NYsquarebird58's Brake System Overhaul and Disc Brake Conversion

[NYsquarebird58]

Maybe the problem is that you have the disc output of the master cyl plumbed to the rear drums? That might explain why you have such good braking on the rear and not so good at the front? In the references below note that the front and rear outputs are reversed on one style of master cyl. Did the master cyl you selected come with the details as to which output goes where?Eric

My reservoirs are the same size on the front and back of my master cylinder and It's my understanding the pressure coming out of the master cylinder is the same on both sides. I don't think I could plumb this particular master cylinder the wrong way.

It appears you have the brake light switch hooked up to the front line? That will cause that switch to go bad sooner with the higher pressure.(hearsay only - no experience on that but the switch was designed for the lower pressure drum system). The switches are pretty cheap - I'd just leave it and see what happens - change it if you need to later.Eric

I spoke with "Old Irish Dave" earlier. He says he prefers the master cylinders with ports on both sides, because he likes to screw the hydraulic brake switch directly to the master cylinder on one of the unused ports. Also, if you look at the original master cylinder on our squarebirds, the brake switch is screwed right to the end of it.

I'm making the assumption here that the line with the switch in it is the output for the front discs since it is plumbed to the front input of the proportioning valve....and from the proportioning valve I'm guessing you ran a new line to each front side from the two front outputs? (at least that's how I did mine).Eric

Correct. Here;'s my setup.

You did separate the front and rear systems right?? (by removing that junction point on the frame near the steering box?)

That is a disc/drum proportioning valve - right? If it were a disc/disc prop. valve with the drums on the rear - hummm.

Just a few guesses. Eric

Yes, I ran all new lines and removed the old junction block up front.

I'm still amazed at how well those booster brackets turned out.Eric

Thank you! Fabricating those was probably the funnest part of the whole project.

Some really good reference.....these are the folks that helped me when I was doing my conversion.
http://www.mpbrakes.com/uploads/docu...lumbingpdf.pdf

http://www.mpbrakes.com/uploads/documents/optomize.pdf
Eric

Great articles. Thank you!

I used a Lincoln Mark V? disc/drum brake master cyl and a disc/drum proportioning valve from master power. No nose dive - no rear lock up and about the same pedal pressure as the drum system. The master cyl lines come out the wrong side but it worked so well I just lived with it (basically it was all I could find that would fit my Frankenstein* system 10+years ago)

*Ahem...... I mean my custom hot rod highly engineered super performance braking system.

Seems I found later that a Mustang ('68?) is the same master cyl with the outputs on the other side - may change it someday. Eric

Those scarebird brackets really made the job so much easier for me!

You've done a super nice job on the documentation here and it's much appreciated. Geezzz I remember those days well. Almost think you cheated by getting to use the scarebird brackets. But then cheating is allowed in Squarebird brake mods..... :-)

Eric

Thank you, Eric. It seems like we all struggle just a little less than the guy before us. Hopefully the nest guy who decides to do a disc brake conversion struggles even less. I'm happy to post and snap off plenty of pictures to help others out.

[NYsquarebird58]

Photos are a bit small for me, but it looks like you are running the same setup I am on our 58. The combination valve is adjustable, I know I had to spend some time adjusting ours because I had mostly rear brake at the start. Also make sure you are using the right output for the front brakes, I think at first I had mine plumbed backwards also. The bigger of the two reservoirs is for the front disc brakes.

What I had to do was take some tools along and start changing the setting on the valve till I had the right amount of Front vs Rear brakes setup in it. Before I did that I could mash on the pedal and the car would slow, but not bite hard on the front.

Hey Bryan,

My master cylinder is a 1" bore MBM MC1921H and my Combination valve is an MBM PV2. My master cylinder has the same size reservoirs for the front and back so I don't think that's an issue.

Where on your proportioning valve do you adjust it? Yours looks similar to mine, but I don't have an adjustment.

Here's a pic of my proportioning valve and how I routed my lines.

[RustyNCa]

OK, so I installed the 1" master cylinder yesterday. It seems to have done the trick regarding pedal travel and effort. It feels good now. I don't have to push down quite as hard, and I have a bit more peddle travel. It's certainly not a night and day difference between the two, but the for my setup the change was just right.

