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Discussion Starter #1
1973 Opel GT
Original booster / MC (from what i can tell)

Before I put the vehicle away for our Canadian winter, on an usually cold morning around 6C (43F) i got to the stop sign at the end of the street and i had weak pressure on the brake pedal and it traveled to the floor and the red failure light came on. The vehicle came to a stop. But not like it has. I chalked it up to cold weather - maybe check the seal on the booster hose - vacuum leak - cold weather issue.
When i pulled it our storage and drove it on warm days - brake travel did feel a bit soft - but vehicle was driving fine and stopping. When i had it out on another cold day - similar temp - low 40s, brake traveled to the floor and warning light came on - BUT NOT EVERY TIME.
Also note - i have had E-brake issues of not working and locking properly unless lever is pulled up to the max.

Last weekend I used a turkey baster and sucked out a 3/4 of the fluid in the brake fluid reservoir. And used the one man method to bleed all 4 points. https://www.youtube.com/watch?v=n1NvtUwfRJc
What i had noticed: was the fluid level was up and around screen filter in the resoiver and screen filter has a bit of rust - water in the lines?
: 8mm wrench for front brakes, 9mm for rear to open bleeders
: fluid in reservoir didn't go down a whole lot after each wheel bleed.
: all 4 wheels - bleed clear brake fluid - no problems.


My question here is: Faulty MC? time to replace?
: brake adjustment issue needed - compounded by e-brake not working?
: time to leave Canada for warmer weather?

Any insight would be helpful.





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When the Master cylinder piston rings fail the result is that the fluid is escaping around the rubber cups in stead of being pushed out to the wheels, causing the the pedal tol go to the floor. THis in turn will allow the failure switch to be triggered when the switch does not have the proper front and back circuts line pressures.

If you found water in the brake fluid this is bad as most brake fluid will absorbe moisture from the air and is causes an the fluid to rust the inside of the brake lines, master cylinder walls and each piston at the wheels. The auto shops sell lithmos paper to test if your brake fluid is contaminated.
Do not just replace the Master cylinder , You need to check and replace all worn and failed parts of the brake system including the brake lines if they have rusted and weakned.

This is a great time to replace all parts including the flex hoses. Ron

PS check your master cylinder cap to make sure it seals well as a source of water getting into the system
 

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The only way the warning light comes on is if the master cylinder fails, the ground for the warning light comes from the master. It is not worth trying to rebuild the master, just buy a new one. I also agree with checking all other parts of the system to see if they are in any way compromised.
 

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Check Boooster too

Usually if the Master cylinder Fails... petal to the floor...like said the seals in master failed..and any water in there when cold would freeze too... Also when the seals fail.. most likely the rear seal too, then the brake fluid ends up inside the power booster... and then it's not long before the brake fluid eats up the rubber diaphragm inside.... after you remove master Cylinder... get a long Q-tip and reach inside the bottom of booster ..see if it's full of brake fluid. I would change master and the booster... OGTS sell a nice Combo deal
Good Luck and keep us posted
 
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The only way the warning light comes on is if the master cylinder fails, the ground for the warning light comes from the master. It is not worth trying to rebuild the master, just buy a new one. I also agree with checking all other parts of the system to see if they are in any way compromised.
I agree with you,I also would buy a new MC or Combo.But the most MC can rebuild with original ATE-Seals,when the cylinder walls inside have NO rust spots or pits.

Repair Set Master Brake Cylinder
 

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Discussion Starter #7
Usually if the Master cylinder Fails... petal to the floor...like said the seals in master failed..and any water in there when cold would freeze too... Also when the seals fail.. most likely the rear seal too, then the brake fluid ends up inside the power booster... and then it's not long before the brake fluid eats up the rubber diaphragm inside.... after you remove master Cylinder... get a long Q-tip and reach inside the bottom of booster ..see if it's full of brake fluid. I would change master and the booster... OGTS sell a nice Combo deal
Good Luck and keep us posted
i took of the brake booster hose and removed the elbow from the booster. Took a q-tip and placed it in a long drink straw and swabbed around the bottom of the booster. Nothing to show that there is fluid or was fluid in there.

