Brake and clutch issues for the new racer platform

[mark kibort]

This car has unknown brake lines, abs and master and slave cylinders. I wanted to get all the old nasty fluid out of the system before I attached them to the brake lines, so I connected the rear lines and left the front lines wide open. I put on a power bleader and forced out the fluid . it started coming out of only the passenger side first, not the driver side. when it got blue from the new fluid, I closed that side off and tried to do the driver side. It was not coming out. I pushed the pedal but nothing came out. when I pushed really hard, it squirted out. then pumped the brakes and got all the gold dirty fluid out util it got blue. for some reason though, with the power bleader attached, it didnt force the fluid out unless the brake pedal was depressed.
clutch was similar . the power bleeder did dribble the fluid out until it turned blue and then of course, the pedal just falls to the floor. an hour later, there was 1/4pedal, but it didnt have any chance of being a real pedal. master cylinder issues for brakes, master for clutch? ABS clogged?
thoughts?
Im puzzled that when the power bleader is connected that the fluidl doesnt flow out of the front lines when completely disconnected. any reason why it wouldnt??

[69gaugeman]

Power bleeder is ~10psi. Foot pedal is MUCH higher. There are solenoid valves in the ABS body that might be at closed or mid position. Can you power up the abs module and have it reset the abs valves?

Im puzzled that when the power bleader is connected that the fluidl doesnt flow out of the front lines when completely disconnected. any reason why it wouldnt??

Disconnected where? Caliper? master cylinder?

[Mrmerlin]

since this was a car that had an engine removed i would inspect the hard lines to all of the systems its quite possible that one or more could have gotten pinched, normally with the lines open they will all leak fluid till the reservoir is empty

[Tom. M]

With the clutch, make sure the master cylinder piston is all the way up in the bore. The pedal can be up but the piston can still be depressed not allowing fluid to pass.

[SharkSkin]

If the fluid in the MC was nasty it would have been better to flush the MC first via the bleeder and/or disconnecting lines rather than force any crud through the ABS.

We tend to think of master cylinders as having a seal that wipes past a port on the wall of the MC, and this port is where the fluid comes in from the reservoir. Looking at P. 24 of the "928s w ABS Infotechnik pub 1985.pdf" document on the tech docs CD, this is not the case at all and the mechanism is much more complicated. There is the rear piston which is activated by the brake rod, and a front floating piston which is activated by hydraulic pressure from the rear piston(referring to position on the car; the rear piston activates the front brakes, the front piston activates the rear brakes). Each piston has a shuttle valve which opens with the brake rod fully released, and it's these shuttle valves that allow fluid to flow into the MC from the reservoir.

Now, none of the above explains why one side of the front circuit behaved differently than the other. The differentiation between right & left front is at the ABS pump where it is divided into two circuits. The reason I mentioned that isto point out that the MC is much more complex than an "old school" MC and there is more that could go wrong to account for the soft pedal. In addition to possible issues with the seals in the bore(more seals than in a conventional MC) the spool valves may not be sealing properly. You may get lucky but IMHO it's very likely that you're going to have to replace the MC; if you have seen signs of rust in the fluid then you're almost certainly going to have to replace it.

Back to the apparently clogged line, you might try disconnecting the lines at the ABS pump and see if you can blow them clear with compressed air. If you don't find any blockage this way it's probably the ABS pump as Rod alluded to. If it becomes clear through diagnosis that you need an ABS unit I have a late one that still has ~6 months on the 928I warranty, but make sure you need it -- no sense in just throwing parts at it. I'll cut you a deal if you want it.

One final note -- don't waste another drop of the ATE fluid on it until you're satisfied it's working perfectly. Get a couple quarts of generic DOT3 at your favorite generic auto parts store and use that to flush and test the system. Until you actually begin tracking it, any compatible fluid will work just as well as the ATE. IMHO you're going to have to get it working, go out and pound on it to activate the ABS a few times, bleed it, and repeat until you can get clean fluid at all 4 corners. Each time you bleed it, make sure you move enough fluid to replace all the fluid in the system. Only when you are sure it's 100%, replace the fluid with ATE.

[mark kibort]

Disconnected at where the brake lines attach to the hard lines at each wheel.

Ill try to power up the system to see if that helps or does anything.

Originally Posted by 69gaugeman

Power bleeder is ~10psi. Foot pedal is MUCH higher. There are solenoid valves in the ABS body that might be at closed or mid position. Can you power up the abs module and have it reset the abs valves?



