brakes broke??

[shmed]

well was cruising down the highway in the GN,
when this clown in front of me decided to do a complete stop????
well i slammed on the brakes, and they hardly pulled the front end down, i tried later on in a parking lot to see if they would lock up, and they wouldn't no matter how hard i pushed...

The pedal felt fine like a normal brake system. so i had the vacuum assist working.

This car has the vacuum brake conversion, new check valve, caspers tta vaccum block, booster was checked with a hand pump and held vacuum,

the can also has a line lock installed on the front brakes??

Where do i start, to find this problem?
Any ideas??

 

[Glen]

Why would you expect the brakes to lock? The ideal braking is maximum brake with NO lock up.

 

[BJM]

No matter what you should be able to lock up the wheels. On dry pavement though it will take a lot of effort even with working boost. Are your pads old and of typical parts store type? If so I find that as you get down to the second half of a lot of pads they get harder and have a lot less friction. Fresh pads should fix the problem. Also a glazing of the rotors due to overheating will make it impossible to lock up the wheels. The brakes will feel quite normal even if they won't lock up.

 

[Glen]

" BKM wrote "No matter what you should be able to lock up the wheels"


I have to take exception to that, the rear perhaps will lock and most often do, but not the fronts, particularly with these cars. With a typical weight of 3500 lbs. and whoafully (pun intended) inadequate front brakes at 10.5", and vehicle dynamics that they are with wieght transfer during braking, the fronts are simply not up to the task, even with 'good' pads. After repeated stops from speed it only gets worse.

Keep in mind that that a wheel that is locked up is out of control, wether it is the front or rear.

 

[BJM]

I have never owned a car that couldn't lock the brakes, but only when they were working right. Yes the rears lock first, Yes the best braking occurs just at the threshold of locking but that is not a measure of proper functioning. Properly working brakes should be able to lock up. My Buick's do but it takes a heck of a big push. GM brakes are barely adequate to do the job for sure but in a single high force stop they will do the job. Repeated high speed stops are obviously secondary for GM designers.

 

[shmed]

Well When i had the powermaster on the car it would lock the front wheels, without a problem.
Now that i have converted to vacuum,
I can use both feet and push as hard as possible and the wheels will not lock up. none of the wheels.

I understand the maximum braking is achieved before wheel lock up.

But i was just concerned with the high amount of force needed to stop this car with vacuum, compared to the powermaster.

The only reason i even switched was the brake light kept comming on after i installed the line lock.

Could the line lock be causing this problem?

 

[Glen]

DISCLAIMER: These are averages, your system may vary

Vacuum assisted brake booster = 800 - 950 PSI of line pressure

PowerMaster assisted brake booster = 1400 - 1700 PSI of line pressure

Hydra - Boost assited brakes = 1850 PSI and up of line pressure

This should help explain the difference in braking power

Snap-on or Matco sells a brake pressure gauge that goes between the pad and rotor to measure pressures.

Yesterday I took out a '96 Miata, '87 Dodge Caravan, '99 Durango and a '91 Probe. Under 'panic' braking not one locked up the front brakes, although the Durango did activate the rear ABS. ALL are equiped with vacuum assisted braking