Funny thing is when i removed the hose i heard an air escaping noise - but i was pretty sure it didn't come out of the booster.

I replaced the gaskets on the elbow from the hole in the booster to the booster hose as a precaution to make sure that seal is air tight.

Brake issues are still the same. Good pressure when i pump the brakes. But pedal still going to floor. Light hasn't come on. Warmer weather in Canada now.
 

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i took of the brake booster hose and removed the elbow from the booster. Took a q-tip and placed it in a long drink straw and swabbed around the bottom of the booster. Nothing to show that there is fluid or was fluid in there.

Funny thing is when i removed the hose i heard an air escaping noise - but i was pretty sure it didn't come out of the booster.

I replaced the gaskets on the elbow from the hole in the booster to the booster hose as a precaution to make sure that seal is air tight.

Brake issues are still the same. Good pressure when i pump the brakes. But pedal still going to floor. Light hasn't come on. Warmer weather in canada now.
If the pedal goes to the floor it is not the booster!!
 

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i took of the brake booster hose and removed the elbow from the booster. Took a q-tip and placed it in a long drink straw and swabbed around the bottom of the booster. Nothing to show that there is fluid or was fluid in there.

Funny thing is when i removed the hose i heard an air escaping noise - but i was pretty sure it didn't come out of the booster.

I replaced the gaskets on the elbow from the hole in the booster to the booster hose as a precaution to make sure that seal is air tight.

Brake issues are still the same. Good pressure when i pump the brakes. But pedal still going to floor. Light hasn't come on. Warmer weather in Canada now.



Good Job now you know the booster is ok ...held vacuum until you released it by taking out fitting
and no fluid inside.... """ The M A S T E R C Y L I N D E R "" is Trashed .. Just replace that if petal going to the floor and the fluid isn't pouring out of the wheel cylinders
I mean you have no leaks anywhere :veryhappy you've done nothing but check the boosters ok now replace the Master Cyl.
 

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Brake problem

For what is worth,I'm rebuilding a 1975 Ascona and have been looking at the options re brakes.Ive pulled apart 5 masters and all are pitted and not good for rebuilding.Get a new one !
 

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FWIW, I bought my first opel in 1981.. A '69, And the master cylinder was trashed already.

Replace the master cylinder.
 

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Discussion Starter #13
update: new master installed. new problems.

As it has finally warmed up here and I need to get the Opel out of storage I can finally attend to this brake master cylinder failure light issue.

when removing old MC, I also took off brass fittings that are attached the lines that attach to MC to clean them.

opel master cylinder part.jpg

Installed new MC. Bench Bleed with MC mounted in car.

With regards to brass fittings. I know there is a tiny hole through the square head bolt at the end that goes into the MC and at the bottom under the bolt and is just a little offset. I am assuming that these holes will line up and when threaded through.

Brass washer on each side.

Lines mounted back on.

Went to start bleeding the lines to get the air out. Rear passenger side wheel first. Opened the bleeder. Nothing. Pumped the brakes. Nothing coming out of lines. Closed bleeder.

When pumping brakes with key turned. All feels fine.

When car is started and running. Very little brake pressure and RED failure light comes on.

Don't know what I am doing wrong here. Either bend bleed wasn't done right. Or the somehow the holes on the brass fittings are not lined up not allowing fluid into the line??
 

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As it has finally warmed up here and I need to get the Opel out of storage I can finally attend to this brake master cylinder failure light issue.

when removing old MC, I also took off brass fittings that are attached the lines that attach to MC to clean them.

View attachment 365738

Installed new MC. Bench Bleed with MC mounted in car.

With regards to brass fittings. I know there is a tiny hole through the square head bolt at the end that goes into the MC and at the bottom under the bolt and is just a little offset. I am assuming that these holes will line up and when threaded through.

Brass washer on each side.

Lines mounted back on.

Went to start bleeding the lines to get the air out. Rear passenger side wheel first. Opened the bleeder. Nothing. Pumped the brakes. Nothing coming out of lines. Closed bleeder.

