I'm trying to track down any leaks in my system, and I've noticed that my brakes don't really seem like power brakes. In looking at the system, I see a large vacuum hose from the intake to a metal tube that runs to the front compartment. There is in the front compartment another hose connecting to the booster itself. I heard there's supposed to be a filter in this hose somewhere, but I can't see one. It might not be required so may have been removed by previous owner. At any rate, the plug in the booster where the vacuum hose attaches seems to rotate freely. Is this right? What would be a good way to check for vaccum leak in this system, and for positive function of the booster itself? The emergency brake lever has no effect at all, and may not be connected either.
All points allong that line must be tight, including the gromit on the booster. The grommit should be replacable but I'm not sure how hard it will be to find one. The Elbow in that gromit is also a check valve I think, been awhile since I fooled with it. make sure that is it is a check valve that it is sealling corectly.
The brake filter was deleted. I forget what year. You may never have had one.
Quick way to tell if the system is even holding vacuume. Start up the car for a few seconds, shut it off. After a minute or so push down the brake pedal. There should still be "assist" for at least one or two "pumps". If not, you have a leak somewhere.
Parking Brake. I don't know what year you have. On pre '88 Fieros, the cables run along the back of the cradle, exposed. Tug on them, they should not have very much play. There is an adjusting nut to tighten them up if needed. On '88 Fieros, the cables run in a "channel" on the front of the cradle. Same procedure to take out any slack.
[This message has been edited by fiero56 (edited 02-24-2000).]
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08:47 AM
DaveL Member
Posts: 425 From: Florida, USA 33952 Registered: Jan 2000
Excellent point, Phil. I never even thought of that test. While your down there checking out the parking brake cables, make sure there is no fluid leakage anywhere around the little "arms" on the caliper where the cable pulls. The seals behind those can go out at some very inopportune times.
I've done a lot of brake work on my 88. I found that there just isn't enough force generated from the power booster, and I don't know why. It's a dual diaphram and is the same diameter as the other GM power boosters. So the only reason for poor brake performance that I can think of is that a) the vacuum isn't good enough because of the distance from the engine, and/or b) the brake pedal setup in our little cars doesn't allow for enough stroke (which could be traded for power if the hydraulics were redesigned).
Before I did my brake upgrade, I did a couple things to improve the vacuum level. First, I moved the check valve to the intake manifold. This is the same as increasing the volume of the booster so that it holds more vacuum. Remember, when you push the brake pedal, you are releasing air into the booster, and the vacuum must be 'replenished' through the long line that comes from the engine. If you start will 'more vacuum', then pushing the pedal won't reduce it as much. BTW, my 88 doesn't have the booster filter on it. If I were you, I'd remove it from your car. If it's blocked, it will reduce your braking power. There's only a small amount of air that enters your engine through the booster, and that comes from the interior of the car. Sure, there may be some dust, but not a lot of bad stuff to worry about.
The other thing I did was get a vacuum booster from an early 80's Skylark w/disk brakes. I put this device in line with the vacuum hose, up front, close to the booster. This practically guaranteed 24" of water vacuum at all times. This helped quite a bit, but still wasn't what I wanted, so that's why I upgraded.
I don't believe any 87 has the filter. Mine doesn't.
Moving the check is a good idea. Just adding a second one in the rear is probly just as easy. Plus a double check on that long line cant hurt any. would provide a backup if one dies.
Plus adding the check nearer the intake would help stablize manifold vac. That long line has to be doing some pretty odd things durring sudden vac changes in the manifold. Now that I think about it this could account for a few odd thing since the mix in the brake boost line could also be storing fuel under some conditions. It could also divert incoming charge from the manifold when you punch it, esentially compeating with the cylinders for charge for a split second.
[This message has been edited by theogre (edited 02-24-2000).]
Actually, adding a second check valve in the line will hurt. It takes a certain amount of pressure (vacuum) to open the valve, and that amount is subtracted from the ultimate vacuum in the system. It acts like a pressure regulator.
It's worth checking out. The extra reserve capacity may make up for the small decrease in overall line vac. If I don't like it I can always eliminate the one up front.
Either way it will keep the relativly large vacuum capacity of the line from parraciting the manifold when you sudenly drop manifold vac. When the manifold vac drops fast the line as it is has enough storage to scramble the intake flow. At least on the 87 4 cyl where it is connected to the #4 cyl runner. In other setups like, I think, the V6, where it is pulling from a more central location, it's not as likely to unbalance the manifold.
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10:50 PM
Feb 25th, 2000
DaveL Member
Posts: 425 From: Florida, USA 33952 Registered: Jan 2000
Lawrence, Where is the check valve located at on the V6. I've been looking in the Haynes manual and can't find a thing about it. I assume you did the Grand Am update? Did you use the stock master cylinder or go with the Blazer master cylinder. I am undecided about which one to use. Any feedback would help. Thanks, Dave
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10:41 AM
Raydar Member
Posts: 41338 From: Carrollton GA. Out in the... country. Registered: Oct 1999
DaveL... What kind of brake pads do you have? I replaced mine with Carbomet pads from the Fiero Store (along with the rotors), and was amazed at how much harder I had to press on the pedal to stop quickly. I understand that the hotter the pads get, the better they work, but I have yet to get them hot enough to be able to lock the wheels. Not spongy at all, so I don't think there is any air in the lines. Merely an observation...
TH125c and most other transverse transmissions I've seen to date use a cable to the throttle to determine engine loading for shift control. Engine vacuum has no bearing at all on this tranny. The only transverse tranny I know of with a vacuum modulator is one of GM's AOD units. That one uses both the vac modulator and a TV cable.
The check valve is located in the angle fitting on the power booster. Pull it out of the booster, then the hose, and blow through it to make sure it's not blocked. If it's plugged, you won't get enough vacuum into the booster, and if it's stuck open, the vacuum won't be trapped in the booster.
I have an 88, and designed my own brake upgrade. If you are interested, click on the link below and look in the Archives.
Lawrence...... Why didn't you just use an adjustable proportioning valve? Would have been a heck of allot easier. More importantly you can tweek it for long periods of bad weather, or to compensate for diferant pads...
[This message has been edited by theogre (edited 02-25-2000).]
I didn't use an adjustable p-valve because I didn't want the plumbing headaches. It's tight enough in there as it is.
I did think of putting an adjusting screw on the end so that I could vary the spring force, but that would have required a fancy seal that I didn't want to worry about.
It's all moot anyway since I removed the spring all together. The fronts lock just before the rears do, and as you read, the car stops very well. Since I don't drive it in snow, and almost never drive it in the rain, I have no need to go back. If I did, then I would simply put a pressure regulator in the line going to the rears (mounted in the interior) so I could reduce the rear braking 'on the run'.
