Brake Problem on 1FATGMC

[1FATGMC]

I went down to Farmington, NM (135 miles) last weekend to visit a friend and stay the night.  I haven't driven the 1FATGMC much in the last couple months and on the way down the brake pedal seemed closer to the floor, but there isn't many places I use the brake between here and there.

In Farmington I had to do some running around and it seemed the pedal kept going further down and pumping did nothing.  After probably about 40-50 stops the pedal was gone and on the floor.  Luckly this happen just as I got back to his house.  We put it in his shop and checked things out.  The fluid in the front reservoir of the master cylinder was low, but not to the point of sucking air, but close to it.  

BTW the brakes on the truck are '73 Camaro disks in the front with the stock Camaro booster/mastercylinder and proportioning valve with a late 60's GM 8.2 inch 10 bolt in the rear.

About a year ago I put new rotors, calipers, pads on the front and wheel cylinders, drums and shoes on the back.  The booster is off the donor car with over 110,000 mile with me and who knows how many before that.  I also don't think I've ever replaced the master cylinder.

My friend had an early 70's booster off of a chevelle.  We had to modify the rod to the pedal and the rod on the otherside to the mastercylinder (his master cylinder was for a drum/drum car).  So with that booster, which was on the car when he got it, and my master cylinder the problem stayed the same.  That either ruled out the booster or his was no good also.

We gave up and went to bed and got up early the next morning and decided to try and bleed the brakes, but couldn't get the bleeders broke loose and were affraid we were going to break them off so we quit.  I personally don't think the brakes need bled as they don't pump up the pedal just goes to the floor.  Since the parts houses didn't have any parts in stock I decided to drive back home.  I left early on Sunday with really light traffic and only had to contend with about 6 traffic lights in the first 30 miles and then it was open country for the other 100 miles home.  I'm glad I have my emergancy brake between the seats and with a handle as that gave me some stopping power along with gearing down.

The truck is parked and I'm not sure when I'm going to get to it, but I'm wondering if anyone has any ideas?  A friend feels it is the mastercylinder gone bad and it isn't pumping any fluid and I tend to agree with that.  I think it is time for a new booster and mastercylinder anyway, so will probably start there.

One thing I'm supprise about is that with the dual reservoir master cylinder you would think I would have braking on one end of the truck or the other.

Thanks for any suggestions,  Sum

[SKR8PN]

Pull the rear drums and check your shoe adjustment first. I kinda doubt you would loose a master cylinder just like that. Normally there is a lot more warning,like a pedal that SLOWLY drops to the floor at a stop light,but if you hit it again,it will usually come right back up.Then I would see about getting those bleeders out and see whether or not there IS any air in the system.

[Jimc]

I am sure you have looked for leaks at wheel cyls, lines, and such.

I tend to think it may be the master cylindar gone bad, too.
My thinking is like you, if there was air present, you could at least get a little pedal by pumping.
Since the emergency brake is stopping the car, at least the back brakes are operating.
I believe you said all brakes were stopping the truck prior to the pedal going away.
With some fluid level, there would have been pedal when you pumped unless the master is not forcing fluid through the system.



Jim

[32tom]

I went down to Farmington, NM (135 miles) last weekend to visit a friend and stay the night.  I haven't driven the 1FATGMC much in the last couple months and on the way down the brake pedal seemed closer to the floor, but there isn't many places I use the brake between here and there.

In Farmington I had to do some running around and it seemed the pedal kept going further down and pumping did nothing.  After probably about 40-50 stops the pedal was gone and on the floor.  Luckly this happen just as I got back to his house.  We put it in his shop and checked things out.  The fluid in the front reservoir of the master cylinder was low, but not to the point of sucking air, but close to it.  

BTW the brakes on the truck are '73 Camaro disks in the front with the stock Camaro booster/mastercylinder and proportioning valve with a late 60's GM 8.2 inch 10 bolt in the rear.

About a year ago I put new rotors, calipers, pads on the front and wheel cylinders, drums and shoes on the back.  The booster is off the donor car with over 110,000 mile with me and who knows how many before that.  I also don't think I've ever replaced the master cylinder.

My friend had an early 70's booster off of a chevelle.  We had to modify the rod to the pedal and the rod on the otherside to the mastercylinder (his master cylinder was for a drum/drum car).  So with that booster, which was on the car when he got it, and my master cylinder the problem stayed the same.  That either ruled out the booster or his was no good also.

We gave up and went to bed and got up early the next morning and decided to try and bleed the brakes, but couldn't get the bleeders broke loose and were affraid we were going to break them off so we quit.  I personally don't think the brakes need bled as they don't pump up the pedal just goes to the floor.  Since the parts houses didn't have any parts in stock I decided to drive back home.  I left early on Sunday with really light traffic and only had to contend with about 6 traffic lights in the first 30 miles and then it was open country for the other 100 miles home.  I'm glad I have my emergancy brake between the seats and with a handle as that gave me some stopping power along with gearing down.

The truck is parked and I'm not sure when I'm going to get to it, but I'm wondering if anyone has any ideas?  A friend feels it is the mastercylinder gone bad and it isn't pumping any fluid and I tend to agree with that.  I think it is time for a new booster and mastercylinder anyway, so will probably start there.

One thing I'm supprise about is that with the dual reservoir master cylinder you would think I would have braking on one end of the truck or the other.

Thanks for any suggestions,  Sum

You can isolate the problem by pinching off the 3 brake hoses. Still no pedal then it's probably in the M/cyl. If you get a pedal, loosen each clamp separately until you lose the pedal. You'll then know where to look.

