My brakes are driving me nuts!

[gr_diver]

Last summer I rebuilt the rear brakes on my car, and last week I rebuilt the front calipers. I also changed the pads, the pins and springs, the flexible hoses, and re-adjusted the rears. Everything was perfect for 4 days! The pulling I had disappeared, the pedal height was significantly raised, there was no interminent pedal, much less effort was needed to stop the car, and the brakes felt very powerful, much like in every new car. I was also using the brakes very carefully to let the pads break-in slowly.

But 4 days later the pedal went again just a tad lower, and the nice "powerful clamping" feeling went away, much like they used to feel before the rebuild. This was also the time that a tiny squeal the brakes produced since the rebuild went away. They also feel more progressive (in relation to pedal effort), whereas at first the nose of the car would sink with minimal effort. The change in feeling was as if pads/rotors were a little slippery. I first re-adjusted the rears (they had not changed), and re-bled all four corners. The pedal was again raised just a hair, but the feeling was not restored. I removed the front wheels, there were no leaks, I cleaned again the friction surfaces with brake cleaner spray but nothing changed.

The calipers are functioning well, there is no pulling, no interminent pedal and they are self-adjusting.

Could it be the pads? I used OEM pads, they are black carbon-like made by A.T.E., and they are the same stuff that was there before (this might be important, as the brakes got the feeling they had before the rebuild). Before installing them I lightly filed the edges all around to remove any sharp points that might score the rotors. Could it be them being a bit coarse at the beginning, and now they have gotten smooth? What experience do you have with pads of this material?

Thank you for your time!


P.S. The pad shape might seem odd to you, because my calipers are GM floating, factory fitted on cars after mid '78, but it is general brake experience I am after, or at least I think so...

[hrcollinsjr]

You didn't say anything about the brakes pulling to either side just lighter braking than you would expect.

Does it brake okay at a panic or sudden stop and then the pedal slowly sinks to the floor? The pedal slowly sinks to the floor while applying steady pressure? Sounds like a master cylinder going out.

Harold

[gr_diver]

No, the pedal does not fade, not even while standing at traffic light for a minute. I had pulling to the right, which was eliminated after the rebuild.

Braking is adequate, even in panic condition.

It is just that immediately after the rebuild, the brakes performed slightly better than a few days later, which I expected to be just the opposite, since I thought brake-in would enhance their ability even more.

[GTJIM]

It soumds like you have been too careful 'bedding' the pads in and they have become glazed (smooth and shining). Remove the front pads and rub the friction surface on a sheet of 180 grit wet & dry sanding paper that is placed on a flat surface. This will remove the 'burnt' surface from the pad and let it bite again - be a bit less gentle 'bedding in' the pads!

[raisinracer]

You also need to clean up your rotors. Either get them turned or use a flpper disc. If you use a filpper be careful not to do it uneven.

[hrcollinsjr]

A failing master cylinder will in my experience work briefly in panic stops but fade as steady pressure is applied.

GTJim may have answered your question correctly.

Harold

[gr_diver]

That could be it, the glazed pads I mean, because they grab, but it feels like they got slippery.

I will try, on first chance, to de-glaze them...

I keep my fingers crossed!!!

Thank you all for your time!!!

[blancojp]

Are you sure these are GM calipers?
They look more like Ford Festiva or Escort than anything else.
In any event, I would try the pad scenario first. If that does not solve your problem and if these are two piece unit assembly, make sure the part that has the cylinder is mounted correctly. I have seen cars that have monster braking power for a few days and then go away because the caliper cylinder is no longer sitting parallel to the pad.

[gr_diver]

blancojp: They are GM floating calipers, made by Delco Moraine, standard fitted to Opel Ascona/Manta B Series from mid '79 to '88, and in some other Opel models including the Vectra and Corsa until 1991. Of course for the latter, they had a bit different casting, but the internal parts are identical. Also, A.T.E. made an interchangeable part for this caliper, that was used by GM as well, somewhere after '85.

Thanks for the recommendation, I will check it as well if I de-glaze the pads...

And I say if, because I took a look at the leaflet that was in the box with the new pads. A.T.E. recommends moderate driving for 400-500 miles for break-in. I only did about 200 miles since the installation, so I will give them some more time... Maybe a little more braking action will even deglaze them in-situ...

[GTJIM]

My memory has just be jogged - At one time Opel sold disc pads with a layer of abrasive on them to "condition" the brake disc surface when installing replacement pads. I would guess that there is a glazing problem with many Opel replacement pads and this was one of their 'cures' - a bit brutal!
Let us know how cleaning up the pad friction surface works out.

[gr_diver]

My pads probably had that coating you mentioned Jim. You made me curious, so I looked at the pictures I took immediately after I removed the calipers, and some more I took when I re-cleaned the rotors, after the issue appeared...

It is the same rotor, just in the "after" pic the caliper was installed. The lighting conditions are very similar (same parking spot, same hour of the day, same camera, almost same angle, same "soft-flash" camera function to eliminate shadows). The difference is clearly is visible...

Maybe now that rotors are "re-conditioned" I need to make a few mild-to-hard 80->20km/h decelerations, without stopping in between to establish a new "transfer-film".

If that doesn't work, out will come the pads for sanding!

[gr_diver]

When I posted the pictures earlier, I did not go to the car because the wind was blowing like crazy, so now that it calmed I went to take a closer look...

I couldn't believe my eyes! The rotors when I removed the calipers were lightly scratched, and the deeper grooves visible in the "before" pic were fingernail catching. Now it is MUCH more smooth, the deep grooves have completely disappeared, and there are only very shallow scratches, that the fingernail does not get caught in...

Nice!!!!

I think I should probably accept that I was braking with the abrasive coating at first, and now that it is gone I start to get the real feeling. But I must confess that today the car started giving me a better braking impression.

Time will tell...

[gr_diver]

A few days have passed, and brakes have stabilized somewhat... The brake feeling is the same all the time, BUT, the interminent pedal came back.

I was browsing through older posts yesterday, and found out that I am having the same issues as GoinManta described almost a year ago, everything rebuilt, low pedal at first application, good afterwards if used little, low pedal when going in traffic.

I am now thinking that this situation can be from a faulty rear proportioning valve. Apart from reducing pressure to the rear brakes to avoid locking, it also has to keep some pressure in the rear circuit for quick take-up. Maybe this valve is gummed-up, and when used a lot (city driving) leaks internally, and is not keeping the rear brakes under pressure. So the pedal goes lower in order to replenish the volume that already should be there... Then, when frequent application is not necessary it finds it's way into the crud and seals somewhat, giving the impression of a better pedal...

This can explain the need for more foot-effort, because the driver also has to add the lost residual pressure of the rear brakes...

What made me think of this scenario is the fact that when with the car stationary I pull up the handbrake, pedal's height does not change, it though has a sharp bottom end feeling. Thus, it is not rear adjustment issues nor air in the system. So it has to do with fluid flow to the rears. With the shoes contacting the drums via the handbrake, the shoe return springs do not "try" to re-tract the cylinder pistons, thus the fluid that goes there stays there. Result, sharp pedal. When the handbrake is released, the springs retract the shoes, they in turn retract the cylinders, and there is back pressure in the circuit. The valve can't hold it -> residual pressure gets lost -> low pedal at next application...

It is just a theory though!