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Old 08-23-2011, 03:45 AM   #1
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Brake fluid or Hydraulic Fluid?

We replaced the master cylinder that has a tee connected for the Tandem Axle w/moe/ryde suspension hydraulic brakes. 1982 HR 33ft Imperial 454 Chevy. The disc brakes are working but there is a noise coming from the drum for the tag axle rear drum brakes. The noise sounds like the drum is empty. The cap reads heavy duty hydraulic fliud is this correct and can someone give me brand type? I have not seen Brake Hydraulic Fliud at auto parts, only jacks and equipment type hydraulic fluids. Also when fluid is added will just the drum brake need to be bleed and is this done the same as the disc brakes by pumping and holding brakes?
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Old 08-23-2011, 02:43 PM   #2
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Far as I know it uses regular DOT 3 brake fluid. Normal jack type fluid would not meet those specs for heat ands such. The posts I have read indicate that bleeding can be difficult but is performed in the same matter as regular brakes. The tag brake is just seperate independent brake system that is controled by primary system. Since you have come this far you should flush the tag system also.

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Old 08-23-2011, 03:46 PM   #3
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Yup. Standard DOT3 brake fluid.

One person at the bleeder on the wheel cylinder. One person pressing on the brakes. Since the tag system uses engine vacuum to work the master cylinder, you need to have the engine running.

Crack open the bleeder screw 1/4 to 1/2 turn, brake pedal down slowly. Close bleeder screw, brake pedal back up. Repeat until no more bubbles. Don't let the master cylinder run dry.

If you are starting with a dry master cylinder, you'll need to bleed it first. Same drill but since there is no bleed screw, crack loose the line coming out of it. Actually, if the master is dry you should probably replace it!

Mini-vacuum pump works good too if you have one.

I just redid my tag brakes so ask away if you have any problems.
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Old 08-23-2011, 06:04 PM   #4
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Thanks guys just a few more questions; The item that Im pointing at, what is it called and can I remove the top bolt and add fluid also too this? This item sends two hoses directly to drum master cylinder, the reason for this question; the lines that go back to the drum brakes have lots of curves and turns, should the drum be dry, would putting fluid at this point also speed up fluid flow to rear? also should engine run from beginning too end of the bleeding process?
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Old 08-23-2011, 07:37 PM   #5
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No you do not add fluid at that point. Those 2 hoses are vacuum lines, not brake lines. The bleeder valve is for the main system, not the tag system. I am Putting together a post describing the system. Will post shortly

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Old 08-23-2011, 08:23 PM   #6
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Sounds like Dave will get you straightened up shortly.

The big "drum" thingy is a vacuum diaphram. It is what pushes on the master cylinder to work the tag brakes.

BTW, have you pulled the tag drums to inspect the brakes? The drums are held on like the front drums on a rear-wheel drive car. Cotter pin and a big nut then they slide off. The drums are HEAVY so watch it. It would be a good time to repack the bearings so you'll need new grease seals too.
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Old 08-23-2011, 10:02 PM   #7
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Here is a diagram of your system:


First, understand that the Tag drum brake system operates at a lower psi pressure (around 800psi) than the chevy disc brake system (around 1000psi). If you operated the tag at the disc pressure then it may damage the drum brakes. The tag sycronyzer valve, booster, and master cylinder are used to operate the tag drum brake system at the proper pressure level. The brake line from the master cylinder you installed connects to the Tag Sychronyzer Relay Valve. That valve is a pressure transducer that controls the vacuum / air supply to the Tag Booster. When you depress the brakes, vacuum is applied to one side of the booster bladder and air is applied to the other side. The bladder is connected to the Tag master cylinder and operates the Tag MC piston which transfer the energy (via the brake fluid) to the drum wheel cylinders.
The bleeder valve you are pointing to here is used with the main system brakes, not the tag. This is the Sycronizer Valve and is only used to control the Air/Vacuum lines to the Tag Booster based on the main system (P30 in your case) hydraulic brake force.


