Chevrolet Astro braking problem

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My Astro is a 1990 model. It has two separate brake fluid reservoir. The master cylinder has just been changed and all the brake components are new (calipers, rear cylinders, etc). Il fill up both reservoir. When I use the brakes for more than 1 hour, the rear brake reservoir is getting empty and the front brake reservoir is filling up with the rear brake reservoir fluid. It overflows and get out of the cover and spill.

What's going on????

Thanks

Rene

posted by  renetousignant

Hmmm, sounds to me like something might be messed up. You''ll have a much better chance of getting helped if you go find the "Introduce Yourself" section" and use it.

posted by  vwhobo

Three words dude. Bad Master Cyinder.

Fluid is kept seperate from each other in the resivoir for a reason. You lose fluid in the front and you still got the rear and vice versa.

The fluid migrating from the rear to the front can only occur one way and thats through the bore of the master cylinder. Since thats not suppose to happen it must be a bad master.

Since you just purchased it you will be able to swap it and if i am wrong you've wasted nothing but time.

One note , if you bought a rebuilt instead of new ask if you can pay the difference and get new. It is usually not a lot more and you get far fewer problems that way. Have you ever heard anyone ask to buy a rebuilt baby seat?

edit: After I wrote this i thank about it a bit more, why did you replace all this to begin with? I was answering on the presumption that the vehicle was operating fine and needed brakes, but replacing the mc usually indicates another problem to start.

posted by  hitchhiker

Which is why you should get as much information from a person as you can BEFORE coming to a conclusion. Giving people an answer without knowing the full situation, which you've shown you like to do, seldom gives you enough information to come up with an educated response.

In other words, the person who answers without all the info is as bad, or maybe worse, than the person who askes the question without all the info.

posted by  vwhobo

I agree with you. It's better to let people know me a little. I just fill the "Introduce yourself" section this morning.

Thanks.

posted by  renetousignant

Thanks for answering!

When I first changes the MC, it was because the pedal could'nt keep the pressure. It was slowly going to the floor. I changed the MC and this fixed this first problem. At this moment, I changed about every thing in the brakes like disk, calipers, drums and cylinders.
Then the other problem occur: the brake fluid going from the rear reservoir to the front one. I changed the MC a second time and it still do the same thing. That's why I am looking for another problem. I am asking myself if the combination valve may be the problem. Is it possible the the brake fluid start from the rear reservoir and transfer to the front reservoir passing by the combination valve?

What do you think of this?

Thanks!

P.S. You can read my "Introduce yourself" in the introduction forum!

posted by  renetousignant

This is exactly why we need to get as much information as possible instead of jumping to conclusions. Are you reading this hitchhiker?

There are only two places in your braking system where the fluid can migrate from the front to rear system, the master cylinder and the combination or prop valve. That is unless you have ABS but we know you don't or else you wouldn't have the combi valve.

So, you've got the same problem with two master cylinders after fixing the first problem. While that doesn't beyond a shadow of a doubt mean they aren't bad, I feel the possibility of that is pretty slim. The other question that needs to be asked is did you have this fluid migration problem before replacing the master cylinder? Inquiring minds need to know.

posted by  vwhobo

No, I did not have this problem before the first fixing. This problem came and grow very slowly after I changed the first MC. It took one complete year before the fluid loss begin to be innacceptable. I should add that this truck does have an 4 wheel ABS system, and it does have a combination valve. I think that my next try will by this combination valve.

Thanks.

posted by  renetousignant

Isn't that exactly what the end of my post says :doh:



I ended my diagnosis with a open ended question. This was to give the poster a opportunity to post back, which he did.



probably

All this aside vwhobo has a great question, just a little out of phase.



The question should be,



You wrote that the first problem was a slowly sinking pedal. After your replaced the master it fixed the problem. Could there be containments in the lines. I did a check for recalls on all data and there was nothing there, except a revised bleeding procedure that i didn't have a chance to look at a work. Will check tommorrow and post back.

posted by  hitchhiker

It sounds like the hitchhiker was on the right track. probably a leaking valve or seal in the mc. if you've got a manual or a few clues you can buy a kit for serviceable parts in the mc.

posted by  diyo

Just out of curioustity, do you know how to read? The man has already replaced to master cylinder TWICE with remanufactured units. Do you really think he wants or needs to rebuild a remanufactered part? Maybe I should have just stopped with the first four words of the previous sentence.

posted by  vwhobo

If your van does in fact have ABS that opens the door to a whole new set of problems. Also the fact that it took a year from the time of the M/C replacement until the fluid migration problen took place sheds some different light on the matter. Before we try to do anymore online diagnostics, are there any other useful tidbits of information we should know?

posted by  vwhobo

After a little reflection, and the four wheel abs clinker thrown in there i still believe its a bad master. But, I think the master was caused to go bad by something else.The fluid build up on one side blew through the seal in the master and the fluid in migrating throught the piston in the master. (has the cap ever been loosen by internal pressure?)

Possibly a bad brake hose or contaminated fluid, wheather by rust in the lines or dirt when the first one got changed. It may also that the brake pressure modulator valve is feeding back through the other side, but usually this is indictitive of erractic brake behavoir which you havn't brought up.
(ie. rear brakes locking or inoperative, or pedal flutter)

You are going to have to do some intense diagnostic work to put your finger on this, rather than replacing the same stuff you already replaced and hopefully i given you the right tools to do it.

In the following links i have copied from All-Data include a flow chart for diagnosis, the correct method for manual bleeding of your brake system, a nice picture on how to inspect brake hoses, how to flush your system(i recommend a power bleeding flush instead) and a way to check for internal bleeding and failure of the brake pressure modulator valve.

Read it all, try whats within your capabilitys. You sound pretty game , good luck. btw. copy these links to your files, i don't have alot of k's to leave em up forever.

URL: http://home.ripway.com/2003-11/40235/brake1.BMP

URL: http://home.ripway.com/2003-11/40235/brake2.BMP

URL: http://home.ripway.com/2003-11/40235/brake3.BMP

URL: http://home.ripway.com/2003-11/40235/brake4.BMP

URL: http://home.ripway.com/2003-11/40235/brake5.BMP

URL: http://home.ripway.com/2003-11/40235/brake6.BMP

URL: http://home.ripway.com/2003-11/40235/brake7.BMP

posted by  hitchhiker

Thank you very much for all the informations. You can remove the URL's , I copied them all. I'll try to fix the problem this weekend using these tips. :thumbs:

posted by  renetousignant

:ohcrap:

Are you always such an asshole VWhobo or do you specifically go out of your way to try to make everyones life as miserable as yours?

all I can see is someone posted for help and someone responded and you bring them down in flames.......

posted by  Cybered

Exactly.

posted by  lOgiC

I just want to thank everybody for their help about my braking problem. It has been fixed this weekend. This was finally the combination valve which was in trouble.

Now my old Astro is braking like a new one!

Thanks again :wink2:

posted by  renetousignant

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