Brake light won't go out

[echo196886]

HI all, Im working on a 1980 CJ7 . My master cylinder was leaking into my power brake booster so I switched them out. The guy at the parts store told me that since I was going to bleed the brakes anyway I did not need to bench bleed the master cylinder. Now my brakes have been bled twice and my brake lights will not go off. In addition I still have no brakes. I plan to bleed the brakes again today since I have never done it before and am sure I did something wrong the first time. Any thoughts?

 

[mtnwhlr]

I hate to say it but the guy at the parts house is dumb @$$. You should always bench bleed a new master cylinder other wise it takes forever to get all of the air out of the hole system.

 

[BusaDave9]

I agree with mtnwhlr, if you replace the master cylinder you should bench bleed the master then bleed each brake.
If you don't bench bleed the master you will get a lot of air in the system that must then be bled out. It's better to avoid getting that much air in the system that must get bled out.

So now the brake lights are on? I assume you are taking about the lights in back not the brake light on the dash. The brake lights in back come on when the brake pedal isn't all the way up.

 

[defibvt]

I agree with mtnwhlr, if you replace the master cylinder you should bench bleed the master then bleed each brake.
If you don't bench bleed the master you will get a lot of air in the system that must then be bled out. It's better to avoid getting that much air in the system that must get bled out.

So now the brake lights are on? I assume you are taking about the lights in back not the brake light on the dash. The brake lights in back come on when the brake pedal isn't all the way up.

This or it could be the brake switch.

 

[echo196886]

I kind of figured out the dumb @$$ thing on my own, lol. I am going to bleed the brakes again, and never ever listen to a parts guy store again. The good news is that at least I know my brake lines are nice and clean now. The only bummer is I'm grounded to my car until I can get the Jeep up and running again.

 

[BusaDave9]

The brake lights in back come on when the brake pedal isn't all the way up.

This or it could be the brake switch.

I think we are saying the same thing. The brake switch is at the top of the brake pedal to detect when the pedal isn't all the way up. It sounds like the pedal won't even come all the way up.

Bleeding your brakes must either be done with 2 people or with a vacuum pump.
Always start bleeding with the tire farthest from the master cylinder (right rear brake). The main problem you need to avoid is sucking air back into the braking system as you bleed the brakes.
There are 2 mistakes that can cause you to suck air into the braking system while bleeding the brakes.
1. Make sure the reservoir NEVER empties when you are bleeding your brakes.
2. If you are using the 2 man method make sure the person in the drivers seat NEVER releases the brake pedal when the bleeder valve is not tight. Communicate good commands when to press and when to release the brake to avoid this mistake.

If you do accidently let air back into the braking system when bleeding then consider yourself back at square one. You have to start bleeding all over again.

Connect a clear tube to the bleeder valve and watch to see if bubbles are coming out of your brake. This means you still have to bleed some more.
Problem: sometimes when I use a vaccum pump I see bubbles and think they are coming from the brake cylinder when actually they are coming from a bad seal on the bleeder valve. These bubbles make me think I have a lot more bleeding to do when actulally I have already bled all the air out.
The solution is to use Teflon pipe seal around the threads of the bleeder valve.

The issue here is you need to add the teflon tape BEFORE you start bleeding. I often see bubbles and wish I would have used teflon tape. If I have already started bleeding it's too late. Adding teflon tape now would add air to the system.
Also make sure to use clear tubing that fits very tight over the bleeder valve.

If you follow these tips and then see bubbles come out of your brake cylinder then you know you have to bleed some more. If bubbles stop coming out the cylinder you are done.

Here is how to use a vacuum pump to bleed your brakes:
How To Bleed Your Brakes or Flush Your Brake Fluid - YouTube

Here is how to use 2 people to bleed your brakes:
How To: Bleed Your Brakes - Feature - Car and Driver

 

[bondo258]

Problem: sometimes when I use a vacuum pump I see bubbles and think they are coming from the brake cylinder when actually they are coming from a bad seal on the bleeder valve. These bubbles make me think I have a lot more bleeding to do when actually I have already bled all the air out.
The solution is to use Teflon pipe seal around the threads of the bleeder valve.

I spent a day looking for the air "leak" in some repair sections I had to make for my CJ.

Re-flaring hardened lines is tough enough without over-tightening/cracking tapered faces, re cutting, gently filing, blowing line out, reconnecting the calipers and having to re-flare them, with a china flare kit.

Now I know why the shops either use the Two-person method or the "pump" style that sits onto the reservoir and forces fluid through the lines.

Never figured on air getting in through the bleeder threads.

Vacuum bleeders are great, if you remember to tape the bleeder threads. That sounds mickey-mouse and hackish, but it's the only thing that works, o-rings don't do the trick, and you don't want pipe dope getting sucked into your caliper.

I cut my tape width down to 3/16ths just in case to avoid getting teflon in the cylinder bore, or the sealing surface of the bleeder screw.

 

[savscj]

Hi: Don't know if this will help you or not but I'm attaching info on correct bleeding procedure. My husband and daughter are almost done rebuilding 1980 CJ7 . Info is from Jeep Service Manual I bought when they started.

View attachment 8873

View attachment 8874

View attachment 8875 I hope this helps you

Not sure if I did this right. If you can't see pics, email me and I will send them to you.

 

[echo196886]

Wow, thank you so much, This manual will be the next thing I purchase for my Jeep. I have a Chilton's but it doesn't give the kind of detail your manual does. I have to say, this site is amazing. I had some trepidation about joining at first because some of the posts I read were a little sexist, but I have absolutely changed my mind. Thank-you to everyone!

 

[savscj]

No prob. I have gotten a lot of help on this site myself. I will try to find the name of the company I got the book from and post it. They had original shop manuals that actual GM/AMC/FORD/DODGE mechanics used in dealer shops.

 

[BajaEdition]

Moved to correct forum