front brake bleed problems

[john d]

Reaching out , upgraded front brakes on 90 convert. 2000 Grand Am now. Have bled accumulator, ABS pump and all calipers. Peddle goes to the floor with abs pump connected. Pump does run. Have excellent peddle when disconnecting pump.

Has anyone any suggestions.

[2seater]

How were the front brakes bled? Just changing the front calipers should not have required the other bleeding procedures unless it was run dry. When the key is turned on and the pump runs, does the pump stop after charging the system? Do the red and amber lights go off as the pump is running and prior to pump shutoff? How much does the fluid level in the brake reservoir drop as the pump is running and the system is being pressurized?

[john d]

Bled front by relieving pressure in acum. pumped 25 times. Then conventional bled by pumping pedal. Pump runs, does stop when charged. Lights go out  prior to pump shut off. Fluid level in res. seems to drop as always before about 1/4 inch below full. Thanks for reply

 

P.S. bled back using abs pump and helper pressure on pedal just for the hell of it. Have upgraded back to 1998 Park Ave Two months ago no problems

[Ronnie]

17 minutes ago, john d said:

Pump runs, does stop when charged. Lights go out  prior to pump shut off.

Does the pump start running again each time you press the brake pedal and it goes to the floor?

[john d]

yes Ronnie it does. 

[Ronnie]

Sounds like you have air in the rear brake lines or calipers. When you bled the brakes did you follow the instructions here on ROJ? When you bled the rear did the helper just hold the pedal down the entire time and let the pump do the work? Or, was there some pedal pumping by the helper during the process?

[john d]

Helper held pedal down pump did the work. Fluid ran clear had no air then. Are you suggesting I do the rear again. Also can pump release pressure with key off, pedal of course hardens as soon as pump pressurizes accum. pedal goes to floor.

[john d]

Have double checked fluid drop in reservoir. seems to be 3/4 inch now, could have been all along. In reviewing the diag for accum. that is to great

[Ronnie]

I'm trying to figure out where the pressure is going when you hit the pedal after the accumulator has pressurized and the pump shuts off. You say the pedal goes to the floor when the pump is running. Does it actually go to the floor, or does it go down to where it gets hard like it does after pumping the pedal 25 times?

[rogold]

Since you changed the calipers, make sure the bleeder screws are at the top of the caliper. Sometimes if left and right calipers are installed on the wrong side, the bleeders end up on the bottom of the caliper, and you will never get all the air out when bleeding.

[2seater]

I was going to ask if they are dual piston for the same reason. My guess is it is air in the front circuit somewhere. The rear brakes work by modulating and applying the boost pressure directly to the calipers. There is little involvement of the master cylinder in the conventional sense. 

 

What size accumulator is installed? If it is the larger Hydac or Wabco, normal fluid drop is greater, but 3/4" is an awful lot.

Edited April 22, 2023 by 2seater

[john d]

Ronnie Pedal goes to the floor. never hard.

Rogold calipers are correct bleeder on top.

2 seater accumulator worked fine with oem calipers. not sure what accumulator is on vehicle

 

Valves on top, can't Id accumulator

 

Thanks to all, keep it coming

[2seater]

Standard size accumulator. Usual fluid drop from empty to full in a perfect world would be 1/2", so it probably needs to be replaced. However, that shouldn't cause the brake pedal issue as long as the pump is working properly.

As Ronnie alluded to, where is the fluid going? Insufficient boost should cause a hard pedal. Does the pedal pump up higher if the pedal is applied several times rapidly? How much pedal pressure does it take to get the pedal to sink to the floor? is it more than normally applied in ordinary circumstances. If it was only the front calipers that were changed, it would seem most likely the problem lies there. Do the front brake work? Do they clamp the rotor solidly at all? Are the front rotors held square with a couple of lugnuts while the wheel is off? I know this is all stuff probably looked at but just speculating.

[john d]

wish I knew where fluid was going, Pedal never comes up is pump engaged, As soon as pedal is pressed with abs on pedal goes to floor, Front brakes work fine without abs connected.

 

 

[2seater]

So we don't get confused, the pump is not the ABS system. It is a necessary part of the braking system. The ABS system is an auxiliary system through which the brake fluid is routed to prevent wheel lockup. The ABS can be disabled and the brakes will work without the anti lock features. I think what we have been discussing is whenever there is pressure from the pump, the brake pedal sinks to the floor?? Do you have a FSM to go through the Teves system diagnostics?

[2seater]

I have browsed through my FSM and the only thing I found under low or spongy pedal is to inspect the front and rear system to be certain it is bled properly. I found this excerpt during a google search from the Turbo T’Bird forum which also used the Teves2 system. Same advice but one addition, fluid bypass in the master cylinder? 

[Ronnie]

20 hours ago, john d said:

Helper held pedal down pump did the work. Fluid ran clear had no air then.

I think there is air in the system since the pump is capable of building pressure and shutting off.  When the pump builds pressure it must be compressing an air bubble in the system somewhere and when you push the brake pedal the air is released quickly and the pressure is gone causing the pump to run and the pedal to go to the floor. Assuming you are certain you have bled the brakes properly, the most likely place for an air bubble to be trapped  is in a bad accumulator. It is the highest point in the system. Air could have got in it when you were working on the brakes. Normally the accumulator has a gas charge on top of a rubber bladder (diaphram) that pushes the fluid and any air out the hole in the bottom when the pressure in the system drops.

 

Take the accumulator off and do this down and dirty test to see if the bladder is ruptured.

-Bleed all the pressure out of the system by pumping the pedal 25 times.

-Immediately remove the accumulator and watch to see how much fluid drains out. There shouldn't be much because the gas pressure pushing on the bladder should have pushed most of it out.

-Next get a small rod that isn't sharp on the end and see how far it will easily go up in the hole in the accumulator. It should only go in a short distance. If the bladder is ruptured it can easily be pushed in a long way as shown in photo #2

 

The first shows the bladder inside a good accumulator pushing against the hole in the bottom.

 

 

 

Photo #1

 

Photo #2

 

[2seater]

This is not to complicate the post above, but just to add a little data gleaned from the FSM. The acceptable gas pre charge range in the accumulator is 580psi minimum to 1160psi maximum. There is also an acceptable leakdown rate for the system fluid pressure to decay after an initial three minute wait after pump shutoff and that is 145psi in five minutes. Admittedly this was a bit of a surprise to me. That would mean the pressure could leak down to pump restart in less than 25 minutes without touching the brakes and be considered normal operation.

 

I too think there is air trapped somewhere. A pressure bleeder for the front brakes would be helpful or using vacuum at the caliper as a second choice may be needed. I have never heard of the master cylinder itself going bad on this system.

[john d]

Ronnie and 2 seater appreciate all your help. will test accumulator tomorrow. I do not have FSM. If this helps you guys help me, system is still charged as of now from yesterday. Excuse any confusion in terminology, we have been discussing whenever pump engaged pedal sinks to floor. 

[john d]

Once again thanks to everyone for their help!!! This started with my finding a front brake 2000 Grand Am upgrade on line. I was unsuccessful with this. My opinion, for whatever it's worth, don't bother. Bleeding did not work at all. even though it seems to. I've changed everything back to OEM. Bled brakes exactly the same everything works. Would seem the problem is the bleeder valve position. OEM is positioned straight up, the Grand Am valve, points inward. perhaps an air pocket remains above it that will not bleed. Maybe a pressure bleeder will work, but my 200,000 mile go anywhere anytime driver, will be staying stock up front. 

 

P.S. The Park Ave 1998 rear upgrade works fine.