98 Brake Problem


ptcfast2
08-04-2010, 09:58 AM
I replaced the Master Cylinder and rebuilt my rear drum brakes on my 98 w/o ABS over the weekend (those flair nut bolts on the MC can be a pain to get off after 12 years, but nothing vice grips couldn't fix! :wink:) and bench bled the cylinder.

Put everything back together and started to bleed the system via the classic two person pump method. Before I actually tried to bleed the system, I checked for leaks at the MC and made sure that when pressing the pedal in the car no hissing was heard at the MC along with no fluid drips due to loose flair nuts.

After about 30 minutes of bleeding I got the following result:

-Front Driver: Gushing Fluid
-Front Passenger: Dribbles Fluid
-Rear Driver: Dribbles Fluid
-Rear Passenger: Gushes Fluid

Brake pedal goes all the way to the floor once the car is started (pumps up when off), and the car will stop if I press the pedal to the floor (which means I can get it to a shop if need be :)). I can definitely notice that the two brakes that gush fluid are doing the work when this I press it to the floor though.

Long story short: I called my mechanic and asked what I should do. He suggested gravity bleeding the lines of the wheels that dribble fluid. He said that if they are dribbling, it means that they have a good connection up at the MC, but air is caught up somewhere in the lines. He said that sometimes gravity bleeding is the only way to get stubborn air out of the system unless you have a power bleeder pump.

Any suggestions/anyone seen this happen before?

maxwedge
08-04-2010, 12:33 PM
All 98 Luminas had abs, look closer. If you emptied the system the abs must be bled with a scanner.

ptcfast2
08-04-2010, 01:16 PM
All 98 Luminas had abs, look closer. If you emptied the system the abs must be bled with a scanner.
The 1998 Lumina had ABS as standard on only the LS and LTZ models. The base model (mine) did not include ABS.

maxwedge
08-04-2010, 08:37 PM
Ok, so back to a regular bleed see if you can get a vacuum bleeding system or borrow/buy one, about 60.00

jeffcoslacker
08-06-2010, 12:38 PM
Split diagonal brake system so makes sense which ones are gushing and which are dribbling.

I worked alone in the shop and never had any problems using just gravity bleeding...but I also never had to bleed the system after installing a MC...only bench bleed of the MC is required.

Any small amount of air trapped in the lines when you attach them should go out on the first couple of strokes, since it's so close to the MC, it will find it's way up and out through there.

You may have a situation where you have an airlocked MC though...you can try doing the two man bleed while cracking open the line fittings at the MC, rather than the bleeders at the wheels...sometimes this will purge it. Be sure to protect your paint and eyes while doing this, it may spray out everywhere. Keep some water handy.

Also, you know you never "bottom out" the pedal/piston when bleeding right? This can damage the MC bore. You want to open/close the bleed point quickly, before the pedal guy bottoms it. I see too many people going all the way to the floor before closing it up, this is WRONG...and can suck air back in.

Another thing you can try, beside a gravity bleed (I'd take both bleeders out completely from the affected brakes and just keep filling the MC until it flows good from both lines) if you don't have specialized equipment is this:

Remove the bleeder screw from one of the affected brakes. Push your thumb tightly over the hole, and keep it pressed hard onto it. Have your pedal guy stroke the pedal repeatedly about 2/3 of the stroke. Keep you thumb tightly pressed down. Any air should "burp" past your thumb, but none will get drawn in. DO NOT LET THE MC RUN DRY! When the fluid gets down there in earnest, you will not be able to resist it, you'll know. With the pedal at rest, take your thumb off, install the bleeder screw and tighten, and bleed normally maybe two strokes just to clear any air from the bleeder screw bore. It should work fine now.

Repeat on the other affected brake.

Kind of a poor man's speed bleeder. Works well. I've found sometimes you need this kind of force and quick pumping to get fluid moving into where you want it to be....

ptcfast2
08-09-2010, 02:28 PM
Well, I attempted to gravity bleed the system the other day before bringing it into the shop I use when I get stumped. No luck with that.

