So I finally got around to doing my brakes, inwhich I replaced my rotors, lines, pads, calipers, master cyl and fliud. SO I went to drive the car and I can slam two feet down on the pedal and it just doesn't GRAB like any other car would. It just creeeeps down to a halt. The brakes were priofessionally bled and the pedal feels good, but the brakes just feel like they are not doing what they should

I was going to get an adj prop valve installefd to boost pressure to the rears, since they dont even hold the drive wheels.

Does anyone think it would be worth it to replace the stock prop valve while Im at it? I doubt the booster is bad since the pedal feels good and not rock hard as it might if the booser were bad.

Thanks fellas

Will

 

I have the same problem. Replaced everything you did and come up with the same result.

 

What gives??? I mean I know from what every says the stock moraine brakes are crap, but come on. They cannot be as bad as what I am feeling... I don't believe a car could have ever made it off the floor with a brake system like this. Something must be wrong. Well I will change the stock prop valve and mod it with a wilwood unit for the rears. But this might take some time as the tranny went out on me and the cars most likely just going to be retired all together

Will

 

Did you bench bleed the master cyl?

The lines don't come out of it at the highest point of the cyl after it's installed; so some air will remain trapped there forever, professional bleeding or no. You can run 10 gallons of fluid through there and that air pocket will still be there.

 

A v12 pheonix should get it out right. Maybe its your booster? I was thinkin of replacing my MC mainly cause the resivoir looks like crud and the MC is prob the original.

 

No.

You have to bench bleed it. No way around it. Even if you replace it, you'll still have to bench bleed the new one.

 

What you're describing sounds like the pads aren't properly seated to the rotors. This is not an uncommon problem, particularly with new metallic pads on freshly-cut or new rotors. If the pads are not broken in properly, the symptoms will be exactly what you describe (good pedal feel, lousy stopping power).

The bedding-in procedure for new pads can be somewhat precarious - the best general advice I can give for new pads is that you don't immediately go out and slam on your brakes to see how well they work. This can put a glaze on both the pads and the rotors, and will necessitate the job be done over again.

A couple of links on bedding in new pads (apologies in advance if you already know this):

http://www.bendixbrakes.com/tech/Bra...Procedures.pdf

http://www.kitcarbooks.com/brakepads.html

-Bob

 

What i mean is the v12 would make the bench bleeding much easier.

 

my brakes feel like garbage too, i didnt get around to bench bleeding , but i think bleeding the calipers made my brakes worst, time to start from where i was suppose to , now i have to slam on the pedal just so i can slow down

 

This is interesting. I purchased this car about a year and ½ ago and completely rebuilt it. I replaced everything on the brakes except the proportioning valve and I have the same experience. I thought I did something wrong so I have taken the car to several mechanics including the authorized GM dealer. I have always received the same answer. They can’t find anything wrong with the brakes. But I put the car up on jacks, put the car in gear and let it idle, hit the brakes and the rear wheels slow down but continue to spin. I have replaced the rear calipers three times. The car has lousy braking. Front brakes seem to work well but you can’t lock the brakes like I would think you should. I have four wheel disc brakes. I wonder if rear drum brakes have the same problem. Why put rear disc brakes on a car with this performance. I have bench bled the MC and put gallons of brake fluid through the system bleeding and re-bleeding. New OEM pads, refinished the rotors with a non-directional finish and still no good. I get plenty of fluid through the rear calipers when I bleed. I just don’t think they were designed properly.

 

Don't shoot me if this sounds silly but I would check your vacuum line and booster. Make sure that it is holding vacuum by pulling the booster vac check valve fitting out when parked with the car off and there should be some vacuum present. Drum brakes are self energizing and work well with no power assist but discs are not self energizing so they require a boat load more force to grab hard. If you ever had to shut down a four wheel disc brake car and stop with no vac assist you will know exactly what i mean here. You practically have to wrap your arms around the steering wheel and push with everything you got to stop. Nine times out of ten i find its the little overlooked "simple" things that are causing problems. I swapped from drums to disc before but I swapped the booster and all and it worked out great. Anyone know if the disc/drum boosters are the same?

 

The problem with your 1986 brakes is that they're the crappy cast-iron Saginaw calipers. Those never have worked well, they generated complaints when they were brand-new.