There is a problem, though... Under moderate braking my rear drums lock up! It's not fun. If I have to make a sudden stop, I'm in trouble. Last night I took the bird up to about 70mph and brought her down to a gradual controlled stop. She stopped fine, but I had to be real gradual on the pedal.

I can lock the rear wheels only going 10 or 15mph. it doesn't take much.

The rear brakes locked up the same way with the 1-1/8" MC as well, so I know it's not that.

Any ideas?

Photos are a bit small for me, but it looks like you are running the same setup I am on our 58. The combination valve is adjustable, I know I had to spend some time adjusting ours because I had mostly rear brake at the start. Also make sure you are using the right output for the front brakes, I think at first I had mine plumbed backwards also. The bigger of the two reservoirs is for the front disc brakes.

What I had to do was take some tools along and start changing the setting on the valve till I had the right amount of Front vs Rear brakes setup in it. Before I did that I could mash on the pedal and the car would slow, but not bite hard on the front.

Maybe the problem is that you have the disc output of the master cyl plumbed to the rear drums?

Eric

No, the MC used on most of these GM based changeover kits is a CORVETTE Disc/Disc MC, the reason (I am assuming is that they can be used on either Disc/Drum or Disc/Disc Kits).

They do not include a Residual Valve for the rear drums so one can use the reservoirs in any position.

It would be interesting to know how much line pressure is generated to the rear wheel cylinders.

[DKheld]

Maybe the problem is that you have the disc output of the master cyl plumbed to the rear drums? That might explain why you have such good braking on the rear and not so good at the front? In the references below note that the front and rear outputs are reversed on one style of master cyl. Did the master cyl you selected come with the details as to which output goes where?

It appears you have the brake light switch hooked up to the front line? That will cause that switch to go bad sooner with the higher pressure.(hearsay only - no experience on that but the switch was designed for the lower pressure drum system). The switches are pretty cheap - I'd just leave it and see what happens - change it if you need to later.

I'm making the assumption here that the line with the switch in it is the output for the front discs since it is plumbed to the front input of the proportioning valve....and from the proportioning valve I'm guessing you ran a new line to each front side from the two front outputs? (at least that's how I did mine).

You did separate the front and rear systems right?? (by removing that junction point on the frame near the steering box?)

That is a disc/drum proportioning valve - right? If it were a disc/disc prop. valve with the drums on the rear - hummm.

Just a few guesses.

I'm still amazed at how well those booster brackets turned out.

Some really good reference.....these are the folks that helped me when I was doing my conversion.
http://www.mpbrakes.com/uploads/docu...lumbingpdf.pdf

http://www.mpbrakes.com/uploads/documents/optomize.pdf

I used a Lincoln Mark V? disc/drum brake master cyl and a disc/drum proportioning valve from master power. No nose dive - no rear lock up and about the same pedal pressure as the drum system. The master cyl lines come out the wrong side but it worked so well I just lived with it (basically it was all I could find that would fit my Frankenstein* system 10+years ago)

*Ahem...... I mean my custom hot rod highly engineered super performance braking system.

Seems I found later that a Mustang ('68?) is the same master cyl with the outputs on the other side - may change it someday.

You've done a super nice job on the documentation here and it's much appreciated. Geezzz I remember those days well. Almost think you cheated by getting to use the scarebird brackets. But then cheating is allowed in Squarebird brake mods..... :-)

Eric

[simplyconnected]

Locking rear drums is a classic symptom of a non-functioning combination proportioning valve. I'm surprised you didn't mention this before you changed master cylinders.

Sometimes coming up with the correct proportions are attained by going to a smaller-bore wheel cylinder on the drum brakes. That's what I did on the Galaxie. The proportioning valve should get you real close by itself.

Before diving in, make sure your brake shoes are bedded-in. When a small surface area of the shoe makes contact with the drum, it usually grabs much harder. - Dave

[NYsquarebird58]

OK, so I installed the 1" master cylinder yesterday. It seems to have done the trick regarding pedal travel and effort. It feels good now. I don't have to push down quite as hard, and I have a bit more peddle travel. It's certainly not a night and day difference between the two, but the for my setup the change was just right.