Anyways, brought the car in to my mechanic (driving with 2 working brakes is fun!), and they did their normal troubleshooting, re-bled the MC, attempted to bleed the brakes via gravity & 2 pedal method. They received the same results as I did before I brought it to them.

They suggested obtaining a new MC to rule the re-manufactured MC causing problems completely. I shipped a new MC overnight from Florida, brought it to them and they installed it. Said it bench bled perfectly (good news I guess) and installed in on the vehicle. No leaks around the fittings when they attempted to bleed the entire system (good news again) but they arrived at the same results!

-Front Driver: Gushing Fluid
-Front Passenger: Dribbles Fluid
-Rear Driver: Dribbles Fluid (Occasionally)
-Rear Passenger: Gushes Fluid

They suspect some form of blockage in the lines (or some really really really stubborn air). I wais told today that they were going to buy some form of "power reverse-bleed" system tomorrow (never heard of it) and attempt to force the blockage/air out that way. I'm still thinking some form of power bleed as originally suggested may be in order.

Upon my original inspection I noted no leaks or obstructions/crimps along the lines having the problem. My mechanic confirmed that he was unable to observe anything that would be causing a blockage.

So, I'm starting to get stumped.I think my mechanic is as well (Hard to stump a guy with 30+ years of experience :frown:) so any additional ideas would be apprenticed. Anything in the system that can get gunked up/clogged? Would the next step be to replace the lines on one of the trouble brakes and see if that fixes it (if power bleeding does not work)?

old_master
08-09-2010, 07:42 PM
As mentioned in an earlier post "Split diagonal brake system". Left front and right rear are on the same hydraulic circuit. Right front and left rear are on a separate hydraulic circuit. If there is a difference in hydraulic pressure from one circuit to the other, (ie blown line or in your case, excessive air) The centering valve automatically shuts off the failed circuit, (it's a safety thing ;) ).

You can manually center the valve and bleed both circuits, they make a special tool for it. Or, you can open one of the bleeders that is bleeding correctly, and give a quick jab and release on the brake pedal. If you do it with the ignition in the RUN position, you'll see the red "brake" light on the dash flicker. The trick is to keep the light off, then bleed as mentioned earlier, very gently.

If the light flickers and the opposite hydraulic circuit dribbles, the valve went overcenter. Open a bleeder on the opposite circuit and jab again. The dash light must be off when the ignition is in the RUN position to bleed all 4 wheels.

jeffcoslacker
08-09-2010, 09:12 PM
As mentioned in an earlier post "Split diagonal brake system". Left front and right rear are on the same hydraulic circuit. Right front and left rear are on a separate hydraulic circuit. If there is a difference in hydraulic pressure from one circuit to the other, (ie blown line or in your case, excessive air) The centering valve automatically shuts off the failed circuit, (it's a safety thing ;) ).

You can manually center the valve and bleed both circuits, they make a special tool for it. Or, you can open one of the bleeders that just dribbles, and give a quick jab and release on the brake pedal. If you do it with the ignition in the RUN position, you'll see the red "brake" light on the dash flicker. The trick is to keep the light off, then bleed as mentioned earlier, very gently.

If the light flickers and the opposite hydraulic circuit dribbles, the valve went overcenter. Open a dribbling circuit bleeder and jab again. The dash light must be off when the ignition is in the RUN position to bleed all 4 wheels.


Good idea, I've only seen that happen once or twice where they got so offcenter I had to manually reset the proportioning valve...can you still do that? I don't even know...

old_master
08-09-2010, 09:26 PM
Air compresses, fluid doesn't, that's why you have to "fool" the valve by opening one bleeder on the circuit that's flowing. By doing it this way, you're creating a "failed" hydraulic circuit and forcing the valve to shut off the system. The trick is making the valve stop in the middle. I usually leave the ignition on and watch the light, if it blinks, close the bleeder and open one on the other circuit and jab it again. Eventually you get the hang of it. Sometimes the valve will get really stuck and you need to jab it a few times to unstick it.

ptcfast2
08-10-2010, 11:51 AM
As mentioned in an earlier post "Split diagonal brake system". Left front and right rear are on the same hydraulic circuit. Right front and left rear are on a separate hydraulic circuit. If there is a difference in hydraulic pressure from one circuit to the other, (ie blown line or in your case, excessive air) The centering valve automatically shuts off the failed circuit, (it's a safety thing ;) ).

