Hey guys, my brakes suddenly failed on me a couple days ago in my Cav. Feels like all the power goes to the rear drums and the fronts dont work at all, when I get on the brakes the rears lock up completely and the rear end of the car suddenly hits the floor like its on bags. I did a full brake fluid job and it didnt seem to fix anything, but the old stuff was filthy. I was wondering if our cars have a proportioning valve or something that might have let go? Maybe I should replace the master cylinder? Let me know what you think, thanks.

Need a little more info on the year of vehicle? I will believe the brake system still isnt free from air. Have u looked at the rear drum brakes?. Could be possibly youre Master cyl, Also could be calipers or front brake lines colapsed?.

Its an 03 and there shouldnt be any air in the lines since the fluid was just changed. The brake lines dont seem to be collapsed and the front brakes are in good shape. I'll need to check out the drums in the back closer, i understand that too much clearance between the shoes and the drum can cause problems for brake feel. It feels like my brakes are an on-off switch, ive got 2 inches of dead pedal and then suddenly the rears lock up completely.

Also, wouldnt a master cylinder problem set off a warning light? Ive got no lights on the dash. Maybe its a brake booster problem?

eco tec wrote:Its an 03 and there shouldnt be any air in the lines since the fluid was just changed.

The oil was changed by whom? Maybe they fudged it up.

fluid*

Maybe, but its the exact same problem before and after the fluid change so i doubt air in the lines is the problem.

eco tec wrote:Maybe, but its the exact same problem before and after the fluid change so i doubt air in the lines is the problem.

Was the proper procedure used to bleed the brakes? ABS brake systems can be tricky to bleed. If the valves in the ABS module are not positioned correctly, the system will not bleed the air out.

Yup, fluid change was done by the book. maybe ill just change the master cylinder and hope for the best?

I had kinda a similar problem when i turned my rotors. After i put them back in i took it for a drive and felt like a had no brakes. i mean i REALLY had to push on my pedal and it would barely slow me down. I know this isnt the same kinda problem but the ABS brake systems are tricky. After a while it finally went back to normal. Maybe try bleeding them again, could be air still in there.

This is the second time the fluid was flushed, which makes me think even more that its the master cylinder. I wonder why my ABS light didnt turn on though since the brakes are obviously busted. Would an OBD2 scanner be able to read ABS light codes?

Sounds to me youre gonna need the Tech II tool help. With this I am assuming.

I bet getting GM to scan the car is going to cost the same as me replacing the master cylinder, so ill just replace the thing and hope for the best. Looks like it shares a mount with the ABS, this is not going to be fun.

Well, Not to sound rude, For just droping cash on a master cyl thinking thats the not issue spend the cash and get the probelm pin pointed, Then replace the part youreself for get the shop to do it. Its a common problem, Once you play around with ABS system and the air isnt completely out of the system the braking system wont work properly. But remember choice is youres.


Good Luck.

You said your fluid change was done "by the book". How exactly was the flush and bleeding procedure done? Like I said earlier, ABS systems need to be bled differently than non-ABS and there are even differences depending on the model of ABS unit you have on your car. These things can be a @#% to bleed if you don't do it properly, and the symptoms you're describing are possible if the system isn't bled properly.

It was done as it says it should be done in the Haynes manual, is there some extra step that might have been missed?

I don't have the Haynes manual for your car, but here is the procedure from Mitchell OnDemand:










Make sure you do it exactly like the instructions say, including waiting the 15 seconds. If not, chances are it won't be bled properly.

Looks like Haynes and the source you listed have slightly different instructions. I'll see if I can get around to using your guide to bleed the brakes again tomorrow. Thanks for the help Chris, will post back with results

Hope you get it sorted out.

Quote:


This is the second time the fluid was flushed, which makes me think even more that its the master cylinder. I wonder why my ABS light didnt turn on though since the brakes are obviously busted. Would an OBD2 scanner be able to read ABS light codes?

No, OBDOII scanners only read engine codes.

I have the same problem with my car. It hits hard on teh back drums after you first start to drive, and then its fine after that. The front brakes work then. BUT if I leave the car sit for some time, it will do it again.


What did you do and did you get it fixed?

Haven't got around to looking at it yet, will let you guys know what happens

Followed the instructions Chris gave and the brakes suddenly work again! To anybody having the same problem I had, do exactly what Chris said and you should be good to go! Thank You!

Glad to be a help, and glad you got it sorted out.