Bleeding master cylinder question...
 

So I guess I'm a dope. I installed my DRM bias spring. Then followed the directions to bleed all four calipers, which took dangerous brakes (full of air) to merely insanely soft.

But I should have read the FSM instead. Apparently if you suspect the master has air in it, there is a procedure to bleed it first.

However, I'd already bled the corners. Does that mean there may be air somewhere else in the system, like maybe in the ABS controller (pulled out of the m/c)? After bleeding the m/c tonight, I fired it up to feel the pedal with the booster. It's raining and at freezing so I don't want to drive it around, but the pedal feels more like normal, though not exactly firm.

The manual actually says you don't have to bleed the calipers after bleeding the m/c if the calipers don't have air in them. I was surprised by that, but am I ok at this point? Or should I bleed the calipers for good measure? Or may there now be air in the ABS unit, and if so what do I do about it? Suggestions? Thanks! :worship:

Re: Bleeding master cylinder question...
 

Bob unless you power vacuum bleed the system its a crapshoot. So with that being said drive it around if the brake pulses while driving you have air in the system. If the brake functions feel the same I would not worry about it.

Which reminds me I need to do my spring from DRM via FU2 as my next project. How much a PITA was that?

Re: Bleeding master cylinder question...
 

You are supposed to bench bleed the master. Just undoing the lines from the master and screw in some adapters and running lines to the reservoir. The lines get minimal air in them while open as they are now the highest point in the system.

Re: Bleeding master cylinder question...
 

The snap ring is the biggest PITA. The spring has to be almost completely compressed and then you have to get the snap ring in there. It can be quick or take forever depending on your luck. I tried screwdrivers, socket extensions, etc to press the spring in, but nothing worked as well as my index finger. Unfortunately after about the millionth attempt, my finger was pretty beat up.

Hey Jeff, what do you mean about adapters? I just unscrewed the lines enough that fluid would run out as the brake pedal was depressed. Basically I (eventually) followed the FSM directions. Is there more to bleeding the m/c than that?

Re: Bleeding master cylinder question...
 

Basically it seals off the port and does not allow any air back into the MC.

http://image.superchevy.com/f/870123...bench_02_z.jpg

Re: Bleeding master cylinder question...
 

Thanks guys, this is right on time with my bias spring on the way and all new brake system on my Z after this long storage.:handshak:

Re: Bleeding master cylinder question...
 

.....:o if you have a spare slave cylinder use the bleeder from it, that works at the larger of the two M/C lines. The smaller of the two @ the M/C takes a caliper bleeder screw....get some rubber tubing & you're in like flint.

I do believe that on the 90 abs system, unless the system is actually used the air you have can not get into the pump. During the self tests, it just works the solenoid valves to make sure they work.....I think I'm correct...:o

It is easier on a bench in a vise. I made a tool from an old slave cylinder push rod fitted into a small block of wood for a hdl...fits the M/C piston like a glove.

:cheers:
tom

Re: Bleeding master cylinder question...
 

What would prevent air from getting in when you remove the adapters to re-install the brake lines?

I didn't remove my m/c from the car. I followed the DRM instructions and picked the proportioning valve out vs beating it against some wood like the FSM suggests.

Thanks for the feedback everyone. I think I will just drive the car (tomorrow should be a nicer day) and see how it feels. If it's not good then I'll bleed all the calipers again.

Re: Bleeding master cylinder question...
 

Good point and IMHO it's valid Bob. I guess it's easier to get the air from the connection point at the lines to the calipers and then out, than to bleed the air in the M/C and the connection point. It sure does take forever to get the air to the calipers, or at least in my car it does. Took me forever!

Also, I was always taught that unless you use a p-bleeder, any M/C work needs to be bench blead to negate the risk of bottoming out the M/C piston at the end of the bore & possibly damaging the piston seals when ya bleed it in the car. Actually, I did have to do a few sharp wacks, used my bench bleeder tool to smack the mount flange a few times and then a coupla hits on the oak block....it came out but it took some right sharp raps. I thought I was gonna break the thing.

:cheers:
tom

Re: Bleeding master cylinder question...
 

I've bleed mine several times by getting a spare MC cap and seal, put a NPT fitting in it and putting 8 psi on the MC, it can be done pretty quick. It needs a hose clamp around the cap also and will still pop off above 10 psi. But if your worried about a brake fluid mess if the cap pops off, mine didn't and it's popped off probably 5 times when I was trying to find the maximum limit. I know some claim gravity bleeding works good, just take all day.