Replacing brake stop light switch

[zuburg]

I replaced the brake stop light switch on my 1956 Thunderbird. This is the part that screws into the brake line block on the frame right under the battery. I assumed I would need to bleed the brakes after, but no brake fluid leaked out when I removed the old one. Do I need to bleed the brakes?

 

[dmsfrr]

I don't know what the inside of that block looks like and it may be possible there is a small bit of corrosion obstructing the opening and it needs to be cleaned out.
If the switch & brake lights work now it's a good thing.

You may be ok but if it's been a while or the fluid is starting to get dark it won't hurt to bleed/flush the whole system anyway. However, do be careful with the wheel cylinder bleeder valves, they have been known to snap off if they're stuck or rusty.
Normally you'd start with the wheel farthest way from the MC, bleeding until the fluid is clear then repeating with the next farthest and ending with the closest wheel (LF).

Where to start may be different if you have a fender mounted power brake booster. It looks to have a bleeder valve on top. (circled in yellow) It's also the highest point in the system, where air would naturally accumulate.
It might need to be bled first(?) or maybe it takes care of itself when the whole system is bled, I don't know and I hope someone else does 'cuz I'll have to do mine soon and need to know too.
.

 

[zuburg]

Yes, as I understand it, you bleed the power booster first, then do right rear, left rear, right front, then left front. I had the new switch and forgot to install it before bleeding the brakes after replacing the hard and soft lines and wheel cylinders. I was hoping to avoid bleeding them again. Maybe I'll bleed them and find no air bubbles, so it won't take too much time and fluid.

 

[paul2748]

You don't have to bleed the brakes if you just replaced the switch. I have replaced a number of these and never had to bleed.

When bleeding the brakes on my 56, I bleed the booster last on the theory that you start at the furthermost point and work forward.

I strongly recommend you install the mechanical switch offered by the TBird parts vendors. Instead of waiting for the correct pressure, the brake lights go on instantly when the pedal is pressed.

 

[Lanny]

When bleeding the brakes on my 56, I bleed the booster last on the theory that you start at the furthermost point and work forward.
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Paul, one reason that you would bleed the Master first, is that it produces the pressure,
so you need get all the air bled out of the Master cly, so you can build pressure.
Then start at the furthest wheel cyl, to purge air from the system and work your way to
the front of the vehicle.








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[paul2748]

Lanny- I agree with you, but the question referred to the power brake booster, not the master. Don't know if this makes a difference.

 

[Milt K from Pa]

Barners,
Earlier this year I replaced the entire brake system including the master. On my T-bird, I flushed the existing steel and flexible lines using fresh silicone fluid, which I was changing to. When the fluid was all purple from all wheels and the power assist, I began the final bleed starting at the power assist on the fender apron. Continued to the farthest rear wheel and etc. It worked out well with no problems.
Good luck.
Milt K from Pa