Alternator light on after brake system work

[Justin71]

Looking for some thoughts on an interesting issue we've had. Front brakes had developed a leak somewhere (still unknown), and the larger master cylinder chamber had drained down to where brakes weren't working.

I pulled the Master cylinder and cleaned it up - it was very dirty everywhere in there even though I had replaced the master cylinder with a new one about a year ago. I also pulled the distribution block for rebuild

To start with, I rebuilt distribution block using the muscle car research kit (very dirty in there too). and emptied and cleaned the master cylinder. I then bench bled the master cylinder, and reinstalled both units.

Come to find out, the back brakes are not even getting fluid - another issue in the rear lines somewhere I guess, not due to master cyl or distro block tho - pretty sure of that.

So, the main question I have is that immediately after this work I have an *alternator light* and a brake light. The brake light I can understand since the back brakes are somehow blocked, but is there anything I could have done that caused the alternator light to come on? I didn't purposefully disconnect any harnessing - is there something in that area that I could have inadvertently broken an electrical connection that would cause that?

Also looking for suggestions on how to clear the back brakes. If you have suggestions on where or how to start looking for the problem, I am all ears.

Thanks for any advice-

Jay

 

[RacerX]

Get someone to pump up the brakes and then try bleeding from the hard line on the chassis near the rear axle. If nothing there then bleed from the distribution block. If you do get fluid at the rear hard line, try the hard lines to the distribution Y on the axle housing. I'd bet the rubber line from the chassis to the axle housing has collapsed and needs replacing.


For the alternator light, do the basic checks with a volt meter at the battery. At idle you should see 13.5 volts or more up to 14.5. If not, check your voltage regulator first. There is a test to jumper 2 wires at the voltage regulator temporarily to make sure the alternator is putting out. You can Google the site for alternator test.

 

[Don C]

Whenever you do any work on the brake system you should bleed the complete system to clear the gunk out, other wise it will mix in with the clean fluid and wind up back in the master cylinder. Start at the distribution block and follow the the brake line back to the rear brakes, and make sure you don't have a pinched or kinked line someplace. Follow RacerX's procedure for bleeding the lines and testing the alternator. You may have some problem with bare wires touching or a problem with the circuit board causing both lights to be on at the same time. Make sure whether or not the alternator is working before you look for bad wires, connectors, or circuit board.

 

[Justin71]

Thx guys. My plan was to bleed the entire system. I tried to start bleeding at right rear being farthest way, but was very surprised to see no fluid. subsequently, I found no fluid on drivers side either. I believe this system was working last year, so something has changed.

I suspect you're right about the flex line to the rear axle, when that liner goes it can plug up even hydraulic pressure - that happened on my 69.

I'll look for some alternator check procedures. Does anyone know what physical change or state (Voltage somewhere or ???) that causes the light to come on? How does this "sensor" actually work? What is it looking at to detect a bad alternator?

 

[Don C]

The ground that turns the alternator light on comes from the I terminal on the voltage regulator. When you turn the key on the alternator and regulator are energized and the regulator applies the ground to the I terminal. When the regulator is charging this ground is removed. Other than the alternator and brake warning lights receiving their positive voltage from the same source the only common factors are their wires being in the same harness and connector. The brake warning light receives its ground from the proportioning valve/distribution block.