1972 opet gt Brakes Issue

[pcsoccer3]

I have a 1972 opel gt that is have issues with the brakes. I have rebuilt the master cylinder and still having the problem. The problem is that I have brakes when i pump the brake pedal several time fast. As soon as i let off the brake it looses brake. I have to pump the brakes several times until they get hard in order to have brakes. I have bleed out the brake lines several times to make sure no air in the lines. If anyone has any suggestions or answers it would be much appreciated. Thanks

[blancojp]

Originally Posted by pcsoccer3 I have a 1972 opel gt that is have issues with the brakes. I have rebuilt the master cylinder and still having the problem. The problem is that I have brakes when i pump the brake pedal several time fast. As soon as i let off the brake it looses brake. I have to pump the brakes several times until they get hard in order to have brakes. I have bleed out the brake lines several times to make sure no air in the lines. If anyone has any suggestions or answers it would be much appreciated. Thanks

There are two possible causes:
1) You rebuilt the master cylinder improperly and it is failing to seal and hold pressure.
2) You did not bleed the master cylinder prior to bleeding the rest of the system.

Sometime you can bleed a system to death and still have air trapped in the master cylinder. The third possibility is you might have a leak somewhere therefore losing pressure and adding air into the system.

[ungermm]

When you rebuild a master cylinder, you must always make sure that the MC cylinder lining is clean and shiny (free of scaring or rust). The new MC rebuild parts must be put in the right position.

Proper bench bleeding of the MC is a must before you bleed the brakes. Also, when you reattach the brake lines to the MC, you must tighten the fittings so that they aren't cross threaded and/or leaking.

Bleed the brakes starting with the shortest brake line to the MC (front drivers side, then front passenger side, then rear drivers side, and lastly rear passenger side). And make sure you keep an eye on the fluid in the MC reservoir so that it never goes empty.

After bleeding...if the brakes are hard on one pump you should be good. If problems arise where they get soft, check to see if your brake fluid has gone down in the reservoir. If so, check each caliper and wheel cylinder for leakage. The other possibility is leakage from the MC into the brake booster.

Another important item to check and replace is the flexible brake lines. There are three. Originals are most likely bad by now.

Jerry

[pcsoccer3]

Im pretty sure that i rebuilt to MC correctly and cleaned it fairly well. I also replaced all the brake lines with new lines. The only thing really that i could do is the bench bleeding of the master. Instead i gravity bleed the master. Also you mention to bleed the brakes in a certain order. Does that make a huge difference to the point where i am experiencing this problem, because the way i did it was from the passenger front to the passenger back to drivers back to drivers front. To me i never thought it would make a difference. Also i have no leaks anywhere the amount of fluid remains the same in the reservoir. The other thing that i have looked at or am not to familiar with is the booster. Ungerman mentioned that there could be a leak from the MC to booster but my question is would that leak out somewhere and see a decrease in fluid. I appreciate all the help in advance from everyone.

[wrench459]

Hows the rear brake adjustment?

I just remembered a wise old owl "don't rely on the internet for brake issues"

Theres many a good mechanic just around the corner. It's your life.

[hrcollinsjr]

I'm in a similar situation. I just rebuilt and installed wheel cylinders & brake calipers, new hoses, and new MC. I tried gravity bleeding and loosening the lines at the MC with someone depressing the pedal for me. Should have bench bled the system which is SOP. I will find a short brake line today and use it to bench bleed the system as I should have done to start with.

Harold

[blancojp]

Originally Posted by pcsoccer3 Im pretty sure that i rebuilt to MC correctly and cleaned it fairly well. I also replaced all the brake lines with new lines. The only thing really that i could do is the bench bleeding of the master. Instead i gravity bleed the master. Also you mention to bleed the brakes in a certain order. Does that make a huge difference to the point where i am experiencing this problem, because the way i did it was from the passenger front to the passenger back to drivers back to drivers front. To me i never thought it would make a difference. Also i have no leaks anywhere the amount of fluid remains the same in the reservoir. The other thing that i have looked at or am not to familiar with is the booster. Ungerman mentioned that there could be a leak from the MC to booster but my question is would that leak out somewhere and see a decrease in fluid. I appreciate all the help in advance from everyone.

If you gravity bled the system, there is the possibility of air pockets inside your master cylinder chamber. Gravity bleeding does not resolve the issue, just makes the problem a mistery.

[wrench459]

Originally Posted by hrcollinsjr I'm in a similar situation. I just rebuilt and installed wheel cylinders & brake calipers, new hoses, and new MC. I tried gravity bleeding and loosening the lines at the MC with someone depressing the pedal for me.

Harold get out your trusty minivac and pull a vacuum on the M/C fill cap vent. Don't work harder work smarter.
Shame on you for not bench bleeding the M/C first.

[hrcollinsjr]

Originally Posted by wrench459 Harold get out your trusty minivac and pull a vacuum on the M/C fill cap vent. Don't work harder work smarter. Shame on you for not bench bleeding the M/C first.

My Mityvac is down for the count as far as I'm concerned, $25 repair kit is too expensive when I can upgrade to a much nicer one for approx. $65.

Too late anyway since I took a bad brake line I had and cut it so that I could bench bleed the cylinder. Worked like it is supposed to. Just need to finish bleeding the rest of the system. My youngest brought me some more brake fluid so I should have brakes later tonight!

Harold