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Mon Aug 25, 2008 7:20 pm

Since I bought my 66 Sedan 2 years ago, the brake lights will not turn off when releasing the brake. I have tried new brake light switches and bleeding the brakes about 10 times. After I bleed the brakes I get one or two pumps, and they stick on again. Any ideas on this crazy problem? Do I need a new master cylinder?

Mon Aug 25, 2008 8:10 pm

It may be the MC hanging up. Keep in mind that if you remove the MC, there are spacers inside the bulkhead for the MC bolts. If the spacers fall down inside the bulkhead, you'll never be able to snug up the MC retaining bolts. Therefore, when you loosen up the MC bolts, dont remove them all the way.

Mon Aug 25, 2008 8:34 pm

Sounds like someone mis-adjusted the pushrod, or never properly adjusted the stop on the pan if the MC had been changed in the past, or both. :)

Mon Aug 25, 2008 9:14 pm

try checking the brake light presure switch. my 66 went thru 3 before one worked right. one time is would not turn the brake lights on then they stayed on and wouldn't go off. When you install the switch make sure to drip some brakefluid in the end so you don't get a air bubble in the switch.

Wed Aug 27, 2008 1:40 pm

You might also check your grounds and the bulbs and wiring connectors. I took the rear light covers off and made sure all of the connectors were tight, bulbs pressed in correctly and that they all had a clean contact. I just had a similar thing happen and for some reason on the passenger side, when the screw that holds the bulb holder to the tail light housing was tightned downed, it casued the brake lights to come on. So I disconnected all wires out back and double checked all contacts.

Wed Aug 27, 2008 4:43 pm

How are your soft lines? They may be expanding internally when you push, then push fluid and pressure back into the MC even after you let up.

Thu Aug 28, 2008 12:52 pm

I do not know if the 66 has the dual circuit master cyl but i know on my 69 it had two switches on the master cyl one of them was faulty and would not open when the pedal was released causing the lights to stay on.
I was able to test it by pulling a wire off each switch to find the culprit.

Thu Sep 25, 2008 6:15 pm

Thanks for all the replies guys. Checked all your suggestions and looks like the MC is bad. Think I'm gonna replce it since only $100.

Fri Sep 26, 2008 3:35 am

FYI - I had all kinds of goofy stuff on the 65 - Wires were a little to short under the passenger side tarboard in the engine compartment and some of the connectors kept coming undone - rear lights did the goofiest stuff - like it was possessed.