There's a recall kit available from GM that you install into the calipers; but auto cars don't qualify for it as a recall. But you can of course buy it and put it in your car. For some reason, rebuilt calipers never have it; seems kind of dumb, but that's the way it is.

Also, there's a proportioning valve mod for those brakes, that supposedly makes them almost somewhat more nearly functional. IIRC it involves removing something and drilling something, but I don't remember the details.

People who do both of those things report that their rear brakes work almost as well as drums afterwards. A huge improvement.

Yes the drum and disc boosters are the same. However, there are other potential differences; specifically the length of the little rod in them. If the rod is too long they will get too little assist, and if the rod is too short, they will be way too touchy.

 

True... true...

 

In my particular case the booster was replaced by the GM dealer. I will check to see if it is holding pressure after I shut down. I am getting about 18 -20" vacuum at idle. Brake peddle feels good and the car will stop with a normal amount of peddle effort.

I have read about the recall but it supposedly only fixes the emergency brake. It gets gummed up and stops working. The reason manual trans. cars go the recall is because GM feels an emergency brake is more important on a manual car. The article said eventually the emergency brakes will stop working anyway even with the recall. The self adjustment feature is lousy.

I have heard GM mechanics talk about the fact that those brakes are the worst in the industry to properly adjust. The service manager says sometimes his people give up. I don’t completely understand this since they “should” be self adjusting by operating the Emergency brake. I still think they designed them wrong.

 

So guys, sorry to ressurect such an old thread, but I want to know if you guys think it would be worth it to replace the stock prop valve as well as add an adj prop valve to get some more line pressure to the rear. The car just doesn't feel like it can stop for ****, and there are only a couple of things that have yet to be replaced. THe prop valve itself, the booster(which seems to be fine) and the lines themselves(hardlines). Does anyone have anymore input before I decide to go ahead and do this? Thanks

Will

 

You never did say why you replaced all these brake parts to begin with - was it because of this problem, or something else? Did this problem start new with the new brake job?

If the former, I'd look at the booster and its vacuum supply. If the latter, and if you still have a good pedal and if the parking brake is properly adjusted, I'm sticking with what I wrote above - the pads never took a seat, and simply aren't generating enough friction to stop the car. They'll get hot and possibly stink a bit, but that's about it. In the seventeen + years I turned wrenches for a living, I saw this happen a million times.

As for bench bleeding the master, that's always solid advice, but probably not the source of your problems in this case if the pedal is good.

IMO, The odds of it being a bad proportioning valve are slim to none. Although anything is possible, I've never, ever in my life seen one go bad. Seen a bunch of them replaced though.

-B

 

The willwood unit is awsome, but what a pain to install. I'm glad i did it with the engine out. I'm also glad i didn't have any leaks the first time around.

 

Norcal,

When you rebuilt the calipers, did you also adjust the "free travel?" I wonder if this adjustment could somehow be causing your difficulties--I used reman loaded calipers, adjusted the free travel, and I've experienced no problems with my PBR's: Not only do the brakes function well, but the parking brake holds on an incline.

Check the following link for more info about free travel:

https://www.thirdgen.org/techbb2/sho...nd+free+travel

Also, did you clean and check the guide pins and their bores for wear and proper lubrication? Could they be hanging up?

Ooops, sorry, Norcal, I thought you'd swapped to PBRs.

JamesC

 

i need comments on the Wilwood Adjustable Proportional Vavle, im swap out my 87 10 bolt drums for 88 10 bolt discs for the rear, i heard everything else is interchangable, except hard axle lines and ebrake setup, but i know im gonna have to get a different prop valve to change the ratio of front to rear breaking. is the wilwood any good? or is it just the name that is attractive?

 

Well the wilwood is one of only a few basic adj prop valves around, and it is only $40. I mean a prop valve isn't a complicated machine. If by good you mean, it won't break, won't leak, easy to install, easy to adjust, and effective, then yes it is good.

 

My rear PBR brakes were so bad they would make horrible noises when trying to stop because the pads were slapping the rotors. They would not stop the rear wheels when the car was jacked up.

I gutted the prop valve and all my problems disappeared. The rears do lock slightly before the fronts, but how often do you lock em up anyways? The car still didn't stop like a Porsche but at least the rears were working.

 

My rear PBR's suck too they wont hold the tire from spinning if in the air or on ice.I remember reading on one of the vette boards that a guy packed little stainless steel washers from home depot in his prop valve for more rear breaking power.Maybe it could work for us.