There is a problem, though... Under moderate braking my rear drums lock up! It's not fun. If I have to make a sudden stop, I'm in trouble. Last night I took the bird up to about 70mph and brought her down to a gradual controlled stop. She stopped fine, but I had to be real gradual on the pedal.

I can lock the rear wheels only going 10 or 15mph. it doesn't take much.

The rear brakes locked up the same way with the 1-1/8" MC as well, so I know it's not that.

Any ideas?

[NYsquarebird58]

I'm currently running an 1-1/8" master cylinder. I'm going to give a 1" master cylinder a try. I'm hoping the smaller bore size will give me more peddle travel and require less peddle effort.

It'll probably be about two weeks until I can give it a try. I'll keep everyone posted.

[Astrowing]

I got a lot better braking performance with a bleed with my Mighty Vac to pull fluid through the system rather than the old fashion pump and release fluid several times. I also used the opportunity to flush the now 2 year old fluid and replace it.

[NYsquarebird58]

Are you sure the rear brakes have been adjusted properly? Remember, they will not make full drum contact until the arc of the shoe lining is the same as the brake drum (wear-in).

Also- http://www.brakeandfrontend.com/issu...ontentid=40440

Thank you for this link; just gave it a read. I'll follow the 30/30/30 Burnish Procedure as suggested in the article.

[NYsquarebird58]

I replaced the vacuum hose going from the manifold to the booster, so now there's only one check valve in the system. At first I didn't think I noticed much difference rolling back and forth around the driveway, but it felt better on the road. I wouldn't say it "puts you through the windshield", but she definitely slows down faster than she did yesterday. I locked up the brakes a few times and she stops straight, but the brakes just don't "grab" as hard as I originally thought they would.

I guess the only way I can compare the feel of the brakes is as if you were stopping a loaded truck. It stops, but not on a dime.

I don't know, maybe they just need to break in a little more. My new rotors got rusty from being mounted on the car and not used for the past five months and the drums and everything else is also new.

I did several things. First I pulled up hard on the parking brake to try and seat the drums. Then I kept on adjusting the shoes just until I got to the point where I could not spin the drums. At that point I backed it off a bit until I could spin the drums with some resistance.

When I finished bleeding the brakes, I gave the pedal a few good pumps to try and seat the drums again and then I readjusted the drums a bit more until I felt some drag while spinning the wheel by hand.

I’m not sure if that’s proper procedure but it made sense to me at the time.

You pretty well covered it. Now remember, as the shoes wear in (arc) to the drums, you will probably lose the self adjusting feature. Give it a few weeks and ratchet them up again and the self adjusters should take over then.

[jopizz]

The self-adjusters you installed work when the car goes in reverse. It helps to go backwards a few times and hit the brakes.

John

[NYsquarebird58]

Good point.

On the initial adjustment, did you run the shoes completely against the drums and then back them off until you could rotate (spin) the wheel by hand one half turn?

You will also have to seat the linings once you have your assist problem fixed.

I did several things. First I pulled up hard on the parking brake to try and seat the drums. Then I kept on adjusting the shoes just until I got to the point where I could not spin the drums. At that point I backed it off a bit until I could spin the drums with some resistance.

When I finished bleeding the brakes, I gave the pedal a few good pumps to try and seat the drums again and then I readjusted the drums a bit more until I felt some drag while spinning the wheel by hand.

I’m not sure if that’s proper procedure but it made sense to me at the time.

I’m getting ready to leave the house now to pick up a new piece of vacuum hose. Hopefully that does the trick. I took the old hose and check valve off and sucked on the end. I did feel some resistance, but I’m not sure if it’s enough to starve the booster of the vacuum needed for full assist.

The rear drums seem to be adjusted properly. I can hear and feel the resistance of the shoes contacting the drums when I spin the wheels by hand. I also have a high pedal. I figured that if my drums were out of adjustment that, my peddle would seem low once I apply the brakes.

Good point.

On the initial adjustment, did you run the shoes completely against the drums and then back them off until you could rotate (spin) the wheel by hand one half turn?

You will also have to seat the linings once you have your assist problem fixed.