my brakes don't make any sense!!

[stosh562]

ok, i had working brakes but a little low. car sat over winter and then i pulled M/C to rebuild. the booster was replaced with another used one because of fluid that leaked into it. new rear cylinders and shoes. drums turned. the front calipers i rebuilt last year and installed new rotors. so i put this all back together. had someone help bleed the brakes. low pedal. used a vaccum for the second time, still a low pedal, almost to the floor. checked the adjustment on the rear shoes, that's good. booster is holding vacuum. don't know what else to try. it would seem that the M/C is still the culprit but don't know if there is something i'm missing. i am really deserate to get the car back on the road since the old Dodge get's only 8 mpg.

[First opel 1981]

Could be the brake rod (whatever its called) needs adjusting. Its the rod that goes through the square tube on the drivers side.

[SpringGT]

Did you check for line leaks at all four corners of the car and at the M/C?

If there are no system fluid leaks, it sounds like the M/C or the lines still have air in them. Did you bench bleed the M/C first? Or did the M/C reservoir run dry during the bleeding process, thereby reintroducing air into the system?

If it is not air in the system, then you may have a bad M/C rebuild and are slipping fluid around the piston cups. It is more likely to be an air problem than a M/C problem since the M/C is new. IMO.
Bob

[Dennis Texas]

With all the stuff you have replaced it almost certainly is the master cylinder even if you rebuild one, the sleeve has to be spotless for the new seals to push fluid. If you have no fluid on the ground at any of the wheels then most likely suspect is the master cylinder. I sent three MC to be rebuilt only 2 out of the 3 were able to be rebuilt all of them looked good to me when I sent them in. They even replace the reservoir rubber seals on the top.

This is where I sent mine and they did a great job cost me 30 bucks each and 5 dollars for the one that could not be rebuilt for an inspection fee.
Auto Parts Fast at RockAuto
I've seen a lot of pricy rebuilt ones, some over a hundred totally ridicules , save your money and try rock auto. Most you will be out is 5 dollars and shipping. Recommend them to everyone they did me such a great job.

[jlthunder]

Or get one from Opel GT Source. They stand behind their parts

[ghcoe]

Old rubber brake hoses can create a spongy pedal too. Also make sure the pedal rod is adjusted properly. You will loose pressure through the reservoir port till the piston passes the port. If you do not have enough piston travel past the port you will not get full breaking function.

[stosh562]

well, i did bench bleed as best i could and there are no other leaks from the lines that i could see. when i started the rebuild i was careful to get everything out and back in right and the inside of the cylinder looked good to me. i did look at Rockauto and was considering that, was just hoping i could get this going quicker but apparently not. my economic situation was also dictating that i try all home remedies first. i was wondering...what are the 2 small screws for on top of the M/C just under the resevoir. those don't have anything to do with bleeding, do they?

[SpringGT]

I somehow missed that you had done the M/C rebuild yourself in your original post.

When you rebuilt it, did you hone the bore of the cylinder or just clean it up and install new cups? The bore gets polished inside where the cups move back and forth and this glazed surface needs to be honed out until you have a uniform "matte" surface on the full length of the bore. Otherwise the new rubber parts will not seat properly and fluid
can slip around them.
Buy a brake cylinder hone at a part store, hone the full length of the bore back and forth, then shine light into it and look for shiny areas in the bore surface . Continue this process until the entire bore surface has a uniform dull surface and all shiny areas have been eliminated. Clean and flush the abrasives out of the M/C, reinstall the new rubber parts and re-bleed everything. HTH
Bob

[GoinManta]

I had a similar problem.. the MC was good.. but it wasnt bleed right and it had air stuck in it. Have you tried bleeding the master again?

Then after re-bleeding it with a vacuum pump, I lifted the rear end high in the air and let the front sit low.. cracked the rear wheel cylinders and let it gravity bleed overnight using the little bottles with the magnet on the back (at advance autoparst for $6) and made sure they were higher than the master.

That seemed to have gotten it for me.

[Dennis Texas]

i did look at Rockauto and was considering that, was just hoping i could get this going quicker but apparently not. my economic situation was also dictating that i try all home remedies first. i was wondering...what are the 2 small screws for on top of the M/C just under the resevoir. those don't have anything to do with bleeding, do they?

You may be on a tight budget, but brakes is something you don't want to chance, this system, brakes, have to be right it could be the difference between life as you know it now and life after the fact. Send it to rock auto or somewhere else, if you have lots of money Jim sells one just like the one from Rock Auto for over a hundred bucks still cheaper than an ambulance ride and also opel gt source, it would be the best money you have spent just to eliminate that as problem. What is your time worth or your life and at 8 mpg on dodge it would pay for it self in several full tanks of fuel. I can only tell you from personal experience this was the best deal I had found to rebuild the Master Cylinder.

