Replace Caliper or Master Cylinder?

[dburgjohn]

Rebuilt driver front caliper (piston came out while off rotor for other work). Have bleed front brakes 3 times and warning light still comes on. It will reset but comes back with next hard brake. Verified it is not e-brake and wire is on sensor good. My guess is something wrong with caliper rebuild (but no visible leaks) or master went bad due to fluid being drained. It was several days between caliper removed and ordered parts coming in.

Any way to troubleshoot farther or just take a guess and R&R one of them? Asked local mechanic who said "I don't rebuild those calipers, I just replace them".

 

[White75]

is this for a C3 or your C4?

Try a full system bleed, not just the front wheel you were working on

 

[6880 Mike]

...or master went bad due to fluid being drained...

Did you bleed the master cylinder after the fluid drained?

 

[Hib Halverson]

Absolutly do a full system bleed per the factory service manual. In addition, you may need to bleed the ABS prime pipe.

Don't replace more parts until you properly bleed the system.

 

[dburgjohn]

Opps

Sorry, I had not changed my picture yet.

My car is a 1981. I have bleed it from master cylinder (had fitting there) and both fronts (did not undo anything in rear system) three times. Clear fluid and not air comes out but the brake light still somes on when I step on the brake. I quick tap will re-set the light but it comes back with the next firm brake action.

 

[wishuwerehere82]

Even though you didn't touch the rear brakes, the fluid through the valve where the brake light switch is still shares the same lines. There is air in the rear lines, and must be bled out to avoid having the light come on, and more importantly to keep the braking system balanced pressure-wise.
The light comes on when it brake fluid fkws at a disproportional rate to one brake cylinder than the other.
You need to bleed them properly, otherwise there will be problems with pulling to one side, Etc.
Rear right inside caliper first, then outside. Then the left rear inside and outside.
Then the front right, and front left.
Drive it awhile, then do it again to make sure.

 

[dburgjohn]

Even if...

So even if you only open the front half of system, the whole thing must be bled?

Could the rubber in the master cylinder have been damaged by having the fluid drained out of it for several days while I waited on the parts to come in?

I don't mind spending the cash for a repair but I don't want to spend what is not needed as there is not a lot of extra around these days.

 

[wishuwerehere82]

Refer to post #4,
Peobably just a little air in the lines near the switch.
Your master is still OK.

 

[dburgjohn]

one and a half

I have run 1 1/2 bottle of fluid through it.

I saw some notes about bench bleed for air trapped above the line tap on the MC. does that still need to be done if you have the bleeders on the MC?

If so can I use jacks to raise rear (level MC) and do it on car?

thanks

 

[JohnZ]

I saw some notes about bench bleed for air trapped above the line tap on the MC. does that still need to be done if you have the bleeders on the MC?

The bleeders on the master cylinder are useless, which is why they were eliminated. What you're trying to get rid of is air that's trapped in the bore, and the only effective way to do that is to bench-bleed the cylinder. Once that's done, you can re-install it and bleed the total system.

 

[dburgjohn]

do I have to

can anyone tell if the car can just be dropped in the front to level the MC for a on-car bench bleed? I really don't want to risk breaking the rear bleeders if I don't have to.

 

[minifridge1138]

I would just try bleeding all 4 wheels and see if that fixes it.
If not, then you have to bench bleed the MC and then bleed all 4 wheels.

 

[6880 Mike]

One of these will help.