When pumping brakes with key turned. All feels fine.

When car is started and running. Very little brake pressure and RED failure light comes on.

Don't know what I am doing wrong here. Either bend bleed wasn't done right. Or the somehow the holes on the brass fittings are not lined up not allowing fluid into the line??
I had a similar problem when I did the restoration on my GT. I had accidentally hooked the lines up wrong to the MC. I don’t remember exactly which pairs were reversed, but I couldn’t bleed the rears.
 

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Discussion Starter #16
UPDATE

let the car sit overnight. Started all over again. Bled the rear passenger side and clear new brake fluid comes out. Proceed to do remaining 3 wheels. Get to Driver side front. THE BLEEDER SCREW SNAPS!!! :pat::pat::pat:

There are a lot of auto repair and supply places around my warehouse where I am storing the vehicle so I thought I would drive it over to a specialty brake place for an inspection and advice. Brake is working - pedal travel is not that great. Go around the blocks a few times and try one hard push on the brake. Pressure at first - then it goes to floor and red light goes on - NO BRAKES. I cautiously head back to the warehouse and drive it back in the bay door.

This is beyond me. I remember replacing my MC on a 72 Olds Delta 88 Royale convertible I had and had to brake hard once shortly thereafter and sprung a leak in the break line somewhere because the pressure of the new MC was too much in a weak spot in the line. Maybe something similar here???

I didnt want to give up. I restarted everything from the bench bleed to bleeding the lines at the wheels. When I got the the front driver wheel. I decided to try and undo the "U" shaped line from the caliper to the brake hose and I snapped that too.

Went down to a specialty brake place. Spotted a few vintage cars on the hoists. Talked to a mechanic there. He said the bleeder screw could be the problem and getting it - its a crap shoot.But judging by the head that i had in my hand - he said it looks like i snapped it of and its probably rusted in there. He said for the time energy and effort - its best if I locate a new caliper and take off the old one.

Sooooo. Thoughts? Where can i source one - OUTSIDE of opelgtsource (I'm in Canada and it takes a while to get here)? I used the parts list - not getting anywhere. Suggestions???
 

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UPDATE

let the car sit overnight. Started all over again. Bled the rear passenger side and clear new brake fluid comes out. Proceed to do remaining 3 wheels. Get to Driver side front. THE BLEEDER SCREW SNAPS!!! :pat::pat::pat:

There are a lot of auto repair and supply places around my warehouse where I am storing the vehicle so I thought I would drive it over to a specialty brake place for an inspection and advice. Brake is working - pedal travel is not that great. Go around the blocks a few times and try one hard push on the brake. Pressure at first - then it goes to floor and red light goes on - NO BRAKES. I cautiously head back to the warehouse and drive it back in the bay door.

This is beyond me. I remember replacing my MC on a 72 Olds Delta 88 Royale convertible I had and had to brake hard once shortly thereafter and sprung a leak in the break line somewhere because the pressure of the new MC was too much in a weak spot in the line. Maybe something similar here???

I didnt want to give up. I restarted everything from the bench bleed to bleeding the lines at the wheels. When I got the the front driver wheel. I decided to try and undo the "U" shaped line from the caliper to the brake hose and I snapped that too.

Went down to a specialty brake place. Spotted a few vintage cars on the hoists. Talked to a mechanic there. He said the bleeder screw could be the problem and getting it - its a crap shoot.But judging by the head that i had in my hand - he said it looks like i snapped it of and its probably rusted in there. He said for the time energy and effort - its best if I locate a new caliper and take off the old one.

Sooooo. Thoughts? Where can i source one - OUTSIDE of opelgtsource (I'm in Canada and it takes a while to get here)? I used the parts list - not getting anywhere. Suggestions???
Don't know if it would be any faster but there's one on Ebay that can be rebuilt. It comes from the United States, though.
 

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Discussion Starter #20
Toronto. If I can’t find one online I’m going to ask Rionheart


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I looked through the old parts spread sheet for Calipers. Is there an update or new compatible part numbers?


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