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1993 Caprice V8 5.0 brake problems


vintshave
05-05-2013, 07:31 PM
Hi,

My 93 Caprice is having brake issues. I replaced the master cylinder and bled each of the lines, but the pedal is still spongy and the brake light comes on as the pedal reaches the floor. I'm not sure what in the system to check/replace next and would welcome any ideas from the forum.

Thanks!

J

Tech II
05-05-2013, 08:25 PM
Why was the M/C replaced?

Does this have ABS?

vintshave
05-05-2013, 09:39 PM
Why was the M/C replaced?

Does this have ABS?

Well, it was original equipment and in my semi-educated mind, it was the most logical suspect.

Yes, it has ABS.

What about the power booster?

silicon212
05-06-2013, 01:12 AM
Well, it was original equipment and in my semi-educated mind, it was the most logical suspect.

Yes, it has ABS.

What about the power booster?

If the pedal is spongy then you have air in the system. Did you bench bleed the master cylinder before installing it?

vintshave
05-06-2013, 01:48 AM
If the pedal is spongy then you have air in the system. Did you bench bleed the master cylinder before installing it?

I did bench bleed the master cylinder. I then bled each of the lines till they ran solid with fluid. Is it possible that I just did not bleed them long enough? I wasn't sure how long I had to bleed each line? Or is it more likely that there is a problem with the replacement master cylinder? How would I be able to tell the difference?

Thanks again!

J

Tech II
05-06-2013, 08:42 AM
If the symptoms are exactly the same as before replacing the M/C, chances are it's not the M/C.....

The booster does not make the brakes spongy....

Were you loosing brake fluid(was level low in reservoir) before replacing the M/C?

Have you checked the rear wheel cylinders for leakage? Adjusted the rear brakes?

Checked rubber hoses for ballooning when when brakes applied?

Does the system have a combination valve, that needs to be reset?

Not sure which ABS system you have...in some cases the pump has to be activated to remove air from it....

vintshave
05-06-2013, 01:08 PM
If the symptoms are exactly the same as before replacing the M/C, chances are it's not the M/C.....

The booster does not make the brakes spongy....

Were you loosing brake fluid(was level low in reservoir) before replacing the M/C?

Have you checked the rear wheel cylinders for leakage? Adjusted the rear brakes?

Checked rubber hoses for ballooning when when brakes applied?

Does the system have a combination valve, that needs to be reset?

Not sure which ABS system you have...in some cases the pump has to be activated to remove air from it....

1. I don't think I was losing fluid, but it's possible
2. I did not check or adjust the rear brakes
3. I have not checked rubber hoses
4. The system has a combination valve below the M/C. I am not sure how to reset it, the book does not tell me
5. I assume it's the standard factory ABS system. How would I activate the pump?

Sorry for all the questions.

vintshave
05-06-2013, 04:04 PM
New info/clues:

1) I disconnected the sensor attached to the combination valve below the M/C. The light no longer goes on, but braking does not improve. Does this mean that there is air in the combo valve? If so, how would i remove it?

2) The parking brake has no effect when I press it. I know that it is hooked up to one of the rear drum braking system. Does this indicate a maladjustment in one or the other of the rear brakes to you?

Thanks!

maxwedge
05-06-2013, 07:49 PM
The combo valve pressure sensor works off pressure differentials in the brake system, I would definitely start by thoroughly checking the rear brakes. But as tech11 says air could be in the abs unit which can be hard to bleed, there is a button on the end of the prop. valve, it should move out when appling the brakes, check that out ( 2 man job) and post back.

vintshave
05-06-2013, 10:12 PM
The combo valve pressure sensor works off pressure differentials in the brake system, I would definitely start by thoroughly checking the rear brakes. But as tech11 says air could be in the abs unit which can be hard to bleed, there is a button on the end of the prop. valve, it should move out when appling the brakes, check that out ( 2 man job) and post back.

MAJOR UPDATE:

Combo Valve
------------
When a helper depressed the pedal, a pin popped out from the side closest to firewall. When he let the pedal up, it returned. Nothing projected from the other side. Is this normal?

Rear Brakes
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I didn't really think to check the rear shoes because I had just replaced them 12 months ago.

But on your suggestion, I removed the back right drum. Those suckers were worn right down to the bone and the drum is severely grooved. The wheel cylinders are pretty rusty too, so they need to be replaced. It's a little weird because I replaced the shoes, drums and wheel cylinders on the back brakes about 12 months ago. This leads me to believe:

1) I either messed them up royally when I installed them
2) there is something else that brought them to an early grave

Not sure which, but it is clear that BOTH rears are going to need new drums, wheel cylinders and shoes.

I would certainly welcome any thoughts on what may have led to the rapid demise of the rear brakes.

While it's not going to be dirt cheap or easy to redo the rear brakes, it certainly beats the hell out of a bad ABS system :runaround:

j cAT
05-07-2013, 12:14 AM
the reason you have spongy brakes with rposting here is because the rear drums/shoes are worn to the limits.

what could have happened is this. the parking brake cable was adjusted to compenste for worn drums and shoes. then you installed new drums and shoes and did not back off the parking brake cable so it had slack in it . then driving around with the rear brakes on the rear brakes worn down very fast.

with new drums shoes park brake adjusted correctly then adjust the shoes you most likely will find much less pedal travel. what can occur when the drums/shoes are worn very badly is the rear brake cylinders will leak. with any rust belt 10 year old vehicle brake line leaks are normal and to be expected.

if the pedal keeps dropping you still have a leak..

vintshave
05-12-2013, 11:12 PM
To everyone who responded:

Thank you, thank you, thank you for all your help! After much dirt, grime, grease, trial, error and fighting with the wife (who wanted to take it to a mechanic), the brakes at back to top notch! Big problems were a completed worn left side shoe (probably from not adjusting the emergency brake cable) and a weird wearing right shoe and a lot of air on the line on that side. Took care of these and we are in business once again. Now If I can only fix the a/c...

Thanks again guys!

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