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K. Wiggins
K. Wiggins, Chevy Technician
Category: Chevy
Satisfied Customers: 2516
Experience:  ASE Certified Technician AA in automotive Technology, 15+ years in the trade
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I have a 1993 K1500 Suburban that has been well maintained

Customer Question

I have a 1993 K1500 Suburban that has been well maintained over the years. Last weekend I noticed a change with the brake pedal. The pedal became ‘softer’ and would slowly ‘sink’ to the floor while waiting at a stop light. The brake warning light does not indicate a problem. Not leaking brake fluid and master cylinder is full. I bench bleed then installed the replacement master cylinder and bleed the air out of the entire brake system. The newly replaced master cylinder acts the exact same way as the previous master cylinder. While testing the brakes, I did a panic stop and braking was about 75% with no ABS event or brake warning light. The front brake pads and rear brake shoes have about 75% of the lining. The rear shoes are properly adjusted with a working emergency brake. Could the ABS modulator be the problem?
Submitted: 1 year ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 1 year ago.

Hi, My name is ***** ***** for the delay.

I will do my best to assist you

Expert:  Tim's Auto Repair replied 1 year ago.

do you have the brake shoes in the rear adjusted all the way against the rear hubs?

Customer: replied 1 year ago.
No, brake shoes are adjusted for the brake drums.
Expert:  Tim's Auto Repair replied 1 year ago.

does it have only rear antilock brakes or all four wheel anti locks brakes?

Customer: replied 1 year ago.
4 wheel abs
Expert:  Tim's Auto Repair replied 1 year ago.

OK,I WOULD THINK YOU HAVE AIR TRAPPED IN THE BRAKE CONTROLM UNIT NOW AFTER REOKACING THE MASTER.

I WILL SHOW YOU HOW TO BLEED IT..if it isnt air,i would think it is the abs module itself

THANKS

PLEASE COPY AND PASTE the link below to your browser, I have uploaded more info on this there please copy and paste the link below to your main browser[INTERNET EXPLORER or FIREFOX]

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https://www.dropbox.com/s/kkocxnnj14jivnf/1119-03-BRAKE-Fig.doc?dl=0

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if the link doesn’t work that way, try it this way

thanks

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www.dropbox.com/s/kkocxnnj14jivnf/1119-03-BRAKE-Fig.doc?dl=0

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If you are satisfied with my answer, Please Rate my answer by clicking the rating button so I can get credit for my work. I’m not always going to be giving you good news, so please don't let this stand in the way of you accepting my answer. .it does not cost you more money and we will still be able to communicate, ,.please understand, i can not see, hear or touch the vehicle and only know what you tell me. Bonuses and positive feedback are appreciated.. if you are not satisfied with my answer, please do not leave bad feed back ,i will gladly opt out and let another expert handle the question. .if i have sent any diagrams, please print them. .sometimes you may need to right click the image [,then save picture as]to save it to your computer so you can open it with your picture program...Please ask if you need more help

Customer: replied 1 year ago.
Replacing the master cylinder did not cause the problem. The master cylinder was replaced in an attempt to fix the problem. What caused the problem?
Expert:  Tim's Auto Repair replied 1 year ago.

hi

i would think the valve on the abs module,,but,do try bleeding the module first..

sometimes ou will just get dirt in the fluid and it will stick the valve,,

bleed it the way i gave you in the link

thanks

\

Customer: replied 1 year ago.
I have not had a chance to work on the suburban. I do not see how a piece of dirt can create an air bubble inside a closed hydraulic system that has been working properly for the past 10 years or more. I will try bleeding the ABS modulator over the Thanksgiving holiday.
Expert:  Tim's Auto Repair replied 1 year ago.

that will be fine

have a happy thanksgiving

Expert:  Tim's Auto Repair replied 1 year ago.

thanks

Customer: replied 1 year ago.
I tried to bleed the Brake Pressure Modulator Valve but only got brake fluid out of one bleeder. I disassembled and cleaned the valve as one of the needle valves was sticking. After reinstalling and bleeding the one bleeder was still not passing brake fluid. I am trying to purchase another Brake Pressure Modulator Valve. The valve is no longer available from GM.
Expert:  Tim's Auto Repair replied 1 year ago.

so,

you get no air or fluid?

Customer: replied 1 year ago.
One bleeder had good brake fluid flow, one bleeder had no brake fluid flow.
Expert:  Tim's Auto Repair replied 1 year ago.

ok

please stand by,perhaps one of the other guys has a better idea of what is going on here.

someone will be right with you

thanks

Expert:  K. Wiggins replied 1 year ago.

Hello, there's a revised bleeding procedure for the modulator valve. I'll post it below, let me know if this helps.

Customer: replied 1 year ago.
I won't be able to get to work on the suburban until the weekend.
Expert:  K. Wiggins replied 1 year ago.

That's no problem, feel free to update me then.

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