powermaster question

[JDSfastGN]

Ok for the past year my foot has slowly dropped to the floor when holding the brakes at a stop light. No brake light or anything so i knew it had to be an internal leak in the mastercylinder. It is a fairly new unit and I was just gonna replace it under warrenty but Oreillys is short on the units due to a lack of core returns. So i decided to swap mastercylinders with a unit i had sitting around. I did this and the brakes are a ton better. I have the LS1 brakes and i finally know how they are supposed to feel. The only problem is now when i turn the key after it has sat overnight the motor does its typical prime, but the light stays on for a good 10 secs. The passengerside also fills up pretty quickly when i turn the key off (accumulator leak?) Ive read the gnttype.org stuff and this tells me to replace the whole thing. It is still the same accumulator and motor as before which worked fine. I bled the motor of air and then the mastercylinder by cracking the lines until i got no more air. I did not however bleed the lines at the calipers or drums. Could there be enough air in the lines to cause the light to stay on for 10 secs. Driving around the light never comes on but the motor runs a lot. It also cycles every 20 secs or so with the key on and no brake input. Could there be air trapped still in the MC? Did another problem arise by coinisidence? Pedal has a nice feel and holds. When i go back home this weekend i will swap out to the other switch on the mastercylinder i replaced. Any other ideas? Sorry for the length just wanted to be thourogh :biggrin:

 

[zeus87gn]

You can't bleed the high pressure side by cracking the lines loose. You will just let in more air, churn up the fluid and spray brake fluid all over the place. You have to 'cycle' the acc (high pressure side) to accomplish this. See the link in my sig for proper procedures. Sometimes it takes more than once or twice to get the job done. I just did a fresh P/M last weekend and it took 15 (or so) cycles.

If the ps of the bowl fills up quickly after turning off the key, it is the acc pushing the fluid back in there past the main piston seals. Now it could be just that there is trapped air still in the power piston by-passing the seals. I have experienced this. If you see frothy air on pump down, you may have found your problem.

Now after you remove all the air, if you find that your motor is still turning on and off in less than 2 minutes (by the book), you have swapped in a bad master cylinder. It is internally leaking and is in need of rebuild/replacement.

HTH

 

[JDSfastGN]

thanks Zeus, we did bleed the high pressure side as the procedure mentioned by cycling the accumulator 4-5 times. I checked yesterday again and did not see any air when i did the procedure. I may try it again today a few more times just to see if it helps. After discussing with my dad he and I came to the conclusion that the master cylinder must have an internal leak as you stated. Thanks for the help Zeus, i was hoping you would reply after reading most of your replies after doing a search.

 

[zeus87gn]

Yea, I seem to have the biggest mouth when it comes to these things.

Personally, if the dang thing ever has to be removed for whatever, it is going to get new seals at minimum. But that's me.

I have to make an update to my procedure, so if you get a fresh rebuild, or rebuild your self, check back.

 

[JDSfastGN]

Yea, I seem to have the biggest mouth when it comes to these things.

Personally, if the dang thing ever has to be removed for whatever, it is going to get new seals at minimum. But that's me.

I have to make an update to my procedure, so if you get a fresh rebuild, or rebuild your self, check back.

Have you been able to match up random Orings? or have you had to by the kit for around $100? I just went out to see if i could get any more air out of the system. I did that a few times and did see a small amount of tiny bubbles. I took the car out to go get a turkey baster to suck some of the fluid out and on the way the brake light came on and there was a strange hissing sound when i wasn't on the brakes. I brought it back and played with it some more and have now royally screwed it up. I can't get the motor to stop running. It primes down to a certain point and then just runs at a constant rpm? Im fixing to do a search to see what comes up but just thought i'd post here first. Thanks man.

 

[JDSfastGN]

ok just a quick update, after playing with the switch and hitting it a few times the motor stops now. Its also weird that i no longer have the high pressure side of the master cylinder filling up when the key is turned off? It also did not cycle on its own once during a 3 minute span. Ugh these things can be a pain, if i wasn't 120 miles away at school it wouldn't be as big a deal haha.

Edit: also there appears to be fluid in the pressure switch... not sure if it could be from a previous spill or if the switch is bad. I ohmed the switch, the two outside connectors have continuity and the inside has nothing with either the of the outside ones if that makes any sense.

 

[zeus87gn]

Have you been able to match up random Orings? or have you had to by the kit for around $100? I just went out to see if i could get any more air out of the system. I did that a few times and did see a small amount of tiny bubbles.

No, I haven't had the time to try and attempt my own kit. There is a materials issue that I don't know about. There are many sizes styles and compounds that can be had. Too many for my knowledge (I'm a wire nut anyway). I bought my kit back when they were cheap and available.

 

[JDSfastGN]

took it to class and on the way home it decided to run constantly again.... dammit. Im thinking about running a wire from the power wire to a switch inside the car just to temporarily get the car home 120 miles away.

 

[zeus87gn]

ok just a quick update, after playing with the switch and hitting it a few times the motor stops now. Its also weird that i no longer have the high pressure side of the master cylinder filling up when the key is turned off? It also did not cycle on its own once during a 3 minute span. Ugh these things can be a pain, if i wasn't 120 miles away at school it wouldn't be as big a deal haha.

Edit: also there appears to be fluid in the pressure switch... not sure if it could be from a previous spill or if the switch is bad. I ohmed the switch, the two outside connectors have continuity and the inside has nothing with either the of the outside ones if that makes any sense.

Hmmmmmmm
Sounds like you may have a malfunctining switch. Without the proper diagnostic tool (that can't be had) all you can do is change it out with a known good one to test.

Your ohm readings need to be taken with the acc pumped down. Then they should all be continuous with eachother. Is this when you did this?

BTW, you shouldn't hit these switches. I consider them delicate because of thier design. They can be damaged easily. I don't even recommend removing them with pliers.

Your issue with it now sealing up can be looked at in a couple of different ways. It can be either 1- you had air in it and it has worked out; or 2- you had an oring that has just reseated itself.

 

[zeus87gn]

took it to class and on the way home it decided to run constantly again.... dammit. Im thinking about running a wire from the power wire to a switch inside the car just to temporarily get the car home 120 miles away.

Even more of a notion that the switch insn't any good.

Don't let that motor run for more than 20 seconds at any given time. You could burn up the motor and/or the pump.

Gotta run, more later...

 

[JDSfastGN]

ok it did ohm ok when the accumulator was depressurized. After letting it sit there for a bit i went out and its turning off just fine. Is the switch getting hot and grounding? Could there be an air bubble right below the switch giving it a false reading? thanks again for the help Zeus. BTW im lacking tools down here at school, does anybody know the wrench size for the pressure switch?

 

[zeus87gn]

The pressure switch is designed into the electrical system to activate either the light in your dash, or the control side of the relay built into the motor. It does this by grounding (therfore completing) the circuit. So yes, it is grounding but it is supposed to do that.

Air may be an issue, but I doubt it if you didn't get anything after cycling the acc.

The proper wrench for these switches is a speciall shaped socket that you can only get from guess where - GM. They ain't coming off with it. I've tried. You may can luck out and find some socket that may fit (I think I did but can't remember the size right off...it's a large deep well metric). If you are careful, you can use appropriately sized pliers to remove/install. The important thing is to remember that they are delicate and can be damaged. You don't need to tighten them as tight as you can. Once it seats, give it a little tug more and you should be good to go.

Have a nice evening.