Disconnected where? Caliper? master cylinder?

[mark kibort]

I also forgot to mention that when the driver side was open and the pedal was acting like the valves were closed, i pushed REAL hard and then it squirted out and I was able to push out fluid fairly normally, but I still didnt get any flow when i wasnt pushing the pedal, like I am used to at 7psi with the bleeder.

[mark kibort]

The fluid looked dirty, but not with any real bad stuff, like pieces or rust. just dirty. So, you are saying I should disconnect at the ABS , each of the lines as they enter the abs unit, so that we can see if the unit is clogged? I tried it again last night and now i cant even get the drive side brake lines to push out fluid. in fact, now when the line is connected , it doesnt even push on the brake pads. ABS controller for the line going to the left or right front caliper? the input line as it goes to the ABS , right?

The chassis is really clean and the master and ABS units look clean too, much cleaner than the Holbert stuff, but that stuff worked flawlessly. I put on the power bleader and it would push fluid out at any side immediately.

I think I may take you up on that Abs controller if we cant solve the problem.

Thanks again,

Mark

Originally Posted by SharkSkin

If the fluid in the MC was nasty it would have been better to flush the MC first via the bleeder and/or disconnecting lines rather than force any crud through the ABS.

We tend to think of master cylinders as having a seal that wipes past a port on the wall of the MC, and this port is where the fluid comes in from the reservoir. Looking at P. 24 of the "928s w ABS Infotechnik pub 1985.pdf" document on the tech docs CD, this is not the case at all and the mechanism is much more complicated. There is the rear piston which is activated by the brake rod, and a front floating piston which is activated by hydraulic pressure from the rear piston(referring to position on the car; the rear piston activates the front brakes, the front piston activates the rear brakes). Each piston has a shuttle valve which opens with the brake rod fully released, and it's these shuttle valves that allow fluid to flow into the MC from the reservoir.

Now, none of the above explains why one side of the front circuit behaved differently than the other. The differentiation between right & left front is at the ABS pump where it is divided into two circuits. The reason I mentioned that isto point out that the MC is much more complex than an "old school" MC and there is more that could go wrong to account for the soft pedal. In addition to possible issues with the seals in the bore(more seals than in a conventional MC) the spool valves may not be sealing properly. You may get lucky but IMHO it's very likely that you're going to have to replace the MC; if you have seen signs of rust in the fluid then you're almost certainly going to have to replace it.

Back to the apparently clogged line, you might try disconnecting the lines at the ABS pump and see if you can blow them clear with compressed air. If you don't find any blockage this way it's probably the ABS pump as Rod alluded to. If it becomes clear through diagnosis that you need an ABS unit I have a late one that still has ~6 months on the 928I warranty, but make sure you need it -- no sense in just throwing parts at it. I'll cut you a deal if you want it.

One final note -- don't waste another drop of the ATE fluid on it until you're satisfied it's working perfectly. Get a couple quarts of generic DOT3 at your favorite generic auto parts store and use that to flush and test the system. Until you actually begin tracking it, any compatible fluid will work just as well as the ATE. IMHO you're going to have to get it working, go out and pound on it to activate the ABS a few times, bleed it, and repeat until you can get clean fluid at all 4 corners. Each time you bleed it, make sure you move enough fluid to replace all the fluid in the system. Only when you are sure it's 100%, replace the fluid with ATE.

[Andrew Olson]

I don't exactly know how the bias/proportioning valve works, but I winder if you were working against it?

[mark kibort]

I just had open lines , before the caliper and was pushing on the brake pedal. one side squirted out like milking a cow, and the other wouldnt budge any fluid.

I guess Ill have to look at the WSM and see the routing. out of the master, there are seveal fittings. one to the front and one to the rear. (then the blue hose fitting to the clutch master) without abs, there is just the bias valve on the rear line coming from the brake master and nothing on the front and they just must "T" where it goes left to right side. with the ABS, think its more complicated.

sounds this could be ABS related

Originally Posted by Andrew Olson

I don't exactly know how the bias/proportioning valve works, but I winder if you were working against it?

[SharkSkin]

Originally Posted by mark kibort

The fluid looked dirty, but not with any real bad stuff, like pieces or rust. just dirty. So, you are saying I should disconnect at the ABS , each of the lines as they enter the abs unit, so that we can see if the unit is clogged? I tried it again last night and now i cant even get the drive side brake lines to push out fluid. in fact, now when the line is connected , it doesnt even push on the brake pads. ABS controller for the line going to the left or right front caliper? the input line as it goes to the ABS , right?

