Power Brake Question

Ron61 · #1 (**permalink**) 04-18-2004, 07:01 AM

I have been running power brakes since the car was built in 1996 and am having a problem which has been with me almost ever since then. I have tried everything but take it to a brake shop of which Redding has none that I trust.
The brakes work great and always have but when I have to get on them hard they will drag the engine down and actually kill it if I don't let off. Pedal stays where it should be, and I can lock the tires up. This has been a problem as I said above from day one. I have tried getting up to speed, putting it in neutral and costing as I applied the brakes. The more I applied them the more it drags the engine down. I think I have a Corvette power brake booster unit on there but can't find any numbers. It is a thin type to fit and clear under the fender where they go on a Classic Roadster type body.
Any suggestions as to what I could try? I don't have vacuum gauges and such, but the unit must be getting vacuum or I couldn't lock the brakes up. Pumping the pedal and holding it shows nothing as it will stay where I pump it up0 to until my leg tires of holding it.

Thanks,

Ron

Bruce Edwards · #2 (**permalink**) 04-18-2004, 08:31 AM

Sounds like a bad booster or a leaking check valve. Have you tried unhooking the vacuum line and driving the car? Chances are the engine will run fine. That will show you have a leak in the booster system. Some of them will only leak when the pedal is pushed past a certain point. When you step on the brakes with the engine running can you here any vacuum leaks? A whistle sound?

Ron61 · #3 (**permalink**) 04-18-2004, 08:58 AM

Bruce,

I have listened for any whistling sounds and have heard none. Haven't tried driving the car with the vacuum line to the booster disconnected. I will try this if the rain ever quits. Is the check valve you refer to in the unit itself and can I get to it? I can put a vacuum plug over the plug that comes out of the intake to block the vacuum. I know then the brakes will be hard to use as I had a power unit go completely out on one of my other cars once. And since this has been this way since 1996 or 97 and has never gotten worse that is what has me really confused as if that takes much. Power brakess are not one of my strong points.

Thanks,

Ron

Bruce Edwards · #4 (**permalink**) 04-18-2004, 09:07 AM

Ron,

The check valve is the part in the booster that the hose hooks to. Small plastic part on most. Take it out and see if you can blow air threw it both on both sides. If you can it is bad. Some get stuck open and the brakes will feel ok at first and start to go away and get harder as you slow down. Another way to check is to start the car then shut it off and after a few minutes step on the brakes. If it is still soft the valve is good.
Let me know what you find.

Ron61 · #5 (**permalink**) 04-18-2004, 04:56 PM

Bruce,

Thanks for the information. I will try to check it tomorrow. I can get it out easy enough. I have just never seen a problem like this and as I said, it has been this way since day one. Brakes work great, just kills the enine if I get on them hard.

Ron

Bruce Edwards · #6 (**permalink**) 04-18-2004, 05:02 PM

Ron,

If the booster leaks when you put on the brakes the sudden drop in vacuum will cause the engine to stumble or shut down at low speeds. Not that unusual.

Junket · #7 (**permalink**) 04-18-2004, 05:44 PM

Ron I think Bruce is correct I belive the early vet were not dual diaphragm and the check valve was about 3-4" from the booster on the hose.
Ken

Ron61 · #8 (**permalink**) 04-18-2004, 07:25 PM

Bruce & Junket,

I may be wrong about this being a vet booster as the plastic valve is a right angle one that the hose plugs to and the other end goes into a hole in the booster. Wish it was a little easier to see so I could look for some numbers. Tomorrow I will pull the valve out of the unit and try blowing through it as Bruce suggested. Dam, I don't have any idea of how hard it would be to get that unit out as it is really difficult to get to now. But I have lived with this for 6 years and am tired of it. I had to get on the brakes quick and hard a couple of days ago when a person not looking pulled out in front of me. Locked the tires up and killed the engine. I was doing about 45 MPH at the time. This booster looks almost identical to the one that I had on a 1975 Comet that I once owned except the booster is not as thick. If I can find some numbers maybe you can help me identify it. I really apperciate the help as I said earlier, brakes are not my area of expertise at all. I will post what I find tomorrow.

