My '65 GT Fastback now has Stainless Steel Brakes Corporation disks on all four wheels and I am looking for some advice on properly setting the proportioning valve. One article I have come across recommends starting with the valve set full open, driving about 30mph and hitting the brakes (expect the backs to lock) and then closing the valve a half turn and repeating the test and adjustment until the rears just don't lock. Any other suggestions or advice? Thanks.

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Thats how I did mine.

I left it so the rear locks up just a wee bit before the front.

Good luck

Gun

 

I am trying to do this same adjustment.

Excuse my ignorance, but how can you tell if the front or back end is locking up first?

Thanks!

 

Get one to lock up...and it'll be easy to tell.

If the front locks up first..you lose your ability to steer.

 

Having an observer?

Keeping the end that locks locked until you stop and seeing where the black marks stop?

BTW, you probably should have the fronts lock up just ahead of the rears in an all-out stop on dry pavement. Locked rear brakes only will let the car slew around toward the low side if the road has any crown to it. You don't have direct steering control over the rear, so it's trickier to deal with, and if you need to brake that hard you won't want to be choosing between the rear end drifting/sliding down toward a curb (or a ditch) and initially steering toward it to avoid the spin. On edit, when you ease up too quickly and a locked-rear-wheel stop goes back to wheels rolling, it can grab and snap the other way.


Norm

 

I was thinking the same thing,, to me if the rears lock first, and the front is stopping fast, the rear end of the car can pass the driver beforehe can say "oh snap".... total loss of control...

If the fronts lock first, the car will "plow" forward in the direction of inertia, but it seems to me that the driver would at least have an opertunity to release the brakes and regain a simblance of control if the car is somewhat straight and there was enough time to do so.... Just my thinking....

 

Thanks for the input.

I got them to lock up, but even with the adjustable proportioning valve set to full increase of pressure to the rear brakes, I never felt as if it wasn't stable.

I am running on grooved concrete rather than asphalt, so it probably isn't ideal for this test.

Also, because the alignment is so far out after doing the disc brake swap, I don't want to run it out to the nearest blacktop before getting that done.

 

Fix your alignment first. Otherwise the car will hunt a bit under braking. DIY methods will get you more than close enough.

Norm

 

You definitely want the front brakes to lock just a micro second before the rear brakes lock.
after all 4 are locked, kiss your *** goodbye because you are no longer in control of your vehicle. But, if the rear locks up first, you can really give a big smack to your behind because the rear will come around on you and you will go sideways or backwards toward the direction you used to be going. Is there any wonder why the ABS system was invented?

 

ABS sucks, but it's better than goober drivers who are too stupid to back out of the brakes. And yeah, you want the fronts to lock up just before the rears do