Hydraulic Tag Axle Brake Information

[Dave78Chief]

I have seen several references to people working on Tag axle brakes on the web but it seems most cannot find parts for them. The original Mfg of the brake system (Master Brake Inc.) is no longer in business. Here is some information I located that might help someone in the future:

Basic diagrams of Electric and Vacuum/Hydraulic brake system: http://www.primotrailersales.com/ima...%20Diagram.pdf
Even though trailer brake systems are shown a tag axle works the same way for the type of system (electric or vacuum/hydraulic) installed.

Midland Vacuum Booster/Master Cylinder (Bottom of pdf page 4 [catalog page 6]): http://www.bepco.biz/Catalogs/VacHydCat/S4_BOOSTERS.pdf. That was from BEPCO Products: Vacuums & Hydraulics

Midland Vacuum Booster/Master Cylinder (bottom of pdf page 100 [catalog page 2-24]): http://www.precisionrebuilders.com/p...ogPHB-0398.pdf.
In the same pdf file you will find the OEM Master Brake Booster/Master Cylinder AND the sycronization valve on pdf page 104 (catalog page 2-28). That pdf is from is from Precision Rebuilders: Welcome to Precision Rebuilders.com

While I do not know if the products from this manufacture are compatable with the older systems you could at least upgrade a hydraulic system to their product if need be: ELECTRIC VACUUM PUMP. Be sure and look at their other pages because they sell both systems and parts for their systems. Their systems are the ones pictured in the first pdf above. You would only need the VB-800 booster (750psi) for a tag axle system. Anything more would to high of a PSI value for the original tag implementation..

Older tag axle systems typically use Dextor axles and brakes. They were produced in both electric and hydrualic brake versions. Electric is controlled by an electric brake controller. There were 2 versions of hydraulic brakes. One has a bolt on wheel cylinder while the other has the wheel cylinder welded to the backing plate. Refer to the Dexter web site for further information. Dexter Axle - Trailer Axles and Running Gear Components - Parts Store_
The Coach Mfg to was the one who decided and installed a given tag axle system, not the chassis Mfg.

Most add-on tag axle systems are from MOR-ryde Corportation: MOR/ryde Home

MOR-ryde Legacy Owners Manual: http://www.morryde.com/downloads/tec...s%20Manual.pdf
MOR-ryde Legacy Service Manual: http://www.morryde.com/downloads/tec...e%20Manual.pdf

I located several pictures showing the installed and dissassembled parts here: Pictures by vicNmin - Photobucket

Again, I hope this helps someone in the future
Dave

[Dave78Chief]

Hydroboost based hydraulic tag system used on P30 chassis:


A Ford F53 chassis implementation is basically the same except that they use a Hydromax booster instead of a hydroboost booster for the main chassis. The tag system would be the same.

A Sychronizer valve:

The short tower section at the top is the hydraulic cylinder section (brake hose is attached to it in this picture). The bleeder zert fitting is for bleeding this portion of the main (hydroboost/hydroma) chassis system.
The large funnel section below that is used to control the vacuum signal to the Tag booster.
The lower half is the atmospheric air section to the other side of the booster.



The small black "U Cup" seal in this next picture is what fails resulting in brake fluid being sucked into the engine vacuum. Should be able to find it through a hydrulic supply house.


Tag Booster and Master Cylinder:



Tag Booster Bladder valve that engine vacuum acts on:


Dave

[Nick-B]

Hey Dave, AWESOME pictures and explanation.

You da MAN!

[96 Wideglide]

Thought I could hear 'air' while standing near the rear axles, and having someone pump the brake pedal .

[Dave78Chief]

There is another thread over on the IRV2 Newmar forum that demonstrates another variation of a tag axle system (Tag axle brake fluid).



IVR2 user Nick-B provides some excellant part resource information in post #17 (Tag axle brake fluid)

NAPA carries the 1950 Ford F3 (3/4 ton) master cylinder for that variation:
New: NMC M4572
Rebuilt: NMC P4572



Dave

[lynns69nova]

I reviewed your response to one of the other listings. I am hopeful you can help me out.

I have 1997 National RV Dolphin RV, w/ 7.5L Ford
Is it a P53 Chassis, is that correct?

my problem...

I have what sounds like a large vacuum leak @ the tag booster. The engine RPM's rev when applying the brake.
The red brake indicator light comes on when brake is applied.
I have inspected all hoses from booster to motor, all shows to be fine.
I know that National RV is no longer in business, do you know of any leads to find a tag booster and cylinder.

Thanks so much.
Lynn

[Dave78Chief]

If you look back at post 1, about 1/3 of the way down I posted links to booster and master cylinder rebuilders. I point to the the pages in their catalogs related to the tag axle components.

For Ford, you would have a F53 Motorhome chassis. The F53 chassis braking system is based on a Hydromax booster system which is a variation of the Hydroboost system I portrayed in the diagram above.

Dave.

[Nick-B]

Quote:

Originally Posted by lynns69nova my problem... I have what sounds like a large vacuum leak @ the tag booster. The engine RPM's rev when applying the brake. Sounds like the diaphram in the booster is torn. The red brake indicator light comes on when brake is applied. If you are saying that the red "Brake" light in the Ford gauge panel is coming on then that means the entire brake system (not just the tag system) is not right. Time for a complete overhaul. I have inspected all hoses from booster to motor, all shows to be fine. Good. I know that National RV is no longer in business, do you know of any leads to find a tag booster and cylinder. Even if they were in business, they would just refer you to Mor-Ryde or Dexter for parts and information.

Lynn,
I think I would find an RV wrecking yard to find a replacement vacuum booster.

Best of luck!