Vacuum Master Brake

GNONYX

Well-Known Member
I finally switched over from powermaster to vacuum brake system, both brake line fittings are the same, so would it make a difference if the rear brake lines is attached to the front master cylinder, or should the rear brake lines be connected to the master cylinder fitting closer to the firewall?
 

KC87

Well-Known Member
If you look close the front line to the PM is bigger than the one attached at the rear. IIrc the vacuum master cylinder pretty much lines up with a slight bending to the lines. Someone else chime in.
 

1986 Buick GX1

GX1 #001 [The One and Only]
I used the master cylinder, dual diaphragm vacuum booster from an ‘86 monte SS when I did my conversion in ‘97, so it’s been a while.
It seems I had to bend the lines forward to line up and I thought the threads or the seats were different sizes, but regardless, KC87 is correct. The large line goes on the front and the small one goes on the rear (closer to the firewall).
I hope I did it right. Lol

D1DE996E-E298-447D-92E7-479C4BBF5989.jpeg
 

GNONYX

Well-Known Member
I used the master cylinder, dual diaphragm vacuum booster from an ‘86 monte SS when I did my conversion in ‘97, so it’s been a while.
It seems I had to bend the lines forward to line up and I thought the threads or the seats were different sizes, but regardless, KC87 is correct. The large line goes on the front and the small one goes on the rear (closer to the firewall).
I hope I did it right. Lol

View attachment 350175
Okay, I asked another well known member in another site and he said being the front disc requires more fluid and being the forward or larger master cylinder bowl is larger, the smaller brake line goes to the front, and the larger brake line goes to the rear of closer to the firewall.
Now, I know when I was gravity bleeding the passenger rear wheel the front/larger master bowl was running low. Which means my master cylinder brake lines are backward. My photo shows the brake fittings are backward. This weekend I have to replace the passenger rear drum brake wheel cylinder. I'm also going to replace all of the brake bleeders with Russell Speed Bleeder.
20200207_185832.jpg
 

1986 Buick GX1

GX1 #001 [The One and Only]
Okay, I asked another well known member in another site and he said being the front disc requires more fluid and being the forward or larger master cylinder bowl is larger, the smaller brake line goes to the front, and the larger brake line goes to the rear of closer to the firewall.
Now, I know when I was gravity bleeding the passenger rear wheel the front/larger master bowl was running low. Which means my master cylinder brake lines are backward. My photo shows the brake fittings are backward. This weekend I have to replace the passenger rear drum brake wheel cylinder. I'm also going to replace all of the brake bleeders with Russell Speed Bleeder.
View attachment 350207
It looks like I better dig a little deeper into mine.
I thought I was unable to connect them differently, but it’s been a while so I’m not sure. They do work well.
 

GNONYX

Well-Known Member
It looks like I better dig a little deeper into mine.
I thought I was unable to connect them differently, but it’s been a while so I’m not sure. They do work well.
Today I tried to reverse the MC brake line but those lines are not reversible.
I believe I would have to get a shorty brake line with a coupling in order to make it right
 

1986 Buick GX1

GX1 #001 [The One and Only]
Today I tried to reverse the MC brake line but those lines are not reversible.
I believe I would have to get a shorty brake line with a coupling in order to make it right
I was thinking the lines were reversed when swapping from PM to vacuum and have been searching for verification, but have not been able to find anything yet.

So far everything I’ve found skips over the brake line specifics. They are very informative otherwise. Maybe it doesn’t matter if they’re not reversible, but I’ll keep looking though.
 

GNONYX

Well-Known Member
I was thinking the lines were reversed when swapping from PM to vacuum and have been searching for verification, but have not been able to find anything yet.

So far everything I’ve found skips over the brake line specifics. They are very informative otherwise. Maybe it doesn’t matter if they’re not reversible, but I’ll keep looking though.
Okay I did found out the way we both have it set up (MC brake line) is correct, but the only question I have is the front MC bowl larger for the disc pads or would it matter?
 

1986 Buick GX1

GX1 #001 [The One and Only]
Okay I did found out the way we both have it set up (MC brake line) is correct, but the only question I have is the front MC bowl larger for the disc pads or would it matter?
I’m glad you verified our lines are correct. I just found this info as well.

Thanks to Earl Brown for the how to on the Vacuum Brake Conversation.

It confirms the brake lines are indeed reversed compared the the Powermaster system. 10th paragraph down.


I installed an SSBC rear disc brake kit prior to the vac swap so I guess I didn’t pay attention to the bowl size.
 
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