major brake issues PLEASE HELP !!!!

[69 rs ss]

OK so i own a 72 olds 442 which i recentley did a brake overhaul on im running kore 3 kit Z06 brake calipers all the way around 6 piston 4 piston. I purchased a tuff stuff 9 inch dual diaphram booster and a wilwood tandam master cylinder 1" bore. I recentley installed everything including new brake lines I also gutted the factory combonation valve and use as a distribution block and installed a summit prop valve to rears. First problem i ran into is when bolting master to booster the booster rod pushes slighty against the master and compresses master piston slighty. Sencond i have excellent brake pressure to the fronts but absolutley zero brake pressure to the rears. ive bench bled master and pumped the brakes to bleed lines. seems like the fluid wont go down in the master for the rears no matter how much i try to pump n bleed. i need major help please
Thanks in advance

[Hydratech®]

I am certain that the MC piston preload is where your problem is. If the vac booster MC pushrod rod is adjustable, make it happen. If the rod is removable by hand (slip in / slip out), buzz it down nicely until you achieve zero MC piston preload. Just to be sure, double check that there is zero preload on the pedal rod under the dash FIRST, as sometimes a brake lamp switch or pedal stop adjustment could be at fault.

Here is our online article that takes this discussion further:

http://hydratechbraking.com/braketech1.html

You may have to get into advanced port plug diagnostics, but I bet your MC piston preload condition is at fault. Here is further discussion regarding the Wilwood MC:

http://www.lateral-g.net/forums/showthread.php4?t=17060


We love our cars, right?

[JRouche]

Yes, the pin needs to be adjusted. I dont think thats the cause for loss of rear brakes though. A too short of a pin "might" cause this, but still dont think so, a too long of a pin wont.

When you bled the rear brakes with new lines how much fluid did you go through? I found it took alot more than I expected. Even after I got new clean fluid out to the rear I had to continue to pump even more through to remove some pockets of air. I dont know where the pockets came from. I was thinking it should have been a nice solid column of fluid once I got some to the rear. NOT. I ended up pumping a pint or more through (no biggy cause I had two quarts of new fluid on hand for the brake job) just for the rear calipers. And you bled it with the valve all the way open right? And with the valve all the way open you still cant drag the rear tires with heavy braking?

Not familiar with your system. Is it a parking brake type caliper? Mine are the cadillac calipers with parking brakes. The parking brake feature on mine can be a bear sometimes. Kinda finicky. The parking brake NEEDS to be used, that is what takes up the slack from normal pad wear. Yer pads are new so thats not the issue. But even first time installations of the cadillac calipers they need to be adjusted so the parking brake is fully seated, bottomed out. Otherwise the pads are so far away from the rotors that the brake pedal travel just takes up the slack and doesnt do any real braking.

Ok, Im going backwards here. I just re-read your post. You aren't moving any fluid out to the rear during bleeding? You said the fluid level isn't going down. I thought you were able to bleed the rear brakes.

You cant bleed them? Is that yer problem? No fluid to the rear? Ok, that easier...

Make sure the proportioning valve is opened all the way. Problem is. If the front is tight, all pumped up and you have a massive air bubble on the rear you wont be able to push the pedal down any further to remove the BIG bubble. The pedal will stop due to the tight front pressure before you can get a full stoke from the pedal to clear the rears air bubble.

I have a vacuum brake bleeder, it helps with those issues. It will pull fluid and air without having to press the pedal.

But you dont need that. Even if you only get a inch or so from each pedal pump you can drive the fluid out to the rear. Its a long and frustrating process, but it works.

Another thing you can do is buy a quart or two of fluid and plan on throwing it away. Crack the front bleeder, just one side, just enough to get some flow. Route a tube to a very clean container with some clean new fluid in it just an inch or two, to cover the end of the tube. ( I like new mason jars) so the front bleeds off into it. It needs to be clean cause the fluid will be drawn back up into the caliper on release of the pedal (along with the big bubble of air thats in the tube, you will need to re-bleed the front brakes).

But what it does is allows more pedal travel so you can push alot of fluid to the wide open rear brake bleeder. You will be able to get a full pedal stroke and move the big gas bubble down the line. Keep an eye on the fluid level in the reservoir, dont wanna drain it.

