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· Senior Contributor
539 Posts
Discussion Starter · #1 ·
i finally got a master cylinder!!! here is the story, i have an old spark plug wire pluging up the brake booster hose that goes into the carb. the car starts and won't idle unless you leave it alone but it will idle really high, if you hit the gas the rpms drop and the car dies. when the car gets warmed up it wont do this. how do i fix it? then i took some old good condition hose and hooked it up to the carb and then the check valve and then the booster and i had the old master cylinder on it.(not bolted on) the car would run but rough, and if i took the master cylinder off it would die. but if i held the master cylinder down and pushed on the back of the booster it wouldnt kill the engine. but the round spring that fits in the rubber gasket is missing, where can i find that gasket with spring? and the front peice on the booster where the hose goes to is loose, it appears to have a gasket under it, where can i that gasket? when i took the booster off it was full of fluid, appeared to be brake fluid.. but it was brown. when i did the "test" i poured all of the fluid i could get out . sound like this is still a useable booster? and does anything sound wrong with my carb? thanks

· Registered
305 Posts
If your booster was full of fluid then it is definately shot. These are virtually a non-repairable item, tho a few members claimed to have some success after a lot of blood, sweat, and cussing. Regarding the poor engine performance, without the booster hooked up properly, you probably have a huge vacuum leak that is causing the ideling problem. Try plugging the carb port itself and then see how the engine runs. You may have to adjust the idle and/or timimg to get the engine to run smooth. With the port properly sealed off you should see a major improvement in performance. When you get a new booster be sure to run a new hose from the port to the booster and be sure it is properly clamped to the fittings so you have no vacuum leaks. Remember, the brakes are your MAIN life saving tool on the car, so you want to make sure everything is working great with new componets and not jury-rigged with something that my let you down when you need to make a quick stop.

· Member
239 Posts
You seem to be chasing your tail!


I've just been through the master cylinder and booster change out and was a bit confused myself, Namba cleared the booster function up for me and I will try too help give you some advice if I can.

first off you haven't said if your car has a Weber or the stock Solex Carb. adjustments differ on the two. Your car sounds to #1 have a vacuum leak via the booster, #2 carb. fast idle cam adjustment is incorrect when it's cold and the choke is engaged. Forget about adjusting the carb. however until the vacuum leaks are sealed. My car has the weber carb. and there is a cam that sets on a screw and comes into play once you depress the pedal, it also doesn't like much gas pedal input when cold. So when I start my 72 GT I get in pump the pedal then take my foot off and turn the key and start her up. I now have my fast idle cam set to around 1500 RPM when it's dead cold and the choke is fully closed, once it has warmed up it idles around 950 in park and about 750 in gear (automatic trans.) As the engine warms up and the choke plate begins to open it will roll off this cam and not come into play via the linkage. The Weber has a cam and screw, the solex has a linkage with an adjustable nut, I would suggest you research carb adjustments for whichever carb you have once you get you vacuum leak fixed.

Now as for your booster, just because it has got brake fluid in it it's not necessarily toast unless the diaphram has got a hole in it. You can clean out the booster housing with brake clean, brake fluid attracts moister and will rust the insides of the booster. The booster has vacuum to the front side where the hose attaches and ambient (outside) air that is drawn into it from the back side when you depress the pedal. If the diaphram was to have a hole you would have a vacuum leak through the booster. I'm somewhat confused at your post #1 you state the brake booster hose going to the carb. This hose should be attached to your intake manifold fitting below the carb!!! with a check valve approx. 6-8" from the manifold connection... The fitting on the carb. (weber or solex) should go to your vacuum advance on your distributor. #2 round spring fitting into the rubber gasket on the booster???? The only spring there is is inside the booster and is a large spring that can't be removed unless you disassemble the booster! ( so I'm unclear what spring you refer to)... #3 there is no way you can check for a vacuum leak by just holding the master cylinder onto the booster with your hand, it has a round o-ring that fits around the base and seals the master to the booster when the two nuts are tightened down!!! So you have to wrench the master down tight to the booster or you'll have a self induced vacuum leak!!! Now as for the hose fitting gasket at the booster OGTS has these, or you could try Kragen in the HELP section where they sell PCV valves and replacement parts like door handles ect...get the master bolted up first then spray this fitting with carb. cleaner WD40 ect... it might not be leaking.

I hope this has shed some light, #1 get the vacuum leaks fixed via your brake system and then look up the adjustment section for your carb. and worry about the idle. Otherwise your just chasing your tail!!!

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