Rear Disc Brakes on Seville

[Tod - North Texas CLC]

This is getting to be ridiculous.  I have a 1979 Seville and I cannot get a good brake pedal. I have replaced all 4 calipers, all brake pads, bled throughly, and couldnt get a good pedal.  So, I replaced the Master Cylinder, bled throughly, and still could get a good pedal.  Spoke to some club members who reminded me of the correct procedures to set the rear caliper e-brake lever, and I am setting it properly - still not a good pedal.  Spoke a brake shop that suggested that the rear calipers might not have been properly rebuilt, so, replaced the rear calipers AGAIN, adjusted parking lever per manual, bled throughly, and STILL have too much pedal travel.

I do have good emergency brakes, and the brakes will stop the car, but the pedal travel is way down there (I am comparing to another Seville, and the difference is substantial).  All of this after going through over 3 gallons of brake fluid with multiple bleeding of the the lines.

Is there anyone out there who can offer me the magic solution for this?

[wm Link]

My guess is the rear calipers, the lever on them HAS to be removed, and then the shaft can be retracted, replace the lever and that should do it. Have you done that?

[Mark]

I sold my 79 Seville - enough was enough after 12 years of doing exactly what you describe.  Just when I thought that the pedal was good then a short time later it was a problem again.  

What I couldnt understand is how a rusty, ugly 78 Eldorado (my winter car) could never give me a problem in that same time span.

[Tod - North TX CLC]

Yep - I have done that.  Using a 9/16" wrench to adjust the shaft so that the pads are firmly against the rotor, then placing the lever on the flat of the shaft so that it is all the way against the return stop.  Just a touch of the e-brake lever will lock the pads firmly to the rotor.

Everyone keeps telling me that it is the rear calipers, but I have now gone through 3 sets of rear calipers (three different stores - NAPA, AutoZone and OReilly), and I still cannot get a good pedal!

[Michael Stamps 19507]

This might be going out on a limb but maybe the rubber lines are swelling under pressure?

Stampie

[Bruce Reynolds # 18992]

Gday Tod,

I am coming in on this thread not knowing exactly what bearings are used to retain the axles, hubs, or whatever holds the rear discs into place, or if it is FWD or RWD, but firstly, have you tried isolating the front and rears to individually test each part of the system.

By that I mean, blocking off the rears, and just braking with the front and measuring the pedal action, then doing the same with the fronts, and seeing which makes any different.

And, secondly, I have had experience in the past with fitting discs to a Chev 12 bolt axle using the "C" Clip axle retention method, and found that the sideways movement of the axle was pushing the pads back too far so that when the brake pedal was pressed, it had to press the pistons out further than normal to apply pressure to the pads.   Stopping the axle movement stopped that.

Also, Ford stopped their rear pad problems by using a double-row bearing that stopped axle flex, but that was with the 9" and the Borg Warner Diffs.

Bruce,
The Tassie Devil(le),
60 CDV

[Joe Abernathy #17524]

Probably a dumb question, but did you bench bleed the new master?  Its almost impossible to get all the air out otherwise.

[Tod - North TX CLC]

The axles are exceptionally tight - no movement of the rotors when the pads are applied - the roller bearings were replaced a few years ago.

I did bench bleed the Master - probably 50-60 long, slow strokes until I was getting absolutely no, not even tiny, bubbles in the bleed lines.

I wish it was the rubber lines - I purposely checked them in the hopes of seeing a swell, but no such luck.

Good idea about segregating the brake lines so I can narrow down the problem.  I will have to hunt down some fittings to block the ports, and see if I can at least identify whether the problem is front or rear lines.

I appreciate all of the ideas - keep em coming.

Tod

[Bruce Reynolds # 18992]

Todd,

Although I dont advocate using them, brake places use a crimping tool to temporarily squash the rubber hoses to isolate fittings when doing work on brakes to save loss of fluid.

But plugging the lines will work, but dont do any testing on the open road with isolated brakes as you might need full braking in an emergency.

By axle movement, I am referring to the sideways movement when the brakes arent applied.   You see, the disc pads rely on slight sideways movement, or run-our, to push the pistons and pads back out of the way when the pedal pressure is released.   In a drum brake system, there are return springs that retract the shoes to the stops, but nothing like that in the disc brake system.

Bruce,
The Tassie Devil(le),
60 CDV

[Mike #19861]

 Tod,

 It seems like you have covered all the likely problem areas at least once. By your description, I would feel that the problem lies in the hydraulic system somewhere.

 One area that is not often adressed is the slider pins and bushings. The must allow the caliper to compensate for brake wear, if not the pedal will get lower. I have seen in many instances where they seize up and cause a low pedal.

 Now, since you say that the calipers have all been replaced, I would suspect that they are all in good shape, but the bushings must be lubricated with silicon grease to allow movement. Since you say the parking brake works fine, I would look at the front calipers first to make sure they are free.

  Mike