Is my proportioning valve shot?

Can somebody help me figure out why I don't have rear brakes in my Mar '96 1 liter hatchback? For the longest time, I've always felt as though braking was poor. I did a rear brake job about 4 years ago, before my son drove it for 1 & 1/2 years in Austin. It's been parked for the last year or so, and I decided to get it back on the road.

It passed the state inspection, but still, I had doubts. I pulled the drums, and there is ZERO wear. No dust. It looks as though it just had a new brake job. The only wear on the shoes is on the leading and trailing edges of both shoes. The left and right pistons acutate, and there is no observable binding. The drums are still within the wear limits, with no scoring.

The pedal is firm. I've got new pads up front. While driving, I get effective braking when I pull up on the parking lever as I depress the brake pedal. I've replaced the fluid and bleed the brakes following the sequenced outling in the GM service manual. There seemed to be an adequate (force) spurt out of the bleed valves. All lines and hoses appear in good condition (147,000 miles).

Anybody got suggestions as to what else could cause the problem?

FYI, my VIN is 2C1MR22XT6774172, and Chevy says I need p/n 30016527 at $157. What year range/model can I use, should I go to the boneyard for a replacement?

I've done front & rear jobs on at least 5 different cars, so I confident that I am doing the work right. This has me stumped. My wife and children drive about 70 miles one way to work and school. We want to stop driving the VW GTI VR6 with its' 2.8L, but the Metros' poor braking worries me.



BTW- my first post. Thanks to this forum, I was able to solve a lighting problem by replacing the multifunction switch and jumpering the junction block.

how many clicks for the hand brake to hold? how far does the brake pedal depress before it engages? if it takes more than 6 clicks on the hand brake and the brake goes down further than 1 inch the rear brake shoes need adjusting. then it should work better. the porpotiong valve should be good if you get fluid out of the bleeder when you bleed the brakes. are you using two people to bleed the brakes one in the car to pumpit up ane one at the rear, if not use to poeple. hope this helps

how many clicks for the hand brake to hold? how far does the brake pedal depress before it engages? if it takes more than 6 clicks on the hand brake and the brake goes down further than 1 inch the rear brake shoes need adjusting. then it should work better. the porpotiong valve should be good if you get fluid out of the bleeder when you bleed the brakes. are you using two people to bleed the brakes one in the car to pumpit up ane one at the rear, if not use to poeple. hope this helps

As of now, the car is in Austin, TX, some 70 miles away, while my wife is at work. My rear shoes have a ratcheting adjuster, not the star wheel type. This adjuster sytsem appears to be working ok. My brake pedal does not travel too far to get a firm pedal. I'd call it a High Pedal Yes, I used the 2 person method to bleed the brakes. Note that the apparent pedal firmness did not change after I replaced the DOT 3 fluid. My perception is that the mechanical brake (parking) syatem works, but the fluid system does not.

Thanks for your advice, I followed the steps you outlined, but still no improvement. Simply put, my back brakes do not work work under pedal pressure, but work under mechanical input.

HELP

I may be way out in left field, but I have always understood that in older cars
(Cars from my days - I am 65) that you adjust the rear drum brakes by
backing up (quickly) on some empty road and then jam on the parking brakes.

That adjusts the rear Brakes.

I back down a hill maybe three times and yank on the parking brake.

My parking brake engages at maybe 3 clicks.

Am I wrong?

DoctorBIll

BTW - What the Heck is a "Proportioning Valve" and how would it work?

Been There Done That Been There Done That.

It seems as though the ratchet system in me Metro adjusts the slack/shoes when the pedal is depressed. This is not the same process that occurs under the star wheel type adjuster. I've seen both. When I depress the brake pedal, the racheting lever takes up the slack, while on jack stands. Done the going back routine, but it does not work. I read in another post about this style of adjuster. My GM service manual describes the adjuster. It is not the star (back up to adjust type).


When I say that my rear brake components look like a new job, I really mean it. My son did not do any services to the car since I gave it to him. The rear brakes were pristeen.

Thanks Doc.

My other alias is DownhillBill- While riding bicycles in a local bike club, someone noted that I go faster downhill rather that uphil. Musta benn my weight.


Bill

I've seen those adjusters fail often. If you notice a difference in the brakes' performance with the emergency handle up a few clicks, I bet the adjusters are not working.

That being said, the rear brakes don't do much on these cars, they can't. Under hard braking about 90% of the weight is on the front tires. If any more than 10% of the braking force is going to the rears, you've lost control and are backing into something. I find that front pads last 50K miles and rear shoes 200K.

The proportioning valve divides the brake system between the front and rear. The service manual says that in the event of a system failure in the front, that all pressure is diverted to the rear brakes, and vice versa. The proportioning valve limits outlet pressure to the rear brakes after a predetermined pressure has been reached. There is no section on servicing the valve.

