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Open Roads Forum  >  Class A Motorhomes  >  Maintenance Issues & Tips

 > ABS module bleed suggestions????

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lonfu

kingman arizona, middle of the desert

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Posted: 03/01/18 06:57am Link  |  Quote  |  Print  |  Notify Moderator

1998 p30 chassis, 4 wheel disc with hydraulic brake boost from the power steering pump. Replaced the master cylinder with a bench bleed. Replaced the hydraulic booster. Replaced all 4 brake calipers. Checked the very short flex brake lines, no expansion obvious. Changed to dot 5.1 or super dot 4. Problem is a spongy brake pedal with no ABS light. I've vacuum bleed and power pedal bled the system several times with clean airless brake fluid coming out. Total of one gallon of fluid. I've tied down the brake pedal for a couple of hours to let air out of the lines to the ABS module. Original service manual says to bleed like regular brakes. No special method for bleeding the ABS module. My tech2 code reader, when I go through special functions, reads that it "can't connect to ABS module". No ABS light.

So, I assume that the ABS module is not tech2 compliant and it won't work. Yes, I have pumped the brake 4 times to bring the system to 35 psi, held and then tried to connect. Tech2 reader works for all other functions. Other sites have suggested that the tech2 will not work on the p30 chassis ABS brake module.

BUT I STILL HAVE SPONGY BRAKES, WHICH INDICATES AIR IN THE LINES...

I can only assume that there must be air trapped in the ABS module. How do I get it out? I don't see any obvious bleeder valves on the module. I do see a hex head bolt/cap that sits flush with the body that is inaccessible without removing the entire module.

It is a real head scratcher for me??? Anybody have any suggestions as to what direction to go here??


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KJINTF

Western Montana

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Posted: 03/01/18 07:11am Link  |  Quote  |  Print  |  Notify Moderator

Check you chassis wiring diagram
Not sure about your chassis

My 2008 W16 chassis has two Data connectors similar to most Mid to large trucks
The standard DTC 16 pin OBDII port where my Tech2 connects

PLUS

A 9 pin round J1939 connector where the ABS module and two CAN Buss are connected - The ABS module is NOT connected to the standard 16 pin DTC Connector in any way

I use the NEXIQ protocol converter along with WABCO Tool box software to access the ABS module - Yes the Tool Box software offers an ABS Bleed function. It works great


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77rollalong

Brighton Ontario

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Posted: 03/01/18 07:15am Link  |  Quote  |  Print  |  Notify Moderator

I have used the scanner tool to bleed the abs pump, not sure exactly what it does within the pump. but it does work, then you re bleed the system again after and you should get a hard pedal.
This is out of Mitchels on demand

1) raise and support Vechicle. Begin at the right rear wheel. Install clear plastic hose to bleed screw. immerse other end of hose in contaimer that is partially filled with clean brake fluid

2) Open bleed screw 1/2 to 1 full turn. Have assistant slowly depress brake pedal untill reaches full travel. Hold pedal untill bleed screw is closed. Release brake pedal and wait 10 -15 sec. repeat untill clean bubble free brake fluid is present at wheel bleed screw.

3) Check master cylinder every 4-6 strokes of brake pedal to avoid running dry. repeat procedure on left rear, then right front, then left front. after bleeding all 4 wheel go to the next step

4) Using scan tool in function test, run function test 4 times consecutivels while appling the brake pedal firmly. release brake pedal between each test.

5) Rebleed all 4 wheels to remove remaining air from brake system. ensure brake pedal feel is appropriat befor attempting to drive vehicle. Re bleed as nessary to obtain appropriate pedal feel.

* This post was edited 03/01/18 07:33am by 77rollalong *

rgatijnet1

Florida

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Posted: 03/01/18 07:55am Link  |  Quote  |  Print  |  Notify Moderator

Did you change the short rubber brake line at the rear of your chassis at the same time you replaced the two front brake lines?

SidecarFlip

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Posted: 03/01/18 08:11am Link  |  Quote  |  Print  |  Notify Moderator

Most ABS modules have a Schrader bleed valve on the body somewhere.


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allbrandauto

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Posted: 03/01/18 01:00pm Link  |  Quote  |  Print  |  Notify Moderator

run into this problem many times pump brake pedal and hold crack open the lines going into the abs module from master cly.

shepfly

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Posted: 03/01/18 09:58pm Link  |  Quote  |  Print  |  Notify Moderator

Buy or borrow a Phoenix reverse brake bleeder, this forces brake fluid from the bleeder screw back thru the ABS pump to the master cylinder. Works for me on MC ABS systems which can be a bear! Dave

rgatijnet1

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Posted: 03/02/18 04:18am Link  |  Quote  |  Print  |  Notify Moderator

You have a 1998 P30 chassis. The brake pedal on this chassis will never be as firm as most other vehicles. Spongy is normal. If you do a search of the internet, you will find many others that have tried. The best thing you can do is to use a premium disc pad material on resurfaced/new rotors.

77rollalong

Brighton Ontario

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Posted: 03/02/18 05:22am Link  |  Quote  |  Print  |  Notify Moderator

The hydro boost does give a sense of a spongy brake, its best not to have the engine running and to pump down the pedal so you have no boost at all when bleeding the brakes, then when you get a hard pedal you know you do indeed have the air out.. with the 4 wheel disk brakes you should not be able to push the pedal down more than an inch or so before it stops.. Years ago i had an old Datsun 510 that i did a master cylinder in, but at the same time added a power brake booster out of a 240Z.. after bleeding the pedal would only drop a 1/2 inch with you foot.. start the motor and i could push the pedal right to the floor with your hand.. it was like driving the school bus i had with air brakes, 4 years later i brought the car in to have a safety check done, and the mechanic came to me after and commented on how well the car stopped..

lonfu

kingman arizona, middle of the desert

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Posted: 03/02/18 07:02am Link  |  Quote  |  Print  |  Notify Moderator

what year of coach do you have?


77rollalong wrote:

I have used the scanner tool to bleed the abs pump, not sure exactly what it does within the pump. but it does work, then you re bleed the system again after and you should get a hard pedal.
This is out of Mitchels on demand

1) raise and support Vechicle. Begin at the right rear wheel. Install clear plastic hose to bleed screw. immerse other end of hose in contaimer that is partially filled with clean brake fluid

2) Open bleed screw 1/2 to 1 full turn. Have assistant slowly depress brake pedal untill reaches full travel. Hold pedal untill bleed screw is closed. Release brake pedal and wait 10 -15 sec. repeat untill clean bubble free brake fluid is present at wheel bleed screw.

3) Check master cylinder every 4-6 strokes of brake pedal to avoid running dry. repeat procedure on left rear, then right front, then left front. after bleeding all 4 wheel go to the next step

4) Using scan tool in function test, run function test 4 times consecutivels while appling the brake pedal firmly. release brake pedal between each test.

5) Rebleed all 4 wheels to remove remaining air from brake system. ensure brake pedal feel is appropriat befor attempting to drive vehicle. Re bleed as nessary to obtain appropriate pedal feel.


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