69 442 brake problems

[will442]

Help needed: About 2 yrs ago the brake booster check valve failed requiring excessive pedal force followed by a brake master cylinder failure. I replaced the brake master cylinder and went to bleed the brakes but sheered off the L front bleed valve and subsequently replaced the caliper. I was never able to bleed the brakes and took it to a local Midas shop. They were also unable to bleed the brakes and concluded the new brake master was bad, replaced it and rebleed the brakes which worked well for about 5 months. I took it back to the Midas place the following Spring, they again were unable to bleed the brakes and again replaced the brake master and rebleed the brakes but the pedal was on the floor within a couple of days. No fluid has leaked out at any of the calipers or the lines as far as I can see. The reservoir is full and yet the pedal goes to the floor (but does return). Has anyone experienced this? Could this have something to do with the other hydrolic device below the brake master? Should I repeat bench bleeding of the brake master, and rebleed all four calipers again, perhaps with colored brake fluid? Would using a "speed bleeder" help? The weather is getting nice, any help or direction would be greatly appreciated.

[joe_padavano]

First, I would avoid Midas for brake work. Not to bash vendors in this forum, but I've personally witnessed Midas employees doing things like using a vice grip pliers to squeeze a brake hose while changing a caliper. I'm very hesitant to take an old car to a repair chain in general, since these places are mainly parts replacers and really don't spend any time trying to diagnose a problem (witness the speed at which they declared a brand new master cylinder "bad"). Their goal is to get cars in and out as quickly as possible.

Next, if you're not doing the work yourself, have a trusted shop check everything in the brake system. A car that old will typically have deteriorated brake hoses. These can fail internally, with the rubber collapsing and acting like a one-way valve. This will prevent proper bleeding and brake function. Also, inspect all the hard lines for rust or other damage.

Since you replaced a caliper, I assume this is a disc brake car. Your car has drums in the back, not calipers, by the way. A 69 with factory discs will have a cylindrical proportioning valve below the master cylinder. This can go bad but even if it does, it won't make the brake pedal go to the floor. Also, the proportioning valve has a button that must be depressed when bleeding the brakes.

Next is the distribution block on the frame. This device has a sliding spool valve inside it that triggers the BRAKE light on the dash if you lose pressure in the system. This valve can get out of place if brakes are not bled properly and can cause a problem if it does.

Finally, find a shop that uses a pressure bleeder. This will absolutely remove all air from the lines if done properly.

On a car this old, consider a wholesale replacement of calipers, rear wheel cylinders, and hoses. These parts are not very expensive and do wear out.

[will442]

Joe: Thank you so much for your thoughtful input, I will look into each of these items and consider replacement of all the non-durable brake items. I will let you know what the final culprit was and we'll both learn something. Many thanks,

Will

[OldsDoug]

May or may not be related, but over the years I've had a couple of problems with failures of the seal between the master cylinder and the power brake booster... it's a rubber cup that fits in the front of the brake booster. If this goes bad, you'll have a hard pedal and a terrific vacuum leak that will cause all sorts of drivability problems. You'll hear a hissing sound between the master cylinder and the booster.

There was a replacement for this thing available from GM the last time I checked, but it's a flat piece instead of a cup. Most cars of similar vintage with Moraine boosters use the same piece - I'd advise picking off a few from your favorite local junkyard, even if this doesn't turn out to be the problem.

Also, I'd replace all wheel cyls, hoses, and calipers, as Joe mentioned. Good luck!

Regards,

Doug

[RoadkingHI]

Quote:

A 69 with factory discs will have a cylindrical proportioning valve below the master cylinder. This can go bad but even if it does, it won't make the brake pedal go to the floor. Also, the proportioning valve has a button that must be depressed when bleeding the brakes.

Next is the distribution block on the frame. This device has a sliding spool valve inside it that triggers the BRAKE light on the dash if you lose pressure in the system. This valve can get out of place if brakes are not bled properly and can cause a problem if it does.

Finally, find a shop that uses a pressure bleeder. This will absolutely remove all air from the lines if done properly.

On a car this old, consider a wholesale replacement of calipers, rear wheel cylinders, and hoses. These parts are not very expensive and do wear out.

Interesting as I have a 73 Toro (disc in front, drum in back) and similar problems. Brakes don't work but it happens after I have been driving a while (20 minutes or longer) and my brakes fade away. Kind of like the rear only is working. (Good thing the 455 engine is there as I down shift quickly to slow down!)
I changed the booster and master cylinder and pedal bleed the brakes. Now the light is on and the problems is the same.
I susepcted the proportional valve but wanted to find out more about it. I believe this year the prop valve and distribution are in the same housing.
I plan on bleeding them again this weekend but am interested in the button on the prop valve.
You seem to have a good knowledge on these any suggestions?