The chassis is really clean and the master and ABS units look clean too, much cleaner than the Holbert stuff, but that stuff worked flawlessly. I put on the power bleader and it would push fluid out at any side immediately.

I think I may take you up on that Abs controller if we cant solve the problem.

Thanks again,

Mark

When all is said and done you may need to have the same vacuum bleeding operation done that Nicole had done to her car. What I'm suggesting is that you remove each line between the ABS pump and front caliper and try to blow them out with compressed air(be sure you find a way to contain the fluid coming out!). If either line is blocked that may be the whole problem. The circuit tees to the two front calipers inside the ABS pump, so if the lines are clear that points to the pump. It's a single line from the master to the ABS pump. The problem is not the proportioning valve either, though that's not to say there is no problem with that -- it just doesn't account for the symptoms re: L/R fluid flow on the front lines.

[mark kibort]

got it. So, in the abs, it splits the two sides. got it. Ill dsconnect those two lines and blow compressed air through with the ends in a bag or something.

then, if that doesnt work, or they are clear, it points to the ABS controler, only after doing the same for the front line going from the master to the abs, which seems to be clear, in that the passenger side leakds with power bleeder and squirts fuild with the pedal depressed. the rears we will see.

thanks

mk

Originally Posted by SharkSkin

When all is said and done you may need to have the same vacuum bleeding operation done that Nicole had done to her car. What I'm suggesting is that you remove each line between the ABS pump and front caliper and try to blow them out with compressed air(be sure you find a way to contain the fluid coming out!). If either line is blocked that may be the whole problem. The circuit tees to the two front calipers inside the ABS pump, so if the lines are clear that points to the pump. It's a single line from the master to the ABS pump. The problem is not the proportioning valve either, though that's not to say there is no problem with that -- it just doesn't account for the symptoms re: L/R fluid flow on the front lines.

[SharkSkin]

I doubt that there is a problem with the line from the MC to the ABS. It's probably better that you don't introduce air into that line if it's not absolutely necessary(and I think it isn't).

[mark kibort]

ok, got it.

So,i was looking at it a little closer today, and it seems there are only 2 lines connected to the master. the rear most located (front brakes) and the and the front located connection (rear brakes). so, at the ABS, there are a bunch of connections. you want me to disconnect the front brake line as it exits the ABS unit. The main line from the master seems to connnect to the bottom rear of the ABS unit. You are saying that since I was able to push fluid out on the passenger side, then, its kind of like the master is working fine. it really has to be in the driver side lines or ABS system side to side splitter system internal to the ABS.

keep that ABS controller warm for me. I bet that is the problem, as I have a hard time believing that a line could be clogged like this.

mk

.

Originally Posted by SharkSkin

the mechanism is much more complicated. There is the rear piston which is activated by the brake rod, and a front floating piston which is activated by hydraulic pressure from the rear piston(referring to position on the car; the rear piston activates the front brakes, the front piston activates the rear brakes). Each piston has a shuttle valve which opens with the brake rod fully released, and it's these shuttle valves that allow fluid to flow into the MC from the reservoir.

Now, none of the above explains why one side of the front circuit behaved differently than the other. The differentiation between right & left front is at the ABS pump where it is divided into two circuits. The reason I mentioned that isto point out that the MC is much more complex than an "old school" MC and there is more that could go wrong to account for the soft pedal. In addition to possible issues with the seals in the bore(more seals than in a conventional MC) the spool valves may not be sealing properly. You may get lucky but IMHO it's very likely that you're going to have to replace the MC; if you have seen signs of rust in the fluid then you're almost certainly going to have to replace it.

Back to the apparently clogged line, you might try disconnecting the lines at the ABS pump and see if you can blow them clear with compressed air. If you don't find any blockage this way it's probably the ABS pump as Rod alluded to. If it becomes clear through diagnosis that you need an ABS unit I have a late one that still has ~6 months on the 928I warranty, but make sure you need it -- no sense in just throwing parts at it. I'll cut you a deal if you want it.
.

[FlyingDog]

Is your clutch blue hose clamped on? If so you should have no problem running the pressure on the power bleeder up to 20-25psi. IIRC, 25 is the stated limit for the bleeder. Only open one line at a time. If the system has lots of air in it, sometimes the power bleeder will just keep compressing the air without really pushing much fluid. Keep the bleeder hooked up and pressurized while pumping the pedal.