[First opel 1981]

What is your time worth or your life and at 8 mpg on dodge it would pay for it self in several full tanks of fuel.

The Rock Auto rebuild would pay for itself in ONE tank of gas! (OK, maybe a tank and a half)

[Dennis Texas]

The Rock Auto rebuild would pay for itself in ONE tank of gas! (OK, maybe a tank and a half)

your correct, depending on tank size, I was just pushing the point that values are of no effect if your hurt while debating cost.

[blancojp]

ok, i had working brakes but a little low. car sat over winter and then i pulled M/C to rebuild. the booster was replaced with another used one because of fluid that leaked into it. new rear cylinders and shoes. drums turned. the front calipers i rebuilt last year and installed new rotors. so i put this all back together. had someone help bleed the brakes. low pedal. used a vaccum for the second time, still a low pedal, almost to the floor. checked the adjustment on the rear shoes, that's good. booster is holding vacuum. don't know what else to try. it would seem that the M/C is still the culprit but don't know if there is something i'm missing. i am really deserate to get the car back on the road since the old Dodge get's only 8 mpg.

On a GT, the brake pedal rod delivers the force of the pedal to the brake booster. However even is the rod is mal adjusted, the end result is a pedal which can be either too high or too low. So I would check to see where the pedal si sitting at the rest position. When I do brakes on any car, the first thing I do is block off the master cylinder ports. I then pump the pedal with the top cap off until it has little movement and gets hard as a rock. The pedal will get hard as a rock since the fluid has no place to go therefore releasing all of the air in the chamber via the reservoir. This method is better and more reliable than bench bleeding since takes the air out and tests the master cylinder at the same time. The plugs can be purchased at any hydraulic supply store for about $1.00 each and three are required.

I then hook up the rear brake line and start the bleeding process. When the rear is fully bled and the E-brake is adjusted properly, the pedal will have little travel and will be hard as a rock once again. It is now time for the front system so attach the front lines and bleed the front brakes. Again, when all of the air is out of the front circuit, the pedal will have little travel and will be hard as a rock.

The final step is to lock the brake pedal in place with a rod. This will serve as if someone is pressing the brake pedal continuosly which will allow you to check for leaks. At 1000psi of delivered pressure, a thought to be tight connection will develop a leak.

Hope this helps.

[wrench459]

Or you could install a pressure bleeder and be done in 5 minutes. :-)

[stosh562]

i am definately not driving the car yet. i value this car more than me at the moment. i didn't hone the master when i rebuilt it. i can try that and try the bleeding process again i've still got a couple days off to try that and see what happens.

[blancojp]

Or you could install a pressure bleeder and be done in 5 minutes. :-)

I have two of them and never used them, do not trust them at all.

[stosh562]

well, i have definately done everything now. i pulled the M/C back off, pulled it apart, honed it, checked my seals, put everything back together, bench bleed, and installed again. had someone help with bleeding the lines, have no air anywhere and no leaks. re-adjusted the rear shoes. the E-brake works but it is up at the top of its height, but it does hold the car very good. my pedal is still low. its is very solid but low and the car does stop. here's a question: is there any adjustment on the rod in the booster? i could not see how it would adjust if there is. on my 78 dodge p/u, there was a simple procedure to adjust the pushrod length for the M/C.

[First opel 1981]

well, i have definately done everything now. i pulled the M/C back off, pulled it apart, honed it, checked my seals, put everything back together, bench bleed, and installed again. had someone help with bleeding the lines, have no air anywhere and no leaks. re-adjusted the rear shoes. the E-brake works but it is up at the top of its height, but it does hold the car very good. my pedal is still low. its is very solid but low and the car does stop. here's a question: is there any adjustment on the rod in the booster? i could not see how it would adjust if there is. on my 78 dodge p/u, there was a simple procedure to adjust the pushrod length for the M/C.

As I recall, there is. Its toward the front of the car, if I remember correctly.

BUT, first adjust the E brake. If the Ebrake isn't adjusted properly, you can have problems.

[tomking]

before you adjust on the e brake, adjust the rear brakes behind the backing plates as described in the FSM. Then go to the e brake.

[First opel 1981]

This explains how to adjust brakes, both at the pedal and the rear brake shoes.

Opel File Downloads - The Classic Opel Forums

The rear brake shoe adjustment is on page 6 and 7.