ABS module bleed suggestions????

[lonfu]

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??

[lonfu]

yes, when I replaced the hydraulic booster that was in the instructions to bleed the pow steer pump. No, the problem for me was air trapped in the ABS module.... just couldn't get it out...tech2 scan tool glitch won't allow it to link up. Only 2 years of chevy 97 to mid 99 won't allow link up. Funny how it showed up on the pass front caliper. Drove to town yesterday and no brake drop at stop lights no pump up and it squats when I'm braking. The "slam on the brakes" method seems to be the answer for these year of P30 chassis. get the rear wheels off the ground, 55mph and "slam on the brakes" then re-bleed all 4 wheels. But I'll bet you only get bubble out of the front right caliper!!!!!

garry1p wrote:
I was having a heck of a time bleeding my brakes until I found the following note after a lot of searching brake problems.

"After bleeding the brakes on the P-30 chassis in the normal manner start engine and rotate steering wheel all the way to the stop in each direction two or three times".
Made a big difference in my brakes but they never work like a car or pick-up.

[garry1p]

I was having a heck of a time bleeding my brakes until I found the following note after a lot of searching brake problems.

"After bleeding the brakes on the P-30 chassis in the normal manner start engine and rotate steering wheel all the way to the stop in each direction two or three times".
Made a big difference in my brakes but they never work like a car or pick-up.

[lonfu]

Update!!!!!

I jacked up the rear of my 98 chevy P30 chassis, put jackstands under the rear axle..... easy peasy with the new 12 ton hydraulic bottle jack that the wife picked up for me at HF. 3 ton jack stands.

Ran it up to 55 mph, gave both rears wheels time to get to an even speed, then slammed on the brake as hard as I could.... did this 3 times, then shut it down and brake pedal bled all calipers with the engine off. Nothing new came out of the rear calipers. BUT... GOT SOME AIR BUBBLES FROM THE FRONT RIGHT CALIPER. So, I did it again and got some more air bubbles from the front right caliper...... Third time, no bubbles....

Pedal firmed right up, still just a bit more of a drop to the braking point than I would like, 1 to 1.5 inches, but the pedal doesn't drop, feels squishy or pump up. Poor wifes legs were jelly after pumping the pedal for hour!!! But couldn't have done it without her... and that hydraulic bottle jack... what a cool new tool!!

So, drove it up the dirt road across the street, pulled into the sand on the shoulder and slammed on the brakes.... I could feel the front wheels releasing and braking, yeah!!!! did this several times then tested on the pavement. It squats just like is did when it was new!!! Yes, I've had it that long... bad news, the power steer pump is wet on the bottom.... rebuild kit here I come...

Lastly, my GM tech2 scan tool, refuses to link up with the ABS module. I checked it on my 96 eldo and it reads it perfectly. It connects with the 7.4L moho engine perfectly. First I went through and pulled all the connectors to check for bent or dirty pins, then cleaned the grounds. No change, no link. When I checked on line other folks were having problems getting their GM tech2 tools to link with Kelsey Hayes 12765501 ABS brake module. So, apparently there is some sort of glitch in the module that prevents it from linking up. These units were used in chevy trucks and P30's 1997 to 1999.

The "slam the brakes" method is the only way to bleed these suckers...

Thanks for the offer of the wiring schematics. I have a complete chevy shop manual for this moho. It says it should connect, wiring schematic says it should connect.... but doesn't.. why??? I can't say....

Thanks everyone for your help!!

[77rollalong]

wondering if you have a problem with the abs system, will the scan tool do any diags of the abs system at all , i do have the wiring diagrams for the 1998 p30 motorhome here

[lonfu]

the problem is the scanner won't link so I can't run the test function to clear the air out of the ABS module. I'll look for another plug on the module.I've tried holding the brake pedal down and running the function too, but it keeps saying it won't link to the module. I suspect it is the year of the chassis. 98 chevy

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.

[lonfu]

I haven't replaced any of the brake lines. When under pressure I've checked them for bulges and all seem ok. The are not cracked or heat damaged and do not bulge.

rgatijnet1 wrote:
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?

[lonfu]

I was thinking about doing this, but how will that get the air out of the abs module? I was thinking the output lines would work better, what do you think?

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

[lonfu]

I've been doing it with the engine off.

77rollalong wrote:
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]

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.

[77rollalong]

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..

[rgatijnet1]

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.

[shepfly]

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

[allbrandauto]

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

[SidecarFlip]

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