Disc Conversion Bleeding Issues
11-23-2017, 06:14 PM
#1
Disc Conversion Bleeding Issues
Hey guys, I just swapped my 85' Trans Am from a drum to 1LE disc rear. Bought brand new calipers, rotors, pads, the whole shabam. The master res was nearly empty and the brake light has been on (the fluid drained out from the rear hoses. Anyways, now that I'm trying to bleed it, I think the combo valve is closed off, as the pedal is firm and fluid shoots out through the master res if you try to force it. Is the ABS or combo valve cutting off flow to the rear? If so, how can I get it to release so I can bleed the brakes?
11-23-2017, 10:30 PM
#2
Re: Disc Conversion Bleeding Issues
If you let the reservoir run dry, you'll probably need to bleed the master cylinder. You can try to stuff several rags around the master cylinder fittings to keep fluid off your paint, and crack the lines open to bleed the master, but it'd probably be best to bench bleed it. It may not be possible to get all the air out with the master in the car.
More likely one or more rubber or steel brake lines is blocked than the combination valve. If the valve has a problem, they'll usually just stick with the warning light switch off-center. The lines however like to rust, and the rubber breaks down and turns to goo. If fluid doesnt run out when you open part of the system it's blocked.
More likely one or more rubber or steel brake lines is blocked than the combination valve. If the valve has a problem, they'll usually just stick with the warning light switch off-center. The lines however like to rust, and the rubber breaks down and turns to goo. If fluid doesnt run out when you open part of the system it's blocked.
11-23-2017, 10:37 PM
#3
Re: Disc Conversion Bleeding Issues
I was going to bench bleed the master anyways, so I should be ok there. All of the lines look likes they're in good shape (from the outside, for what it's worth). I'm going to try to unstick the pressure differential switch first because the light is on. How exactly can I get it unstuck? Nobody seems to have a foolproof way of doing it.
11-24-2017, 12:11 AM
#4
Re: Disc Conversion Bleeding Issues
Unscrew the switch, look down in the hole and you'll see a rod. There is a low spot machined in the rod, that pushes the tit on the switch up when an imbalance occurs. Kinda like ===V===. Anyway, you can reach down in there with a pick and push the rod back to center, but that's not going to do anything except turn the light off. Whatever created the imbalance will just trip it again if the problem isn't solved.
The best way to go is to fix the problem, then when you apply the brakes, the pressures in the front/rear circuits should be equal and the switch SHOULD move back to center. If and only if the brakes are working fine, and the light is stuck on, would I bother resetting the switch.
If your switch is sticking, your brake lines are shot and your brake fluid is or was full of sludge. In other words, a sticking switch would go hand in hand with blocked lines and black fluid, etc.
The lines can "look fine" and get totally crapped up on the inside. It's the nature of the beast. You've got brake fluid, which absorbs moisture. The moisture in the fluid eventually will cause steel parts to rust, like the fittings on the end of all the brake hoses that have those tiny little passages that plug up so easily. Then you've got the rubber that swells as it rots, and further contaminates the fluid, etc.
The solution is to periodically flush the brake fluid. But no one ever flushes brake fluid, because they don't run commercials during NASCAR, about the latest wonder fluid and flushing your brakes like they do the newest, BS motor oil, and 3k mile oil change intervals.
The best way to go is to fix the problem, then when you apply the brakes, the pressures in the front/rear circuits should be equal and the switch SHOULD move back to center. If and only if the brakes are working fine, and the light is stuck on, would I bother resetting the switch.
If your switch is sticking, your brake lines are shot and your brake fluid is or was full of sludge. In other words, a sticking switch would go hand in hand with blocked lines and black fluid, etc.
The lines can "look fine" and get totally crapped up on the inside. It's the nature of the beast. You've got brake fluid, which absorbs moisture. The moisture in the fluid eventually will cause steel parts to rust, like the fittings on the end of all the brake hoses that have those tiny little passages that plug up so easily. Then you've got the rubber that swells as it rots, and further contaminates the fluid, etc.
The solution is to periodically flush the brake fluid. But no one ever flushes brake fluid, because they don't run commercials during NASCAR, about the latest wonder fluid and flushing your brakes like they do the newest, BS motor oil, and 3k mile oil change intervals.
11-24-2017, 07:32 AM
#5
Re: Disc Conversion Bleeding Issues
Since this occurred after swapping out the rear, isn't it possible I don't have a line issue but that the switch tripped because I had the rear lines unhooked and stepped on the pedal? And couldn't I just reset the switch, gravity bleed the whole system (after bench bleeding the master) and call it a day?
11-24-2017, 11:22 AM
#6
Re: Disc Conversion Bleeding Issues
Gravity bleed? A thirdgen? *laughing so hard I fell off my dinosaur*
If you're gravity bleeding, that's your problem. Have yet to see that work on a thirdgen. Not to say it's impossible, but nah. Helper. Pump up, crack bleeder, close bleeder, release, wait, pump up, crack bleeder, close bleeder, release, wait.... Avoid letting the brake pedal bottom out.
Do the brakes work? Yes / No
-Yes, but the light is still on : Try manually resetting the switch
-No : Fix the brakes first, worry about the light later.
The light really doesn't effect anything. When the brakes are properly bled, the equal pressure in the system SHOULD reset the switch without any intervention.
If you're gravity bleeding, that's your problem. Have yet to see that work on a thirdgen. Not to say it's impossible, but nah. Helper. Pump up, crack bleeder, close bleeder, release, wait, pump up, crack bleeder, close bleeder, release, wait.... Avoid letting the brake pedal bottom out.
Do the brakes work? Yes / No
-Yes, but the light is still on : Try manually resetting the switch
-No : Fix the brakes first, worry about the light later.
The light really doesn't effect anything. When the brakes are properly bled, the equal pressure in the system SHOULD reset the switch without any intervention.
11-24-2017, 03:03 PM
#7
Re: Disc Conversion Bleeding Issues
So I played around with it a bit more today, and I got everything to work right. For anyone in the future: here's how it went
1. Bench bleed the master
2. My pressure differential switch piston was all the way to one side, so I couldn't reset it with a pick (no valley to put the pick into)
3. My rear lines were full of air, as all the fluid had drained out, I hooked up the air filled rear lines to their calipers.
4. Open one of the lines to the front brakes at the combo valve.
5. Firmly press the brake, the air pressure in the rear (because air is largely compressible) will force the piston to re-center but it was not so much pressure as to send it all the way to the forward position.
6. Optional but I did this: open all lines (post-combo valve) to verify fluid is dripping straight from the master through the combo valve and the switch is not engaged.
7. Gravity bleed (requires raising the front end quite a bit, I chose to gravity bleed so as not to offset the pressure differential switch again).
8. Once everything is bled properly, a few hard presses of the pedal should re-center the pressure differential switch.
1. Bench bleed the master
2. My pressure differential switch piston was all the way to one side, so I couldn't reset it with a pick (no valley to put the pick into)
3. My rear lines were full of air, as all the fluid had drained out, I hooked up the air filled rear lines to their calipers.
4. Open one of the lines to the front brakes at the combo valve.
5. Firmly press the brake, the air pressure in the rear (because air is largely compressible) will force the piston to re-center but it was not so much pressure as to send it all the way to the forward position.
6. Optional but I did this: open all lines (post-combo valve) to verify fluid is dripping straight from the master through the combo valve and the switch is not engaged.
7. Gravity bleed (requires raising the front end quite a bit, I chose to gravity bleed so as not to offset the pressure differential switch again).
8. Once everything is bled properly, a few hard presses of the pedal should re-center the pressure differential switch.