way of testing the system so you do not have to take the wheels on and off all day. when all is right, the master cylinders "stroke" should be stopped half way by the drums, or ratchet straps/ clamp. Is there an adjustment nut at the base of the shoes to spread them to the proper width?
I am a little worried about the upper cylinder not bleeding as well as the lower. Double check for any leakes in the lines. You may not see them, and when you suck on the bleeder, all you are doing is pulling air thru the leak. Also check the bleeder valve on the cylinder. It has a little hole in the side that allows the fluid to pass around the thread.
I would not be afraid to get a section of clear hose and manually suck the air out of the system. Make sure it i clear so you can see the fluid coming before you cet a mouth full. It sounds silly, but it allows you to guage the pressure needed and you can "feel" if you have a leek, or an obstruction or if fluid is slowly advancing. I would when ever possible avoid pumping the master cylinder rapidly. All that movement in the cylinder just allows for air to get in.

Another method I have heard of is gravity and time. Attach sections of hose to both bleeder valves. that are long enough to be placed just above the resevoir. Fill the resevoir and open the bleeder valves and than go to bed. By morning the bubbles have risen out of the system and you are good to go. Good luck.

nektai · Post by **nektai** » Fri Dec 02, 2005 10:43 am

Update;

I purchased a long section of hose, attached it to the bottom bleeder valve and sucked a massive amount of air out of the system. Next I gently pumped the master cylinder until the fluid in the tube was solid liquid without any bubbles. I thought I had it so I moved the bottle and tube to the floor so that I would not make too much of a mess when I disconnected the tube from the bleeder valve.

Gravity took over and fluid started to move and much to my dismay lots of air bubbles started to appear. I cycled a fir amount of fluid through the system but in the end I lost confidence in what i was doing.

Mr Douglas T,

I should have taken you up on your generous offer to send my your pump. I am out of time, I have a stack of maple that I have to resaw, so today I will buy a pump as that seems to be the best way to get the air out. Also the adjustment for the spacing of the pads is controlled by screws that can be reached from the back of the saw.

nektai · Post by **nektai** » Mon Dec 05, 2005 3:35 pm

I bought a pump and made a mess and then I found a leak!!

I cracked MSC to find a replacement for the copper tubing but I do not know what i am looking for. I need a tube or hose that can slink like a snake and hopefully be easier to work with than the copper. I have to replace the long piece that travels from the master cylinder to the bottom wheel. This is not going to be fun.

the leak is at the drip in the above picture.

mr douglas t · Post by **mr douglas t** » Tue Dec 06, 2005 12:43 am

What a relief to find the problem. Copper tubing is by far the most flexible. Home depot and most hardware stores sell it. In that size, it is commonly used to plumb the ice makers in fridgerators. You will need a flaring tool to flare the ends. Auto parts stores sell a fancy little hand held plier like tool for bending the lines with out kinking them. It is an artform to bend the lines to fit. Good luck.

crzypete · Post by **crzypete** » Tue Dec 06, 2005 10:06 am

Nico, I can't really tell from the photo, But you might be able to patch a small piece in- rather than slink the entire new piece. There are plenty of different couplings around for the flexible copper.

It is like douglas said, used for ice makers, but also for propane and natural gas. buy a cheap flaring tool, do a few samples, then when you do the reall thing, make sure you remember to but the nut on before you flare it- oldest mistake in the book.

Also, There are small tubing benders available, which would make that u-turn much easier.

Glad to hear you found the leak.

Pete

nektai · Post by **nektai** » Tue Dec 06, 2005 8:06 pm

Thanks for the info on the tube and the tools. I have ruined one piece of copper due to my stupidity. I bought a cheap flaring tool and a bending spring that will allow me to achieve the tight curves.

tomorrow should be a day of progress

Nico

nektai · Post by **nektai** » Thu Dec 08, 2005 7:40 pm

Tubing is all new and tight.

Brakes still sucked- no action at all so i pulled the master cylinder. It was all crudded up so i cleaned it and put it back on. There is still something wrong and I suspect that tomorrow night I will have to pull it again as seems to be hanging up on the return stroke.

I have pictures but will post over the weekend as right now I think I will trade the brake fluid for a glass of wine.

a humble Nico

nektai · Post by **nektai** » Fri Dec 09, 2005 8:48 pm

Success!!!

Here is the pic of the master cylinder as it came off the saw.

The crud that you see looks like it built up a long time ago. This would mean that i have been operating with a limited stroke. This was not too big a deal to me because if you remember I had two frozen pistons in the wheel cylinders so i must have had some sort of crippled balance. Everything was thrown out of whack when I drained the system while working on the bottom wheel cylinder. My theory is that the limited stroke on the Master cylinder prevented one of the chambers from filling up with fluid. The result was the same as having a leak and I could not get pressure even after fixing the actual leak that I had caused.

The episode that drove me to drink revolved around the gasket on the dumbbell like plunger on the right

The first time I took apart the master cylinder I was afraid to pry off the gasket. I did not want to break it and I was not sure if it was meant to come off. When I decided it had to go I found gunk and corrosion that had acted to expand the diameter of the gaskets seat. The result was that the spring did not have enough force to return the plunger to it proper position. Once the gunk was gone the master cylinder acted like it was supposed to and I was able to properly bleed the wheel cylinders.

The bottom line is that I was afraid of the brake system and as a result i treated its components one by one. My fear did not allow me to think of the system as a whole. Once I found a frozen part I should have realized that there were probably gunked parts elsewhere in the system. The moral of the story is if you are in a similar situation save yourself some time and drain the system and rebuild both cylinders and the master- you will save yourself a lot of work as the whole thing could be done in a few hours.

Nico

dadude · Post by **dadude** » Mon Mar 20, 2006 9:52 am

you guys amaze me at the fury in which you attack these machine rebuilds. just read your brake story and i must say that i am impressed with efforts and results, good stuff!

brad