I converted my 1972 front drums to disc. My problem is I can’t deliberately get the brakes to lock up. Under normal braking the car stops fine, the petal feels a little stiff on a hard brake. I replaced all parts required for this conversion, (parts list below) and I did a complete/thorough brake bleed. A mechanic friend told me to try a few things, install better brake pads, ceramic, so I did, and maybe install an adjustable proportioning valve, but my problem is not the rear brakes locking up. I did some other research on-line and on Master Power Brakes website they mention doing a brake Pressure test with this tool, http://www.mpbrakes.com/tools.htm but I still don’t think that is the problem, but maybe I’m wrong.

Please reply with any suggestions/help.

Parts replaced are new, Stock.
booster/master/ proportioning valve, all new front brake lines, Spindles, Calipers, Pads, rotors, caliper mounting brackets, backing plates, new bearings.

Usually a problem of not being able to lock the front brakes is due to the pads not 'clamping' on the rotor hard enough... this can be from one or more issues. First off, have you 'broken in' the brake rotors and pads? You actually do need to break them in and get the rotors and pads mated to each other. A series of progressively longer/harder stops. but not enough to get the brakes hot, just need to warm them a little and do it several times. I usually go for a little ride where I can slowly stop from about 10MPH, just gently pushing on the brakes. I then do it from about 20 MPH, them about 30 MPH. I will then start over at about 10MPH, but this time will apply more pressure than the last time and stop quicker. Do it from 20, 30 and even 40 MPH. Between each stop, I try to drive a mile or two and give the brakes a chance to cool down a little. After the last stop, I park the car for an hour or two to let everything completely cool down, them I drive as normal, still trying to take it easy for a bit. I can generally feel a difference in the brakes after that.

You mentioned brake pads, did you actually swap in new ones? What is the rating on them? They should have a two digit code stamped or written on them... it will be two letters like "FF". This is there actual stopping rating and I'd suggest you get least an FF rating... that means they will stop good in both cold and hot temps.

Are all the parts new? You said they were stock... where did you buy them? Did you bench bleed everything real well? I'd bleed the fronts again just to be sure.

By this time, you nned to make sure you haven't 'glazed' the rotors by trying to stop hard... make sure they are not really smooth and shiny.

Finally, did you move the brake pedal pushrod to the other hole in the brake pedal? This helps get better leverage.

That's about all I can think of for now... keep us posted.

Bill C.

I don't think I can lock the front discs on my 68 either, I used stock 72 discs.

The stock sized brakes are sorta small, given the size and weight of the car. And if you have wide front tires, it will be harder to lock them.... so if after checking up on stuff that BC mentioned, you might not find anything wrong. And that might mean that the brakes are fine... for what they are.

There are a lot of people who swapped on larger front brakes from a B-body, or aftermarket units, and I suspest it's due to the undersize of the factory brakes. Don't get me wrong, I'm perfectly happy with mine, as they are still 100X better than the drums I replaced with them!

Chris

Bulb has a good point... a lot of times if you go to a wider tire, it will not allow the brakes to lock up anymore! I've had this happen in two cars and more recently in my '90 Suburban. I know the brakes on the 'Burb were good before the swap to larger/wider tires... now they will not lock up! Going to swap out the cheap brake pads and go for the nice ceramic ones to try and help.

Check it all out and if it seems ok, then maybe there is no problem.

Bill C.