99 Tahoe brake problems

[JDN]

My neighbor asked me to check his tahoe out by driving it and telling him what I thought of the way the brakes felt. I picked it up to 30mph and stepped on the brakes. The truck stopped but the peddle was spongy and went to the bottom. I told him that a spongy peddle usually meant air in the system and that the peddle going all the way down was not good. He said that it had been like that for years, ever since he took it to the local chevy dealer for work on the brakes. So we took all wheels off and found many problems. One of the rotors was so bad it couldn't be turned, we replaced both along with new pads. The wheel cylinders were both leaking in the rear, replaced both. The shoes had a lot of meat but all were cracked down the middle, put new shoes.
We then bled the system starting with RR wheel, then LR, RF, and finally LF, the peddle firmed up but if I held firm pressure on the peddle it would eventually go down. We re-bled system again and the peddle would still go down. We next replaced the master cylinder after bench bleeding and the peddle still goes down. I don't know what else to do. We did some research and found that this truck has a Kelsy Hayes EHCU and that this might need to be bled first then the rest of the system. We don't know what this is. Can anyone HELP US?

 

[kev2]

First is the ABS or any other warning light on?

The procedure requires a SCAN tool bleed procedure...I cannot link that at this time.. am posting base bleeding to see if you did the correct sequence
...



Two Person Procedure
Raise the vehicle in order to access the system bleed screws.
Bleed the system at the right rear wheel first.
Install a clear hose on the bleed screw.
Immerse the opposite end of the hose into a container partially filled with clean DOT 3 brake fluid.
Open the bleed screw 1/2 to one full turn.
Slowly depress the brake pedal. While the pedal is depressed to its full extent, tighten the bleed screw.
Release the brake pedal and wait 10-15 seconds for the master cylinder pistons to return to the home position.
Repeat the previous steps for the remaining wheels. The brake fluid which is present at each bleed screw should be clean and free of air.
This procedure may use more than a pint of fluid per wheel. Check the master cylinder fluid level every four to six strokes of the brake pedal in order to avoid running the system dry.
Press the brake pedal firmly and run the Scan Tool Automated Bleed procedure (below 15,000 GVW) once, or run the Function Test (above 15,000 GVW) four times. Release the brake pedal between each test.
Bleed all four wheels again using Steps 3-9. This will remove the remaining air from the brake system.
Evaluate the feel of the brake pedal before attempting to drive the vehicle.
Bleed the system as many times as necessary in order to obtain the appropriate feel of the pedal.

 

[JDN]

Thanks for the help. No warning lights were on. We did the bleeding like you pointed out but only that. We know only basic mechanics and so know nothing about scan tools. Is this something that we can purchase and use without previous experience?

 

[kev2]

did you pay attention to the @15second wait time between pumps?


Sorry the scanner with that feature would be unreasonable expensive for one use....

Some of the "brake" specality shops provide a brake fluid flush and that would require the same procedure- worth checking prices..

I am still checking some resources will post if anything new...

 

[JDN]

I just talked to my neighbor about that and he said that he remembers that we talked about it but doesn't remember for sure if he waited the full 15 seconds. Why is this important? We just did it because the instructions said to? Also forgot to mention that on the fourth attempt at bleeding we kept getting air in both rear wheels and no matter how many times we bled, air would still come out. That's why we started to look into other causes. Sorry for my forgetfullness.

 

[kev2]

Release the brake pedal and wait 10-15 seconds for the master cylinder pistons to return to the home position.