Thanks,

Ron

Bruce Edwards · #9 (**permalink**) 04-18-2004, 08:02 PM

Ron,

Does not matter what it is off of they all work the same way. My bet is a bad valve. Wouldn't you feel bad for living with that for all that time for a $10.00 part?
Hope that is all it is and keep us up to date.

Ron61 · #10 (**permalink**) 04-19-2004, 06:47 AM

Bruce,

Guess I can feel better. I took the check valve off and inspected it thourghly. It looks ok, and I can blow through it one way but not at all in the other direction. I checked the whole dam unit with mirrors and flashlight and can't find a number, word, or letter on it. I think your statement of maybe a leaking diaphram may be the problem but wouldn't it have gotten really bad over the years until I had no brakes or am I reasoning off in the wrong direction. Also checked the connections to all vacuum ports and everything is good. Removing that unit, even if I could find another that wouold fit in there is about a two day job. Do you know where I could look to find any numbers or codes that would tell me what it is from?

Thanks,

Ron

Bruce Edwards · #11 (**permalink**) 04-19-2004, 07:02 AM

Most of them only have a sticker on them that is "Cleaned" off when they are rebuilt or cleaned and painted. I have seen some go for a long time and never get any worse. How many miles do you really put on your car every year? Most Cobra's are not driven that much so the problem can go on or years.
Still need to see if that is the problem. You really should drive the car with out the booster hooked up to see how the car runs. If you still have the same problem your 351 may have the floats in the carb set to high so as you slow down fuel is forced out of the vents and down the carb flooding it out.
When it dies how hard is it to start back up?

Ron61 · #12 (**permalink**) 04-19-2004, 07:59 AM

Bruce,

As soon as the RAIN goes away for a day or so I will drive the car with the booster disconnected. I drive the car quite a bit and normally pretty hard. That is why it is all beat up and has paint chips. It was so bad that the Gasholes made me park four cars down from them at the convention center. When it dies it will start right back up with no cranking at all. Fires right off.

Thanks,

Ron

Bruce Edwards · #13 (**permalink**) 04-19-2004, 08:17 AM

Ron,

Sounds like a bad booster but it is still best to double check. Make sure before you start pulling it all apart. Nothing like thinking you found the problem and doing all the work only to find out you missed something. That can be a real pain in the back side.

trularin · #14 (**permalink**) 04-19-2004, 09:52 AM

Ron,

I have a spare vaccumn gauge ( I think ) I can send you to check this out.

Email and send me your address. When your done, send it back. This will allow you to check the booster and the check valve ( I think the check valve is probably okay, sounds more like a leak in the diaphram ).

Get ready for spring!

Let me know.

Ron61 · #15 (**permalink**) 04-19-2004, 10:18 AM

Bruce,

Believe me as hard as it is going to be to get that unit out, I am not going to ruah into it. The car stops great and I can wait until next Winter if it turns out the booster is bad.

Trularin,

You have e-mail. I am to dumb to understand power brakes I guess. I have listened for any vacuum leaks, did the check all fittings thing, pushed the pedal until the brakes are locked and held it there and it never moves until I release it, and even tried getting down under the dash and pushing the pedal with my hand while the car was running at a fast idle to see if I could hear anything. I will try driving the car with the booster disconnected if the rain ever stops. I know that the brakes will be very hard to use, but at least that should tell me something. I am just not sure what. Oh, it is embarassing to be so dumb about something like this.

Ron

trularin · #16 (**permalink**) 04-19-2004, 11:52 AM

Ron,

If the engine runs fien with the booster out of the circuit, then I would venture to say the diaphram is leaky.

If you have a vac gauge connected and the car is stopped with your pedal all the way down, the needle should be still. If it is waving or moving back and forth, you most likely have a leak.

Speculation at it's best.