So obviously, I dont get where you are having problems. Dont know if the rears were bleeding or not. If not try some of the stuff. If they were bled, bleed again. You have an obstruction (air bubble, or caliper travel issue). Hydraulics are actually pretty simple because the fluid doesn't compress. With force applied there should be some movement, the fluid, an air bubble or the caliper or physical blockage. A solid column of fluid. JR

[69 rs ss]

thanks for the great info i will try this out asap. is it possible i hAVE a bad master cylinder when i compress piston manually on MC it makes a wiered noise? front line bleeds fine and front brakes work great but nothing to rear

[Hydratech®]

Did you bench bleed the MC first? It is my opinion that you must thoroughly bench bleed a master cylinder in a bench vise with the MC being secured LEVEL or NOSE DOWN. Any upward angle on the MC during bench bleeding will want to make you life difficult, as air will want to rise to front (which will sit there in the tops of the cylinders and not want to come out). I always hear about guys that are convinced that they can conlusively bleed out a brake master cylinder when bolted in the car, never mind that the factory upward angle on the vacuum booster is a whopping 17 degrees (1st gen F body and '64-72 A body). Even with a pressure pot / bleeder, there are air bubbles that will not come out due to this upward angle. With the MC level or rear of the MC tilted upward, all air will migrate upward and rearward towards the compensation ports (piston fluid feed ports) in the bottoms of the brake fluid wells of a master cylinder. Bench bleeding will also tell you what the MC is up to, as you have removed all variables and should see fluid production out of both ports. Let's put this into the simplest form: If you can't get the MC to behave in a bench vise, nothing magic is going to happen when you put it on the vehicle to make it work any better, which is why you have to start here.

While messy, I like to use my finger tips as one way directional check valves on the brake line output ports while bench bleeding. I suggest you have a tray ready to catch the brake fluid and also a larger towel handy. Fill the MC fluid wells about half to 3/4 of the way. Wait for brake fluid to start dripping out the brake line ports. Plug the ports on the MC by applying firm fingertip pressure to the ports, stroke the pistons inward using your other hand, allowing whatever pressure built up to escape past your finger tip "check valves" (by relaxing fingertip pressure on the brake line ports while storking the MC pistons inward)). Then seal the ports by applying firm fingertip pressure again when releasing the MC pistons back to the rear of the MC. You will feel the activity of the MC building pressure against your fingertups when stroking the MC pistons inward, though not allow air to get sucked back in while allowing the MC pistons to retract back rearward. The primary piston (front port on the Wilwood 260-8555 1") will be producing the majority of pressure and volume as compared to the rear (as this is how MC's work)(not a dead linear output between the front and rear ports as some would believe). Once you have fluid pressure building conclusively in both ports every time you stroke inward, you should be comfortable in knowing that you do not have a bad MC, as it is doing its job with fluid production out of both ports. The noise you state you are hearing is likely the rear piston being completely dry, with the piston and seal not being fully lubricated (by being fully immersed in brake fluid).

Once the above sequence is completed, then plug the ports on the MC (hopefully you have some plastic or metal fittings you can do this with)(run up to the parts store ahead of time if needed). With the brake line ports plugged, you should not be able to stroke the MC pistons inward more than a 1/4" IF the MC is fully bled, as the fluid has nowhere to go (as the ports are plugged). If you still have a spongy MC piston apply at this point, you very likely still have air trapped in the MC pistons. Leave the plugs in the ports, and now stroke the MC pistons in firmly and release. Do this in rapid succession and you should see little air bubbles gurgling up out of the ports in the bottoms of the brake fluid wells. As you get the last of these little bubbles out, you should find the MC pistons getting harder to push in, which indicates you are winning the game (by ridding the MC of the last air still trapped in the MC pistons).

Leave the port plugs in the brake line ports. Fill the fluid reservoirs to about 3/4" below the tops of the fluid reservoirs. Install the lid on the MC. Wipe the MC down of all brake fluid. Now go see what preload you may have when installing the MC onto the face of the vacuum booster. You should feel a clean fit of the MC to the face of the booster, and NOT have to draw it down to the vac booster the rest of the way with the mounting fasteners. If there is a preload, this will apply the MC pistons when bolted down. Interestingly, this will usally allow the fronts to bleed out, but will typically prevent the rear from allowing any fluid! (which is exactly what is happening to you). Sometimes you can even just loosen the MC mounting bolts and find that all of a sudden you get rear brake fluid! (as you have allowed the MC piston to release all the way against the snap ring in the back end of the MC casting).

Make sure you have a big towel under the MC first to catch any brake fluid. Leave the MC lid on, connect the brake lines to their respective ports LOOSELY. FYI - on this particular MC, it is front port = front brakes / rear port = rear brakes. Now remove the lid from the MC and wait for the brake fluid to start dripping out of the brake line connections at the MC - loosen them up further or temporarily disconnect the lines if the fluid doesn't want to start dripping out of the line connections at the MC ports. With a steady drip, drip, drip coming out of both loose brake line connections, this proves out that the MC pistons are in a full state of release as installed on the vac booster, the MC is not airlocked, and that you can now move onto capillary / gravity bleeding. Refer back to our online article for the rest of the gravity bleeding sequence. In speaking with Dustin Burr at Wilwood, 99% of the MC's they receive back under warranty actually have nothing they can find wrong with them, so the odds are that you do not have a bad MC.

[quarterbooty]

I have a similar installation in my '72 Monte Carlo. With regard to little or no fluid flow to the rear circuit, I had a similar issue that I finally resolved as described here:

https://www.pro-touring.com/showthre...ht=#post711703

Hope that helps.