Bleeding master cylinder question...

[Aurora40]

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:

[GOLDCYLON]

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?

[Jeffvette]

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.

[Aurora40]

How much a PITA was that?
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.

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.

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?

[Jeffvette]

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?


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

http://image.superchevy.com/f/8701238/0509sc_bench_02_z.jpg

[HAWAIIZR-1]

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:

[tomtom72]

.....: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

[Aurora40]

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.

[tomtom72]

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.

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

[lbszr]

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.

[xlr8nflorida]

:thumbsup:

[Jeffvette]

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


The air in the brake lines at the connection will be nill, unless you are horsing the lines around. The big issue is you need to bleed the master so it is primed and ready to go. You can't effectively bleed the master when it's all hooked up as the air compresses as the piston is pushed in.

[GOLDCYLON]

Im waiting to see Bob what you report about how well the spring works.

[xlr8nflorida]

Im waiting to see Bob what you report about how well the spring works.

I don't have it, I was told that I had to be careful with the 6 piston setup or I would be replacing the master cylinder. I'm sure it makes a decent difference on a stock system.

[tomtom72]

I love my DRM bias spring!

I have a stock set up...well DRM GS calipers w/ss pistons up front & rebuilt stockers out back all on ss lines and a stock M/C & Power stop semi's (the dusty kind)...oh, forgot, rotors swapped out for some 'bling'...all four are drilled & slotted from Rotorsonline.com...last Dec they had a fire sale all four shipped for $200.00. The local NAPA wanted that much for stock replacements!

Anyway, over all the spring took away some of the severe nose dive under sudden braking, ya know when ya get cut off....yea, imagine that happening in Metro/NYC :neutral:

Other than it seemed to make the car "feel" more balanced under braking, which maybe my imagination....I did the brakes in stages. Spring, M/C kit, ss lines, caliper kits all on OEM rotors & pads. GS/DRM calipers & "bling" rotors & power stop semi-metallic pads were all the finish step. Now the total package seems to be much better than the either the pure OEM stuff and the phase 1 stuff.....the phase one comparo could be my imagination, but the end result is way different than the OEM configuration. Way more initial bite, less pedal effort / stopping power increment (does that make any sense?), nearly level sudden braking, waaaay more dust even on the rear wheels!......and the rotors look cool behind my chrome fake A-molds!:sign10:

:cheers:
tom

[xlr8nflorida]

This is not exactly ZR-1 related but maybe you guys can help me. On my 93 LT1, the pedal feels very hard to push and the car seems to take longer to stop then it used to. Now to be completely honest, this car has sat about a year, other then starting up every few weeks, pumping the pedal and a few occasional drives, the car has not seen alot of use. My 92 seemed to do this as well before I sold it. It's hard for me to remember what stock is anymore. My father drove it the other day and said the brakes are shitty. He has an Acura TL which has brakes that really bite. On my ZR-1, I have the 6 pistons and C5 I have the stock brakes so I told him the system is just older. Deep down, I think there might be something wrong with it. Also, come to think of it, I'm not too good about draining brake fluid on my daily drivers, could that cause the issue? The best way to explain it is that when you hit the brakes, it dosen't really bite, it more or less stops smoothly but very slow smoothly. LOL

Thanks!

[tomtom72]

XLR8,

Two things pop out at me right away:
Booster issues:...symptoms could overly high pedal effort to stop = bad booster, and a hissing sound when you step on pedal = internal leak in booster, or a bad vacuum check valve &/or vacuum feed line.

Something like glazed rotors or pads.....which I doubt, oh, and one more thing maybe stuck parts like water in old brake fluid causing some corrosion in the caliper reservior or just stuck pistons......okay so sue me that's more than two....:sign10:

:cheers:
Tom

[xlr8nflorida]

XLR8,

Two things pop out at me right away:
Booster issues:...symptoms could overly high pedal effort to stop = bad booster, and a hissing sound when you step on pedal = internal leak in booster, or a bad vacuum check valve &/or vacuum feed line.

Something like glazed rotors or pads.....which I doubt, oh, and one more thing maybe stuck parts like water in old brake fluid causing some corrosion in the caliper reservior or just stuck pistons......okay so sue me that's more than two....:sign10:

:cheers:
Tom

I'm not getting hissing. Not glazed rotors or pads as I drive that 93 like an old lady. I haven't changed out the brake fluid in like 5 years, maybe I'll start there LOL

Thanks for your help.

[tomtom72]

okay on all the stuff in left field.

One of the symptoms of a bad or going bad booster is high pedal effort. The car stops, but it's eventually and the pedal feels hard, not mushy. The worse the booster is internally, the harder the pedal feels and the harder you have to step on it to get to stopping. It's like "man, I got a rock solid pedal, but the car don't stop!" is the usual observation.

:cheers:

[Aurora40]

FYI, so the battery in the car died incredibly suddenly and severely (less than 1v when attached to the car, about 8v when unhooked). I got a new one, and after trimming off the big fat flare for the handle that was on the ACDelco replacement, I drove the car today.

The brakes are pretty crapola, the pedal moves a ton before they engage. So hopefully there is still air, but they actually feel fairly firm once they start working. I'll try bleeding at the calipers again and cross my fingers.

I think I've definitely hit that point where I realize (for the millionth time) that if something works, leave it alone. The stock brakes were perfectly fine. And more importantly, they worked correctly. I don't know why I always have to re-learn that lesson...

[tomtom72]

True words in that last paragraph! I wish I'd remember that, for the zillionth time too!:redface:

[Aurora40]

So bleeding the calipers again seems to have helped. It feels like it did initially after upgrading the front calipers, which is to say the pedal has a fairly long initial travel, but then works well.

I can't really tell if it has more rear-bias though. I'll have to find some unoccupied road to do some hard braking tests.