[1FATGMC]

Then I would see about getting those bleeders out and see whether or not there IS any air in the system.

Thanks, I've had problems with the bleeders not coming out before.  I'm wondering if putting some type of anti-seize on them is a good idea.

It seemed that over the hour or so I was driving in traffic each time I put the brakes on the pedal just went a little closer to the floor and pumping wouldn't do anything.  I've wondered if the rears were out of adjustment, but they worked fine last August going and coming to B'ville, just ask George   .  After that trip I took the truck and the teardrop to Calif. and Oregon in Oct. and everything seemed fine.  Then it sat until I used it this last weekend.

I'm just going to have to find time to work on it.

c ya, Sum

[1FATGMC]

You can isolate the problem by pinching off the 3 brake hoses. Still no pedal then it's probably in the M/cyl. If you get a pedal, loosen each clamp separately until you lose the pedal. You'll then know where to look.

That sounds like a good place to start.  Just use vise grips on the rubber lines?

c ya, Sum

[WZ JUNK]

I use teflon tape on the bleeder screws.

I am going out on a limb and speculate that one side of the master cylinder is bleeding over into the other side.  I think the master cylinder is bad and I think the seal between the two sides is bad.  This is assuming that you have not noticed any fluid loss anywhere.  The other place the master cylinder could fail is the seal near the vacuum booster and then the fluid could actually be drawn through your engine by the vacuum link.  If this is happening you can fill the master clinder, start the vehicle, have someone pump the brakes, you should be able to smell the odor of brake fluid in the engine exhaust.

[phat46]

I'd try a new master cyl. too.  Sounds like the problem i had with my daughters car last fall. Same symptoms as you, but in my case i replaced the M/C after trying all the bleeding and adjusting stuff...but, the new M/C was bad right out of the box, that really had me scratching my head for a couple days. The second one was good and fixed the prob in an hour.

[32tom]

You can isolate the problem by pinching off the 3 brake hoses. Still no pedal then it's probably in the M/cyl. If you get a pedal, loosen each clamp separately until you lose the pedal. You'll then know where to look.

That sounds like a good place to start.  Just use vise grips on the rubber lines?

c ya, Sum

Yes. Vise grips or their clones make special vise grips just for this purpose. Smooth rounded jaws that wont damage the hose. (not absolutely necessary) You can also buy brake hose clamps from the tool guys. They are handy to prevent draining the m/cyl when removing a caliper for service. They are cheap and they help cut down on the wild goose chases. If you've ever chased a low pedal/air in the sytem problem you'll want them in your tool box.

[tomslik]

hey, check your spindles!make damnm sure they ain't cracking/breaking just before the seal area.
had one do that on a 68 chevelle w'disc....

went thru 3 m/c's before going on a test drive and THEN the spindle breaks clean off...

only time i EVER seen that stuff!
scared me + that ain't easy to do.

[C9]

I think a couple of things are going on.
The self adjusters in the back are not working as they should.
Part of that may be that we tend to back our vehicles up and stop gently.
That does not allow the self-adjuster mechanism to 'cock' so that it will roll the adjuster star wheel up a notch on the next forward stop.

Couple of things you can do there.
Do some firm stops in both directions - very low speed works just fine and the rear brakes should adjust up.
Or - adjust them manually up to spec.

This part is a could be/couldn't be deal since your E-brake is working ok.
I find when my roadster E-brake is getting up toward the top end - Gennie handle, Vega style - adjusting the rear brakes is indicated.

Even so, if I remember I make a firm rearward stop in the driveway whenever I go somewhere in the car and that seems to be doing the trick.

Other thing is, you have an internal M/C leak.
Hone it and put a kit in it.
Then bench bleed it and that may take care of things.

With strong discs on the front, many times we don't recognize the drums aren't doing their part in the stopping equation.

[1FATGMC]

I think a couple of things are going on.
The self adjusters in the back are not working as they should.
Part of that may be that we tend to back our vehicles up and stop gently.
That does not allow the self-adjuster mechanism to 'cock' so that it will roll the adjuster star wheel up a notch on the next forward stop.

I have a feeling this is what is happening as I don't go backwards much    and the handle on the e-brake is pulling pretty high.  I'll adjust them and I think the mastercylinder is bad.

Tom I'll check the spindles just to be sure

Thanks for everyone's help and I'll post when I finally get things fixed as that might help someone else in the future with the same problem.

c ya, Sum

[enjenjo]

I'm wondering if putting some type of anti-seize on them is a good idea.

I use anti seize on them. just make sure you don't get any on the sealing area at the bottom. The anti seize helps when vacuum bleeding, it keeps air from leaking past the threads.

[mrloboy]

It sounds like a master cylinder problem to me. You have no apparant leakage, there is fluid in the resevoir. If the adjusters were not functioning, then pumping the peddle would provide efficient brake force. Eliminating each of these scenarios points to the loss of pressure within the master cylinder. This is assuming you have located the master cylinder on your firewall.

If you have located the booster/ master cylinder in the under floor location, you may have cause a back-bleed scenario leaving an airlock in the system. If you mount your master cylinder below the floor, you should always include a residual pressure valve on both sides of the cylinder, 2 lbs on disc brakes and 10 lbs on drum assemblies.

If you have used your vehicle in the past with no problems, I feel replacing the master cylinder will put you safely back on the street. rj

[1FATGMC]

This is assuming you have located the master cylinder on your firewall.

Yep it is on the firewall.  

Thanks for the reply and welcome to RRT.  If I had all of those projects laying out in the back yard I would really have a hard time knowing where to start  :? .

c ya, Sum