The service manual says to adjust (reset) the rear brakes by pressing the pedal 3-5 times with a force of aproximately 66 lbs. I've done this, and the backing up routine today. No help.

I am aware that the front brakes do most of the braking. Still, the back brakes must play a role besides parking, otherwise they would only be mechanically acutated. I pulled the drum off another Metro, and it was just filled with dust, so they must contribute. Why don't mine?

It would be strange to find two seized wheel cylinders out back... but I suppose it's possible. Confirm movement of the brake shoes with the drums off while pressing the brake pedal.

If they move, replace your worn out adjusters.

-MechanicMatt

That would be my question - HOW DO YOU KNOW THE REAR BRAKES EVEN MOVE?

If you drained the system at the rear brakes, but see no evidence that the are
being used, I would make sure the cylinders are working.

If the cylinders are really old, maybe the rubber seal is shot (O-Rings?).

Just a thought - Did you buy the car used?

Could someone have installed the incorrect brake shoes? Too small, maybe?
Could the wrong Brake Drum have been installed or switched at some time?
Maybe someone playing around with larger wheel sizes?

Jack the rear end up, take off a wheel and have someone slowly press the brake
pedal and if the piston is working, yell for them to stop - don't want the piston to exit
the cylinder.....Both sides.

Would a bubble in the rear lines cause this effect. I suspect the brakes would
be mushie if you had a big bubble.

BTW - Where is this Proportioning valve located? Do all Geo Metros have one?

DoctorBill

try putting a bunch of wieght in the back then brake and see if you notice a difference in the back brakes. if you do then the brakesare working ok.

What's weight going to do? Don't understand that one.

Yes Doc, all cars have a proportioning valve because you need much more braking force in front, and also because disks and drums require different things. It's mounted on the firewall, just follow the metal lines from the master cylinder.

Thanx for the input folks. I won't be able to examine or work on the car till this weekend. Yup, I bought it used in 2002. Don't know exactly when I did a 4 wheel brake job; but I'd guess within a year after I got it.

Good idea about the shoes. I'll pull one side and compare it side by side to a set at Auto Zone and Advanced Auto. But, last week I did look at a new set, and my lining is as thick as a new shoe.

I sized up to 13" wheels, but the drums are the same. I noticed that the drum from a Metro XFI has a different bearing layout, and the studs have a smaller diameter. Both the XFI and my drums have a Max Diameter of 182mm, or 7.1653 inches, which is the spec from the service manual. My drums measure 7.095 inches.

the wieght in the rear will readjust the porpotioning valve to put more braking force to the rear. Yes they work that way.

Not on a Metro. Some cars do adjust proportioning by weight, but no Metro/Swift ever has.

Besides doing the 'backing up - pulling the Parking Brake Handle up' (PBH) thing to adjust
the rear brakes, can't you also adjust them as to when they engage by tightening up the link
to the rear brakes (to make the Parking Brake engage with the PBH just off the floor)?

Makes the Rear Brakes come closer to the drum....

Yes?

DoctorBill

The adjusters in the brake drum adjust the rest position of the shoes and affect both how far the handle needs to be pulled up and how far the pedal needs to be pressed down. While the parking brake cable could be adjusted to do the same thing, you'd have to adjust it a ton to get to the right point, it's not designed for that.

Our rear brake adjusters are supposed to take up the slack every time you apply the brakes in normal use, they have tiny little serrations that strip off easily. One of mine went when I put the parking brake on, it came up the normal amount, then went "POP" and the handle came up about two inches further. If you remove the console, you can easily see that one cable is farther forward than the other. On my other car, I didn't notice that the handle was up too high but it did seem that the pedal was mushy. I was jacking the car up to do something else and noticed that I could turn one of the rear wheels by hand.

Simple tests are the best. Jack up the rear of the car, have someone press the brakes at varying pressures and make sure the rear tires won't spin with moderate to firm pressure. If the brakes grab they are working. The wear at the front and back of the pad may be all the wear you see until they wear down a bit. The amount of wear and dust you get is going to depend heavily on driving style. Lead foot it for a couple of weeks and break hard and you will probably see a bit more wear.

So how did this story end? Did I miss it?

On my 96 Metro I am troubleshooting a front brake sticking problem but not sure if there is a bearing that could be causing the heating of the rotor. There is no leaking front the cylinder.

Can these brake cylinders be rebuilt, cleaned up, or is it best to just replace it?

Ended the way many of these end, with the original poster disappearing, we'll never know if we helped him fix his problem or if he's dead because of his bad brakes and bad advice. :sarcasmsign:


Sticking front brakes are either stuck caliper pistons, stuck caliper sliders, or collapsed rubber hoses.