[gmoney]

Gentlmen: Years ago I had a similar priblem on my 69 Cutlass. After money spent and much vexing thought, I had to replace the little 90 degree check valve when it fell apart. All the problem went away. I since learned to start with the little things first. This is the plastic fitting on the power booster that is vacume fed from the engine. I hope this helps, Mike

[joe_padavano]

Quote:

Gentlmen: Years ago I had a similar priblem on my 69 Cutlass. After money spent and much vexing thought, I had to replace the little 90 degree check valve when it fell apart. All the problem went away. I since learned to start with the little things first. This is the plastic fitting on the power booster that is vacume fed from the engine. I hope this helps, Mike

Starting with the simple things is always a good plan for diagnosing a problem, but in this case the plastic check valve on the booster won't cause the "BRAKE" light on the dash to come on. Only a hydraulic problem (or a sticking e-brake pedal) will cause that.

Quote:

Interesting as I have a 73 Toro (disc in front, drum in back) and similar problems. Brakes don't work but it happens after I have been driving a while (20 minutes or longer) and my brakes fade away. Kind of like the rear only is working. (Good thing the 455 engine is there as I down shift quickly to slow down!)
I changed the booster and master cylinder and pedal bleed the brakes. Now the light is on and the problems is the same.
I susepcted the proportional valve but wanted to find out more about it. I believe this year the prop valve and distribution are in the same housing.
I plan on bleeding them again this weekend but am interested in the button on the prop valve.
You seem to have a good knowledge on these any suggestions?

Yes, your 73 will have the combo valve that incorporates the proportioning valve, the residual pressure valve, and the differential pressure switch all into one housing. If you pedal bled the brakes and the light stays on, your differential pressure switch spool is offset to one side in the housing. If sludge builds up in the housing this can cause the spool to stick, which keeps the light on and can also upset the flow of hydraulic fluid. Depending on which way the spool is stuck, cracking the bleeder screws on the other end of the system can help recenter the spool. Since your rear brakes seem to work, try bleeding the fronts to get the spool recentered.

Yes, you do need to keep the button depressed during bleeding. This actually disables the residual pressure valve during bleeding.

[RoadkingHI]

Thanks for the info. I will try this tomorrow and hopefully cruzin' by the afternoon (not too far since gas is up again :-)
Really appreciate your help!

[RoadkingHI]

Ok, I did some work this weekend on the Toro.
Pushed the button in, I had to use a little force to get it to move in but it worked and I bled all of the brakes. Good flow on the front, little slower on the back but all bled ok.
Pedal is "hard" so don't think air is any problem.
The system still has the "brake" light on.
The stopping is still not up to par, actually gets worse as I drive it. If I slam the brakes after a 20 to 30 minute cruise at about 30 MPH the car will stop but no "face on the dash" type of stop.
It stops evenly, no pulling or pulsating in the system.

I plan on pulling each wheel to check all shoes, calipers and etc. But if you have any other recommendations I would appreciate it.
Little confusing in that I can't pinpoint the problem. I am inclined to just replace the proportional valve as that appears to be the center of the distribution and I tend to think this may be my head ache.

The car set for several years with minimal use until about 3 years ago when I drove it from Northern CA to Seattle. No problem then but my annual trip last year the brakes started to act up. Funny is that they would fade before then come back, fade off again and a few miles later would work ok.... Stumps me.

Again, any info is REALLY appreciated.

[imported_Kerry]

If you haven't already done so, replace all of the brake fluid from the master cylinder to the wheels. Old brake fluid absorbs water from the atmosphere & if there is any drag in the system, it will generate enough heat to boil the water & give you lousy brake response. If that doesn't help, replace all of the rubber components in the system.

[joe_padavano]

Quote:

If you haven't already done so, replace all of the brake fluid from the master cylinder to the wheels.

This may be good advice, but it won't solve your brake idiot light problem. The slow flow from the back brakes is indicative that the differential pressure valve spool is likely stuck in the rear position. The first troubleshooting thing is to disconnect the wire going to the proportioning valve. If the light goes out, the spool valve is your problem. If not, you have an electrical problem. Next, try just cracking one of the front bleeder screws a little and have a helper press hard on the brake pedal. This should dislodge the spool valve. If not, you should probably replace the proportioning valve.

[RoadkingHI]

I posted info on the latest results under "73 Toronado....."
Thanks for the help!