 

[tombtomb]

With any hydraulic system if the pedal sinks there is a loss of pressure. Either a fluid leak or the fluid is bypassing inside the master cylinder. First check very closely for fluid leaks.Since you have already replaced the master cyl it is possible that one of the rubber brake hoses is swelling thus absorbing the pressure. Thomas

 

[JDN]

OK, this is where I'm at. And again thanks for the replies, I removed the master cylinder and again bled it according to the instructions that came with the unit and this time the cylinder would not firm up. According to the instructions the cylinder is supposed to firm up to the point that I would not be able to push it more than 1/8in. This is not happening. I then called my brother and he told me to install the master and plug the ports and step on the brakes. He said that if the brakes are solid and do not move, that the master is good. So now I'm confused, when bleeding the master it didn't firm up like the instructions said, yet when installed and plugged, it does firm up where it won't move. Now what?

 

[kev2]

should NOT firm up if exhausted to reservoir.....

should be hard when plugged....

 

[JDN]

Today with the master again bled and filled with fresh fluid and all the lines checked for leaks and swelling as tombtomb suggested (all was fine) we proceeded to bleed system at the wheels starting with RR. This time we made sure we followed the process as you suggested with the 15 second intervals all around and again the pedal firmed up OK but when I started the engine the pedal again got spongy and went down to about an inch from the bottom. We bled everything according to not only the instructions we got from you guys but also to what the manual said and still no luck. Any other suggestions will be greatly appreciated.

 

[tombtomb]

Have you drivin the trk since last bleeding? The pedal should drop when the engine is started indicating the booster is working. You said that the pedal deropped to an inch from the floor but if you are driving the trk the brakes may lock up well before the pedal gets that low.

 

[Transman]

There are two things you can try. The first is go to your nearest parts house like Napa and buy the bleed tool for the abs unit. It is around 5 bucks. It looks like a C with another piece of metal on top that tightens down with a wing nut. The whole tool is about 2 inches or so long. Find the valve on the side of the ABS unit, it will have a soft rubber cover on it. Pick off the protector and apply the tool, tighten the wing nut and bleed again. If this process does not work then take it to a competent repair shop that can use the scanner to bleed the ABS system for you. They should not charge over 50 bucks and it takes 5 minutes.
We do them all the time for people that can't bleed the ABS unit. We only charge $22.50 for this service as long as the air is out of the rest of the system. Post back, Transman

 

[JDN]

I did drive the truck and the brakes worked enough to stop it but the pedal had 1/4 maybe 1/3 the resistance of the normal feel of the pedal when applying the brakes. This is about half worse than when we first started this ordeal. That is why I told him it needed to be fixed in the first place.
My neighbor(the owner) decided to call the local Chevy dealer to ask if they would bleed the system for him and was told that since they have no way of knowing what was done to the truck that it would take about four hours to check and if need be bleed it, this he said was because of the complexity of the process.
After driving it I told him how it felt and he suggested we'd bleed it with a vacuum bleeder. We went to the RR wheel and opened the bleeder 1/4 to 1/2 turn, attached the hose and started to pump. To our surprise we got nothing but air. We did this for about fifteen minutes and were never able to get a solid stream of fluid. We stopped everything at this point. Needless to say we are confused. It's from one thing to an other.
Transman, you say to bleed the ABS unit, when I first wrote in I was asking about the EHCU, this we had never heard of and I think we are talking about the same thing. We read that if this had air in it that no matter what we did at the wheels that we would never be able to bleed the system correctly, and so I think that that is what you are saying we should do. Right?
P. S Doesn't 4 hours at about $500 bucks sound like a tad to much?

 

[Gus]

4 hours to check and bleed? Run, don't walk away from that dealership....

You don't have to go to a Chevy dealership.....any GM dealership can do the job for under an hour, provided there are no codes in the system and there are no parts to replace.....

 

[JDN]

Well guys I guess we'll never find out if we could have fixed this Tahoe. My neighbor gave up and took it to the dealership yesterday morning. He had hinted about doing it but I really thought that he would give us a chance to work it out. I guess he just got tired of it. With that I would like to Thank You all for your time and effort and say that what you guys do for the rest of us mortals is greatly appreciated. Again Thanks and best wishes. Oh ya! Also thanks to the other mortals that took the time to put their in. BYE!