Because the tag system is seperated from the chevy system via the sychronyzer valve, you would not feel the lost pressure when you open a tag wheel cylinder bleeder. The engine has to be running in order to have vacuum for the tag booster to operate.

While some tag systems use electric brakes controlled via a electronic Brake Controler, your system is not. The controller in your rig is installed for an actually trailer brake system, not your tag brake system.

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Old 08-23-2011, 10:11 PM   #8
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Good idea to pull the tag drums and look for a leak there. There is a reason the tag master cylinder is empty.
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Old 08-24-2011, 12:00 AM   #9
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thanks Dave diagram big help, my only fear was getting air into disc brakes line but the vacuum/air system solves that. We have filled reservoir twice with fluid removed line and fluid is flowing from MC. now it just a matter of PATIENCE. There is still ugly sound coming from tag booster, after fluid reaches back wheels hope enough fluid will have filled lines too stop noise. We will remove the drum brakes too check condition, sure we will be purchasing them also, its a 1982 what else. Should this noise not stop in the drum(tag Booster) will removing the brass T disconnect this tag axle? and would that be a option for me. A safe option? T picture below connected to rubber hose.
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Old 08-24-2011, 08:20 AM   #10
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Tag axles are added when the coach Mfg wants to increase the GVWR rating by increasing the rear GAWR. The brakes on the tag axle assists in stopping that additional weight. Could you disconnect them by eliminating the brass "T" at the main MC? Yes you could but from a safety perspective I do not feel many would agree with doing that. Additionally, you run the risk of falling periodic safety inspections (yearly here in VA).

Booster noise: Depends on what the noise is. Is this the sound of air rushing into the booster? Is the noise constant or is it just there when the pedal is pushed and/or released? Trying to determine if it is just normal air/vacuum noise flowing in and out of the chamber. Or is this a mecahnical noise from say a rusty Master cylinder bore?
As you can see there is not much to the inside of the booster. The part with the spring is the bladder. The rod in the center of it is the pushrod that pushes the tag master cylinder piston back and forth. As I said before, the Sycronizer Valve does nothing more than apply a vacuum to one side of the bladder resulting in the bladder pushing the pushrod into the master cylinder. Question is, is your bladder leaking resulting in the noise you hear?



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Old 08-24-2011, 04:02 PM   #11
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Problem Solved! we took MH too a local tire shop and got both sets back wheels off for disc brake system and re-bleed the whole system, also did same for the tag axle, noise stopped brake paddle firm, its a good chance that first bleed was poorly done, we were on soft ground and worked fast. Now everything seems to be fine, no leaks found, didnt remove drums,because checkbook stayed home. Trip planned for mid Sept will see what has to be replaced when we get back!! Thanks for the help you guys are the best!! I wanted the convertible!!!
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Old 08-24-2011, 05:56 PM   #12
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Dave, that is the best diagram of the tag axle I have seen, and I have looked a lot. Thanks for going to all the trouble. I have been wanting to work on my tag axle for awhile, but other things took more priority. You have really broken it down to something I can understand. Thanks.
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Old 08-24-2011, 08:20 PM   #13
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dspowers,
Thats great. You did the bulk of the work. The shop helped you finnese the end result. Enjoy the comfort of a good brake system.

Quietwater,
Glad the drawing helped. I noticed the limited amount of information on the net myself while trying to understand the system also. I also put together a lot of additional information on seperate thread:
Hydraulic Tag Axle Brake Information

Good luck,
Dave
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Old 08-24-2011, 08:25 PM   #14
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Quote:
Originally Posted by dspowers View Post
Problem Solved! we took MH too a local tire shop and got both sets back wheels off for disc brake system and re-bleed the whole system, also did same for the tag axle, noise stopped brake paddle firm, its a good chance that first bleed was poorly done, we were on soft ground and worked fast. Now everything seems to be fine, no leaks found, didnt remove drums,because checkbook stayed home. Trip planned for mid Sept will see what has to be replaced when we get back!! Thanks for the help you guys are the best!! I wanted the convertible!!!
Thank you for the update, they are important.
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