You can manually center the valve and bleed both circuits, they make a special tool for it. Or, you can open one of the bleeders that is bleeding correctly, and give a quick jab and release on the brake pedal. If you do it with the ignition in the RUN position, you'll see the red "brake" light on the dash flicker. The trick is to keep the light off, then bleed as mentioned earlier, very gently.

If the light flickers and the opposite hydraulic circuit dribbles, the valve went overcenter. Open a bleeder on the opposite circuit and jab again. The dash light must be off when the ignition is in the RUN position to bleed all 4 wheels.

Read through the last few posts, printed them all out, and brought them down to the shop. I was hoping one of these responses would be my golden ticket out of brake hell, but alas it seems that we're still stuck. Buying a new MC did help the pedal firmness (not all the way to the floor now! :)) when compared to the reman one I had on there a few days before.

BTW: One of the mechanics down at the shop remembers the procedure you mentioned about resetting the centering valve by jabbing the brake pedal. He was like haha...he said that he was taught that trick went he went to a class a year ago. He's never had to use it before...

So, anyways, after we got the car back on a lift, we discovered (as I thought was the case) that the 4 lines from the MC run directly to the brakes. The car itself does not have a separate centering/proportion valve...so maybe it's built into the MC? Sorry for the questions...we're getting into areas I don't exactly know anything about now! :uhoh:

After I left I got a call saying that they tried the brake "jab" method... but light won't go on/off really fast like you said. They opened the left front bleeder (good circuit) and when the hit the pedal no light flickering, no nothing. They tested the opposite circuit for fluid after this...same results as before. The repeated it a few times to no avail.

jeffcoslacker
08-10-2010, 07:22 PM
Did you try rapidly pumping like I described above?

I've had front brakes on motorcycles so airlocked I had to do this for 5 mins or so before getting a firm lever and fluid flow...and that's with only a couple of feet of line/hose in the circuit...it can take a while in a car if the line ran dry...

kevinb70
08-13-2010, 08:38 PM
have you checked for pinched lines? much of the brake system is crushable metal tubing

ptcfast2
08-13-2010, 10:18 PM
Just wanted to let everyone know that this problem has been fixed!

Went to a Chevy dealership and one of the mechanics that has worked there for quite a few years suggested a power bleed (which I was planning on doing anyways once I found a power bleeder cap that fit the new MC!). Stopped by AutoZone on the way home from the dealership and saw a MightyVac on sale...figured hell...it's worth a shot.

Went down to my mechanic and drove the car back home using the e-brake...and proceeded for about an hour using the MightyVac on the two problem wheels. The tank for the MightyVac filled with OLD fluid...which I thought was interesting seeing that these lines were bled and bled and bled....

So, I using the vac until I got some new fluid out of both lines. Got another person to pump the brakes up, I opened the bleeder and fluid started to gush out. Did the same for the other line and had success as well. Started her up, had a squishy pedal...drove for a bit and the pedal firmed right up! I was ecstatic at this point!

Anyways, it seems that so much air was in the system that a traditional bleed was unable to solve the problem. Luckily the MightyVac was able to pull the fluid out before I needed to use the power bleeder (which I am happy to return as it was damn expensive!).

Thanks for all the suggestions and help guys....it's nice to have a place on the web where I can get some solid advice that makes sense. Now I'm off to change the intake & head gaskets... :)

maxwedge
08-14-2010, 09:46 AM
Hmm, see post #4.

ptcfast2
08-14-2010, 09:56 AM
Hmm, see post #4.
Your post is why I bought both. Before I decided to spend another few days tinkering with it, I left it with my mechanic for a week. Sometimes the only way to fix things is doing it yourself it seems! :)

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