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Old 04-24-2008, 01:08 PM
jor jor is offline
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Brake Warning Light

87 Suburban 4wd

Wondering if anyone can help me with a brake issue. I put 3/4 ton running gear under my 1/2 Suburban. The rear end is a 14 bolt Chevy. I put on 13" drum brakes that I got off of an 84 pickup. I replaced about everything (master and wheel cylinders, shoes, bearings, races, brake line) and I bled them and bled them but couldn't get the back brakes to work properly. They would not lock up, even on gravel. Anyhow, I installed a new combination (proportioning) valve (photo below) and they work well now - or at least a lot better than they were working. Now the darn brake warning light won't go out. If I stomp them in my driveway (gravel) the backs lock up immediately and the fronts, just a sec after. Thanks.
jor

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Old 04-24-2008, 02:42 PM
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Did you try to center the switch? Here's an excerpt from a brake manual I have:

Whenever work on the brake system is done it is possible that the brake warning light will come on and refuse to go off when the work is finished. Sometimes the switch needs to be centered.

Raise and support the truck.

Attach a bleeder hose to the rear brake bleed screw and immerse the other end of the hose in a jar of clean brake fluid.

Be sure that the master cylinder is full.

When bleeding the brakes, the pin in the end of the metering portion of the combination valve must be held in the open position.

Turn the ignition key ON. Open the bleed screw while an assistant applies heavy pressure on the brake pedal. The warning lamp should light if not already lit. Close the bleed screw before the helper releases the pedal.

To reset the switch, apply heavy pressure to the pedal. This will apply hydraulic pressure to the switch which will re-center it.

Repeat for the front bleed screw.

If the warning lamp does not light during Step 5, the switch is defective and must be replaced.
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Old 04-24-2008, 03:19 PM
jor jor is offline
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I thought I had but that's not the technique I used. I'll give it a try. Thanks for the tip.
jor
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Old 04-27-2008, 11:28 AM
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Man, I just can't get that darn light to go out. I bled the brakes again with the combo valve depressed per the instructions. Then I removed the tool holding the combo valve button in and followed yours and the shop manual's instructions for centering the valve. I got the light to show some activity. Off until the brake is depressed, then fluttering and then, BACK ON!!! The brakes are functioning well. The only thing I can think to do is just keep doing the same thing! (isn't that the definition of stupidity!)
jor
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Old 04-27-2008, 12:01 PM
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Check the piston depth in the rear of the master cylinder you took off, and the master cylinder you put on. The rod in the power brake unit that pushes the master cylinder might need adjusting.
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Old 04-27-2008, 01:06 PM
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Quote:
Check the piston depth in the rear of the master cylinder you took off
Neither is adjustable but thanks for the idea. I know I'm getting good fluid movement to all wheels.
jor
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Old 04-27-2008, 01:35 PM
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Quote:
Originally Posted by jor
Neither is adjustable but thanks for the idea. I know I'm getting good fluid movement to all wheels.
jor
I have never seen a power brake unit that the rod that pushes the master cylinder piston is not adjustable.

If you are getting good fluid movement to all wheels, the proportioning valve is centered correctly.

Is this the same brake light that is on when the emergency brake is applied?
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Old 04-27-2008, 01:43 PM
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Yes, it's the same light. It goes on if the e-brake is engaged and also if there is an imbalance in brake pressure front to rear. The rod is definitely not adjustable. I've put two different units in this thing in the past and both were not adjustable. But, like I said before, it's moving the fluid to all wheels. The book says you have to re-center it after bleeding to make the light go off and that is what I'm having trouble with.
jor
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Old 04-27-2008, 01:51 PM
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Double check your rear brake adjustment now that the brake shoes are centered in the drums. It is quite possible they are not adjusted out enough, or one wheel is way too loose, causing the switch in the proportioning valve to not center exactly.
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Old 04-27-2008, 01:59 PM
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Ahhh... that's a good idea. I know I had them adjusted properly but maybe... Thanks.
jor
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Old 04-27-2008, 02:02 PM
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jor

This also brings to mind a truck with 13" brakes I put a new set of brakes on.
The new drums I put on the center hole was .028 larger than the old drums I took off. This kept the rears from not getting centered, and adjusted correctly. It also acted like it had a tire out of balance too.
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Old 04-27-2008, 02:09 PM
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Quote:
he new drums I put on the center hole was .028 larger
I'm OK there as they are the same size (whew!). I had 11 5/32" on it before and it all bolted right up nice and tight. Thanks.
jor
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Old 04-27-2008, 02:17 PM
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Sadly those drums were made in china along with a pair of rotors on a 2005 Toyota 4-Runner that were supposed to measure 39mm on the outside, and measured a loose 37mm, causing the front brake pads to ride .012 above the rotor and squeal like mad cold only.

The list of "junk" made in china stuff is long for me.
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Old 04-27-2008, 04:42 PM
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going out on a limb here but does the speedo work?
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Old 04-27-2008, 05:00 PM
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Originally Posted by Holder350
going out on a limb here but does the speedo work?
Get OFF that Limb and climb down that "tree" to a stiffer branch near the bottom.
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